Atmospheric degradation of volatile organic compounds

Quantification for photochemical loss of volatile organic compounds upon ozone formation chemistry at an industrial city (Zibo) in North China Plain

Volatile organic compounds (VOCs) are consumed by photochemical reactions during transport, leading to inaccuracies in estimating the local ozone (O3) formation mechanism and its subsequent strategy for O3 attainment. To comprehensively quantify the deviations in O3 formation mechanism by consumed VOCs (C-VOCs), a 5-month field campaign was conducted in a typical industrial city in Northern China over incorporating a 0-D box model (implemented with MCMv3.3.1). The averaged C-VOCs concentration was 6.8 ppbv during entire period, and Alkenes accounted for 62% dominantly. Without considering C-VOCs, the relative incremental reactivity (RIR) of anthropogenic VOCs (AVOC, overestimated by 68%-75%) and NOx (underestimated by 137%-527%) demonstrated deviations at multiple scenarios, and the RIR deviations for precursors in High-O3-periods (HOP) were lower than Low-O3-periods (LOP). The RIR deviations from individual species involved C-VOCs calculation did not impact the identification for the high-ranking-RIR AVOC species but non-negligible. Monthly comparisons showed that higher C-VOCs concentrations would lead to higher RIR deviations. The daily maximum of net Ox production rate (P(Ox)) and the regional transport Ox (Trans(Ox)) without C-VOCs were underestimated by 56%-194% and 81%-243%, respectively. After considering C-VOCs, the contribution of HO2+NO for Ox gross production (G(Ox)) decreased by 7% (LOP) and 7% (HOP), but OH + NO2 for Ox destruction (D(Ox)) decreased by 16% (LOP) and 23% (HOP), and alkenes + O3 increased for D(Ox) by 12% (LOP) and 22% (HOP). This implies that VOCs-NOx-O3 sensitivity was deviated between with/without C-VOCs, and severe O3 pollution rendered deviations in O3 formation, especially via NOx-driving chemistry. Based on RIR(NOx)/RIR(AVOC) with/without C-VOCs, the sensitivity regime shifted from VOCs-limited (-0.93) to transition (1.38) at LOP, and from VOCs-limited (0.19) to NOx-limited (3.79) at HOP. Our results reflected that the NOx limitation degree was underestimated without constraint C-VOCs, especially HOP, and provided implication to more precise O3 pollution control strategies.

Promoted oxygen adsorption on porous CeO2 cubes with abundant oxygen vacancies for efficient gaseous formaldehyde removal

Photocatalytic degradation stands as a promising method for eliminating gas-phase pollutants, with the efficiency largely hinging on the capture of photogenerated electrons by oxygen. In this work, we synthesized a porous CeO2 single crystal cube with abundant oxygen vacancies as photocatalyst, employing urea as a pore-forming agent and for gas-phase formaldehyde degradation. Compared with the CeO2 cubes without pores, the porous ones were superior in specific surface area, akin to conventional CeO2 nanoparticles. The photocatalytic degradation for gas-phase formaldehyde on porous CeO2 cubes was significantly accelerated, of which degradation rate is 3.3 times and 2.1 times that of CeO2 cubes without pores and CeO2 nanoparticles, respectively. Photoelectric tests and DFT calculations revealed that this enhancement stemmed from facilitated oxygen adsorption due to pronounced oxygen vacancies. Consequently, the capture of photoelectrons by oxygen was promoted and its recombination with holes was suppressed, along with an accelerated generation of curial free radicals such as ·OH. This work reveals the pivotal role of surface oxygen vacancies in promoting adsorbed oxygen, proposing a viable strategy to enhance the photocatalytic degradation efficiency for gas-phase pollutants.

The characteristics and environmental significance of BVOCs released by aquatic macrophytes

Biogenic volatile organic compounds (BVOCs) emitted by plants serve crucial biological functions and potentially impact atmospheric environment and global carbon cycling. Despite their significance, BVOC emissions from aquatic macrophytes have been relatively understudied. In this study, for the first time we identified there were 68 major BVOCs released from 34 common aquatic macrophytes, and these compounds referred to alcohols, aldehydes, alkanes, alkenes, arenes, ethers, furans, ketones, phenol. For type of BVOC emissions from different life form and phylogenetic group of aquatic macrophytes, 34 of the 68 BVOCs from emergent and submerged macrophytes are classified into alkene and alcohol compounds, over 50% BVOCs from dicotyledon and monocotyledon belong to alcohol and arene compounds. Charophyte and pteridophyte emitted significantly fewer BVOCs than dicotyledon and monocotyledon, and each of them only released 12 BVOCs. These BVOCs may be of great importance for the growth and development of macrophytes, because many BVOCs, such as azulene, (E)-β-farnesene, and dimethyl sulfide are proved to play vital roles in plant growth, defense, and information transmission. Our results confirmed that both life form and phylogenetic group of aquatic macrophytes had significantly affected the BVOC emissions form macrophytes, and suggested that the intricate interplay of internal and external factors that shape BVOC emissions from aquatic macrophytes. Thus, further studies are urgently needed to investigate the influence factors and ecological function of BVOCs released by macrophytes within aquatic ecosystem.

Temporal evolution of speciated volatile organic compound (VOC) emissions from solvent use sources in the Pearl River Delta Region, China (2006-2019)

Volatile organic compounds (VOCs) emitted from solvent use sources constitute an important part of ozone (O3) and secondary organic aerosols (SOA) in the Pearl River Delta (PRD) region, China. While stringent control measures targeting VOCs have been implemented in recent years, an assessment of historical trends is imperative to evaluate their effectiveness. In this study, trends of VOC emissions, compositions, and reactivity from solvent use sources in the PRD region from 2006 to 2019 were estimated using a developed methodology, which considered the improvement of manufacturing equipment and removal efficiency. Results showed that total VOC emissions from solvent use sources displayed an overall increase from 277 kt in 2006 to 400 kt in 2019 despites some fluctuations, with metal products contributing more than 20 % each year. Aromatics and oxygenated VOCs (OVOCs) accounted for over 70 % of total VOC emissions, increasing by 21 kt and 52 kt respectively. OFP and SOAFP increased by 40 % and 23 % respectively from 2006 to 2019. Specific aromatic species, including m/p-xylene, toluene, 1,2,3,5-tetramethylbenzene, o-xylene and ethylbenzene were identified as key species in both VOC emission amount and reactivity. This study aims to facilitate the understanding of VOC emission evolution from solvent use sources in the region and provide insights into the impact of enacted measures, aiding in the future development of more targeted and efficient strategies in the PRD region.

Mechanisms of isomerization and hydration reactions of typical β-diketone at the air-droplet interface

Acetylacetone (AcAc) is a typical class of β-diketones with broad industrial applications due to the property of the keto-enol isomers, but its isomerization and chemical reactions at the air-droplet interface are still unclear. Hence, using combined molecular dynamics and quantum chemistry methods, the heterogeneous chemistry of AcAc at the air-droplet interface was investigated, including the attraction of AcAc isomers by the droplets, the distribution of isomers at the air-droplet interface, and the hydration reactions of isomers at the air-droplet interface. The results reveal that the preferential orientation of two AcAc isomers (keto- and enol-AcAc) to accumulate and accommodate at the acidic air-droplet interface. The isomerization of two AcAc isomers at the acidic air-droplet interface is more favorable than that at the neutral air-droplet interface because the "water bridge" structure is destroyed by H3O+, especially for the isomerization from keto-AcAc to enol-AcAc. At the acidic air-droplet interface, the carbonyl or hydroxyl O-atoms of two AcAc isomers display an energetical preference to hydration. Keto-diol is the dominant products to accumulate at the air-droplet interface, and excessive keto-diol can enter the droplet interior to engage in the oligomerization. The photooxidation reaction of AcAc will increase the acidity of the air-droplet interface, which indirectly facilitate the uptake and formation of more keto-diol. Our results provide an insight into the heterogeneous chemistry of β-diketones and their influence on the environment.

Spatiotemporal characterization of PM2.5, O3, and trace gases associated with East Asian continental outflows via drone sounding

East Asian continental outflows with PM2.5, O3, and other species may determine the baseline conditions and affect the air quality in downwind areas via long-range transport (LRT). To gain insight into the impact and spatiotemporal characteristics of airborne pollutants in East Asian continental outflows, a versatile multicopter drone sounding platform was used to simultaneously observe PM2.5, O3, CO2, and meteorological variables (temperature, specific humidity, pressure, and wind vector) above the northern tip of Taiwan, Cape Fuiguei, which often encounters continental outflows during winter monsoon periods. By coordinating hourly high-spatial-resolution profiles provided by drone soundings, WRF/CMAQ model air quality predictions, HYSPLIT-simulated backward trajectories, and MERRA-2 reanalysis data, we analyzed two prominent phenomena of airborne pollutants in continental outflows to better understand their physical/chemical characteristics. First, we found that pollutants were well mixed within a sounding height of 500 m when continental outflows passed through and completely enveloped Cape Fuiguei. Eddies induced by significant fluctuations in wind speeds coupled with minimal temperature inversion and LRT facilitated vertical mixing, possibly resulting in high homogeneity of pollutants within the outflow layer. Second, the drone soundings indicated exceptionally high O3 concentrations (70-100 ppbv) but relatively low concentrations of PM2.5 (10-20 μg/m3), CO2 (420-425 ppmv), and VOCs in some air masses. The low levels of PM2.5, CO2, and VOCs ruled out photochemistry as the cause of the formation of high-level O3. Further coordination of spatiotemporal data with air mass trajectories and O3 cross sections provided by MERRA-2 suggested that the high O3 concentrations could be attributed to stratospheric intrusion and advection via continental outflows. High-level O3 concentrations persisted in the lower troposphere, even reaching the surface, suggesting that stratospheric intrusion O3 may be involved in the rising trend in O3 concentrations in parts of East Asia in recent years in addition to surface photochemical factors.

Gas-Phase Kinetic Investigation of the OH-Initiated Oxidation of a Series of Methyl-Butenols under Simulated Atmospheric Conditions

Five biogenic unsaturated alcohols have been investigated under simulated atmospheric conditions regarding their gas-phase OH reactivity. The gas-phase rate coefficients of OH radicals with 2-methyl-3-buten-2-ol (k1), 3-methyl-2-buten-1-ol (k2), 3-methyl-3-buten-1-ol (k3), 2-methyl-3-buten-1-ol (k4), and 3-methyl-3-buten-2-ol (k5) at 298 ± 2 K and 1000 ± 10 mbar total pressure of synthetic air were determined under low- and high-NOx conditions using the relative kinetic technique. The present work provides for the first time the rate coefficients of gas-phase reactions of hydroxyl radicals with 2-methyl-3-buten-1-ol and 3-methyl-3-buten-2-ol. The following rate constants were measured (in 10-11 cm3 molecule-1 s-1): k1 = 6.32 ± 0.49, k2 = 14.55 ± 0.93, k3 = 10.04 ± 0.78, k4 = 5.31 ± 0.37, and k5 = 11.71 ± 1.29. No significant differences in the measured rate coefficients were obtained when either 365 nm photolysis of CH3ONO in the presence of NO or 254 nm photolysis of H2O2 was used as a source of OH radicals. Reactivity toward other classes of related compounds such as alkenes and saturated alcohols is discussed. A comparison of the structure-activity relationship (SAR) estimates derived from the available accepted methodologies with experimental data available for unsaturated alcohols is provided. Atmospheric lifetimes for the investigated series of alkenols with respect to the main atmospheric oxidants are given and discussed.

Obscured Contribution of Oxygenated Intermediate-Volatility Organic Compounds to Secondary Organic Aerosol Formation from Gasoline Vehicle Emissions

Secondary organic aerosol (SOA) formation from gasoline vehicles spanning a wide range of emission types was investigated using an oxidation flow reactor (OFR) by conducting chassis dynamometer tests. Aided by advanced mass spectrometric techniques, SOA precursors, including volatile organic compounds (VOCs) and intermediate/semivolatile organic compounds (I/SVOCs), were comprehensively characterized. The reconstructed SOA produced from the speciated VOCs and I/SVOCs can explain 69% of the SOA measured downstream of an OFR upon 0.5-3 days' OH exposure. While VOCs can only explain 10% of total SOA production, the contribution from I/SVOCs is 59%, with oxygenated I/SVOCs (O-I/SVOCs) taking up 20% of that contribution. O-I/SVOCs (e.g., benzylic or aliphatic aldehydes and ketones), as an obscured source, account for 16% of total nonmethane organic gas (NMOG) emission. More importantly, with the improvement in emission standards, the NMOG is effectively mitigated by 35% from China 4 to China 6, which is predominantly attributed to the decrease of VOCs. Real-time measurements of different NMOG components as well as SOA production further reveal that the current emission control measures, such as advances in engine and three-way catalytic converter (TWC) techniques, are effective in reducing the "light" SOA precursors (i.e., single-ring aromatics) but not for the I/SVOC emissions. Our results also highlight greater effects of O-I/SVOCs to SOA formation than previously observed and the urgent need for further investigation into their origins, i.e., incomplete combustion, lubricating oil, etc., which requires improvements in real-time molecular-level characterization of I/SVOC molecules and in turn will benefit the future design of control measures.

Seasonal and height dynamics of volatile organic compounds in rubber plantation: Impacts on ozone and secondary organic aerosol formation

Rubber trees emit a range of volatile organic compounds (VOCs), including isoprene, monoterpenes, and sesquiterpenes, as part of their natural metabolism. These VOCs can significantly influence air quality through photochemical reactions that produce ozone and secondary organic aerosols (SOAs). This study examines the impact of VOCs detected in a rubber tree plantation in Northeastern Thailand on air quality, highlighting their role in atmospheric reactions that lead to the formation of ozone and SOAs. VOCs were collected at varying heights and seasons using Tenax-TA tubes paired with an atmospheric sampler pump and identified by gas chromatography-mass spectrometry. In total, 100 VOCs were identified, including alkanes, alkenes, terpenes, aromatics, and oxygenated VOCs. Principal Coordinate Analysis (PCoA) revealed distinct seasonal VOC profiles, with hydrocarbons, peaking in summer and terpenes in the rainy season. The Linear Mixed-Effects (LME) model indicates that VOC concentrations are more influenced by seasonal changes than by sampling heights. Secondary organic aerosol potential (SOAP) and ozone formation potential (OFP) of selected VOC species were also determined. The total SOAP ranged from 67.24 μg/m3 in summer to 17.87 μg/m3 in winter, while the total OFP ranged from 377.87 μg/m3 in summer to 139.39 μg/m3 in winter. Additionally, positive matrix factorization (PMF) analysis identified four main VOC sources: gasoline combustion (18.3 %), microbial activity (38.6 %), monoterpene emissions during latex production (15.0 %), and industrial sources (28.1 %). These findings provide essential information for managing air pollution in rubber tree plantations. By adopting focused air quality management strategies, plantation operators can mitigate the adverse effects of VOCs, promoting a healthier and more sustainable future.

Climatic conditions and concentrations of BTEX compounds in atmospheric media

Climatic and meteorological conditions are among the factors affecting the ambient concentrations of BTEX compounds. This systematic review and meta-analysis aimed to interrogate the seasonal effect of climatic conditions on the concentrations of BTEX compounds. Three electronic bibliographic databases including Scopus, PubMed, and Web of Science were systematically searched up to November 14, 2023. The search algorithm followed PRISMA guidance and consisted of three groupings of keywords and their possible combinations. For various climatic conditions, the overall mean and 95% confidence interval (CI) of effect size related to BTEX concentrations were calculated using a random-effect model. In total, 104 articles were included for evaluation in this review. BTEX ambient concentration was higher in winter (ranging from 36 out of 79 relevant studies for xylene to 52 out of 97 relevant studies for benzene) followed by summer and autumn. For humidity conditions, the highest exposure values for BTEX were detected for rainy weather (ranging from 3 out of 5 relevant studies for toluene and xylene to 4 out of 5 relevant studies for benzene and ethyl benzene) compared to dry conditions. The pooled concentration (μg/m3) of benzene, toluene, ethyl benzene, and xylene were computed as 2.61, 7.12, 2.21, and 3.61 in spring, 2.13, 7.53, 1.61, and 2.75 in summer, 3.04, 9.59, 3.14, and 5.50 in autumn, and 3.56, 8.71, 2.35, and 3.91 in winter, respectively. Moreover, the pooled concentrations (μg/m3) of BTEX were measured as 2.98, 7.22, 1.90, and 3.03 in dry weather and 3.15, 6.30, 2.14, and 3.86 in rainy or wet weather, respectively. In most seasons, the ambient concentrations of BTEX were higher in countries with low and middle incomes and in Middle Eastern countries and East/Southeast Asia compared to those in other regions (P < 0.001). The increasing concentrations of BTEX in winter and autumn followed by the summer season and during rainy/wet weather appear to be reasonably consistent despite variations in study methods, quality, or geography. Therefore, it is recommended that more serious control measures are considered for decreasing exposure to BTEX in these climatic conditions.

A high-level ab initio study of the photodissociation of acetaldehyde

Acetaldehyde is a very relevant atmospheric species whose photodissociation has been extensively studied in the first absorption band both experimentally and theoretically. Very few works have been reported on acetaldehyde photodissociation at higher excitation energies. In this work, the photodissociation dynamics of acetaldehyde is investigated by means of high-level multireference configuration interaction ab initio calculations. Five different fragmentation pathways of acetaldehyde are explored by calculating the potential-energy curves of the ground and several excited electronic states along the corresponding dissociating bond distances. The excitation energy range covered in the study is up to 10 eV, nearly the ionization energy of acetaldehyde. We intend to rationalize the available experimental results and, in particular, to elucidate why some of the studied fragmentation pathways are experimentally observed in the different excitation energy regions and some others are not. Based on the shape of the calculated potential curves, we are able to explain the main findings of the available experiments, also suggesting possible dynamical dissociation mechanisms in the different energy regions. Thus, the reported potential curves are envisioned as a useful tool to interpret the currently available experiments as well as future ones on acetaldehyde photodissociation at excitation wavelengths in the range studied here.

Quantitative kinetics reveal that reactions of HO2 are a significant sink for aldehydes in the atmosphere and may initiate the formation of highly oxygenated molecules via autoxidation

Large aldehydes are widespread in the atmosphere and their oxidation leads to secondary organic aerosols. The current understanding of their chemical transformation processes is limited to hydroxyl radical (OH) oxidation during daytime and nitrate radical (NO3) oxidation during nighttime. Here, we report quantitative kinetics calculations of the reactions of hexanal (C5H11CHO), pentanal (C4H9CHO), and butanal (C3H7CHO) with hydroperoxyl radical (HO2) at atmospheric temperatures and pressures. We find that neither tunneling nor multistructural torsion anharmonicity should be neglected in computing these rate constants; strong anharmonicity at the transition states is also important. We find rate constants for the three reactions in the range 3.2-7.7 × 10-14 cm3 molecule-1 s-1 at 298 K and 1 atm, showing that the HO2 reactions can be competitive with OH and NO3 oxidation under some conditions relevant to the atmosphere. Our findings reveal that HO2-initiated oxidation of large aldehydes may be responsible for the formation of highly oxygenated molecules via autoxidation. We augment the theoretic studies with laboratory flow-tube experiments using an iodide-adduct time-of-flight chemical ionization mass spectrometer to confirm the theoretical predictions of peroxy radicals and the autoxidation pathway. We find that the adduct from HO2 + C5H11CHO undergoes a fast unimolecular 1,7-hydrogen shift with a rate constant of 0.45 s-1. We suggest that the HO2 reactions make significant contributions to the sink of aldehydes.

Impact of volatile organic compounds in large municipal solid waste landfills on regional environment

Landfill disposal is a major approach of disposing municipal solid waste (MSW) in China. In order to explore the impact of volatile organic compounds (VOCs) generated by landfill on the air quality of regional environment, Jiangcungou landfill in Xi'an and its surrounding area were taken as a research object to analyze the spatial distribution and seasonal variation patterns of non-methane hydrocarbon (NMHC) and VOCs components through seasonal sampling of regional NMHC concentration and VOCs concentration (116 species). CALPUFF model was adopted to analyze the regional dispersion characteristics of NMHC on landfill. In addition, propylene equivalent concentration (PEC) and maximum incremental reactivity (MIR) methods were used to estimate O3 formation potential of the landfill, while fraction aerosol coefficient (FAC) and SOA potential (SOAP) methods were used to estimate SOA formation potential of the landfill. It was indicated that, the component with the highest concentration of VOCs on the working surface and the surrounding area of landfill was p + m-xylene (41.0 μg/m3) and halohydrocarbon (111.2 μg/m3-156.3 μg/m3), respectively. The component with the greatest impact on the surrounding air was acetone, which accounts for 75 %-87 % of the corresponding substance concentration on the landfill. In summer, the surrounding area was affected most by NMHC from landfill, whose emissions contributed 9.5 mg/m3 to the surrounding area. The component making the largest contribution to O3 formation was p + m-xylene (8 %-24 %), while ethylbenzene was the component making the largest contribution to SOA formation (20 %-24 %).

Emerging investigator series: secondary organic aerosol formation from photooxidation of acyclic terpenes in an oxidation flow reactor

One major challenge in predicting secondary organic aerosol (SOA) formation in the atmosphere is incomplete representation of biogenic volatile organic compounds (BVOCs) emitted from plants, particularly those that are emitted as a result of stress - a condition that is becoming more frequent in a rapidly changing climate. One of the most common types of BVOCs emitted by plants in response to environmental stress are acyclic terpenes. In this work, SOA is generated from the photooxidation of acyclic terpenes in an oxidation flow reactor and compared to SOA production from a reference cyclic terpene - α-pinene. The acyclic terpenes used as SOA precursors included β-myrcene, β-ocimene, and linalool. Results showed that oxidation of all acyclic terpenes had lower SOA yields measured after 4 days photochemical age, in comparison to α-pinene. However, there was also evidence that the condensed organic products that formed, while a smaller amount overall, had a higher oligomeric content. In particular, β-ocimene SOA had higher oligomeric content than all the other chemical systems studied. SOA composition data from ultra-high performance liquid chromatography with electrospray ionization mass spectrometry (UHPLC-ESI-MS) was combined with mechanistic modeling using the Generator for Explicit Chemistry and Kinetics of Organics in the Atmosphere (GECKO-A) to explore chemical mechanisms that could lead to this oligomer formation. Calculations based on composition data suggested that β-ocimene SOA was more viscous with a higher glass transition temperature than other SOA generated from acyclic terpene oxidation. This was attributed to a higher oligomeric content compared to other SOA systems studied. These results contribute to novel chemical insights about SOA formation from acyclic terpenes and relevant chemistry processes, highlighting the importance of improving underrepresented biogenic SOA formation in chemical transport models.

Comparative analysis for the impacts of VOC subgroups and atmospheric oxidation capacity on O3 based on different observation-based methods at a suburban site in the North China Plain

The persistent O3 pollution in the Beijing-Tianjin-Hebei (BTH) region remains unresolved, largely due to limited comprehension of O3-precursor relationship and photochemistry drivers. In this work, intraday O3 sensitivity evolution from VOC-limited (volatile organic compound) regime in the forenoon to transition regime in the late afternoon was inferred by relative incremental reactivity (RIR) in summer 2019 at Xianghe, a suburban site in BTH region, suggesting that VOC-focused control policy could combine with stringent afternoon NOx control. Then detailed impacts of VOC subgroups on O3 formation were further comprehensively quantified by parametric OH reactivity (KOH), O3 formation potential (OFP), as well as RIR weighted value and O3 formation path tracing (OFPT) approach based on photochemical box model. O3 episode days corresponded to stronger O3 formation, depicted by higher KOH (10.4 s-1), OFP (331.7 μg m-3), RIR weighted value (1.2), and F(O3)-OFPT (15.5 ppbv h-1). High proportions of isoprene and OVOCs (oxygenated VOCs) to the total KOH and the OFPT method were demonstrated whereas results of OFP and RIR-weighted presented extra great impacts of aromatics on O3 formation. The OFPT approach captured the process that has already happened and included final O3 response to the original VOC, thus reliable for replicating VOC impacts. The comparison results of the four methods showed similarities when utilizing KOH and OFPT methods, which reveals that the potential applicability of simple KOH for contingency VOC control and more complex OFPT method for detailed VOC- and source-oriented control during policy-making. To investigate propulsion of VOC-involved O3 photochemistry, atmospheric oxidation capacity (AOC) was quantified by two atmospheric oxidation indexes (AOI). Both AOIp_G (7.0 × 107 molec cm-3 s-1, potential AOC calculated by oxidation reaction rates) and AOIe_G (8.5 μmol m-3, estimated AOC given redox electron transfer for oxidation products) were stronger on O3 episode days, indicating that AOC promoted the radical cycling initiated from VOC oxidation and subsequent O3 production. Result-oriented AOIe_G reasonably characterized actual AOC inferred by good linear correlation between AOIe_G and O3 concentrations compared to process-oriented AOIp_G. Therefore, with continuous NOx abatement, AOIe_G should be considered to represent actual AOC, also O3-inducing ability.

Spatiotemporal variations, sources, and atmospheric transformation potential of volatile organic compounds in an industrial zone based on high-resolution measurements in three plants

Industrial emissions are significant sources of volatile organic compounds (VOCs). This study conducted a field campaign at high temporal and spatial resolution to monitor VOCs within three plants in an industrial park in southern China. VOC concentrations showed significant spatial variability in this industrial zone, with median concentrations of 75.22, 40.53, and 29.41 μg/m3 for the total VOCs in the three plants, respectively, with oxygenated VOCs (OVOCs) or aromatics being the major VOCs. Spatial variability within each plant was also significant but VOC-dependent. Seasonal variations in the VOC levels were governed by their industrial emissions, meteorological conditions, and photochemical losses, and they were different for the four groups of VOCs. The temporal and spatial variations in the VOC compositions suggest similar sources of each class of VOCs during different periods of the year in each plant. The diurnal patterns of VOCs (unimodal or bimodal) clearly differed from those at most industrial/urban locations previously, reflecting a dependence on industrial activities. The secondary transformation potential of VOCs also varied temporally and spatially, and aromatics generally made the predominant contributions in this industrial park. The loss rate of OH radicals and ozone formation potential were highly correlated, but the linear relationship substantially changed in summer and autumn due to the intensive emissions of an OVOC species. The lifetime cancer and non-cancer risks via occupational inhalation of the VOCs in the plants were acceptable but merit attention. Taking the secondary transformation potential and health risks into consideration, styrene, xylene, toluene, trichloroethylene, and benzene were proposed to be the priority VOCs regulated in the plants.

Mn-Based Mullites for Environmental and Energy Applications

Mn-based mullite oxides AMn2O5 (A = lanthanide, Y, Bi) is a novel type of ternary catalyst in terms of their electronic and geometric structures. The coexistence of pyramid Mn3+-O and octahedral Mn4+-O makes the d-orbital selectively active toward various catalytic reactions. The alternative edge- and corner-sharing stacking configuration constructs the confined active sites and abundant active oxygen species. As a result, they tend to show superior catalytic behaviors and thus gain great attention in environmental treatment and energy conversion and storage. In environmental applications, Mn-based mullites have been demonstrated to be highly active toward low-temperature oxidization of CO, NO, volatile organic compounds (VOCs), etc. Recent research further shows that mullites decompose O3 and ozonize VOCs from -20 °C to room temperature. Moreover, mullites enhance oxygen reduction reactions (ORR) and sulfur reduction reactions (SRR), critical kinetic steps in air-battery and Li-S batteries, respectively. Their distinctive structures also facilitate applications in gas-sensitive sensing, ionic conduction, high mobility dielectrics, oxygen storage, piezoelectricity, dehydration, H2O2 decomposition, and beyond. A comprehensive review from basic physicochemical properties to application certainly not only gains a full picture of mullite oxides but also provides new insights into designing heterogeneous catalysts.

Ozonolysis of 2-Methyl-2-pentenal: New Insights from Master Equation Modeling

Experimental and theoretical studies were carried out to investigate the ozonolysis of trans-2-methyl-2-pentenal. The experiments were conducted in atmospheric simulation chambers coupled to a Fourier transform infrared (FTIR) spectrometer and a gas chromatograph-mass spectrometer at room temperature and atmospheric pressure in the presence of an excess of cyclohexane in dry conditions (RH < 1%). The ozonolysis reaction was investigated theoretically from the results of accurate density functional (M06-2X) and ab initio [CCSD(T)] computations, employing the AVTZ basis set. The sequence of reaction steps was established, and the system of kinetics equations was modeled using MESMER. In the first step, a primary ozonide is formed, which then decomposes along two pathways. The principal ozonolysis products are propanal, methylglyoxal, ethylformate, and a secondary ozonide. An interesting competition between sequential reaction steps and well-skipping is found, which leads to an inversion of the expected methylglyoxal/propanal product ratio at temperatures below 210 K. The mechanism of the "hot ester" reaction channel of the Criegee intermediate was revisited. The computed ozonolysis rate constant and product branching ratio are in excellent agreement with the experimental data that are also reported in the present work.

Additional HONO and OH Generation from Photoexcited Phenyl Organic Nitrates in the Photoreaction of Aromatics and NOx

HONO acts as a major OH source, playing a vital role in secondary pollutant formation to deteriorate regional air quality. Strong unknown sources of daytime HONO have been widely reported, which significantly limit our understanding of radical cycling and atmospheric oxidation capacity. Here, we identify a potential daytime HONO and OH source originating from photoexcited phenyl organic nitrates formed during the photoreaction of aromatics and NOx. Significant HONO (1.56-4.52 ppb) and OH production is observed during the photoreaction of different kinds of aromatics with NOx (18.1-242.3 ppb). We propose an additional mechanism involving photoexcited phenyl organic nitrates (RONO2) reacting with water vapor to account for the higher levels of measured HONO and OH than the model prediction. The proposed HONO formation mechanism was evidenced directly by photolysis experiments using typical RONO2 under UV irradiation conditions, during which HONO formation was enhanced by relative humidity. The 0-D box model incorporated in this mechanism accurately reproduced the evolution of HONO and aromatic. The proposed mechanism contributes 5.9-36.6% of HONO formation as the NOx concentration increased in the photoreaction of aromatics and NOx. Our study implies that photoexcited phenyl organic nitrates are an important source of atmospheric HONO and OH that contributes significantly to atmospheric oxidation capacity.

Analyzing ozone formation sensitivity in a typical industrial city in China: Implications for effective source control in the chemical transition regime

Volatile organic compounds (VOCs) play a major role in O3 formation in urban environments. However, the complexity in the emissions of VOCs and nitrogen oxides (NOx) in industrial cities has made it challenging to identify the key factors influencing O3 formation. This study used observation-based-model (OBM) to analyze O3 sensitivities to VOCs and NOx during summer in a typical industrial city in China. The OBM model results were coupled with a receptor model to analyze the sources of O3. Higher concentrations of O3 precursors were observed during polluted periods indicating that precursor accumulation contributed to the higher maxima of the net ozone formation rate and HOx concentrations. Analyses of ROx· budgets and relative incremental reactivity (RIR) indicated that O3 production is in a chemical transition regime and was sensitive to both VOCs and NOx. Results from Positive Matrix Factorization (PMF) analysis indicated that gasoline vehicle emissions, industrial processes, and coal combustion were major sources of O3 precursors. The sensitivities of O3 production to these sources depend on if both VOC and NOx sensitivities are considered. If only VOCs sensitivity is considered, in contrast, the contribution of anthropogenic sources to O3 production was significantly underestimated. This study highlights the importance of accounting for both VOCs and NOx sensitivities when O3 chemistry is in a transition regime in O3 production attribution studies.

A prediction index of the volatile organic compounds pollution conditions in a chemical industrial park based on atmospheric stability

Volatile organic compounds (VOCs), as common precursors of ozone (O3) and fine particulate matter (PM2.5), are a focus of air pollution prevention and control. Furthermore, with the rapid development of industry, industrial sources have become the largest source of anthropogenic VOCs emissions, leading to economic development while causing great harm to the environment. It is becoming meaningful to efficiently predict the future total volatile organic compounds (TVOC) pollution conditions in chemical industrial parks (CIPs), which can assist managers in carrying out corporate emission management in advance. In this study, TVOC monitoring data and meteorological data from January 1, 2022, to December 31, 2022, were used to innovatively construct the TVOC pollution index. This index comprehensively considers the atmospheric stability and localized horizontal diffusion conditions and can quickly and accurately predict the variations in the TVOC in a CIP in the next 7 days. In addition, we used synoptic weather patterns and backward trajectory analysis to explore the mechanism of VOCs pollution formation in a CIP. The results show that the combined influences of a westerly wind pattern, temperatures above 30 °C, a subtropical high pressure system, more upwind pollutants, and the horizontal and vertical diffusion conditions in the CIP were unfavorable, leading to VOCs pollution.

Characteristics and source apportionment of ambient volatile organic compounds and ozone generation sensitivity in urban Jiaozuo, China

In recent years, many cities have taken measures to reduce volatile organic compounds (VOCs), an important precursor of ozone (O3), to alleviate O3 pollution in China. 116 VOC species were measured by online and offline methods in the urban area of Jiaozuo from May to October in 2021 to analyze the compositional characteristics. VOC sources were analyzed by a positive matrix factorization (PMF) model, and the sensitivity of ozone generation was determined by ozone isopleth plotting research (OZIPR) simulation. The results showed that the average volume concentration of total VOCs was 30.54 ppbv and showed a bimodal feature due to the rush-hour traffic in the morning and at nightfall. The most dominant VOC groups were oxygenated VOCs (OVOCs, 29.3%) and alkanes (26.7%), and the most abundant VOC species were acetone and acetylene. However, based on the maximum incremental reactivity (MIR) method, the major VOC groups in terms of ozone formation potential (OFP) contribution were OVOCs (68.09 µg/m3, 31.5%), aromatics (62.90 µg/m3, 29.1%) and alkene/alkynes (54.90 µg/m3, 25.4%). This indicates that the control of OVOCs, aromatics and alkene/alkynes should take priority. Five sources of VOCs were quantified by PMF, including fixed sources of fossil fuel combustion (27.8%), industrial processes (25.9%), vehicle exhaust (19.7%), natural and secondary formation (13.9%) and solvent usage (12.7%). The empirical kinetic modeling approach (EKMA) curve obtained by OZIPR on O3 exceedance days indicated that the O3 sensitivity varied in different months. The results provide theoretical support for O3 pollution prevention and control in Jiaozuo.

Pollution characteristics, source appointment and environmental effect of oxygenated volatile organic compounds in Guangdong-Hong Kong-Macao Greater Bay Area: Implication for air quality management

Same as other bay areas, the Guangdong-Hong Kong-Macao Greater Bay Area (GBA) is also suffering atmospheric composite pollution. Even a series of atmospheric environment management policies have been conducted to win the "blue sky defense battle", the atmospheric secondary pollutants (e.g., O3) originated from oxygenated volatile organic compounds (OVOCs) still threaten the air quality in GBA. However, there lacks a systematic summary on the emission, formation, pollution and environmental effects of OVOCs in this region for further air quality management. This review focused on the researches related to OVOCs in GBA, including their pollution characteristics, detection methods, source distributions, secondary formations, and impacts on the atmosphere. Pollution profile of OVOCs in GBA revealed that the concentration percentage among total VOCs from Guangzhou and Dongguan cities exceeded 50 %, while methanol, formaldehyde, acetone, and acetaldehyde were the top four highest concentrated OVOCs. The detection technique on regional atmospheric OVOCs (e.g., oxygenated organic molecules (OOMs)) underwent an evolution of off-line derivatization method, on-line spectroscopic method and on-line mass spectrometry method. The OVOCs in GBA were mainly from primary emissions (up to 80 %), including vehicle emissions and biomass combustion. The anthropogenic alkenes and aromatics in urban area, and natural isoprene in rural area also made a significant contribution to the secondary emission (e.g., photochemical formation) of OVOCs. About 20 % in average of ROx radicals was produced from photolysis of formaldehyde in comparison with O3, nitrous acid and rest OVOCs, while the reaction between OVOCs and free radical accelerated the NOx-O3 cycle, contributing to 15 %-60 % cumulative formation of O3 in GBA. Besides, the heterogeneous reactions of dicarbonyls generated 21 %-53 % of SOA. This review also provided suggestions for future research on OVOCs in terms of regional observation, analytical method and mechanistic study to support the development of a control and management strategy on OVOCs in GBA and China.

Photochemical oxidation of VOCs and their source impact assessment on ozone under de-weather conditions in Western Taiwan

The application of statistical models has excellent potential to provide crucial information for mitigating the challenging issue of ozone (O3) pollution by capturing its associations with explanatory variables, including reactive precursors (VOCs and NOX) and meteorology. Considering the large contribution of O3 in degrading the air quality of western Taiwan, three-year (2019-2021) hourly concentration data of VOC, NOX and O3 from 4 monitoring stations of western Taiwan: Tucheng (TC), Zhongming (ZM), Taixi (TX) and Xiaogang (XG), was evaluated to identify the effect of anthropogenic emissions on O3 formation. Owing to the high-ambient reactivity of VOCs on the underestimation of sources, photochemical oxidation was assessed to calculate the consumed VOC (VOCcons) which was followed by the source identification of their initial concentrations. VOCcons was observed to be highest in the summer season (16.7 and 22.7 ppbC) at north (TC and ZM) and in the autumn season (17.8 and 11.4 ppbC) in southward-located stations (TX and XG, respectively). Results showed that VOCs from solvents (25-27%) were the major source at northward stations whereas VOCs-industrial emissions (30%) dominated in south. Furthermore, machine learning (ML): eXtreme Gradient Boost (XGBoost) model based de-weather analysis identified that meteorological factors favor to reduce ambient O3 levels at TC, ZM and XG stations (-67%, -47% and -21%, respectively) but they have a major role in accumulating the O3 (+38%) at the TX station which is primarily transported from the upwind region of south-central Taiwan. Crucial insights using ML outputs showed that the finding of the study can be utilized for region-specific data-driven control of emission from VOCs-sources and prioritized to limit the O3-pollution at the study location-ns as well as their accumulation in distant regions.

Photochemical loss with consequential underestimation in active VOCs and corresponding secondary pollutions in a petrochemical refinery, China

The photochemical loss of volatile organic compounds (VOCs) significantly alters the capturing source profiles in high-reactivity VOC species and results in an underestimation of secondary pollutants such as ozone (O3) and secondary organic aerosol (SOA). Utilising speciated VOC data from large petrochemical refineries, the research assesses the photochemical loss of various VOC species. Air samples from multiple sites revealed over 99 VOCs, with initial concentrations estimated via a photochemical age-based parameterisation method. The comparative analysis of initial and measured VOC values provided insights into the VOCs' photochemical degradation during transport. Findings highlight that the average photochemical loss of total VOCs (TVOCs) across different refinery process areas varied between 4.9 and 506.8 ppb, averaging 187.5 ± 128.7 ppb. Alkenes dominated the consumed VOCs at 83.1 %, followed by aromatic hydrocarbons (9.3 %), alkanes (6.1 %), and oxygenated VOCs (OVOCs) at 1.6 %. The average consumption-based ozone formation potential (OFP) and SOA formation potential (SOAP) were calculated at 1767.3 ± 1251.1 ppb and 2959.6 ± 2386.3 ppb, respectively. Alkenes, primarily isoprene, 1,3-butadiene, and acetylene, were the most significant contributors to OFP, ranging from 19.9 % to 95.5 %. Aromatic hydrocarbons, predominantly monocyclic aromatics like toluene, xylene, styrene, and n-dodecane, were the primary contributors to SOAP, accounting for 5.0 % to 81.3 %. This research underscores the significance of considering photochemical losses in VOCs for accurate secondary pollution assessment, particularly in high-reactivity VOC species. It also provides new detection methods and accurate data for the characterization, source analysis and chemical conversion of volatile organic compounds in the petroleum refining industry.

Sources and environmental impacts of volatile organic components in a street canyon: Implication for vehicle emission

Street canyons serve as a representative environment that directly reflects the impact of vehicular emissions. Volatile organic compounds (VOCs) sampling during an O3 pollution event and a PM2.5 pollution episode was conducted at an urban site and a street canyon in Zhengzhou, China. It has been determined that street canyons suffer from more severe particle and NOx pollution than the urban site. Additionally, O3 has been identified as a significant or emerging pollutant in street canyon environments. In terms of VOCs, the street canyon exhibits 1.4 and 1.1 times higher total VOC concentrations compared to the urban site during the O3 and PM2.5 pollution episodes, respectively. In the street canyon location, there was a slight increase in the proportion of alkanes and aromatics, while the proportions of oxygenated VOCs and halogenated hydrocarbons decreased. Source apportionment analysis reveals that street canyons were more susceptible to the accumulation of VOCs from coating solvent, liquid petroleum gas (LPG), and gasoline additives. Consequently, the environmental impacts of VOCs originating from coating solvent and LPG were more pronounced in the street canyon location compared to the urban site. The trends of NOx concentration indicate that future continuously stricter vehicle emission standards and control policies can further reduce vehicle exhaust emissions and more attention needs to be focused on the reduction of non-exhaust emissions (i.e., coating solvent) and LPG vehicles.

Role of Hydroperoxyl Radicals in Heterogeneous Oxidation of Oxygenated Organic Aerosols

Heterogeneous oxidative aging of organic aerosols (OA) occurs ubiquitously in the atmosphere, initiated by oxidants, such as the hydroxyl radicals (•OH). Hydroperoxyl radicals (HO2•) are also an important oxidant in the troposphere, and its gas-phase chemistry has been well studied. However, the role of HO2• in heterogeneous OA oxidation remains elusive. Here, we carry out •OH-initiated heterogeneous oxidation of several OA model systems under different HO2• conditions in a flow tube reactor and characterize the molecular oxidation products using a suite of mass spectrometry instrumentation. By using hydrogen-deuterium exchange (HDX) with thermal desorption iodide-adduct chemical ionization mass spectrometry, we provide direct observation of organic hydroperoxide (ROOH) formation from heterogeneous HO2• and peroxy radicals (RO2•) reactions for the first time. The ROOH may contribute substantially to the oxidation products, varied with the parent OA chemical structure. Furthermore, by regulating RO2• reaction pathways, HO2• also greatly influence the overall composition of the oxidized OA. Last, we suggest that the RO2• + HO2• reactions readily occur at the OA particle interface rather than in the particle bulk. These findings provide new mechanistic insights into the heterogeneous OA oxidation chemistry and help fill the critical knowledge gap in understanding atmospheric OA oxidative aging.

Sources of elevated organic acids in the mountainous background atmosphere of southern China

Formic acid (FA) and acetic acid (AA) are pivotal organic acids in the troposphere, significantly influencing atmospheric chemistry. However, their abundance and sources in the mountainous background atmosphere remain underexplored. We undertook continuous measurements of FA and AA in Nanling mountains, southern China, during autumn 2020 using a high-resolution time-of-flight chemical ionization mass spectrometer (HR-ToF-CIMS). Both acids registered higher concentrations than in other global high-altitude or forested locations, averaging at 0.89 (max: 3.91) and 0.95 (max: 3.52) ppbv for FA and AA, respectively. High concentrations of FA and AA in this forested background area arose from secondary formation and biomass burning, collectively contributing 71 % to 89 %. During episodes, FA and AA concentrations surged 2-3 times, owing to the enhanced atmospheric oxidation capacity. The secondary FA production was predominantly due to isoprene oxidation among the VOC precursors studied. However, observed inconsistencies between calculated and actual FA concentrations suggest overlooked precursors or mechanisms warranting further investigation. Our findings can enhance the understanding of organic acid characteristics and the interplay of biogenic and anthropogenic sources in the background atmosphere.

Investigation on ozone formation mechanism and control strategy of VOCs in petrochemical region: Insights from chemical reactivity and photochemical loss

To investigate disparities in VOCs pollution characteristics, O3 generation activity, and source apportionment outcomes resulting from photooxidation, online monitoring of 106 VOCs was conducted in Jinshan District, Shanghai from April to October 2020. The observed VOCs concentrations (VOCs-obs) were 47.1 ppbv and 59.2 ppbv for clear days (CD) and O3-polluted days (OPD), respectively. The increase in daytime concentrations of alkenes is a significant factor contributing to the enhanced atmospheric photochemical activity during the OPD period, corroborated by VOCs-loss, ozone formation potential (OFP), propy-equiv concentration, and LOH. The sensitivity analysis of O3-NOx-VOCs indicated that O3 formation was in a transitional regime towards NOx-limited conditions. The results of positive matrix factorization (PMF) demonstrated that refining and petrochemicals (20.8-25.0 %), along with oil and gas evaporation (15.6-16.7 %) were the main sources of VOCs concentrations. Notably, source apportionment based on VOCs-obs underestimated the contributions from sources of reactive components. It is worth highlighting that the sunlight impact & background source was identified as the major contributor to LOH (21.6 %) and OFP (25.3 %), signifying its significant role in O3 formation. This study reiterates the importance of controlling reactive VOC components to mitigate O3 pollution and provides a scientific foundation for air quality management, with emphasis on priority species and controlling sources.

Nonlinear effect of NOx concentration decrease on secondary aerosol formation in the Beijing-Tianjin-Hebei region: Evidence from smog chamber experiments and field observations

During the COVID-19 lockdown in the Beijing-Tianjin-Hebei (BTH) region in China, large decrease in nitrogen oxides (NOx) emissions, especially in the transportation sector, could not avoid the occurrence of heavy PM2.5 pollution where nitrate dominated the PM2.5 mass increase. To experimentally reveal the effect of NOx control on the formation of PM2.5 secondary components (nitrate in particular), photochemical simulation experiments of mixed volatile organic compounds (VOCs) under various NOx concentrations with smog chamber were performed. The proportions of gaseous precursors in the control experiment were comparable to ambient conditions typically observed in the BTH region. Under relatively constant VOCs concentrations, when the initial NOx concentration was reduced to 40% of that in the control experiment (labelled as NOx,0), the particle mass concentration was not significantly reduced, but when the initial NOx concentration decreased to 20 % of NOx,0, the mass concentration of particles as well as nitrate and organics showed a sudden decrease. A "critical point" where the mass concentration of secondary aerosol started to decline as the initial NOx concentration decreased, located at 0.2-0.4 NOx,0 (or 0.18-0.44 NO2,0) in smog chamber experiments. The oxidation capacity and solar radiation intensity played key roles in the mass concentration and compositions of the formed particles. In field observations in the BTH region in the autumn and winter seasons, the "critical point" exist at 0.15-0.34 NO2,0, which coincided mostly with the laboratory simulation results. Our results suggest that a reduction of NOx emission by >60% could lead to significant reductions of secondary aerosol formation, which can be an effective way to further alleviate PM2.5 pollution in the BTH region.

Characteristics and sources of oxygenated VOCs in Hong Kong: Implications for ozone formation

To investigate the characteristics of oxygenated volatile organic compounds (OVOCs) and their potential contribution to ozone (O3) generation, we conducted 3-h high-resolution observations during the summertime of 2022 and the wintertime of 2021. This study focused on a total of 28 OVOCs in five different chemical classes, which were encompassed at two representative sites in Hong Kong, including a roadside and an urban area. During the summertime, the total concentrations of quantified OVOCs (∑OVOCs) were 45 ± 12 and 63 ± 20 μg m-3 at the roadside and urban sites, respectively, whereas the ∑OVOCs decreased by 31 ± 11 % and 38 ± 13 %, respectively, during the wintertime. Among the classes of OVOCs, carbonyls and alcohols were the two predominant at both sites, with relatively higher concentration levels of acetone, methanol, butanaldehyde, and acrolein. The sources of OVOCs have significant spatial and temporal characteristics. Spatially, OVOCs were predominately attributed to primary emission and background at the roadside site, whereas they were a combination of primary emission, secondary formation, and background at the urban site. Temporally, background sources dominated the summertime OVOCs, while the contribution of primary emissions increased for the wintertime OVOCs. The O3 formation potential (OFP) for the OVOCs was calculated. The OFPs were 67 ± 16 and 119 ± 31 μg m-3 at the roadside and urban sites during the summertime, whereas the winter OFPs declined 30 % at the roadside and 38 % at the urban site. The background sources of carbonyls and alcohols at the roadside and of carbonyls and acrylates in the urban area were the major contributors to the summer OFP. Controlling the OVOC sources from local non-combustion sources such as gasoline-fuel evaporation and volatile chemical-containing products could lead to a reduction of OVOCs in the background and subsequently mitigate the OFP. This is beneficial for local O3 reduction in Hong Kong and surrounding regions.

Long-term prediction of the effects of climate change on indoor climate and air quality

Limiting the negative impact of climate change on nature and humans is one of the most pressing issues of the 21st century. Meanwhile, people in modern society spend most of the day indoors. It is therefore surprising that comparatively little attention has been paid to indoor human exposure in relation to climate change. Heat action plans have now been designed in many regions to protect people from thermal stress in their private homes and in public buildings. However, in order to be able to plan effectively for the future, reliable information is required about the long-term effects of climate change on indoor air quality and climate. The Indoor Air Quality Climate Change (IAQCC) model is an expediant tool for estimating the influence of climate change on indoor air quality. The model follows a holistic approach in which building physics, emissions, chemical reactions, mold growth and exposure are combined with the fundamental parameters of temperature and humidity. The features of the model have already been presented in an earlier publication, and it is now used for the expected climatic conditions in Central Europe, taking into account various shared socioeconomic pathway (SSP) scenarios up to the year 2100. For the test house examined in this study, the concentrations of pollutants in the indoor air will continue to rise. At the same time, the risk of mold growth also increases (the mold index rose from 0 to 4 in the worst case for very sensitive material). The biggest problem, however, is protection against heat and humidity. Massive structural improvements are needed here, including insulation, ventilation, and direct sun protection. Otherwise, the occupants will be exposed to increasing thermal discomfort, which can also lead to severe heat stress indoors.

Impact of temperature-dependent non-PAN peroxynitrate formation, RO2NO2, on nighttime atmospheric chemistry

The formation of peroxynitrates (RO2NO2) from the reaction of peroxy radicals (RO2) and nitrogen dioxide (NO2) and their subsequent redissociation are typically not included in chemical mechanisms. This is often done to save computational time as the assumption is that the equilibrium is strongly towards the RO2 + NO2 reaction for most conditions. Exceptions are the reactions of the methyl peroxy radical due to its abundance in the atmosphere and of acyl-RO2 radicals due to the long lifetime of peroxyacyl nitrates RO2NO2 (PANs). In this study, the nighttime oxidation of cis-2-butene and trans-2-hexene in the presence of NO2 is investigated in the atmospheric simulation chamber SAPHIR, Forschungszentrum Jülich, Germany, at atmospherically-relevant conditions at different temperatures (≈276 K, ≈293 K, ≈305 K). Measured concentrations of peroxy and hydroperoxy radicals as well as other trace gases (ozone, NO2, volatile organic compounds) are compared to state-of-the-art zero-dimensional box model calculations. Good model-measurement agreement can only be achieved when reversible RO2 + NO2 reactions are included for all RO2 species using literature values available from the latest SAR by [Jenkin et al., Atmos. Chem. Phys., 2019, 19, 7691]. The good agreement observed gives confidence that the SAR, derived originally for aliphatic RO2, can be applied to a large range of substituted RO2 radicals, simplifying generalised implementation in chemical models. RO2NO2 concentrations from non-acyl RO2 radicals of up to 2 × 10 cm-3 are predicted at 276 K, impacting effectively the kinetics of RO2 radicals. Under these conditions, peroxy radicals are slowly regenerated downwind of the pollution source and may be lost in the atmosphere through deposition of RO2NO2. Based on this study, 60% of RO2 radicals would be stored as RO2NO2 at a temperature of 10 °C and in the presence of a few ppbv of NO2. The fraction increases further at colder temperatures and/or higher NO2 mixing ratios. This does not only affect the expected concentrations of RO2 radicals but, as the peroxynitrates can react with OH radicals or photolyse, they could comprise a net sink for RO2 radicals as well as increase the production of NOx (= NO + NO2) in different locations depending on their lifetime. Omitting this chemistry from the kinetic model can lead to misinterpreted product formation and may prevent reconciling observations and model predictions.

Characterization of a smog chamber for studying formation of gas-phase products and secondary organic aerosol

Smog chambers provide a potent approach to explore the secondary organic aerosol formation under varied conditions. This study describes the construction and characterization of a new smog chamber facility for studying the formation mechanisms of gas-phase products and secondary organic aerosol from the photooxidation of volatile organic compounds. The chamber is a 5.4 m3 Fluorinated Ethylene Propylene (FEP) Teflon reactor with the potential to perform photooxidation experiments at controlled temperature and relative humidity. Detailed characterizations were conducted for evaluation of stability of environmental parameters, mixing time, background contamination, light intensity, and wall losses of gases and particles. The photolysis rate of NO2 (JNO2) ranged from (1.02-3.32) ×10-3 sec-1, comparable to the average JNO2 in ambient environment. The wall loss rates for NO, NO2, and O3 were 0.47 × 10-4, 0.37 × 10-4, and 1.17 × 10-4 min-1, while wall loss of toluene was obsoletely found in a 6 hr test. The particle number wall loss rates are (0.01-2.46) ×10-3 min-1 for 40-350 nm with an average lifetime of more than one day. A series of toluene photooxidation experiments were carried out in absence of NOx under dry conditions. The results of the simulation experiments demonstrated that the chamber is well designed to simulate photolysis progress in the atmosphere.

Effects of NO2 and SO2 on the secondary organic aerosol formation from β-pinene photooxidation

Elucidating the effects of anthropogenic pollutants on the photooxidation of biogenic volatile organic compounds is crucial to understanding the fundamental mechanisms of secondary organic aerosol (SOA) formation. Here, the impacts of NO2 and SO2 on SOA formation from the photooxidation of a representative monoterpene, β-pinene, were investigated by a number of laboratory studies. The results indicated NO2 enhanced the SOA mass concentrations and particle number concentrations under both low and high β-pinene conditions. This could be rationalized that the increased O3 concentrations upon the NOx photolysis was helpful for the generation of more amounts of O3-oxidized products, which accelerated the SOA nucleation and growth. Combing with NO2, the promotion of the SOA yield by SO2 was mainly reflected in the increase of mass concentration, which might be due to the elimination of the newly formed particles by the initially formed particles. The observed low oxidation degree of SOA might be attributed to the fast growth of SOA, resulting in the uptake of less oxygenated gas-phase species onto the particle phase. The present findings have important implications for SOA formation affected by anthropogenic-biogenic interactions in the ambient atmosphere.

Comparison of the ozone formation mechanisms and VOCs apportionment in different ozone pollution episodes in urban Beijing in 2019 and 2020: Insights for ozone pollution control strategies

Ground-level ozone (O3) pollution has been a tough issue in urban areas of China in the past decade. Clarifying the formation mechanisms of O3 and the sources of its precursors is necessary for the effective prevention of O3 pollution. In this study, a comparative analysis of O3 formation mechanisms and VOCs apportionment for five O3 pollution episodes was carried out at two urban sites (CRAES and CGZ) in Beijing in 2019 and 2020 by applying an observation-based modeling approach in order to obtain insights into O3 pollution control strategies. Results indicated that O3 pollution levels were generally more severe in 2019 than in 2020 during the observation periods. O3 formation at the two sites was both VOCs-limited on O3 polluted days and non-O3 polluted days. Stronger atmospheric oxidation capacity and ROx radicals cycling processes were found on O3 polluted days which could accelerate the local production of O3, and local photochemical production dominated the observed O3 concentrations at the two sites even on non-O3 polluted days. Emission reduction of VOCs should be a priority for mitigating O3 pollution, and alkenes and biogenic VOCs was the priority species at the CRAES and CGZ sites, respectively. Additionally, the reduction of oxygenated VOCs should also be important for the ozone control. Gasoline exhaust at the CRAES site, and solvent utilization and fuel evaporation at the CGZ site were main anthropogenic sources of VOCs. Therefore, local control measures should be further strengthened and differentiated control strategies of VOCs in the aspects of area, time, sources and species should be adopted in urban Beijing in the future. Overall, the findings of this study could provide a scientific understanding of the causes of O3 pollution and significant guidelines for formulating O3 control strategies from the perspective of different ozone pollution episodes in urban Beijing.

ON-SITE monitoring OF BVOCS emission in Tremiti island, Italy

A measurement campaign was conducted on San Domino Island, part of the Tremiti Islands archipelago, located in Foggia, Italy. The area is almost entirely covered by vegetation, dominated by the following main species: Juniperus turbinata, Helichrysum italicum, Myrtus communis, Rosmarinus officinalis, Pistacia lentiscus and Pinus halepensis.This study focused on the BVOCs emitted by plants and the ground, employing a simple, economical, and efficient sampling and analysis method. The main known BVOC species emitted by Mediterranean plant species as α-pinene, β-pinene, camphene and limonene were detected. The measurements highlighted a daily complementarity between plant and soil emissions. The daily variations in BVOCs emitted by both plants and the soil are differ, ensuring an almost constant concentration throughout the day. At the same time, the composition of sea spray aerosol (SSA) was also measured. The measurement sites were selected based on botanical characterization to account for the predominant species on San Domino Island, and the sampling was conducted at human height to accurately identify the species for potential use. The combination of beneficial effects of the substances emitted by plant species and soil, along with the simultaneous presence of SSA, are factors that could enhance the effectiveness of forest therapy in a previously unexplored location.

Origin and transformation of volatile organic compounds at a regional background site in Hong Kong: Varied photochemical processes from different source regions

Volatile organic compounds (VOCs) are important gaseous constituents in the troposphere, impacting local and regional air quality, human health, and climate. Oxidation of VOCs, with the participation of nitrogen oxides (NOx), leads to the formation of tropospheric ozone (O3). Accurately apportioning the emission sources and transformation processes of ambient VOCs, and effectively estimation of OH reactivity and ozone formation potential (OFP) will play an important role in reducing O3 pollution in the atmosphere and improving public health. In this study, field measurements were conducted at a regional background site (Hok Tsui; HT) in Hong Kong from October to November 2020 with proton-transfer-reaction time-of-flight mass spectrometry (PTR-ToF-MS). VOC data coupled with air mass back trajectory cluster analysis and receptor modelling were applied to reveal the pollution pattern, emission sources and transformation of ambient VOCs at HT in autumn 2020. Seven sources were identified by positive matrix factorization (PMF) analysis, namely vehicular + industrial, solvent usage, primary oxygenated VOCs (OVOCs), secondary OVOCs 1, secondary OVOCs 2 (aged), biogenic emissions, and background + biomass burning. Secondary formation and vehicular + industrial emissions are the vital sources of ambient VOCs at HT supersite, contributing to 20.8 % and 46.7 % of total VOC mixing ratios, respectively. Integrated with backward trajectory analysis and correlations of VOCs with their oxidation products, short-range transport of air masses from inland regions of southeast China brought high levels of total VOCs but longer-range transport of air masses brought more secondary OVOCs in aged air masses. Photolysis of OVOCs was the most important contributor to OH reactivity and OFP, among which aldehyde was the dominant contributor. The results of this study highlight the photochemical processing of VOCs from different source regions which should be considered in strategy making for pollution reduction.

Comprehensive observations of carbonyls of Mt. Hua in Central China: Vertical distribution and effects on ozone formation

Oxygenated volatile organic compounds (OVOCs) play important roles in tropospheric chemistry, regulating the oxidation capacity and ozone (O3) formation potential of the atmosphere. However, the evolution of OVOCs composition during vertical transport from the near surface to the upper atmosphere layer and the roles of OVOCs in the alpine atmospheric O3 formation are still poorly understood. In this study, we investigated the carbonyl compounds, the most important chemical group of OVOCs, and other gaseous pollutants simultaneously collected at the top (2060 m a.s.l, Top) and the foot (402 m a.s.l, Foot) of Mt. Hua in August 2020. The average concentrations of the total quantified carbonyl compounds (∑carbonyls) at the Top and Foot were 16.05 ± 3.69 and 15.32 ± 5.63 ppbv, respectively. Acetone was the most abundant carbonyl (4.19 ± 1.01 ppbv) at the Top, followed by formaldehyde and n-Nonanal, accounting for ∼58.8 % of ∑carbonyls, while formaldehyde (5.40 ± 2.26 ppbv), acetone, and acetaldehyde were the three most abundant species at the Foot, accounting for 64.7 % of ∑carbonyls. The n-Nonanal, acetone and acetaldehyde showed positive correlations between the Top and Foot during daytime, confirming the vertical transport of carbonyls from the foot to the top of Mt. Hua under the influence of valley winds. The direct emissions from vegetation, transport processes of anthropogenic emissions and photochemical oxidation contributed significantly to the measured carbonyls at the Top, especially for acetone. Formaldehyde, acetaldehyde, glyoxal, and methylglyoxal were the most important contributors to the O3 generation in Mt. Hua. This study could advance our understanding of the vertical distribution of the carbonyls and the effects on O3 formation in the alpine region of China.

Identification of volatile organic compounds and their sources driving ozone and secondary organic aerosol formation in NE Spain

Volatile organic compounds (VOCs) play a crucial role in the formation of ozone (O3) and secondary organic aerosol (SOA). We conducted measurements of VOC ambient mixing ratios during both summer and winter at two stations: a Barcelona urban background station (BCN) and the Montseny rural background station (MSY). Subsequently, we employed positive matrix factorization (PMF) to analyze the VOC mixing ratios and identify their sources. Our analysis revealed five common sources: anthropogenic I (traffic & industries); anthropogenic II (traffic & biomass burning); isoprene oxidation; monoterpenes; long-lifetime VOCs. To assess the impact of these VOCs on the formation of secondary pollutants, we calculated the ozone formation potential (OFP) and secondary organic aerosol formation potential (SOAP) associated with each VOC. In conclusion, our study provides insights into the sources of VOCs and their contributions to the formation of ozone and SOA in NE Spain. The OFP was primarily influenced by anthropogenic aromatic compounds from the traffic & industries source at BCN (38-49 %) and during winter at MSY (34 %). In contrast, the summer OFP at MSY was primarily driven by biogenic contributions from monoterpenes and isoprene oxidation products (45 %). Acetaldehyde (10-35 %) and methanol (13-14 %) also made significant OFP contributions at both stations. Anthropogenic aromatic compounds originating from traffic, industries, and biomass burning played a dominant role (88-93 %) in SOA formation at both stations during both seasons. The only exception was during the summer at MSY, where monoterpenes became the primary driver of SOA formation (41 %). These findings emphasize the importance of considering both anthropogenic and biogenic VOCs in air quality management strategies.

Theoretical study on the potential environmental and ecological risk of 4-ethylphenol induced by hydroxyl radical

This study closely examines the environmental fate of 4-ethylphenol (4-EP), a significant byproduct of biomass combustion. We employed quantum chemical calculations to investigate the reaction mechanism, kinetics, and ecotoxicity of 4-EP initiated by OH radicals in various environments (aqueous, atmospheric liquid, atmospheric and inhomogeneous phases). Our findings highlight that solvent effects contribute to a higher OH-addition reaction branching ratio (Γadd) of 0.68 for 4-EP in an aqueous solution, compared to 0.26 in the gas-phase environment and 0.22 in the inhomogeneous environment at 298 K. We determined the rate constants for the liquid-phase, gas-phase, and nonhomogeneous phase to be 1.14 × 109 s-1 M-1, 3.09 × 109 s-1 M-1, and 6.19 × 1014 s-1 M-1, respectively. Notably, the adsorption of mineral particles considerably enhances the reaction rate of 4-EP with OH radicals. 4-ethylbenzene-1,2-diol, 4-hydroxycyclohexa-3,5-diene-1,2-dione, 1-ethyl-6-methyl-6H-benzo(c)chromene-4,9-diol, 5-ethyl-6'-(1-hydroxyethyl)-(1,1'-biphenyl)-2,3,3'-triol and 2-ethyl-4,6,9-trimethyl-6H-benzo(c) chromene are major products in both gas-phase and liquid-phase reactions, and (2Z, 4Z)-4-ethyl-6-oxohexa-2,4-dienoic acid is also one of the major products in gas-phase reactions. Toxicological predictions indicate that the ecotoxicity of 4-ethyl-6-methyl-6H-benzo(c)chromene-1,9-diol, 2-ethyl-6-methyl-6H-benzo(c)chromene-3,9-diol, and 2-ethyl-4,6,9-trimethyl-6H-benzo(c) chromene surpassed that of 4-EP. However, the toxicity of the reaction products is reduced in the presence of NOx. This investigation provides an exhaustive theoretical foundation for comprehending the degradation behavior of 4-EP and underscores the need to consider various environmental factors in assessing the potential risk of biomass combustion by products.

Kinetic and mechanism of the reaction between Cl and several mono-methyl branched alkanes

Branched alkanes are ubiquitous in the troposphere and play an important role in the chemical processes. In this work, the rate constants and products for the reaction of Cl atoms with 3-methylhexane and 2-methylheptane were measured at room temperature (298 ± 0.2 K) and atmospheric pressure using a conventional relative rate method. The rate constants of 3-methylhexane and 2-methylheptane in units of cm3/(mol·sec) are (3.09 ± 0.31) × 10-10 and (3.67 ± 0.40) × 10-10, respectively. Furthermore, the corresponding atmospheric lifetime of the studied branched alkanes with Cl was 6.92-89.90 hours and 5.82-75.69 hours, respectively. The estimated atmospheric lifetimes indicated that the reaction with Cl atoms could be the most important atmospheric degradation pathway for 3-methylhexane and 2-methylheptane. Primary gas-phase products of the reactions were identified and quantified, and particle-phase products were also obtained. The atmosphere oxidation mechanism of Cl atoms with 3-methylhexane and 2-methylheptane is proposed. The SOA yields of 3-methylhexane and 2-methylheptane from the reaction of Cl atoms were determined to be 7.96% ± 0.89% and 13.35% ± 1.50% respectively. Overall, the results reveal that the primary loss process of branched alkanes is the reaction with Cl atoms, which impacts its degradation on a regional scale.

Drivers and impacts of decreasing concentrations of atmospheric volatile organic compounds (VOCs) in Beijing during 2016-2020

China has implemented various policies and measures for controlling air pollutants. However, our knowledge of the long-term trends in ambient volatile organic compounds (VOCs) after the implementation of these action plans in China remains limited. To address this, we conducted a five-year analysis (2016-2020) of VOC compositions and concentrations in Beijing. The annual VOC concentration decreased from 44.0 ± 28.8 to 26.2 ± 16.4 ppbv, with alkanes being the most prevalent group. The annual average concentrations of alkenes, alkynes, and aromatics have experienced a significant decrease of over 50 %. Seasonal variations indicated higher VOC concentrations in winter and autumn, with more significant reductions observed in winter and autumn. The impact of meteorological conditions caused variations in VOC reductions during the Chinese Spring Festival. Satellite-based measurements of formaldehyde (HCHO) columns confirmed the reduction of VOC emissions during the Coronavirus (COVID-19) lockdown. The normalized annual average VOC concentration decreased by 2.9ppbv yr-1 from 2016 to 2020, and emission reduction contributed to 58.8 % of VOC reduction from 2016 to 2020 after meteorological normalization, indicating the effectiveness of implemented control measures. Based on receptor model, vehicle emissions and industrial sources were identified as the largest contributors to VOC concentrations. Vehicle emissions, liquefied petroleum gas/natural gas (LPG/NG) use, and coal combustion were major drivers of VOC reduction. Potential source region analysis revealed that air masses transported from northwestern and southern regions significantly contributed to VOC concentrations in Beijing. The range of source regions shrunk in both northwestern and southern regions with the reduction in VOC concentrations. The annual variations of ozone formation potential indicated a significant decrease in VOC reactivities through emission control. These results could provide insights into future emission control and coordinated efforts to improve PM2.5 and ozone levels in China.

VOC emitted by biopharmaceutical industries: Source profiles, health risks, and secondary pollution

The biopharmaceutical industry contributes substantially to volatile organic compounds (VOCs) emissions, causing growing concerns and social developmental conflicts. This study conducted an on-site investigation of the process-based emission of VOCs from three biopharmaceutical enterprises. In the workshops of the three enterprises, 26 VOCs were detected, which could be sorted into 4 classes: hydrocarbons, aromatic hydrocarbons, oxygen-containing compounds, and nitrogen-containing compounds. Ketones were the main components of waste gases, accounting for 44.13%-77.85% of the overall VOCs. Process-based source profiles were compiled for each process unit, with the fermentation and extraction units of tiamulin fumarate being the main source of VOC emissions. Dimethyl heptanone, vinyl acetate, diethylamine, propylene glycol methyl ether (PGME), and benzene were screened as priority pollutants through a fuzzy comprehensive evaluation system. Ground level concentration simulation results of the Gauss plume diffusion model demonstrated that the diffusivity of VOCs in the atmosphere was relatively high, indicating potential non-carcinogenic and carcinogenic risks 1.5-2 km downwind. Furthermore, the process-based formation potentials of ozone and secondary organic aerosols (SOAs) were determined and indicated that N-methyl-2-pyrrolidone, dimethyl heptanone, and PGME should be preferentially controlled to reduce the ozone formation potential, whereas the control of benzene and chlorobenzene should be prioritized to reduce the generation of SOAs. Our results provide a basis for understanding the characteristics of VOC emission by biopharmaceutical industries and their diffusion, potentially allowing the development of measures to reduce health risks and secondary pollution.

A study on wildfire impacts on greenhouse gas emissions and regional air quality in South of Orléans, France

Wildfire events are increasing globally which may be partly associated with climate change, resulting in significant adverse impacts on local, regional air quality and global climate. In September 2020, a small wildfire (burned area: 36.3 ha) event occurred in Souesmes (Loir-et-Cher, Sologne, France), and its plume spread out over 200 km on the following day as observed by the MODIS satellite. Based on measurements at a suburban site (∼ 50 km northwest of the fire location) in Orléans and backward trajectory analysis, young wildfire plumes were characterized. Significant increases in gaseous pollutants (CO, CH4, N2O, VOCs, etc.) and particles (including black carbon) were found within the wildfire plumes, leading to a reduced air quality. Emission factors, defined as EF (X) = ∆X/∆CO (where, X represents the target species), of various trace gases and black carbon within the young wildfire plumes were determined accordingly and compared with previous studies. Changes in the ambient ions (such as ammonium, sulfate, nitrate, chloride, and nitrite in the particle- and gas- phase) and aerosol properties (e.g., aerosol water content, aerosol pH) were also quantified and discussed. Moreover, we estimated the total carbon and climate-related species (e.g., CO2, CH4, N2O, and BC) emissions and compared them with fire emission inventories. Current biomass burning emission inventories have uncertainties in estimating small fire burned areas and emissions. For instance, we found that the Global Fire Assimilation System (GFAS) may underestimate emissions (e.g., CO) of this small wildfire while other inventories (GFED and FINN) showed significant overestimation. Considering that it is the first time to record wildfire plumes in this region, related atmospheric implications are presented and discussed.

Source apportionment and ozone formation mechanism of VOCs considering photochemical loss in Guangzhou, China

Understanding the sources and impact of volatile organic compounds (VOCs) on ozone formation is challenging when the traditional method does not account for their photochemical loss. In this study, online monitoring of 56 VOCs was carried out in summer and autumn during high ozone pollution episodes. The photochemical age method was used to evaluate the atmospheric chemical loss of VOCs and to analyze the effects on characteristics, sources, and ozone formation of VOC components. The initial concentrations during daytime were 5.12 ppbv and 4.49 ppbv higher than the observed concentrations in the summer and autumn, respectively. The positive matrix factorization (PMF) model identified 5 major emission sources. However, the omission of the chemical loss of VOCs led to underestimating the contributions of sources associated with highly reactive VOC components, such as those produced by biogenic emissions and solvent usage. Conversely it resulted in overestimating the contributions from VOC components with lower chemical activity such as liquefied petroleum gas (LPG) usage, vehicle emissions, and gasoline evaporation. Furthermore, the estimation of ozone formation may be underestimated when the atmospheric photochemical loss is not taken into account. The ozone formation potential (OFP) method and propylene-equivalent concentration method both underestimated ozone formation by 53.24 ppbv and 47.25 ppbc, respectively, in the summer, and by 40.34 ppbv and 26.37 ppbc, respectively, in the autumn. The determination of the ozone formation regime based on VOC chemical loss was more acceptable. In the summer, the ozone formation regime changed from the VOC-limited regime to the VOC-NOx transition regime, while in the autumn, the ozone formation regime changed from the strong VOC-limited regime to the weak VOC-limited regime. To obtain more thorough and precise conclusions, further monitoring and analysis studies will be conducted in the near future on a wider variety of VOC species such as oxygenated VOCs (OVOCs).

Source characterization of volatile organic compounds at Carlsbad Caverns National Park

Carlsbad Caverns National Park (CAVE), located in southeastern New Mexico, experiences elevated ground-level ozone (O3) exceeding the National Ambient Air Quality Standard (NAAQS) of 70 ppbv. It is situated adjacent to the Permian Basin, one of the largest oil and gas (O&G) producing regions in the US. In 2019, the Carlsbad Caverns Air Quality Study (CarCavAQS) was conducted to examine impacts of different sources on ozone precursors, including nitrogen oxides (NOx) and volatile organic compounds (VOCs). Here, we use positive matrix factorization (PMF) analysis of speciated VOCs to characterize VOC sources at CAVE during the study. Seven factors were identified. Three factors composed largely of alkanes and aromatics with different lifetimes were attributed to O&G development and production activities. VOCs in these factors were typical of those emitted by O&G operations. Associated residence time analyses (RTA) indicated their contributions increased in the park during periods of transport from the Permian Basin. These O&G factors were the largest contributor to VOC reactivity with hydroxyl radicals (62%). Two PMF factors were rich in photochemically generated secondary VOCs; one factor contained species with shorter atmospheric lifetimes and one with species with longer lifetimes. RTA of the secondary factors suggested impacts of O&G emissions from regions farther upwind, such as Eagle Ford Shale and Barnett Shale formations. The last two factors were attributed to alkenes likely emitted from vehicles or other combustion sources in the Permian Basin and regional background VOCs, respectively.Implications: Carlsbad Caverns National Park experiences ground-level ozone exceeding the National Ambient Air Quality Standard. Volatile organic compounds are critical precursors to ozone formation. Measurements in the Park identify oil and gas production and development activities as the major contributors to volatile organic compounds. Emissions from the adjacent Permian Basin contributed to increases in primary species that enhanced local ozone formation. Observations of photochemically generated compounds indicate that ozone was also transported from shale formations and basins farther upwind. Therefore, emission reductions of volatile organic compounds from oil and gas activities are important for mitigating elevated O3 in the region.

Observations of ozone, acyl peroxy nitrates, and their precursors during summer 2019 at Carlsbad Caverns National Park, New Mexico

Carlsbad Caverns National Park (CAVE) is located in southeastern New Mexico and is adjacent to the Permian Basin, one of the most productive oil and natural gas (O&G) production regions in the United States. Since 2018, ozone (O3) at CAVE has frequently exceeded the 70 ppbv 8-hour National Ambient Air Quality Standard. We examine the influence of regional emissions on O3 formation using observations of O3, nitrogen oxides (NOx = NO + NO2), a suite of volatile organic compounds (VOCs), peroxyacetyl nitrate (PAN), and peroxypropionyl nitrate (PPN). Elevated O3 and its precursors are observed when the wind is from the southeast, the direction of the Permian Basin. We identify 13 days during the July 25 to September 5, 2019 study period when the maximum daily 8-hour average (MDA8) O3 exceeded 65 ppbv; MDA8 O3 exceeded 70 ppbv on 5 of these days. The results of a positive matrix factorization (PMF) analysis are used to identify and attribute source contributions of VOCs and NOx. On days when the winds are from the southeast, there are larger contributions from factors associated with primary O&G emissions; and, on high O3 days, there is more contribution from factors associated with secondary photochemical processing of O&G emissions. The observed ratio of VOCs to NOx is consistently high throughout the study period, consistent with NOx-limited O3 production. Finally, all high O3 days coincide with elevated acyl peroxy nitrate abundances with PPN to PAN ratios > 0.15 ppbv ppbv-1 indicating that anthropogenic VOC precursors, and often alkanes specifically, dominate the photochemistry.Implications: The results above strongly indicate NOx-sensitive photochemistry at Carlsbad Caverns National Park indicating that reductions in NOx emissions should drive reductions in O3. However, the NOx-sensitivity is largely driven by emissions of NOx into a VOC-rich environment, and a high PPN:PAN ratio and its relationship to O3 indicate substantial influence from alkanes in the regional photochemistry. Thus, simultaneous reductions in emissions of NOx and non-methane VOCs from the oil and gas sector should be considered for reducing O3 at Carlsbad Caverns National Park. Reductions in non-methane VOCs will have the added benefit of reducing formation of other secondary pollutants and air toxics.

Characterization of photochemical losses of volatile organic compounds and their implications for ozone formation potential and source apportionment during summer in suburban Jinan, China

Volatile organic compounds (VOCs) undergo substantial photochemical losses during their transport from emission sources to receptor sites, resulting in serious implications for their source apportionment and ozone (O3) formation. Based on the continuous measurements of VOCs in suburban Jinan in August 2022, the effects of photochemical losses on VOC source contributions and O3 formation were evaluated in this study. The observed and initial concentrations of total VOCs (TVOC) were 12.0 ± 5.1 and 16.0 ± 7.4 ppbv, respectively. Throughout the observation period, alkenes had the most prominent photochemical losses (58.2%), followed by aromatic hydrocarbons (23.1%), accounting for 80.6% and 6.9% of the total losses, respectively. During high O3 episodes, the photochemical loss of VOCs was 6.9 times higher than that during the cleaning period. Alkene losses (exceeding 67.3%), specifically losses of isoprene, propylene, ethylene, and n-butene, dominated the total losses of VOCs during the O3 increase period. Eight sources of VOCs were identified by positive matrix factorization (PMF) based on the observed and initial concentration data (OC-PMF and IC-PMF, respectively). Concentrations of all emission sources in the OC-PMF were underestimated by 2.4%-57.1%. Moreover, the contribution of each emission source was over- or underestimated compared with that in case of the IC-PMF. The contributions of biogenic and motor vehicle exhaust emissions were underestimated by 5.3 and 2.8 percentage points, respectively, which was associated with substantial oxidation of the emitted high-reactive species. The contributions of coal/biomass burning and natural gas were overestimated by 2.4 and 3.9 percentage points, respectively, which were related to the emission of low-reactive species (acetylene, ethane, and propane). Based on our results, the photochemical losses of VOCs grossly affect their source apportionment and O3 formation. Thus, photochemical losses of VOCs must be thoroughly accounted to establish a precise scientific foundation for air-pollution control strategies.