Characteristics of carbonaceous aerosols: Impact of biomass burning and secondary formation in summertime in a rural area of the North China Plain

Sources and composition of elemental carbon during haze events in North China by a high time-resolved study

Despite the implementation of stringent emission reduction measures in the past year, severe winter haze events still occurred frequently in North China, with only marginal decreases observed in elemental carbon (EC) concentrations. EC not only constitutes a fraction of particle mass but also interacts with boundary layer and influences haze formation. Given the complex composition of EC, characterizing its sources and composition during haze processes is challenging yet crucial for understanding haze formation and evolution. Here, hourly-resolution PM2.5 samples were collected during three different haze event (P1-P3) in the North China Plain to investigate dynamic changes in EC source across different haze processes. The average EC concentrations and char/soot ratios were 9.94 ± 4.80 μgC·m-3, 14.5 ± 6.93 μgC·m-3, 15.9 ± 5.54 μgC·m-3, and 2.42 ± 0.98, 2.70 ± 0.88, 2.61 ± 0.95 for P1, P2 and P3, respectively. Backward trajectory analysis showed distinct variations in EC concentration and composition under the influence of different air masses during the three haze events, with local air masses influenced days exhibiting higher EC concentrations and char/soot ratios. The char/soot ratio based diagnostic method suggested that EC was predominantly influenced by coal combustion and vehicle emissions. Further positive matrix factorization analysis suggested that biomass burning and residential coal combustion were the main contributors of EC (58 %) and played a dominant role in driving variations in EC concentrations during haze episodes. Potential source contribution function analysis results highlight that local biomass burning and residential coal combustion could be major reason for the EC elevation in different haze events. Our results provide valuable insights into the sources and composition of EC during haze events, facilitating the implementation of effective measures for mitigating both EC and PM pollution.

Particulate organic nitrates at Mount Tai in winter and spring: Variation characteristics and effects of mountain-valley breezes and elevated emission sources

Particulate organic nitrates, among the major components of secondary organic aerosols and fine particles, play important roles in regional nitrogen cycle, ozone budget, and cloud condensation nuclei formation. However, the pollution characteristics of particulate organic nitrates at mountain areas and the effects of anthropogenic pollutant transport remain poorly understood. In this study, field sampling and measurements were conducted at a high-elevation mountain site over North China Plain in winter and spring. Total five kinds of particulate organic nitrates in fine particles were determined by ultra-high performance liquid chromatography-electrospray mass spectrometry. The average total concentrations of particulate organic nitrates were 330 ± 121 ng m^-3 and 247 ± 63 ng m^-3 in winter and spring. The monoterpene-derived organic nitrates were the dominant components in both seasons with their contribution higher than 70%, accounting for 1.2 ± 0.8% and 2.0 ± 1.0% in organic aerosols in winter and spring, respectively. The significantly higher levels of particulate organic nitrates in winter than spring was ascribed to the strong effects of mountain-valley breezes and coal combustion plumes. The increasing concentrations of NO_x and particulate matters brought by the valley breeze at daytime facilitated the formation of MHN215, OAKN359, and OAHN361, while the rising SO₂ abundance and the sulfate aerosols transported by elevated emission sources affected the formation of MDCN247 at nighttime.

Impacts of chemical degradation of levoglucosan on quantifying biomass burning contribution to carbonaceous aerosols: A case study in Northeast China

Biomass burning (BB) is an important source of carbonaceous aerosols in Northeast China (NEC). Quantifying the original contribution of BB to organic carbon (OC) [BB-OC] can provide an essential scientific information for the policy-makers to formulate the control measures to improve the air quality in the NEC region. Daily PM_2.5 samples were collected in the rural area of Changchun city over the NEC region from May 2017 to May 2018. In addition to carbon contents, BB tracers (e.g., levoglucosan and K⁺_BB, defined as potassium from BB) were also determined, in order to investigate the relative contribution of BB-OC. The results showed that OC was the dominant (28%) components of PM_2.5 during the sampling period. Higher concentrations of OC, levoglucosan, and K⁺_BB were observed in the autumn followed by the winter, spring, and summer, indicating that the higher BB activities during autumn and winter in Changchun. By using the Bayesian mixing model, it was found that burning of crop residues were the dominant source (65-79%) of the BB aerosols in Changchun. During the sampling period, the aging in air mass (AAM) ratio was 0.14, indicating that ~86% of levoglucosan in Changchun was degraded. Without considering the degradation of levoglucosan in the atmosphere, the BB-OC ratios were 23%, 28%, 7%, and 4% in the autumn, winter, spring, and summer, respectively, which were 1.4-4.8 time lower than those (14-42%) with consideration of levoglucosan degradation. This illustrated that the relative contribution of BB to OC would be underestimated (~59%) without considering degradation effects of levoglucosan. Although some uncertainty was existed in our estimation, our results did highlight that the control of straw burning was an efficient way to decrease the airborne PM_2.5, improving the air quality in the NEC plain.

Atmospheric Reactivity of Methoxyphenols: A Review

Methoxyphenols emitted from lignin pyrolysis are widely used as potential tracers for biomass burning, especially for wood burning. In the past ten years, their atmospheric reactivity has attracted increasing attention from the academic community. Thus, this work provides an extensive review of the atmospheric reactivity of methoxyphenols, including their gas-phase, particle-phase, and aqueous-phase reactions, as well as secondary organic aerosol (SOA) formation. Emphasis was placed on kinetics, mechanisms, and SOA formation. The reactions of methoxyphenols with OH and NO₃ radicals were the predominant degradation pathways, which also had significant SOA formation potentials. The reaction mechanism of methoxyphenols with O₃ is the cycloaddition of O₃ to the benzene ring or unsaturated C═C bond, while H-abstraction and radical adduct formation are the main degradation channels of methoxyphenols by OH and NO₃ radicals. Based on the published studies, knowledge gaps were pointed out. Future studies including experimental simulations and theoretical calculations of other representative kinds of methoxyphenols should be systematically carried out under complex pollution conditions. In addition, the ecotoxicity of their degradation products and their contribution to SOA formation from the atmospheric aging of biomass-burning plumes should be seriously assessed.

Existence and Formation Pathways of High- and Low-Maturity Elemental Carbon from Solid Fuel Combustion by a Time-Resolved Study

Elemental carbon (EC) from various sources contains different sub-fractions with different properties; however, this variability poses several challenges for the accurate assessment of EC emission inventory. EC is defined using thermo-optical analysis (TOA), and its different fractions have different maturation and formation pathways. High- and low-maturity ECs have similar detection signals to those of Soot-EC and Char-EC in TOA. The emission characteristics of Soot-EC and Char-EC were affected by fuel composition and combustion temperatures. Biomass combustion generated more Char-EC than coal combustion, resulting in lower Soot-EC to Char-EC ratios. Soot-EC emissions always increased with an increasing temperature. Char-EC emissions increased with an increasing temperature at 300-900 °C in biomass combustion and decreased in coal combustion when the temperature was >600 °C, suggesting that the two ECs have different formation pathways. Time-resolved analyses of organic carbon (OC), EC, and polycyclic aromatic hydrocarbons showed that Char-EC was preferentially generated in the ignition stage with the rapid emission of OC through direct conversion of OC, whereas Soot-EC was preferentially generated during the flaming stage through gas-phase polymerization of small molecules generated from the decomposition of OC.

Physicochemical and toxicological characteristics of nanoparticles in aerosols in southern Thailand during recent haze episodes in lower southeast Asia

Transboundary haze from biomass burning is one of the most important air pollutions in Southeast Asia. The most recent serious haze episode occurred in 2015. Southern Thailand was affected by the haze during September to October when the particulate matter concentration hit a record high. We investigated physical and chemical characteristics of aerosols, including concentration and aerosol size distribution down to sub-micron sizes during haze episodes in 2013 and 2015 and, for reference, an insignificant haze period in 2017. The highest total suspended particulates and PM₁₀ levels in Hat Yai city were 340.1 and 322.5 µg/m³. The mass fractions were nanoparticles (< 100 nm) 3.1%-14.8% and fine particles (< 1 µm) 54.6%-59.1%. Polycyclic aromatic hydrocarbon size distributions in haze periods peaked at 0.75 µm and the concentrations are 2-30 times higher than the normal period. High molecular weight (4-6 ring) PAHs during the haze episode contribute to about 56.7%-88.0% for nanoparticles. The average values of benzo(a)pyrene toxic equivalency quotient were 3.34±2.54ng/m³ in the 2015 haze period but only 0.89±0.17 ng/m³ in 2017. It is clear that particles smaller than 1 µm, were highly toxic. Nanoparticles contributed 19.4%-26.0% of total BaP-TEQ, whereas the mass fraction is 13.1%-14.8%. Thus the nanoparticles were more carcinogenic and can cause greater health effect than larger particles. The fraction of BaP-TEQ for nanoparticles during 2017 non-haze period was nearly the same, while the mass fraction was lower. This indicates that nanoparticles are the significant source of carcinogenic aerosols both during haze and non-haze periods.

A Climatological Satellite Assessment of Absorbing Carbonaceous Aerosols on a Global Scale

A global climatology of absorbing carbonaceous aerosols (ACA) for the period 2005–2015 is obtained by using satellite MODIS (Moderate Resolution Imaging Spectroradiometer)-Aqua and OMI (Ozone Monitoring Instrument)-Aura aerosol optical properties and by applying an algorithm. The algorithm determines the frequency of presence of ACA (black and brown carbon) over the globe at 1° × 1° pixel level and on a daily basis. The results of the algorithm indicate high frequencies of ACA (up to 19 days/month) over world regions with extended biomass burning, such as the tropical forests of southern and central Africa, South America and equatorial Asia, over savannas, cropland areas or boreal forests, as well as over urban and rural areas with intense anthropogenic activities, such as the eastern coast of China or the Indo-Gangetic plain. A clear seasonality of the frequency of occurrence of ACA is evident, with increased values during June–October over southern Africa, during July–November over South America, August–November over Indonesia, November–March over central Africa and November–April over southeastern Asia. The estimated seasonality of ACA is in line with the known annual patterns of worldwide biomass-burning emissions, while other features such as the export of carbonaceous aerosols from southern Africa to the southeastern Atlantic Ocean are also successfully reproduced by the algorithm. The results indicate a noticeable interannual variability and tendencies of ACA over specific world regions during 2005–2015, such as statistically significant increasing frequency of occurrence over southern Africa and eastern Asia.

Assessment of satellite-estimated near-surface sulfate and nitrate concentrations and their precursor emissions over China from 2006 to 2014

China is the largest anthropogenic aerosol-generating country worldwide; however, few studies have analyzed the PM_2.5 chemical components and their underlying precursor emissions over long periods and across the national domain. First, global 3-D tropospheric chemistry and transport model (GEOS-Chem)-integrated satellite-retrieved aerosol optical depth (AOD) and vertical profiles were used to estimate near-surface sulfate and nitrate levels at 10-km resolution over China from 2006 to 2014. Ground measurement validation of our satellite model yielded correlation coefficients (r) of 0.7 and 0.73 and normalized mean bias (NMB) values of -37.96% and - 32.73% for sulfate and nitrate, respectively. Second, analyses of the spatiotemporal distributions of sulfate and nitrate as well as the vertical density Ozone Monitoring Instrument (OMI)-measured SO₂ (PBL_SO₂) and NO₂ (TVCD_NO₂) indicated that the highest nitrate and sulfate levels occurred in the North China Plain (~25 μg/m³) and Sichuan Basin (SCB) (~30 μg/m³), respectively. The long-term variations in the estimated components and precursor gases indicated that the large sulfate decline was positively correlated with the SO₂ emission reduction due to the mandatory desulfurization implemented in 2007. The annual growth rate of sulfate relative to the national mean was -6.19%/yr, and the concentration decreased by 17.10% from 2011 to 2014. Energy consumption increases and a lack of control measures for NO₂ resulted in persistent increases in NO₂ emissions and nitrate concentrations from 2006 to 2010, particularly in the SCB. With energy consumption structure advancements, reductions in NO₂ emissions and corresponding nitrate levels over three typical regions were prominent after 2012. Third, the estimated national-scale uncertainties of satellite datasets at 0.1° × 0.1° were 26.88% for sulfate and 25.55% for nitrate. Differences in the spatial distributions and temporal trends between our estimated components and precursor gases were mainly attributed to the dataset accuracy, the data pre-processing strategy, inconsistent column density and near-surface mass concentration, meteorological variables and complex chemical reactions.

Secondary organic aerosols in Jinan, an urban site in North China: Significant anthropogenic contributions to heavy pollution

Secondary organic aerosols (SOAs) are an important component of particulates, but whether biogenic SOAs (BSOAs) or anthropogenic SOAs (ASOAs) are the dominant contributors to haze pollution remains poorly characterized. In this study, particulate samples were collected from September 2014 to August 2015 at an urban site in Jinan, which is the capital of Shandong Province and a typical city in the North China Plain. The PM_2.5 samples were analyzed for BSOA (isoprene (SOA_I) and monoterpenes (SOA_M)) and ASOA (aromatic (SOA_A)) tracers. The concentrations of the SOA_A tracer (1.1 ± 1.0 ng/m³) were lowest, and those of SOA_I tracers (41.8 ± 86.2 ng/m³) were highest, with the concentrations of SOA_M tracers (19.4 ± 9.9 ng/m³) being intermediate. The SOA_I tracers were more abundant in the summer and less abundant in the winter. Both SOA_I and SOA_M increased with increasing ozone level but decreased with increasing NOx level. Correlation analysis revealed a good correlation between 2,3-dihydroxy-4-oxopentanoic acid and levoglucosan levels in three seasons. These results suggested that biomass burning activities occurring in the NCP can enhance the emissions of aromatics and should be controlled, especially in the autumn and winter. SOA tracers were classified according to pollution degree, and the results showed that as pollution increases, the contributions of SOA_A increase. These results indicate that reducing anthropogenic emissions is necessary to prevent SOA pollution, especially during heavy pollution episodes.

Water-soluble ions in dust particles depending on meteorological conditions in urban environment

The particle size distribution of particulate matter (PM) and concentrations of water-soluble ions were observed in airborne aerosol in the City of Ostrava (the Czech Republic, Moravian-Silesian Region) during winter 2016. The Ostrava area ranks among the most polluted areas not only within the Czech Republic but also in Europe due to the high concentration of industry, especially metallurgy, in this area. The selected water-soluble ions: were studied in different grain size classes of particulate matter separated into 7 fractions (from 0.0175 to 9.93 μm) collected by an electrical low pressure impactor ELPI⁺. Assessment of the influence of meteorological parameters and various sources of contamination (transportation, industry, and residential burning) in heavily environmentally-burdened urban areas was attempted. This study proved that (K)⁺ is related to metallurgical processes and its role as an indicator of biomass combustion is negligible. The highest concentrations of all water-soluble ions were determined in particles below 0.952 μm that is generally related to combustion processes. At increased air temperature (in the interval from 0 °C to 10 °C), concentrations of both dust particles and the sum of water-soluble ions are decreasing.

Size distribution of bioaerosols from biomass burning emissions: Characteristics of bacterial and fungal communities in submicron (PM1.0) and fine (PM2.5) particles

The North China Plain is the agricultural heartland in China. High PM_2.5 levels and elevated chemical pollutants have been observed during crop harvest seasons due to open biomass burning. Biomass burning in the wheat-harvest season may significantly deteriorate the regional air quality. The harmful ingredients in smoke particles also have severe implications for toxicity and health effects. Previous studies have illustrated the potential role of bioaerosols as ice-nuclei and cloud condensation nuclei and highlighted their influence on biochemical cycles and human health effects. In a monthly field observation campaign of biomass burning conducted at the summit of Mount Tai in July 2015, we reported the composition, potential role, size distribution of microorganisms in particulate matters PM_1.0, PM_2.5, and estimated their contribution to particles. The wide-range particle spectrometer suggested that the predominant particles were distributed in submicron particles (PM_1.0), which resulted in a similar community structure for bacteria and fungi in PM_1.0 and PM_2.5. Among bacteria, the predominant Pseudomonas accounted for 18.06% and 21.29% in PM_1.0 and PM_2.5, respectively. Alternaria covered up to 69.01% and 72.76% of the fungal community in PM_1.0 and PM_2.5, respectively. A disparity between bacterial communities was identified by the abundance of rare species, such as Bacilli being higher in PM_1.0 (2.4%) than in PM_2.5 (1.8%), and Defluviicoccus being higher in PM_2.5 (2.5%) than in PM_1.0 (0.5%), which may be related to cell size and cell growth patterns. Quantitative PCR revealed that microbial cell numbers in PM_2.5 were higher than in PM_1.0, and that the bacterial cell number was about an order of magnitude greater than the fungal cell number. However, the mass concentration and contribution of fungi to particulate matter was much higher than that of bacteria, suggesting the underestimated role of fungi in atmospheric aerosols. Airborne microorganisms in alpine areas remained less characterized. The findings presented here illustrated the potentially important impacts on air quality and bioaerosol pollution by biomass burning, which provides an essential reference for understanding the transmission and health effects of bioaerosols.

Composition and origin of PM2.5 in Mediterranean Countryside

In this work PM_2.5 was collected during winter and summer in a Sardinian village (Gonnostramatza, Italy) highly affected by biomass burning emissions. A multi-technique approach was adopted for the complete PM chemical characterization. The bulk characterization was performed by IC (Ion Chromatography), HPAEC (High-Performance Anion-Exchange Chromatography), TOT (Thermal Optical Transmittance) and ED-XRF (Energy-Dispersive X-Ray Fluorescence) while XPS (X-ray Photoelectron Spectroscopy) was used for the surface characterization. Using levoglucosan as specific tracer of biomass burning emissions, the assessment of the impact of this source was carried out and it represent the major PM source at the investigate site during winter. In winter the average levoglucosan concentration is 2096 ± 324 ng/m³ while during summer its concentration is negligible (18 ± 7 ng/m³). Levoglucosan content in PM_2.5 during winter is on average 13.7%; it is estimated that 65% of PM_2.5 is due to wood burning. XPS has been exploited in this work aiming at highlighting possible differences between surface and bulk composition of PM_2.5. The surface of the particulate matter resulted enriched in carbon compared to the bulk. Among the components of XPS C1s signals recorded on the samples collected during winter, it was found that the signal at 286.5 eV, which is due to the presence of COH, reflects the bulk composition of levoglucosan.

Seasonal variation of chemical characteristics of fine particulate matter at a high-elevation subtropical forest in East Asia

The aim of this study was to chemically characterize the fine particulate matter (PM_2.5) at a subtropical forest in East Asia under the influences of anthropogenic and biogenic sources and a complex topographic setting. Four seasonal campaigns were conducted at the Xitou Experimental Forest in central Taiwan from the winter of 2013 to the autumn of 2014. The results indicated that the ambient levels and chemical features of PM_2.5 exhibited pronounced seasonal variations. Non-sea-salt sulfate (nss-SO₄^2-) constituted the major component of PM_2.5, followed by ammonium (NH₄⁺) and nitrate (NO₃^-) during winter, summer and autumn. However, it was revealed that the mass fraction of NO₃^- increased to be comparable with that of nss-SO₄^2- in springtime. The mass contribution of secondary organic carbon (SOC) to PM_2.5 peaked in summer (13.2%), inferring the importance of enhanced photo-oxidation reactions in SOC formation. Diurnal variations of O₃ and SO₂ coincided with each other, suggesting the transport of aged pollutants from distant sources, whereas CO and NO_x were shown to be under the influences of both local and regional sources. Notably high sulfur oxidation ratio (SOR) and nitrogen oxidation ratio (NOR) were observed, which were 0.93 ± 0.05 and 0.39 ± 0.20, respectively. Precursor gases (i.e. SO₂ and NO_x) could be converted to sulfate and nitrate during the transport by the uphill winds. Furthermore, due to the high relative humidity at Xitou, enhanced aqueous-phase and/or heterogeneous reactions could further contribute to the formation of sulfate and nitrate at the site. This study demonstrated the significant transport of urban pollutants to a subtropical forest by the mountain-valley circulations as well as the long-range transport from regional sources, whereas the implications of which for regional climate change necessitated further investigation.

Characteristics of atmospheric bacterial and fungal communities in PM2.5 following biomass burning disturbance in a rural area of North China Plain

Biomass burning (BB) in North China Plain has been urgent issue in recent years due to the severe environmental impaction. Bacteria and fungi are ubiquitous in particulate matter. Their taxonomic composition, concentration, ecophysiological functions have potentially important implications in atmospheric biochemical cycle and human health. However, current knowledge about airborne microbes during biomass burning period is scant. Here we investigated bacterial and fungal community composition, abundance and potential function in Yucheng, the center of the North China Plain during summer harvest season in 2014. Monthly field observation suggested serious pollution with high concentration of PM_2.5 and water-soluble ions during biomass burning period. Elevated total bacterial and fungal concentration determined by real-time quantitative PCR was observed for samples during burning events. The predominant bacterial taxa were gram-negative, e.g. Acinetobacter, Cyanobacterium, Janthinobacterium, Massilia, Pseudomonas, accounted for 70.9% of total bacteria. The filamentous fungi Alternaria, Aspergillus, Cladosporium and Penicillium were predominant fungal genera. Metastats analysis showed significant disparity in terms of carbohydrate, amino acids metabolism, human and plant disease predicted by PICRUSt analysis between BB and non-BB events. Microbial community structure were mainly influenced by organic carbon and water-soluble ions (magnesium and potassium) suggested by redundancy analysis (RDA) and co-occurrence analysis. Our data yielded insights into microbial community dynamics following biomass burning disturbance. This study may provide potentially important reference for environmental, agricultural and health management.

Partitioning of volatile organic compounds to aerosols: A review

Although volatile organic compounds (VOCs) exist mainly in the gas-phase rather than in aerosols, the concentrations of VOCs measured from aerosols are comparable to those of semi-volatile organic compounds, which preferentially partition into aerosols. VOCs that partition into aerosols may raise health effects that are generally not exerted by aerosols or by VOCs alone. So far, only scant reports on VOC/aerosol partitioning are available in the extant literature. In this review, we discuss findings presented in recent studies on the partition mechanism, factors affecting the partition process, existing knowledge gaps, and recommendations to help address these gaps for future research. Also, we have surveyed the different models that can be applied to predict partition coefficients and the inherent advantage and shortcoming of the assumptions in these models. A better understanding of the partition mechanism and partition coefficient of VOCs into aerosols can improve prediction of the global fate and transport of VOCs in the environment and enhance assessment of the health effects from exposure to VOCs.

Comparison of Measurement-Based Methodologies to Apportion Secondary Organic Carbon (SOC) in PM2.5: A Review of Recent Studies

Secondary organic aerosol (SOA) is known to account for a major fraction of airborne particulate matter, with significant impacts on air quality and climate at the global scale. Despite the substantial amount of research studies achieved during these last decades, the source apportionment of the SOA fraction remains difficult due to the complexity of the physicochemical processes involved. The selection and use of appropriate approaches are a major challenge for the atmospheric science community. Several methodologies are nowadays available to perform quantitative and/or predictive assessments of the SOA amount and composition. This review summarizes the current knowledge on the most commonly used approaches to evaluate secondary organic carbon (SOC) contents: elemental carbon (EC) tracer method, chemical mass balance (CMB), SOA tracer method, radiocarbon (14C) measurement and positive matrix factorization (PMF). The principles, limitations, challenges and good practices of each of these methodologies are discussed in the present article. Based on a comprehensive—although not exhaustive—review of research papers published during the last decade (2006–2016), SOC estimates obtained using these methodologies are also summarized for different regions across the world. Conclusions of some studies which are directly comparing the performances of different methodologies are then specifically discussed. An overall picture of SOC contributions and concentrations obtained worldwide for urban sites under similar conditions (i.e., geographical and seasonal ones) is also proposed here. Finally, further needs to improve SOC apportionment methodologies are also identified and discussed.

Trends in heterogeneous aqueous reaction in continuous haze episodes in suburban Shanghai: An in-depth case study

Heterogeneous aqueous reaction plays important roles in the enhanced formation of secondary aerosols during haze. However, its occurrence in haze episodes remains poorly understood. In this study, the trends in heterogeneous aqueous reaction in continuous haze episodes were investigated by an in-depth case analysis. The highly time-resolved measurements of water-soluble inorganic ions of PM_2.5 were conducted in a suburban of Shanghai, China, and continuous haze episodes, which occurred from Feb. 18 to Feb. 28, were selected as studied cases. Results showed that fine particle pollution in Baoshan was serious. High concentrations of secondary inorganic aerosol ions and the higher sulfur oxidation ratio (SOR) and nitrogen oxidation ratio (NOR) on haze days indicated enhanced conversions from SO₂ and NO_x to their corresponding particulate phases. The high-nitrate haze episode and the high-sulfate haze episode were identified. Further simulations revealed that the PM_2.5 particles had strong acidity during the high-nitrate and high-sulfate haze episodes whether they were calculated by E-AIM 4 or by ISORROPIA II. It was found that particulate liquid water was more sensitive to nitrate than sulfate, and played significant roles in the heterogeneous aqueous reactions of NO₂ and secondary nitrate formation during haze episodes, especially in the high-sulfate haze episode. Further analysis indicated that the high-nitrate haze episode favoured the occurrence of heterogeneous aqueous phase oxidation of SO₂, and the more water was in the particles, the more SO₂ was converted to sulfate aerosols. This work provides an important field measurement-based evidence for understanding the important contributions of the heterogeneous aqueous reactions to secondary aerosol pollution and the tendencies of heterogeneous aqueous reactions in the formation of secondary sulfate and nitrate aerosols in suburban Shanghai.

Nitro and oxy-PAHs bounded in PM2.5 and PM1.0 under different weather conditions at Mount Tai in Eastern China: Sources, long-distance transport, and cancer risk assessment

Fourteen nitro-PAHs and five oxy-PAHs associated with PM_2.5 and PM_1.0 were analyzed by GC-MS/MS at Mount Tai, China. 85% of the nitro-PAHs and 65% of oxy-PAHs were found in PM_1.0. The combined concentration of nitro-PAHs in PM_2.5 was highest in air masses associated with biomass burning (270.50pg/m³) compared with measurements from heavily polluted days (93.21pg/m³) and clean days (81.22pg/m³). A similar trend was also reflected in measurements of PM_1.0. 9-FO, 9,10-ANQ, and 1-NALD were the most abundant oxy-PAHs in both PM_2.5 and PM_1.0 at Mount Tai. The concentration of 2+3N-FLA was markedly increased compared with other species on heavily polluted days and biomass burning days, and 9N-ANT was more concentrated in measurements from days with biomass burning emissions. Secondary generation of nitro-PAHs was also more active during periods with biomass burning. The main formation pathway of nitro-PAHs during the sampling campaign was through reactions with OH radicals, but NO₃ radicals also played a significant role at night. The incremental lifetime cancer risk (ILCR) was highest during periods with biomass burning, indicating that biomass burning has a significant impact on human health. By analyzing the results of back trajectory clustering under different meteorological conditions, we determined that a large area of straw burning in the North China Plain (NCP) was the dominant source of nitro and oxy-PAHs at Mount Tai during the measurement campaign.

A Global Perspective of Fine Particulate Matter Pollution and Its Health Effects

Fine particulate matter (PM) in the ambient air is implicated in a variety of human health issues throughout the globe. Regulation of fine PM in the atmosphere requires information on the dimension of the problem with respect to variations in concentrations and sources. To understand the current status of fine particles in the atmosphere and their potential harmful health effects in different regions of the world this review article was prepared based on peer-reviewed scientific papers, scientific reports, and database from government organizations published after the year 2000 to evaluate the global scenario of the PM_2.5 (particles <2.5 μm in aerodynamic diameter), its exceedance of national and international standards, sources, mechanism of toxicity, and harmful health effects of PM_2.5 and its components. PM_2.5 levels and exceedances of national and international standards were several times higher in Asian countries, while levels in Europe and USA were mostly well below the respective standards. Vehicular traffic has a significant influence on PM_2.5 levels in urban areas; followed by combustion activities (biomass, industrial, and waste burning) and road dust. In urban atmosphere, fine particles are mostly associated with different health effects with old aged people, pregnant women, and more so children being the most susceptible ones. Fine PM chemical constituents severely effect health due to their carcinogenic or mutagenic nature. Most of the research indicated an exceedance of fine PM level of the standards with a diverse array of health effects based on PM_2.5 chemical constituents. Emission reduction policies with epidemiological studies are needed to understand the benefits of sustainable control measures for fine PM mitigation.

Contributions and source identification of biogenic and anthropogenic hydrocarbons to secondary organic aerosols at Mt. Tai in 2014

Ambient fine particulate matter (PM_2.5) and volatile organic compounds (VOCs) collected at Mt. Tai in summer 2014 were analysed and the data were used to identify the contribution of biogenic and anthropogenic hydrocarbons to secondary organic aerosols (SOA) and their sources and potential source areas in high mountain regions. Compared with those in 2006, the 2014 anthropogenic SOA tracers in PM_2.5 aerosols and VOC species related to vehicular emissions exhibited higher concentrations, whereas the levels of biogenic SOA tracers were lower, possibly due to decreased biomass burning. Using the SOA tracer and parameterisation method, we estimated the contributions from biogenic and anthropogenic VOCs, respectively. The results showed that the average concentration of biogenic SOA was 1.08 ± 0.51 μg m^-3, among which isoprene SOA tracers were dominant. The anthropogenic VOC-derived SOA were 7.03 ± 1.21 μg m^-3 and 1.92 ± 1.34 μg m^-3 under low- and high-NO_x conditions, respectively, and aromatics made the greatest contribution. However, the sum of biogenic and anthropogenic SOA only contributed 18.1-49.1% of the total SOA. Source apportionment by positive matrix factorisation (PMF) revealed that secondary oxidation and biomass burning were the major sources of biogenic SOA tracers. Anthropogenic aromatics mainly came from solvent use, fuel and plastics combustion and vehicular emissions. However, for > C6 alkanes and cycloalkanes, vehicular emissions and fuel and plastics combustion were the most important contributors. The potential source contribution function (PSCF) identified the Bohai Sea Region (BSR) as the major source area for organic aerosol compounds and VOC species at Mt. Tai.