Secondary organic aerosol association with cardiorespiratory disease mortality in the United States

Decomposing PM2.5 concentrations in urban environments into meaningful factors 2. Extracting the contribution of traffic-related exhaust emissions

Vehicle-emitted fine particulate matter (PM2.5) has been associated with significant health outcomes and environmental risks. This study estimates the contribution of traffic-related exhaust emissions (TREE) to observed PM2.5 using a novel factorization framework. Specifically, co-measured nitrogen oxides (NOx) concentrations served as a marker of vehicle-tailpipe emissions and were integrated into the optimization of a Non-negative Matrix Factorization (NMF) analysis to guide the factor extraction. The novel TREE-NMF approach was applied to long-term (2012-2019) PM2.5 observations from air quality monitoring (AQM) stations in two urban areas. The extracted TREE factor was evaluated against co-measured black carbon (BC) and PM2.5 species to which the TREE-NMF optimization was blind. The contribution of the TREE factor to the observed PM2.5 concentrations at an AQM station from the first location showed close agreement (R2=0.79) with monitored BC data. In the second location, a comparison of the extracted TREE factor with measurements at a nearby Surface PARTiculate mAtter Network (SPARTAN) station revealed moderate correlations with PM2.5 species commonly associated with fuel combustion, and a good linear regression fit with measured equivalent BC concentrations. The estimated concentrations of the TREE factor at the second location accounted for 7-11 % of the observed PM2.5 in the AQM stations. Moreover, analysis of specific days known to be characterized by little traffic emissions suggested that approximately 60-78 % of the traffic-related PM2.5 concentrations could be attributed to particulate traffic-exhaust emissions. The methodology applied in this study holds great potential in areas with limited monitoring of PM2.5 speciation, in particular BC, and its results could be valuable for both future environmental health research, regional radiative forcing estimates, and promulgation of tailored regulations for traffic-related air pollution abatement.

Long-term source apportionment of PM2.5 across the contiguous United States (2000-2019) using a multilinear engine model

Identifying PM2.5 sources is crucial for effective air quality management and public health. This research used the Multilinear Engine (ME-2) model to analyze PM2.5 from 515 EPA Chemical Speciation Network (CSN) and Interagency Monitoring of Protected Visual Environments (IMPROVE) sites across the U.S. from 2000 to 2019. The U.S. was divided into nine regions for detailed analysis. A total of seven source types (tracers) were resolved across the country: (1) Soil/Dust (Si, Al, Ca and Fe); (2) Vehicle emissions (EC, OC, Cu and Zn); (3) Biomass/wood burning (K); (4) Heavy oil/coal combustion (Ni, V, Cl and As); (5) Secondary sulfate (SO42-); (6) Secondary nitrate (NO3-) and (7) Sea salt (Mg, Na, Cl and SO42-). Furthermore, we extracted and calculated secondary organic aerosols (SOA) based on the secondary sulfate and nitrate factors. Notably, significant reductions in secondary sulfate, nitrate, and heavy oil/coal combustion emissions reflect recent cuts in fossil-fueled power sector emissions. A decline in SOA suggests effective mitigation of their formation conditions or precursors. Despite these improvements, vehicle emissions and biomass burning show no significant decrease, highlighting the need for focused control on these persistent pollution sources for future air quality management.

Indoor air quality in subway microenvironments: Pollutant characteristics, adverse health impacts, and population inequity

Rapidly increasing urbanization in recent decades has elevated the subway as the primary public transportation mode in metropolitan areas. Indoor air quality (IAQ) inside subways is an important factor that influences the health of commuters and subway workers. This review discusses the subway IAQ in different cities worldwide by comparing the sources and abundance of particulate matter (PM2.5 and PM10) in these environments. Factors that affect PM concentration and chemical composition were found to be associated with the subway internal structure, train frequency, passenger volume, and geographical location. Special attention was paid to air pollutants, such as transition metals, volatile/semi-volatile organic compounds (VOCs and SVOCs), and bioaerosols, due to their potential roles in indoor chemistry and causing adverse health impacts. In addition, given that the IAQ of subway systems is a public health issue worldwide, we calculated the Gini coefficient of urban subway exposure via meta-analysis. A value of 0.56 showed a significant inequity among different cities. Developed regions with higher per capita income tend to have higher exposure. By reviewing the current advances and challenges in subway IAQ with a focus on indoor chemistry and health impacts, future research is proposed toward a sustainable urban transportation systems.

Unequal Health Risks and Attributable Mortality Burden of Source-Specific PM2.5 in China

Anthropogenic emissions, originating from human activities, stand as the primary contributors to PM2.5, which is recognized as a global health threat. The disease burden associated with PM2.5 has been extensively documented. However, the prevailing estimations have predominantly relied on PM2.5 exposure-response functions, neglecting the distinct risks posed by PM2.5 from various sources. China has experienced a significant reduction in the PM2.5 concentration due to stringent emission controls. With diverse sources and abundant mortality data, this situation provides a unique opportunity to estimate short-term source-specific attributable mortality. Our approach involves an integrated unequal health risk-oriented modeling in China, incorporating a source-oriented Community Multiscale Air Quality model, an adjustment and downscaling method for exposure measurement, a generalized linear model with random-effects meta-analysis, and premature mortality estimation. Adhering to the unequal health risk concept, we calculated the attributable mortality of multiple PM2.5 sources by determining the source risk-adjusted factor. In this study, we observed varying excess risks associated with multiple PM2.5 sources, with transportation-related PM2.5 exhibiting the most substantial association. An interquartile range increase (7.65 μg/m3) was linked to a 1.98% higher daily nonaccidental mortality. Residential use- and transportation-related PM2.5 emerged as the two principal sources of premature mortality. In 2018, a remarkable 53,381 avoiding deaths were estimated compared to 2013, and over 67% of these were attributed to reductions in coal-dependent sources. Notably, transportation-related PM2.5 emerged as the largest contributor to premature mortality in 2018. This study underscores the significance of a new source-oriented health risk assessment to support actions aimed at reducing air pollution. It strongly advocates for heightened attention to PM2.5 reductions in the transportation sector in China.

Development, Demonstration, and Evaluation of Routine Monitoring of Aerosol Carbon, Oxygen, and Sulfur Content

Traditional online measurements of the chemical composition of particulate matter have relied on expensive and complex research-grade instrumentation based on mass spectrometry and/or chromatography. However, routine monitoring requires lower-cost alternatives that can be operated autonomously, and such tools are lacking. Routine monitoring of particulate matter, especially organic aerosol, relies instead on offline techniques such as filter collection that require significant operator effort. To address this gap, we present here a new online instrument, the "ChemSpot", that provides information on organic aerosol mass loading, volatility, and degree of oxygenation, along with sulfur content. The instrument grows particles with water condensation, impacts them onto a passivated surface with low heat capacity, and uses stepped thermal desorption of analytes to a combination of flame ionization detector (FID) and flame photometric detector (FPD) and then to a CO2 detector downstream of the FID/FPD setup. By relying on detectors designed for gas chromatography, calibration is achieved almost entirely through the introduction of gases without the need for regular introduction of particle-phase calibrants. Particle collection efficiency of greater than 95% was achieved consistently, and the collection cell was shown to rapidly and precisely heat to ∼800 °C at a rate as fast as 10 °C per second. Measurements of total organic carbon, volatility distribution of organic aerosol, total sulfur, and oxygen-to-carbon ratio (O:C) collected during a continuous multi-week period are presented here to demonstrate the autonomous operation of "ChemSpot". Colocated measurements with a mass spectrometer, an aerosol chemical speciation monitor (ACSM), show good correlation and relatively low bias between the instruments (mean absolute percentage error of 21% and 27% for organic carbon and equivalent sulfate measurements, respectively).

Differences in aerosol chemistry at a regional background site in Hong Kong before and during the COVID-19 pandemic

Restrictions on human-related activities implemented in Hong Kong to curb the spread of the coronavirus disease 2019 (COVID-19) pandemic provided an opportunity to investigate the anthropogenic impact on organic aerosols (OA) composition. In this study, we conducted a comparative analysis of online measurements of non-refractory submicron particulate matters (NR-PM1) at a regional background site in Hong Kong, covering the periods before the COVID-19 control (November 2018) and during the COVID-19 control (October to November 2020), to investigate changes in OA sources and formation mechanisms. Among the measured NR-PM1 components, organics were the most dominant species with an average percentage of 51.0 ± 0.5 %, exceeding pre-control levels of 44.0 ± 0.7 %. Moreover, 88 % of the organics were attributed to oxygenated OA (OOA). Diurnal variations of all bulk components in NR-PM1 consistently showed afternoon peaks, indicating photochemical processes during COVID-19 control. Similar to the pre-restriction period, the positive matrix factorization (PMF) model showed that OOA was composed of three factors, including two less-oxidized oxygenated factors (LO-OOA1 and LO-OOA2) and one more-oxidized oxygenated factor (MO-OOA). The contribution of the LO-OOA2 factor remained small and stable during both sampling campaigns, which might imply background levels of OOA at this site. The formation of the two predominant components of organics (e.g., LO-OOA1 and MO-OOA) was further discussed. Compared with before control, observational evidence showed that the levels of MO-OOA exceeded LO-OOA1 during the control period, and the average concentration of odd oxygen (Ox = ozone + nitrogen dioxide) increased by 53 % during the COVID-19 control. Besides, the results showed that both LO-OOA1 and MO-OOA exhibited similar diurnal variations to Ox, and their concentrations generally enhanced with increasing Ox levels. This suggested that the formation of OOA was closely related to the photochemical oxidation processes when anthropogenic emissions were reduced. By correlating LO-OOA1 and MO-OOA with speciated OA markers, we found that the formation of LO-OOA1 remained associated with anthropogenic sources, while biogenic emissions contributed to the formation of MO-OOA during the COVID-19 control. Our findings highlight the interplay between emissions, atmospheric conditions, and aerosol composition, providing valuable insights to guide strategic decisions for future air quality improvement.

Heterogeneous Reactions of Phenol on Different Components of Mineral Dust Aerosol: Formation of Oxidized Organic and Nitro-Phenolic Compounds

Phenol, a common semi-volatile compound associated with different emissions including from plants and biomass burning, as well as anthropogenic emissions and its derivatives, are important components of secondary organic aerosols (SOAs). Gas and aqueous phase reactions of phenol, in the presence of photochemical drivers, are fairly well understood. However, despite observations showing aromatic content within SOA size and mass increases during dust episodes, the heterogeneous reactions of phenol with mineral dusts are poorly understood. In the current study, surface reactions of phenol at the gas/solid interface with different components of mineral dust including SiO2, α-Fe2O3, and TiO2 have been investigated. Whereas reversible surface adsorption of phenol occurs on SiO2 surfaces, for both α-Fe2O3 and TiO2 surfaces, phenol reacts to form a wide range of OH substituted aromatic products. For α-Fe2O3 surfaces that have been nitrated by gas-phase reactions of nitric acid prior to exposure to phenol, unique compounds form on the surface including nitro-phenolic compounds. Moreover, additional surface chemistry was observed when adsorbed nitro-phenolic products were exposed to gas-phase SO2 as a result of the formation of adsorbed nitrite from nitrate redox chemistry with adsorbed SO2. Overall, this study reveals the extensive chemistry as well as the complexity of reactions of prevalent organic compounds leading to the formation of SOA on mineral surfaces.

Synthesis and Characterization of Organic Peroxides from Monoterpene-Derived Criegee Intermediates in Secondary Organic Aerosol

Ozonolysis of alkenes is known to produce reactive intermediates─stabilized Criegee intermediates (SCIs), and their subsequent bimolecular reactions with various carboxylic acids can form α-acyloxyalkyl hydroperoxides (AAHPs), which is considered a major class of organic peroxides in secondary organic aerosol (SOA). Despite their atmospheric and health importance, the molecular-level identification of organic peroxides in atmospheric aerosols is highly challenging, preventing further assessment of their environmental fate. Here, we synthesize 20 atmospherically relevant AAHPs through liquid-phase ozonolysis, in which two types of monoterpene-derived SCIs from either α-pinene or 3-carene are scavenged by 10 different carboxylic acids to form AAHPs with diverse structures. These AAHPs are identified individually by liquid chromatography coupled with high-resolution mass spectrometry. AAHPs were previously thought to decompose quickly in an aqueous environment such as cloud droplets, but we demonstrate here that AAHPs hydrolysis rates are highly compound-dependent with rate constants differing by 2 orders of magnitude. In contrast, the aqueous-phase formation rate constants between SCI and various carboxylic acids vary only within a factor of 2-3. Finally, we identified two of the 20 synthesized AAHPs in α-pinene SOA and two in 3-carene SOA, contributing ∼0.3% to the total SOA mass. Our results improve the current molecular-level understanding of organic peroxides and are useful for a more accurate assessment of their environmental fate and health impact.

Multiscale computational simulation of pollutant behavior at water interfaces

The investigation of pollutant behavior at water interfaces is critical to understand pollution in aquatic systems. Computational methods allow us to overcome the limitations of experimental analysis, delivering valuable insights into the chemical mechanisms and structural characteristics of pollutant behavior at interfaces across a range of scales, from microscopic to mesoscopic. Quantum mechanics, all-atom molecular dynamics simulations, coarse-grained molecular dynamics simulations, and dissipative particle dynamics simulations represent diverse molecular interaction calculation methods that can effectively model pollutant behavior at environmental interfaces from atomic to mesoscopic scales. These methods provide a rich variety of information on pollutant interactions with water surfaces. This review synthesizes the advancements in applying typical computational methods to the formation, adsorption, binding, and catalytic conversion of pollutants at water interfaces. By drawing on recent advancements, we critically examine the current challenges and offer our perspective on future directions. This review seeks to advance our understanding of computational techniques for elucidating pollutant behavior at water interfaces, a critical aspect of water research.

Wildfire plume ageing in the Photochemical Large Aerosol Chamber (PHOTO-LAC)

Plumes from wildfires are transported over large distances from remote to populated areas and threaten sensitive ecosystems. Dense wildfire plumes are processed by atmospheric oxidants and complex multiphase chemistry, differing from processes at typical ambient concentrations. For studying dense biomass burning plume chemistry in the laboratory, we establish a Photochemical Large Aerosol Chamber (PHOTO-LAC) being the world's largest aerosol chamber with a volume of 1800 m3 and provide its figures of merit. While the photolysis rate of NO2 (jNO2) is comparable to that of other chambers, the PHOTO-LAC and its associated low surface-to-volume ratio lead to exceptionally low losses of particles to the walls. Photochemical ageing of toluene under high-NOx conditions induces substantial formation of secondary organic aerosols (SOAs) and brown carbon (BrC). Several individual nitrophenolic compounds could be detected by high resolution mass spectrometry, demonstrating similar photochemistry to other environmental chambers. Biomass burning aerosols are generated from pine wood and debris under flaming and smouldering combustion conditions and subsequently aged under photochemical and dark ageing conditions, thus resembling day- and night-time atmospheric chemistry. In the unprecedented long ageing with alternating photochemical and dark ageing conditions, the temporal evolution of particulate matter and its chemical composition is shown by ultra-high resolution mass spectrometry. Due to the spacious cavity, the PHOTO-LAC may be used for applications requiring large amounts of particulate matter, such as comprehensive chemical aerosol characterisation or cell exposures under submersed conditions.

Oligomerization Mechanism of Methylglyoxal Regulated by the Methyl Groups in Reduced Nitrogen Species: Implications for Brown Carbon Formation

Uncertain chemical mechanisms leading to brown carbon (BrC) formation affect the drivers of the radiative effects of aerosols in current climate predictions. Herein, the aqueous-phase reactions of methylglyoxal (MG) and typical reduced nitrogen species (RNSs) are systematically investigated by using combined quantum chemical calculations and laboratory experiments. Imines and diimines are identified from the mixtures of methylamine (MA) and ammonia (AM) with MG, but not from dimethylamine (DA) with the MG mixture under acidic conditions, because deprotonation of DA cationic intermediates is hindered by the amino groups occupied by two methyl groups. It leads to N-heterocycle (NHC) formation in the MG + MA (MGM) and MG + AM (MGA) reaction systems but to N-containing chain oligomer formation in the MG + DA (MGD) reaction system. Distinct product formation is attributed to electrostatic attraction and steric hindrance, which are regulated by the methyl groups of RNSs. The light absorption and adverse effects of NHCs are also strongly related to the methyl groups of RNSs. Our finding reveals that BrC formation is mainly contributed from MG reaction with RNSs with less methyl groups, which have more abundant and broad sources in the urban environments.

Nitroaromatic Compounds from Secondary Nitrate Formation and Biomass Burning Are Major Proinflammatory Components in Organic Aerosols in Guangzhou: A Bioassay Combining High-Resolution Mass Spectrometry Analysis

The limited characterization and detection capacity of unknown compounds hinder our understanding of the molecular composition of toxic compounds in PM2.5. The present study applied Fourier transform ion cyclotron resonance mass spectrometry coupled with negative and positive electrospray ionization sources (ESI-/ESI+ FT-ICR-MS) to probe the molecular characteristics and dynamic formation processes of the effective proinflammatory components in organic aerosols (OAs) of PM2.5 in Guangzhou for one year. We detected abundant proinflammatory molecules in OAs, mainly classified as CHON compounds (compounds composed of C, H, O, and N atoms) in elemental and nitroaromatic compounds (NACs) in structures. From the perspective of the formation process, we discovered that these proinflammatory molecules, especially toxic NACs, were largely driven by secondary nitrate formation and biomass burning (in emission source), as well as SO2 (in atmospheric evolution). In addition, our results indicated that the secondary processes had replaced the primary emission as the main contributing source of the toxic proinflammatory compounds in OAs. This study highlights the importance of community measures to control the production of nitroaromatic compounds derived from secondary nitrate formation and biomass burning in urban areas.

Modeling of secondary organic aerosols (SOA) based on two commonly used air quality models in China: Consistent S/IVOCs contribution but large differences in SOA aging

Secondary organic aerosol (SOA) is an important component of atmospheric fine particulate matter (PM2.5), with contributions from anthropogenic and biogenic volatile organic compounds (AVOC and BVOC) and semi- (SVOC) and intermediate volatility organic compounds (IVOC). Policymakers need to know which SOA precursors are important but accurate simulation of SOA magnitude and contributions remain uncertain. Findings from existing SOA modeling studies have many inconsistencies due to differing emission inventory methodologies/assumptions, air quality model (AQM) algorithms, and other aspects of study methodologies. To address some of the inconsistencies, we investigated the role of different AQM SOA algorithms by applying two commonly used models, CAMx and CMAQ, with consistent emission inventories to simulate SOA concentrations and contributions for July and November 2018 in China. Both models have a volatility basis set (VBS) SOA algorithm but with different parameters and treatments of SOA photochemical aging. SOA generated from BVOC (i.e., BSOA) is found to be more important in southern China. In contrast, SOA generated from anthropogenic precursors is more prevalent in the North China Plain (NCP), Yangtze River Delta (YRD), Sichuan Basin and Central China. Both models indicate negligible SOA formation from SVOC emissions compared to other precursors. In July, when BVOC emissions are abundant, SOA is predominantly contributed by BSOA (except for NCP), followed by IVOC-SOA (i.e., SOA produced from IVOC) and ASOA (i.e., SOA produced from anthropogenic VOC). In contrast, in November, IVOC became the leading SOA contributor for all selected regions except PRD, illustrating the important contribution of IVOC emissions to SOA formation. While both models generally agree in terms of the spatial distributions and seasonal variations of different SOA components, CMAQ tends to predict higher BSOA, while CAMx generates higher ASOA concentrations. As a result, CMAQ results suggest that BSOA concentration is always higher than ASOA in November, while CAMx emphasizes the importance of ASOA. Utilizing a conceptual model, we found that different treatment of SOA aging between the two models is a major cause of differences in simulated ASOA concentrations. The step-wise SOA aging scheme implemented in the CAMx VBS (based on gas-phase reactions with OH radical and similar to other models) exhibits a strong enhancement effect on simulated ASOA concentrations, and this effect increases with the ambient organic aerosol (OA) concentrations. The CMAQ aerosol module implements a different SOA aging scheme that represents particle-phase oligomerization and has smaller impacts on total OA. Different structures and/or parameters of the SOA aging schemes are being used in current models, which could greatly affect model simulations of OA in ways that are difficult to anticipate. Our results indicate that future control policies should aim at reducing IVOC emissions as well as traditional VOC emissions. In addition, aging schemes are the major driver in CMAQ vs. CAMx treatments of ASOA and their resulting predicted mass. More sophisticated measurement data (e.g., with resolved OA components) and/or chamber experiments (e.g., investigating how aging influences SOA yields) are needed to better characterize SOA aging and constrain model parameterizations.

Mortality risks from a spectrum of causes associated with sand and dust storms in China

Sand and Dust Storms (SDS) pose considerable health risks worldwide. Previous studies only indicated risk of SDS on overall mortality. This nationwide multicenter time-series study aimed to examine SDS-associated mortality risks extensively. We analyzed 1,495,724 deaths and 2024 SDS events from 1 February to 31 May (2013-2018) in 214 Chinese counties. The excess mortality risks associated with SDS were 7.49% (95% CI: 3.12-12.05%), 5.40% (1.25-9.73%), 4.05% (0.41-7.83%), 3.45% (0.34-6.66%), 3.37% (0.28-6.55%), 3.33% (0.07-6.70%), 8.90% (4.96-12.98%), 12.51% (6.31-19.08%), and 11.55% (5.55-17.89%) for ischemic stroke, intracerebral hemorrhagic stroke, hypertensive heart disease, myocardial infarction, acute myocardial infarction, acute ischemic heart disease, respiratory disease, chronic lower respiratory disease, and chronic obstructive pulmonary disease (COPD), respectively. SDS had significantly added effects on ischemic stroke, chronic lower respiratory disease, and COPD mortality. Our results suggest the need to implement public health policy against SDS.

Reactive organic carbon air emissions from mobile sources in the United States

Mobile sources are responsible for a substantial controllable portion of the reactive organic carbon (ROC) emitted to the atmosphere, especially in urban environments of the United States. We update existing methods for calculating mobile source organic particle and vapor emissions in the United States with over a decade of laboratory data that parameterize the volatility and organic aerosol (OA) potential of emissions from on-road vehicles, nonroad engines, aircraft, marine vessels, and locomotives. We find that existing emission factor information from Teflon filters combined with quartz filters collapses into simple relationships and can be used to reconstruct the complete volatility distribution of ROC emissions. This new approach consists of source-specific filter artifact corrections and state-of-the-science speciation including explicit intermediate-volatility organic compounds (IVOCs), yielding the first bottom-up volatility-resolved inventory of US mobile source emissions. Using the Community Multiscale Air Quality model, we estimate mobile sources account for 20 %-25 % of the IVOC concentrations and 4.4 %-21.4 % of ambient OA. The updated emissions and air quality model reduce biases in predicting fine-particle organic carbon in winter, spring, and autumn throughout the United States (4.3 %-11.3 % reduction in normalized bias). We identify key uncertain parameters that align with current state-of-the-art research measurement challenges.

Indoor Air Quality Implications of Germicidal 222 nm Light

One strategy for mitigating the indoor transmission of airborne pathogens, including the SARS-CoV-2 virus, is irradiation by germicidal UV light (GUV). A particularly promising approach is 222 nm light from KrCl excimer lamps (GUV222); this inactivates airborne pathogens and is thought to be relatively safe for human skin and eye exposure. However, the impact of GUV222 on the composition of indoor air has received little experimental study. Here, we conduct laboratory experiments in a 150 L Teflon chamber to examine the formation of secondary species by GUV222. We show that GUV222 generates ozone (O3) and hydroxyl radicals (OH), both of which can react with volatile organic compounds to form oxidized volatile organic compounds and secondary organic aerosol particles. Results are consistent with a box model based on the known photochemistry. We use this model to simulate GUV222 irradiation under more realistic indoor air scenarios and demonstrate that under some conditions, GUV222 irradiation can lead to levels of O3, OH, and secondary organic products that are substantially elevated relative to normal indoor conditions. The results suggest that GUV222 should be used at low intensities and in concert with ventilation, decreasing levels of airborne pathogens while mitigating the formation of air pollutants.

Mechanism of the noncatalytic oxidation of soot using in situ transmission electron microscopy

Soot generation is a major challenge in industries. The elimination of soot is particularly crucial to reduce pollutant emissions and boost carbon conversion. The mechanisms for soot oxidation are complex, with quantified models obtained under in situ conditions still missing. We prepare soot samples via noncatalytic partial oxidation of methane. Various oxidation models are established based on the results of in situ transmission electron microscopy experiments. A quantified maturity parameter is proposed and used to categorize the soot particles according to the nanostructure at various maturity levels, which in turn lead to different oxidation mechanisms. To tackle the challenges in the kinetic analysis of soot aggregates, a simplification model is proposed and soot oxidation rates are quantified. In addition, a special core-shell separation model is revealed through in situ analysis and kinetic studies. In this study, we obtain important quantified models for soot oxidation under in situ conditions.

Oxidized and Unsaturated: Key Organic Aerosol Traits Associated with Cellular Reactive Oxygen Species Production in the Southeastern United States

Exposure to ambient fine particulate matter (PM2.5) is associated with millions of premature deaths annually. Oxidative stress through overproduction of reactive oxygen species (ROS) is a possible mechanism for PM2.5-induced health effects. Organic aerosol (OA) is a dominant component of PM2.5 worldwide, yet its role in PM2.5 toxicity is poorly understood due to its chemical complexity. Here, through integrated cellular ROS measurements and detailed multi-instrument chemical characterization of PM in urban southeastern United States, we show that oxygenated OA (OOA), especially more-oxidized OOA, is the main OA type associated with cellular ROS production. We further reveal that highly unsaturated species containing carbon-oxygen double bonds and aromatic rings in OOA are major contributors to cellular ROS production. These results highlight the key chemical features of ambient OA driving its toxicity. As more-oxidized OOA is ubiquitous and abundant in the atmosphere, this emphasizes the need to understand its sources and chemical processing when formulating effective strategies to mitigate PM2.5 health impacts.

Combined Smog Chamber/Oxidation Flow Reactor Study on Aging of Secondary Organic Aerosol from Photooxidation of Aromatic Hydrocarbons

Secondary organic aerosol (SOA) is a significant component of atmospheric fine particulate matter (PM2.5), and their physicochemical properties can be significantly changed in the aging process. In this study, we used a combination consisting of a smog chamber (SC) and oxidation flow reactor (OFR) to investigate the continuous aging process of gas-phase organic intermediates and SOA formed from the photooxidation of toluene, a typical aromatic hydrocarbon. Our results showed that as the OH exposure increased from 2.6 × 1011 to 6.3 × 1011 molecules cm-3 s (equivalent aging time of 2.01-4.85 days), the SOA mass concentration (2.9 ± 0.05-28.7 ± 0.6 μg cm-3) and corrected SOA yield (0.073-0.26) were significantly enhanced. As the aging process proceeds, organic acids and multiple oxygen-containing oxidation products are continuously produced from the photochemical aging process of gas-phase organic intermediates (mainly semi-volatile and intermediate volatility species, S/IVOCs). The multigeneration oxidation products then partition to the aerosol phase, while functionalization of SOA rather than fragmentation dominated in the photochemical aging process, resulting in much higher SOA yield after aging compared to that in the SC. Our study indicates that SOA yields as a function of OH exposure should be considered in air quality models to improve SOA simulation, and thus accurately assess the impact on SOA properties and regional air quality.

Global Health and Climate Effects of Organic Aerosols from Different Sources

The impact of aerosols on human health and climate is well-recognized, yet many studies have only focused on total PM2.5 or changes from anthropogenic activities. This study quantifies the health and climate effects of organic aerosols (OA) from anthropogenic, biomass burning, and biogenic sources. Using two atmospheric chemistry models, CAM-chem and GEOS-Chem, our findings reveal that anthropogenic primary OA (POA) has the highest efficiency for health effects but the lowest for direct radiative effects due to spatial and temporal variations associated with population and surface albedo. The treatment of POA as nonvolatile or semivolatile also influences these efficiencies through different chemical processes. Biogenic OA shows moderate efficiency for health effects and the highest for direct radiative effects but has the lowest efficiency for indirect effects due to the reduced high cloud, caused by stabilized temperature profiles from aerosol-radiation interactions in biogenic OA-rich regions. Biomass burning OA is important for cloud radiative effect changes in remote atmospheres due to its ability to be transported further than other OAs. This study highlights the importance of not only OA characteristics such as toxicity and refractive index but also atmospheric processes such as transport and chemistry in determining health and climate impact efficiencies.

A Narrative Review on the Impact of Air Pollution on Heart Failure Risk and Exacerbation

Air pollution is a risk factor for many cardiovascular diseases, including heart failure (HF). Although the links between air pollution and HF have been explored, the results are scattered and difficult to piece together into a cohesive story. Therefore, we undertook a narrative review of all aspects of the relationship between HF and air pollution exposure, including risks of developing HF when exposed to air pollution, the exacerbation of HF symptoms by air pollution exposure, and the increased susceptibility that individuals with HF have for air pollution-related health risks. We also examined the literature on environmental justice as well as air pollution interventions for HF. We found substantial evidence linking air pollution exposure to HF incidence. There were a limited number of studies that examined air pollution exposure in clearly defined populations with HF to explore exacerbation of HF or the susceptibility of individuals with HF to air pollution health risks. However, there is substantial evidence that HF-related hospitalisations are increased under air pollution exposure and that the air pollution associated increase in HF-related hospitalisations is greater than hospitalisations for other chronic diseases, supporting links between air pollution and both exacerbation of HF and susceptibility of individuals with HF. There is emerging evidence for interventions that can decrease air pollution health risks for individuals with HF, and more studies are needed, particularly randomised controlled trials. Thus, although the air pollution-related health risks for HF incidence and hospitalisations are clear, further studies specifically targeted at identified data gaps will greatly improve our knowledge of the susceptibility of individuals with HF and interventions to reduce risks.

Multiphase Kinetic Modeling of Air Pollutant Effects on Protein Modification and Nitrotyrosine Formation in Epithelial Lining Fluid

Exposure to ambient air pollution is a major risk factor for human health. Inhalation of air pollutants can enhance the formation of reactive species in the epithelial lining fluid (ELF) of the respiratory tract and can lead to oxidative stress and oxidative damage. Here, we investigate the chemical modification of proteins by reactive species from air pollution and endogenous biological sources using an extended version of the multiphase chemical kinetic model KM-SUB-ELF 2.0 with a detailed mechanism of protein modification. Fine particulate matter (PM2.5) and nitrogen dioxide (•NO2) act synergistically and increase the formation of nitrotyrosine (Ntyr), a common biomarker of oxidative stress. Ozone (O3) is found to be a burden on the antioxidant defense system but without substantial influence on the Ntyr concentration. In simulations with low levels of air pollution, the Ntyr concentration in the ELF is consistent with the range of literature values for bronchoalveolar lavage fluid from healthy individuals. With high levels of air pollution, however, we obtain strongly elevated Ntyr concentrations. Our model analysis shows how chemical reactions of air pollutants can modify proteins and thus their functionality in the human body, elucidating a molecular pathway that may explain air pollutant effects on human health.

Policy-Related Gains in Urban Air Quality May Be Offset by Increased Emissions in a Warming Climate

Air quality policies have made substantial gains by reducing pollutant emissions from the transportation sector. In March 2020, New York City's activities were severely curtailed in response to the COVID-19 pandemic, resulting in 60-90% reductions in human activity. We continuously measured major volatile organic compounds (VOCs) during January-April 2020 and 2021 in Manhattan. Concentrations of many VOCs decreased significantly during the shutdown with variations in daily patterns reflective of human activity perturbations, resulting in a temporary ∼28% reduction in chemical reactivity. However, the limited effect of these dramatic measures was outweighed by larger increases in VOC-related reactivity during the anomalously warm spring 2021. This emphasizes the diminishing returns from transportation-focused policies alone and the risk of increased temperature-dependent emissions undermining policy-related gains in a warming climate.

The effects of city morphology on airborne transmission of COVID-19. Case study: Port Said City, Egypt

Looking beyond COVID-19 outbreak, Scholars continue to develop innovative approaches to bring the city on to health and safety. Recent studies have indicated that urban spaces could produce or propagate pathogens, which is an urgent topic at the city level. However, there is a dearth of studies investigating the interrelationship between urban morphology and pandemics outbreak at the neighborhood level. Accordingly, this research will trace the effect of cities morphologies on the rate of spread of COVID-19 through a simulation study held on five areas that form the urban morphology of Port Said City, using Envi-met software. Results are explored based on the degree of concentration and rate of diffusion of coronavirus particles. It was observed on a regular basis that wind speed has a directly proportional relationship with the diffusion of the particles and an inversely proportional relationship with the concentration of the particles. However, certain urban characteristics led to inconsistent and opposing results like wind tunnels, shaded arcades, height variance, and spacious in-between spaces. Moreover, it is obvious that the city morphology is being transformed over time toward safer conditions; urban areas constructed recently have low vulnerability to respiratory pandemics outbreak compared to older areas.

Changes in tropospheric air quality related to the protection of stratospheric ozone in a changing climate

Ultraviolet (UV) radiation drives the net production of tropospheric ozone (O3) and a large fraction of particulate matter (PM) including sulfate, nitrate, and secondary organic aerosols. Ground-level O3 and PM are detrimental to human health, leading to several million premature deaths per year globally, and have adverse effects on plants and the yields of crops. The Montreal Protocol has prevented large increases in UV radiation that would have had major impacts on air quality. Future scenarios in which stratospheric O3 returns to 1980 values or even exceeds them (the so-called super-recovery) will tend to ameliorate urban ground-level O3 slightly but worsen it in rural areas. Furthermore, recovery of stratospheric O3 is expected to increase the amount of O3 transported into the troposphere by meteorological processes that are sensitive to climate change. UV radiation also generates hydroxyl radicals (OH) that control the amounts of many environmentally important chemicals in the atmosphere including some greenhouse gases, e.g., methane (CH4), and some short-lived ozone-depleting substances (ODSs). Recent modeling studies have shown that the increases in UV radiation associated with the depletion of stratospheric ozone over 1980-2020 have contributed a small increase (~ 3%) to the globally averaged concentrations of OH. Replacements for ODSs include chemicals that react with OH radicals, hence preventing the transport of these chemicals to the stratosphere. Some of these chemicals, e.g., hydrofluorocarbons that are currently being phased out, and hydrofluoroolefins now used increasingly, decompose into products whose fate in the environment warrants further investigation. One such product, trifluoroacetic acid (TFA), has no obvious pathway of degradation and might accumulate in some water bodies, but is unlikely to cause adverse effects out to 2100.

Pollution from fine particulate matter and atherosclerosis: A narrative review

According to the WHO, the entire global population is exposed to air pollution levels higher than recommended for health preservation. Air pollution is a complex mixture of nano- to micro-sized particles and gaseous components that poses a major global threat to public health. Among the most important air pollutants, causal associations have been established between particulate matter (PM), mainly < 2.5 μm, and cardiovascular diseases (CVD), i.e., hypertension, coronary artery disease, ischemic stroke, congestive heart failure, arrhythmias as well as total cardiovascular mortality. Aim of this narrative review is to describe and critically discuss the proatherogenic effects of PM_2.5 that have been attributed to many direct or indirect effects comprising endothelial dysfunction, a chronic low-grade inflammatory state, increased production of reactive oxygen species, mitochondrial dysfunction and activation of metalloproteases, all leading to unstable arterial plaques. Higher concentrations of air pollutants are associated with the presence of vulnerable plaques and plaque ruptures witnessing coronary artery instability. Air pollution is often disregarded as a CVD risk factor, in spite of the fact that it is one of the main modifiable factors relevant for prevention and management of CVD. Thus, not only structural actions should be taken in order to mitigate emissions, but health professionals should also take care to counsel patients on the risks of air pollution.

Toxicological Effects of Secondary Air Pollutants

Secondary air pollutants, originating from gaseous pollutants and primary particulate matter emitted by natural sources and human activities, undergo complex atmospheric chemical reactions and multiphase processes. Secondary gaseous pollutants represented by ozone and secondary particulate matter, including sulfates, nitrates, ammonium salts, and secondary organic aerosols, are formed in the atmosphere, affecting air quality and human health. This paper summarizes the formation pathways and mechanisms of important atmospheric secondary pollutants. Meanwhile, different secondary pollutants' toxicological effects and corresponding health risks are evaluated. Studies have shown that secondary pollutants are generally more toxic than primary ones. However, due to their diverse source and complex generation mechanism, the study of the toxicological effects of secondary pollutants is still in its early stages. Therefore, this paper first introduces the formation mechanism of secondary gaseous pollutants and focuses mainly on ozone's toxicological effects. In terms of particulate matter, secondary inorganic and organic particulate matters are summarized separately, then the contribution and toxicological effects of secondary components formed from primary carbonaceous aerosols are discussed. Finally, secondary pollutants generated in the indoor environment are briefly introduced. Overall, a comprehensive review of secondary air pollutants may shed light on the future toxicological and health effects research of secondary air pollutants.

Chronic Exposure to Secondary Organic Aerosols Causes Lung Tissue Damage

Recently, secondary organic aerosols (SOAs) emerged as a predominant component of fine particulate matter. However, the pathogenic mechanism(s) of SOAs are still poorly understood. Herein, we show that chronic exposure of mice to SOAs resulted in lung inflammation and tissue destruction. Histological analyses found lung airspace enlargement associated with massive inflammatory cell recruitment predominated by macrophages. Concomitant with such cell influx, our results found changes in the levels of a series of inflammatory mediators in response to SOA. Interestingly, we observed that the expression of the genes encoding for TNF-α and IL-6 increased significantly after one month of exposure to SOAs; mediators that have been largely documented to play a role in chronic pulmonary inflammatory pathologies. Cell culture studies confirmed these in vivo findings. Of importance as well, our study indicates increased matrix metalloproteinase proteolytic activity suggesting its contribution to lung tissue inflammation and degradation. Our work represents the first in vivo study, which reports that chronic exposure to SOAs leads to lung inflammation and tissue injury. Thus, we hope that these data will foster new studies to enhance our understanding of the underlying pathogenic mechanisms of SOAs and perhaps help in the design of therapeutic strategies against SOA-mediated lung injury.

Sources of Organic Aerosol in China from 2005 to 2019: A Modeling Analysis

Organic aerosol (OA) is a key component of fine particulate matter (PM_2.5) and affects the human health and leads to climate change. With strict control measures for air pollutants during the last decade, the OA concentration in China declined slowly, while its sources remain unclear. In this study, we simulate the primary OA (POA) and secondary OA (SOA) concentrations from 2005 to 2019 with a state-of-the-art air quality model, Community Multiscale Air Quality (CMAQ, version 5.3.2) coupled with a Two-Dimensional Volatility Basis Set (2D-VBS) module, and a long-term emission inventory of full-volatility organic compounds in China and conduct source apportionment and sensitivity analysis. The simulation results show that, from 2005 to 2019, the OA concentration in China decreased from 24.0 to 12.8 μg/m³ with most of the reduction from POA. The OA pollution from residential biomass burning declined 75% from 2005 to 2019, while it is still the major OA source in China. OA pollution from VCP increased by more than 2-fold and became the largest SOA source in China. From 2014 to 2019, the NO_x control in China slightly offset the decrease of SOA concentration due to elevated oxidation capacity.

Future air quality and premature mortality in Korea

We simulate air quality in Korea for the present, the near-term, and the long-term future conditions under the Shared Socioeconomic Pathways (SSP1: most sustainable pathway with strong emissions control, SSP3: most challenging pathway with mild emissions control) using a chemical transport model. Simulated future concentrations of NO₂, SO₂, and fine particulate matter (PM_2.5), show, in general, lower values compared to the present with varying degrees depending on SSP scenarios. Significant reductions in precursor emissions result in a decrease in O₃ concentrations under a NO_x-limited environment in the long-term future under SSP1. Under SSP3, O₃ increases in the future under a VOC-limited regime, driven by increased CH₄ levels and biogenic VOC emissions under the warming climate. Concentrations of PM_2.5 and its components, including sulfate, nitrate, ammonium, and organic aerosols (OA), generally decrease in the long-term future under both scenarios. However, the contribution of biogenic secondary OA (BSOA) to PM_2.5 will increase in the future. Simulated results are used to estimate cardiorespiratory mortality changes with concentration-response factors from epidemiologic studies in Korea based on national health surveys and Korean cohorts, using projected population structures from the SSP database. The cardiorespiratory health burden of long-term exposure to O₃, NO₂, SO₂, and PM_2.5 is estimated to be 10,419 (95 % confidence interval: 1271-17,142), 8630 (0-18,713), 3958 (0-9272), and 10,431 (1411-20,643) deaths in 2019. We find that the total cardiorespiratory excess mortality due to air pollutants under SSP1 decreases by 8 % and 95 % in 2045 and 2095, respectively. Under SSP3, excess mortality increases by 80 % in 2045, and decreases by 22 % in 2095, resulting in a substantial difference in the health outcomes depending on the emission scenario. We also find that the BSOA contribution to total PM_2.5 will differ by region, emphasizing the potential health impact of BSOA on a local scale in the future.

Characterizing variations in ambient PM2.5 concentrations at the U.S. Embassy in Dhaka, Bangladesh using observations and the CMAQ modeling system

We analyze hourly PM2.5 (particles with an aerodynamic diameter of ≤ 2.5 μm) concentrations measured at the U.S. Embassy in Dhaka over the 2016 - 2021 time period and find that concentrations are seasonally dependent with the highest occurring in winter and the lowest in monsoon seasons. Mean winter PM2.5 concentrations reached ~165-175 μg/m3 while monsoon concentrations remained ~30-35 μg/m3. Annual mean PM2.5 concentration reached ~5-6 times greater than the Bangladesh annual PM2.5 standard of 15 μg/m3. The number of days exceeding the daily PM2.5 standard of 65 μg/m3 in a year approached nearly 50%. Daily-mean PM2.5 concentrations remained elevated (>65 μg/m3) for more than 80 consecutive days. Night-time concentrations were greater than daytime concentrations. The comparison of results obtained from the Community Multiscale Air Quality (CMAQ) model simulations over the Northern Hemisphere using 108-km horizontal grids with observed data suggests that the model can reproduce the seasonal variation of observed data but underpredicts observed PM2.5 in winter months with a normalized mean bias of 13-32%. In the model, organic aerosol is the largest component of PM2.5, of which secondary organic aerosol plays a dominant role. Transboundary pollution has a large impact on the PM2.5 concentration in Dhaka, with an annual mean contribution of ~40 μg/m3.

A high-precision aerosol retrieval algorithm for FY-3D MERSI-II images

The Medium Resolution Spectral Imager-II (MERSI-II) onboard the recently launched Chinese Fengyun-3D (FY-3D) satellite has great capability in detecting global aerosols as it includes aerosol bands similar to Moderate Resolution Imaging Spectroradiometer (MODIS). However, to date, aerosol retrieval based on MERSI-II is still limited to dark target regions and there is no official aerosol products for the MERSI-II. This study focuses on developing a high-precision algorithm to retrieve aerosol optical depth (AOD) suitable for entire land areas (except snow/ice and inland waters) based on MERSI-II measurements. Considering both the accuracy and retrieval efficiency, a new cost function is constructed based on (1) the fact that the AOD (550 nm) retrieved independently from different bands should be the same with the correct aerosol model, and (2) the assumption that the aerosol types are the same in the 5 × 5 km spatial range. The retrieval method based on the new cost function is nearly 50 times faster than most current methods using iterative calculations. To extend the application adaption of the FY-3D MERSI-II AOD retrieval and avoid the errors caused by the surface Lambertian hypothesis, a bidirectional reflectance distribution function (BRDF) database is built using MODIS products. Eight candidate aerosol models in different natural zones of China are constructed based on AERONET aerosol products from 2010 - 2021. The new method is applied to MERSI-II images over China and validated against ground-based measurements at 14 stations from 2020 to 2021. MODIS aerosol products from three operational algorithms are also used for comparison purposes. The results show that MERSI-II AOD retrievals agree well with the ground-based measurements with correlation coefficient (R), root mean square error (RMSE), and relative mean bias (RMB) of 0.913, 0.123, and 0.955, respectively. In addition, 72.19 % of AOD matchups fall within the expected error (EE) envelopes. The MERSI-II retrievals show higher accuracy than that of MODIS dark target (DT) and deep blue (DB) products and comparable accuracy of the MODIS Multi-Angle Implementation of Atmospheric Correction (MAIAC) product. MERSI-II AOD also shows higher stability in terms of spatial and temporal and better performance under heavy aerosol loading conditions than MODIS products. A good AOD agreement with R from 0.777 to 0.863 between MERSI-II and MODIS products is found over the land of China. The new method showing high retrieval efficiency and accuracy has great potential to be operationally applied on AOD retrieval for MERSI-II.

Controlled air exchange rate method to evaluate reduction of volatile organic compounds by indoor air cleaners

Air cleaning technologies are needed to reduce indoor concentrations and exposure to volatile organic compounds (VOCs). Currently, air cleaning technologies lack an accepted test standard to evaluate their VOC removal performance. A protocol to evaluate the VOC removal performance of air cleaning devices was developed and piloted with two devices. This method injects a VOC mixture and carbon dioxide into a test chamber, supplies outdoor air at a standard building ventilation rate, periodically measures the VOC concentrations in the chamber using solid phase microextraction-gas chromatography-mass spectrometry over a 3-h decay period, and compares the decay rate of VOCs to carbon dioxide to measure the VOC removal air cleaning performance. The method was demonstrated with both a hydroxyl radical generator and an activated carbon air cleaner. It was shown that the activated carbon air cleaner device tested had a clean air delivery rate an order of magnitude greater than the hydroxyl radical generator device (72.10 vs 6.32 m3/h).

Linking Cell Health and Reactive Oxygen Species from Secondary Organic Aerosols Exposure

Oxidative stress is a possible mechanism by which ambient fine particulate matter (PM) exerts adverse biological effects. While multiple biological effects and reactive oxygen species (ROS) production have been observed upon PM exposure, whether the biological effects are ROS-mediated remains unclear. Secondary organic aerosols (SOA) constitute a major fraction of fine PM and can contribute substantially to its toxicity. In this work, we measured three types of cell responses (mitochondrial membrane potential (MMP), caspase 3/7 activity, and ROS) and investigated their associations upon exposure to SOA formed from anthropogenic (naphthalene) and biogenic (α-pinene) precursors. MMP and caspase 3/7 activity (an early indicator of apoptosis) are key indicators of cell health, and changes of them could occur downstream of ROS-mediated pathways. We observed a significant increase in caspase 3/7 activity after SOA exposure, suggesting that apoptosis is an important pathway of cell death induced by SOA. We further found strong associations between a decrease in MMP and increase in caspase 3/7 activity with an increase in cellular ROS level. These results suggest that cell health is largely dependent on the cellular ROS level, highlighting oxidative stress as a key mechanism for biological effects from SOA exposure. Linear regression analyses reveal greater changes of the three cellular responses with increasing carbon oxidation state (OSc) of SOA, suggesting that SOA are more toxic when they are more oxidized. Overall, our work provides critical insights into the associations between cell health and ROS level upon SOA exposure and proposes that OSc could be a suitable proxy to assess the overall SOA toxicity.

Organic Peroxides in Aerosol: Key Reactive Intermediates for Multiphase Processes in the Atmosphere

Organic peroxides (POs) are organic molecules with one or more peroxide (-O-O-) functional groups. POs are commonly regarded as chemically labile termination products from gas-phase radical chemistry and therefore serve as temporary reservoirs for oxidative radicals (HOx and ROx) in the atmosphere. Owing to their ubiquity, active gas-particle partitioning behavior, and reactivity, POs are key reactive intermediates in atmospheric multiphase processes determining the life cycle (formation, growth, and aging), climate, and health impacts of aerosol. However, there remain substantial gaps in the origin, molecular diversity, and fate of POs due to their complex nature and dynamic behavior. Here, we summarize the current understanding on atmospheric POs, with a focus on their identification and quantification, state-of-the-art analytical developments, molecular-level formation mechanisms, multiphase chemical transformation pathways, as well as environmental and health impacts. We find that interactions with SO2 and transition metal ions are generally the fast PO transformation pathways in atmospheric liquid water, with lifetimes estimated to be minutes to hours, while hydrolysis is particularly important for α-substituted hydroperoxides. Meanwhile, photolysis and thermolysis are likely minor sinks for POs. These multiphase PO transformation pathways are distinctly different from their gas-phase fates, such as photolysis and reaction with OH radicals, which highlights the need to understand the multiphase partitioning of POs. By summarizing the current advances and remaining challenges for the investigation of POs, we propose future research priorities regarding their origin, fate, and impacts in the atmosphere.

PM2.5 air pollution components and mortality in Denmark

BACKGROUND

Ambient fine particulate matter (PM_2.5) causes millions of deaths every year worldwide. Identification of the most harmful types of PM_2.5 would facilitate efficient prevention strategies.

OBJECTIVES

The aim of this study was to investigate associations between components of PM_2.5 and mortality in a nation-wide Danish population.

METHODS

Our study base was Danes born 1921-1985 and aged 30-85 years, who were followed up for mortality from 1991 to 2015. We included 678,465 natural cause mortality cases and selected five age, sex and calendar time matched controls to each case from the study base. We retrieved the address history of the study population from Danish registries and assessed five-year average concentrations of eight PM_2.5 components using deterministic Chemistry-Transport Models air pollution models. We estimated mortality rate ratios (MRRs) by conditional logistic regression and adjusted for socio-demographical factors at individual and neighborhood level.

RESULTS

Single pollutant models showed the strongest associations between natural cause mortality and an interquartile increase in sulfate particles (SO₄^--) (MRR: 1.123; 95 % CI: 1.100-1.147 per 1.5 µg/m³) and secondary organic aerosol (SOA) (MRR: 1.054; 95 % CI: 1.048-1.061 per 0.050 µg/m³). Two-pollutant models showed robust associations between SO₄^-- and SOA and natural cause mortality. Elemental carbon and mineral dust showed robust associations with higher respiratory and lung cancer mortality.

CONCLUSION

This nation-wide study found robust associations between natural cause mortality and SO₄^-- particles and SOA, which is in line with the results of previous studies. Elemental carbon and mineral dust showed robust associations with higher respiratory and lung cancer mortality.

Heterogeneous Formation of Organonitrates (ON) and Nitroxy-Organosulfates (NOS) from Adsorbed α-Pinene-Derived Organosulfates (OS) on Mineral Surfaces

Organonitrates (ON) and nitroxy-organosulfates (NOS) are important components of secondary organic aerosols (SOAs). Gas-phase reactions of α-pinene (C₁₀H₁₆), a primary precursor for several ON compounds, are fairly well understood although formation pathways for NOS largely remain unknown. NOS formation may occur via reactions of ON and organic peroxides with sulfates as well as through radical-initiated photochemical processes. Despite the fact that organosulfates (OS) represent a significant portion of the organic aerosol mass, ON and NOS formation from OS is less understood, especially through nighttime heterogeneous and multiphase chemistry pathways. In the current study, surface reactions of adsorbed α-pinene-derived OS with nitrogen oxides on hematite and kaolinite surfaces, common components of mineral dust, have been investigated. α-Pinene reacts with sulfated mineral surfaces, forming a range of OS compounds on the surface. These OS compounds when adsorbed on mineral surfaces can further react with HNO₃ and NO₂, producing several ON and NOS compounds as well as several oxidation products. Overall, this study reveals the complexity of reactions of prevalent organic compounds leading to the formation of OS, ON, and NOS via heterogeneous and multiphase reaction pathways on mineral surfaces. It is also shown that this chemistry is mineralogy-specific.

Traffic-related PM2.5 and its specific constituents on circulatory mortality: A nationwide modelling study in China

BACKGROUND

Short-term fine particulate matter (PM_2.5) exposure and increased circulatory mortality have been well documented. However, there are inconsistent findings on mortality effects of traffic-related pollutants from the perspective of sources or constituents. Few studies have examined such associations using source and constituents simultaneously, and even less are based on large-scale, nationally representative data. We aimed to conduct a comprehensive analysis to investigate source- and constituent-specific mortality effects due to traffic-related PM_2.5 pollution in China.

METHODS

We extracted daily mortality data in 280 counties from the China Disease Surveillance Points system (DSPs) from January 2013 to December 2018. Daily concentrations of traffic-related PM_2.5 and specific constituents were simulated using the Community Multiscale Air Quality (CMAQ) model. The downscaling and adjustment methods were carried out to generate a refined exposure assessment. We estimated the circulatory mortality risk using a standard two-stage approach, combining generalized linear model (GLM) with a quasi-Poisson distribution and random-effects meta-analysis.

RESULTS

We observed that traffic-related PM_2.5 and specific constituents were significantly associated with increased circulatory mortality. An increase of interquartile range of traffic-related PM_2.5, elemental carbon (EC), organic carbon (OC), and nitrate (NO₃^-) were associated with elevated circulatory mortality risks of 1.80 % (95 % confidence interval, CI: 1.27, 2.33), 1.85 % (1.33, 2.37), 1.42 % (0.90, 1.94), and 1.10 % (0.55, 1.66) at 3-day moving average (lag 0-2 days), respectively. We also found relatively high associations between traffic-related PM_2.5 and EC exposures and cardiovascular mortality, and OC exposure and cerebrovascular mortality. Moreover, our stratified analysis demonstrated such mortality risks tended to be stronger in males, individuals age 65 years or older, and during the cold season.

CONCLUSION

Our findings provided robust evidence on significant associations of traffic-related PM_2.5 and specific constituents with circulatory mortality. Further emissions abatement from the transportation sector and corresponding pollutants should merit a particular focus in China.

Ammonium-adduct chemical ionization to investigate anthropogenic oxygenated gas-phase organic compounds in urban air

Volatile chemical products (VCPs) and other non-combustion-related sources have become important for urban air quality, and bottom-up calculations report emissions of a variety of functionalized compounds that remain understudied and uncertain in emissions estimates. Using a new instrumental configuration, we present online measurements of oxygenated organic compounds in a U.S. megacity over a 10-day wintertime sampling period, when biogenic sources and photochemistry were less active. Measurements were conducted at a rooftop observatory in upper Manhattan, New York City, USA using a Vocus chemical ionization time-of-flight mass spectrometer with ammonium (NH4 +) as the reagent ion operating at 1 Hz. The range of observations spanned volatile, intermediate-volatility, and semi-volatile organic compounds with targeted analyses of ~150 ions whose likely assignments included a range of functionalized compound classes such as glycols, glycol ethers, acetates, acids, alcohols, acrylates, esters, ethanolamines, and ketones that are found in various consumer, commercial, and industrial products. Their concentrations varied as a function of wind direction with enhancements over the highly-populated areas of the Bronx, Manhattan, and parts of New Jersey, and included abundant concentrations of acetates, acrylates, ethylene glycol, and other commonly-used oxygenated compounds. The results provide top-down constraints on wintertime emissions of these oxygenated/functionalized compounds with ratios to common anthropogenic marker compounds, and comparisons of their relative abundances to two regionally-resolved emissions inventories used in urban air quality models.

Four year long simulation of carbonaceous aerosols in India: Seasonality, sources and associated health effects

India's air quality is in a dismal state, with many studies ascribing it to PM_2.5. Most of these corroborate that carbonaceous aerosol (CA) constitute significant fraction of PM_2.5. However, investigations on the effect of long-term meteorological or emission changes on PM_2.5 and its components, and their associated health effects are rare. In this work, WRF-Chem simulations for three seasons over four years (2016-2019) were carried out to cogitate the spatial and temporal changes in PM_2.5 and its components in India. Model predicted PM_2.5 concentrations were in good agreement with the ground-based observations for 25 cities. PM_2.5 was highest in winter and lowest in pre-monsoon. PM_2.5 reduced by ∼8% in Indo-Gangetic Plain (IGP) but increased by ∼38% and ∼130% in south and northeast India, respectively, from 2016 to 2019. IGP witnessed three times higher average PM_2.5 concentrations than south India. No significant interannual change in CA contributions was observed, however, it peaked in the winter season. Other inorganics (OIN) were the major component of PM_2.5, contributing more than 40%. Primary organic aerosol (POA) fractions were higher in north India, while secondary inorganic aerosol (SIA) dominated south India. Transport and residential sectors were the chief contributors to CA across India. Biomass burning contributed up to ∼23% of PM_2.5 in regions of IGP during post-monsoon, with CA fractions up to 50%. Associations between PM_2.5 and its components with daily inpatient admissions from a tertiary care centre in Delhi showed that PM_2.5 and OIN had lower associations with daily hospital admissions than CA. Every 10 μg/m³ increase in POA, black carbon (BC), and secondary organic aerosol (SOA) were associated with ∼1.09%, ∼3.07% and ∼4.93% increase in the risk of daily hospital admissions. This invigorates the need for more policies targeting CA rather than PM_2.5 to mitigate associated health risks, in India.

Analysis of the impact of success on three dimensions of sustainability in 173 countries

The United Nations have announced 17 Sustainable Development Goals and 169 targets, which are indivisible and integrated, and which balance the economic, social, and environmental dimensions of sustainable development. This indicates that the performance of successful nations is generally good across many sustainability indicators. Our results, based on multi-criteria and statistical analysis across 173 countries, suggest an interconnection between a country’s sustainability 12 indicators and success. This article focuses on the Country Success and Sustainability (CSS) Maps and Models of the World, which show that improvements in environmental, social, and economic sustainability indicators lead to improvements in the country's success, and vice versa. The CSS Models explain 98.2% of national success and 80.8% of the three dimensions of average sustainability dispersions. When a nation’s success increases by 1%, the 12 indicators of the three dimensions of sustainability improve by 0.85% on average. The human development index and GDP per capita were the success variables with the most substantial impact on 12 sustainability indicators in 173 countries. Calculations made using equal and different weights of 17 criteria show a deviation of 5.34% for the priorities of these 173 countries.

Initial pH Governs Secondary Organic Aerosol Phase State and Morphology after Uptake of Isoprene Epoxydiols (IEPOX)

Aerosol acidity increases secondary organic aerosol (SOA) formed from the reactive uptake of isoprene-derived epoxydiols (IEPOX) by enhancing condensed-phase reactions within sulfate-containing submicron particles, leading to low-volatility organic products. However, the link between the initial aerosol acidity and the resulting physicochemical properties of IEPOX-derived SOA remains uncertain. Herein, we show distinct differences in the morphology, phase state, and chemical composition of individual organic-inorganic mixed particles after IEPOX uptake to ammonium sulfate particles with different initial atmospherically relevant acidities (pH = 1, 3, and 5). Physicochemical properties were characterized via atomic force microscopy coupled with photothermal infrared spectroscopy (AFM-PTIR) and Raman microspectroscopy. Compared to less acidic particles (pH 3 and 5), reactive uptake of IEPOX to the most acidic particles (pH 1) resulted in 50% more organosulfate formation, clearer phase separation (core-shell), and more irregularly shaped morphologies, suggesting that the organic phase transitioned to semisolid or solid. This study highlights that initial aerosol acidity may govern the subsequent aerosol physicochemical properties, such as viscosity and morphology, following the multiphase chemical reactions of IEPOX. These results can be used in future studies to improve model parameterizations of SOA formation from IEPOX and its properties, toward the goal of bridging predictions and atmospheric observations.

Heterogeneous Reactions of α-Pinene on Mineral Surfaces: Formation of Organonitrates and α-Pinene Oxidation Products

Organonitrates (ON) are important components of secondary organic aerosols (SOAs). α-Pinene (C₁₀H₁₆), the most abundant monoterpene in the troposphere, is a precursor for the formation of several of these compounds. ON from α-pinene can be produced in the gas phase via photochemical processes and/or following reactions with oxidizers including hydroxyl radical and ozone. Gas-phase nitrogen oxides (NO₂, NO₃) are N sources for ON formation. Although gas-phase reactions of α-pinene that yield ON are fairly well understood, little is known about their formation through heterogeneous and multiphase pathways. In the current study, surface reactions of α-pinene with nitrogen oxides on hematite (α-Fe₂O₃) and kaolinite (SiO₂Al₂O₃(OH)₄) surfaces, common components of mineral dust, have been investigated. α-Pinene oxidizes upon adsorption on kaolinite, forming pinonaldehyde, which then dimerizes on the surface. Furthermore, α-pinene is shown to react with adsorbed nitrate species on these mineral surfaces producing multiple ON and other oxidation products. Additionally, gas-phase oxidation products of α-pinene on mineral surfaces are shown to more strongly adsorb on the surface compared to α-pinene. Overall, this study reveals the complexity of reactions of prevalent organic compounds such as α-pinene with adsorbed nitrate and nitrogen dioxide, revealing new heterogeneous reaction pathways for SOA formation that is mineralogy specific.

Pathogenic Mechanisms of Secondary Organic Aerosols

Air pollution represents a major health problem and an economic burden. In recent years, advances in air pollution research has allowed particle fractionation and identification of secondary organic aerosol (SOA). SOA is formed from either biogenic or anthropogenic emissions, through a mass transfer from the gaseous mass to the particulate phase in the atmosphere. They can have deleterious impact on health and the mortality of individuals with chronic inflammatory diseases. The pleiotropic effects of SOA could involve different and interconnected pathogenic mechanisms ranging from oxidative stress, inflammation, and immune system dysfunction. The purpose of this review is to present recent findings about SOA pathogenic roles and potential underlying mechanisms focusing on the lungs; the latter being the primary exposed organ to atmospheric pollutants.

The mediating role of scientifical-medical satisfaction between COVID-19 conspiracy beliefs and vaccine confidence: a two-waves structural equation model

Vaccine confidence has emerged as one of the most relevant psychological factors implied in the worldwide affecting the fight against COVID-19-as well as public trust in doctors, medicine, and science. Indeed, the vaccine confidence is crucial to maximize the trust in vaccines and their use for prevention, with several implications for public health. This study aimed to analyse the relationships among between vaccine confidence, conspiracy beliefs about COVID-19, and satisfaction with science and medicine in handling the COVID-19 pandemic. A longitudinal observational survey was administered to a convenience sample (n = 544; mean age 52.76 y.o., SD = 15.11; females 46.69%) from the Italian general population. A two-waves mediation model-a structural equation model technique-was used. The survey was part of a larger international project ( https://osf.io/qy65b/ ). The model highlighted that the conspiracy beliefs about COVID-19 had a negative effect on the satisfaction with medicine and science (β = - 0.13, se = 0.03, p < .001). The latter, in turn, had a positive effect on vaccine confidence (β = 0.10, se = .05, p < .001). Interestingly, the effect of conspiracy beliefs on vaccine confidence was completely mediated by the scientifical-medical satisfaction (β = - 0.02, se = 0.01, p < .05). These results highlight how the scientifical-medical satisfaction can fully mediate the relationship between conspiracy beliefs about COVID-19 and vaccine confidence. These findings about vaccine hesitancy and confidence and disclose have implications for psychological and social interventions that could promote vaccine confidence by targeting the satisfaction with science and medicine.

Volatile Chemical Product Enhancements to Criteria Pollutants in the United States

Volatile chemical products (VCPs) are a significant source of reactive organic carbon emissions in the United States with a substantial fraction (>20% by mass) serving as secondary organic aerosol (SOA) precursors. Here, we incorporate a new nationwide VCP inventory into the Community Multiscale Air Quality (CMAQ) model with VCP-specific updates to better model air quality impacts. Model results indicate that VCPs mostly enhance anthropogenic SOA in densely populated areas with population-weighted annual average SOA increasing 15-30% in Southern California and New York City due to VCP emissions (contribution of 0.2-0.5 μg m^-3). Annually, VCP emissions enhance total population-weighted PM_2.5 by ∼5% in California, ∼3% in New York, New Jersey, and Connecticut, and 1-2% in most other states. While the maximum daily 8 h ozone enhancements from VCP emissions are more modest, their influence can cause a several ppb increase on select days in major cities. Printing Inks, Cleaning Products, and Paints and Coatings product use categories contribute ∼75% to the modeled VCP-derived SOA and Cleaning Products, Paints and Coatings, and Personal Care Products contribute ∼81% to the modeled VCP-derived ozone. Overall, VCPs enhance multiple criteria pollutants throughout the United States with the largest impacts in urban cores.

Detailed Characterization of Solid and Volatile Particle Emissions of Two Euro 6 Diesel Vehicles

The solid particle number emissions of Diesel vehicles are very low due to the particulate filters as exhaust aftertreatment devices. However, periodically, the trapped particles are oxidized (i.e., active regeneration) in order to keep the backpressure at low levels. The solid particle number emissions during regenerations are only partly covered by the regulations. Many studies have examined the emissions during regenerations, but their contribution to the overall emissions has not been addressed adequately. Furthermore, the number concentration of volatile particles, which is not included in the regulations, can be many of orders of magnitude higher. In this study, the particulate emissions of two light-duty Euro 6 vehicles were measured simultaneously at the tailpipe and the dilution tunnel. The results showed that the weighted (i.e., considering the emissions during regeneration) solid particle number emissions remained well below the applicable limit of 6 × 1011 #/km (solid particles > 23 nm). This was true even when considering solid sub-23 nm particles. However, the weighted volatile particle number emissions were many orders of magnitude higher, reaching up to 3 × 1013 #/km. The results also confirmed the equivalency of the solid particle number results between tailpipe and dilution tunnel locations. This was not the case for the volatile particles which were strongly affected by desorption phenomena. The high number of volatiles during regenerations even interfered with the 10 nm solid particle number measurements at the dilution tunnel, even though a catalytic stripper equipped instrument was also used in the dilution tunnel.

Human-health impacts of controlling secondary air pollution precursors

Exposure to ozone and fine particle (PM_2.5) air pollution results in premature death. These pollutants are predominantly secondary in nature and can form from nitrogen oxides (NO_X), sulfur oxides (SO_X), and volatile organic compounds (VOCs). Predicted health benefits for emission reduction scenarios often incompletely account for VOCs as precursors as well as the secondary organic aerosol (SOA) component of PM_2.5. Here, we show that anthropogenic VOC emission reductions are more than twice as effective as equivalent fractional reductions of SO_X or NO_X at reducing air pollution-associated cardiorespiratory mortality in the United States. A 25% reduction in anthropogenic VOC emissions from 2016 levels is predicted to avoid 13,000 premature deaths per year, and most (85%) of the VOC-reduction benefits result from reduced SOA with the remainder from ozone. While NO_X (-5.7 ± 0.2 % yr^-1) and SO_X (-12 ± 1 % yr^-1) emissions have declined precipitously across the U.S. since 2002, anthropogenic VOC emissions (-1.8 ± 0.3 % yr^-1) and concentrations of non-methane organic carbon (-2.4 ± 1.0 % yr^-1) have changed less. This work indicates preferentially controlling VOCs could yield significant benefits to human health.

Revisiting Total Particle Number Measurements for Vehicle Exhaust Regulations

Road transport significantly contributes to air pollution in cities. Emission regulations have led to significantly reduced emissions in modern vehicles. Particle emissions are controlled by a particulate matter (PM) mass and a solid particle number (SPN) limit. There are concerns that the SPN limit does not effectively control all relevant particulate species and there are instances of semi-volatile particle emissions that are order of magnitudes higher than the SPN emission levels. This overview discusses whether a new metric (total particles, i.e., solids and volatiles) should be introduced for the effective regulation of vehicle emissions. Initially, it summarizes recent findings on the contribution of road transport to particle number concentration levels in cities. Then, both solid and total particle emission levels from modern vehicles are presented and the adverse health effects of solid and volatile particles are briefly discussed. Finally, the open issues regarding an appropriate methodology (sampling and instrumentation) in order to achieve representative and reproducible results are summarized. The main finding of this overview is that, even though total particle sampling and quantification is feasible, details for its realization in a regulatory context are lacking. It is important to define the methodology details (sampling and dilution, measurement instrumentation, relevant sizes, etc.) and conduct inter-laboratory exercises to determine the reproducibility of a proposed method. It is also necessary to monitor the vehicle emissions according to the new method to understand current and possible future levels. With better understanding of the instances of formation of nucleation mode particles it will be possible to identify its culprits (e.g., fuel, lubricant, combustion, or aftertreatment operation). Then the appropriate solutions can be enforced and the right decisions can be taken on the need for new regulatory initiatives, for example the addition of total particles in the tailpipe, decrease of specific organic precursors, better control of inorganic precursors (e.g., NH3, SOx), or revision of fuel and lubricant specifications.