Molecular signatures and formation mechanisms of water-soluble chromophores in particulate matter from Karachi in Pakistan.

Excitation-emission matrix (EEM) fluorescence spectroscopy is a widely-used method for characterizing the chemical components of brown carbon (BrC). However, the molecular basics and formation mechanisms of chromophores, which are decomposed by parallel factor (PARAFAC) analysis, are not yet fully understood. In this study, we characterized the water-soluble organic carbon (WSOC) in aerosols collected from Karachi, Pakistan, using EEM spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). We identified three PARAFAC components, including two humic-like components (C1 and C2) and one phenolic-like species (C3). We determined the molecular families associated with each component by performing Spearman correlation analysis between FT-ICR MS peaks and PARAFAC component intensities. We found that the C1 and C2 components were associated with nitrogen-enriched compounds, where C2 with the longest emission wavelength exhibited a higher level of aromaticity, N content, and oxygenation than C1. The C3 associated formulas have fewer nitrogen-containing species, a lower unsaturation degree, and a lower oxidation state. An oxidation pathway was identified as an important process in the formation of C1 and C2 components at the molecular level, particularly for the assigned CHON compounds associated with the gas-phase oxidation process, despite their diverse precursor types. Numerous C2 formulas were found in the "potential BrC" region and overlapped with the BrC-associated formulas. It can be inferred that the compounds that fluoresce C2 contributed considerably to the light absorption of BrC. These findings are essential for future studies utilizing the EEM-PARAFAC method to explore the sources, processes, and compositions of atmospheric BrC.

Pollution source and chemicals structure of the water-soluble fractions in PM2.5 that induce apoptosis in China.

Identify risk drivers is the key condition in air pollution control, and biological effect-directed analysis is the most commented method for combing chemical identify and human health. The water-soluble organic matter contained in PM2.5 plays an important role in human health, while it is also the most difficult to identify its chemical information. Exploring the structural characteristics and pollution sources of its key toxic components is the optimized strategy to meet this question. In this study, the induction of apoptosis by the water-soluble fractions (WSF) of PM2.5 samples collected in 10 major cities in China over a period of 1 year was observed in vitro in Beas-2b cells. Organic carbon structures were examined using nuclear magnetic resonance; air potential sources were identified using δ13C and 14C isotopic markers. Apoptosis induction by WSF in PM2.5 was generally stronger in northern cities than in southern cities, and in winter than in summer. Organic compounds with aromatic and double-bond carbon structures from secondary products of motor vehicle exhausts, coal-derived emissions, and emissions derived from the burning of core residues may be primarily responsible for apoptosis induction by PM2.5. Our results will contribute to understanding the toxic substances contained in WSF and provide basic data for accurate pollution control.

Aquatic environmental fates and risks of benzotriazoles, benzothiazoles, and p-phenylenediamines in a catchment providing water to a megacity of China.

Wearing of vehicle parts could release many chemical additives into the environment, such as benzotriazoles (BTRs), benzothiazoles (BTHs), and p-phenylenediamines (PPDs), which are potentially toxic to wildlife and humans. This study investigated the occurrence, source, and risks of BTRs, BTHs, and PPDs in a source catchment providing water to Guangzhou, a megacity in South China, covering groundwater, surface water, and stormwater. The results showed that BTRs and BTHs were predominant in surface water and groundwater. Unexpectedly, the BTR and BTH concentrations were lower in surface water than groundwater in a third of the paired samples. For the first time, 6PPD-quinone, a toxic ozonation product of N-(1,3-dimethylbutyl)-N'-phenyl-1,4-phenylenediamine (6PPD), was extensively detected in source waters. Stormwater decreased the BTR concentrations but increased the 6PPD-quinone concentrations in surface water owing to their affiliation to suspended particles. From natural to urban segments of Liuxi river, a downstream increasing trend in BTR and BTH concentrations was observed, confirming that they are indicative of urban anthropogenic activities. Strong correlations between industrial activities and BTR or BTH concentrations in surface water indicated that industrial activities were their main sources. Six compounds were prioritized as potentially persistent, mobile, and toxic (PMT) chemicals, combing our monitoring results and REACH criterion. This study improves our understanding of the environmental fates and risks of water-soluble tire-wear chemicals, which provides important information for chemical management, and indicates attention should be paid to the risk posed by 6PPD-quinone in the source water.

Regional monitoring of biomass burning using passive air sampling technique reveals the importance of MODIS unresolved fires.

Field-based sampling can provide more accurate evaluation than MODIS in regional biomass burning (BB) emissions given the limitations of MODIS on unresolved fires. Polyurethane foam-based passive air samplers (PUF-PASs) are a promising tool for collecting atmospheric monosaccharides. Here, we deployed PUF-PASs to monitor monosaccharides and other BB-related biomarkers and presented a dataset of 31 atmospheric BB-related biomarkers in the Indo-China Peninsula (ICP) and Southwest China. The peak concentrations of monosaccharides in the ICP occurred before monsoon season. The highest concentrations were in the eastern Mekong plain, while the lowest were along the eastern coast. BB-related biomarkers displayed elevated concentrations after April, particularly in the monsoon season; however, fewer active fires were recorded by MODIS. This revealed the importance of MODIS unresolved fires (e.g., indoor biofuel combustion, small-scale BB incidents, and charcoal fires) to the regional atmosphere. The PAS derived levoglucosan concentrations indicated that, with the inclusion of MODIS unresolved fires, the estimated top-down emissions of PM (4194-4974 Gg/yr), OC (1234-1719 Gg/yr) and EC (52-384 Gg/yr) would be higher than previous bottom-up estimations in the ICP. Future studies on these MODIS unresolved fires and regional monitoring data of BB are vital for improving the modeling of regional BB emissions.

Polycyclic Aromatic Carbon: A Key Fraction Determining the Light Absorption Properties of Methanol-Soluble Brown Carbon of Open Biomass Burning Aerosols.

The composition and radiative forcing of light-absorbing brown carbon (BrC) aerosol remain poorly understood. Polycyclic aromatics (PAs) are BrC chromophores with fused benzene rings. Understanding the occurrence and significance of PAs in BrC is challenging due to a lack of standards for many PAs. In this study, we quantified polycyclic aromatic carbon (PAC), defined as the carbon of fused benzene rings, based on molecular markers (benzene polycarboxylic acids, BPCAs). Open biomass burning aerosols (OBBAs) of 22 rainforest plants were successively extracted with water and methanol for the analysis of water- and methanol-soluble PAC (WPAC and MPAC, respectively). PAC is an important fraction of water- and methanol-soluble organic carbon (WSOC and MSOC, respectively). WPAC/WSOC ranged from 0.03 to 0.18, and MPAC/MSOC was even higher (range: 0.16-0.80). The priority polycyclic aromatic hydrocarbons contributed less than 1% of MPAC. The mass absorption efficiency (MAE) of MSOC showed a strong linear correlation with MPAC/MSOC (r = 0.60-0.95, p < 0.01). The absorption Ångström exponent (AAE) of methanol-soluble BrC showed a strong linear correlation with the degree of aromatic condensation of MPAC, which was described by the average number of carboxylic groups of BPCA (r = -0.79, p < 0.01). This result suggested that PAC was a key fraction determining the light absorption properties (i.e., light absorptivity and wavelength dependence) of methanol-soluble BrC in OBBAs.

The application of land use regression model to investigate spatiotemporal variations of PM2.5 in Guangzhou, China: Implications for the public health benefits of PM2.5 reduction.

Understanding the intra-city variation of PM2.5 is important for air quality management and exposure assessment. In this study, to investigate the spatiotemporal variation of PM2.5 in Guangzhou, we developed land use regression (LUR) models using data from 49 routine air quality monitoring stations. The R2, adjust R2 and 10-fold cross validation R2 for the annual PM2.5 LUR model were 0.78, 0.72 and 0.66, respectively, indicating the robustness of the model. In all the LUR models, traffic variables (e.g., length of main road and the distance to nearest ancillary) were the most common variables in the LUR models, suggesting vehicle emission was the most important contributor to PM2.5 and controlling vehicle emissions would be an effective way to reduce PM2.5. The predicted PM2.5 exhibited significant variations with different land uses, with the highest value for impervious surfaces, followed by green land, cropland, forest and water areas. Guangzhou as the third largest city that PM2.5 concentration has achieved CAAQS Grade II guideline in China, it represents a useful case study city to examine the health and economic benefits of further reduction of PM2.5 to the lower concentration ranges. So, the health and economic benefits of reducing PM2.5 in Guangzhou was further estimated using the BenMAP model, based on the annual PM2.5 concentration predicted by the LUR model. The results showed that the avoided all cause mortalities were 992 cases (95% CI: 221-2140) and the corresponding economic benefits were 1478 million CNY (95% CI: 257-2524) (willingness to pay approach) if the annual PM2.5 concentration can be reduced to the annual CAAQS Grade I guideline value of 15 µg/m3. Our results are expected to provide valuable information for further air pollution control strategies in China.

Probing Legacy and Alternative Flame Retardants in the Air of Chinese Cities.

An increasing number of alternative flame retardants (FRs) are being introduced, following the international bans on the use of polybrominated diphenyl ether (PBDE) commercial mixtures. FRs' production capacity has shifted from developed countries to developing countries, with China being the world's largest producer and consumer of FRs. These chemicals are also imported with e-waste to China. Therefore, it is important to understand the current status of regulated brominated FRs, their phase-out in China, and their replacement by alternatives. In this study, a broad suite of legacy and alternative FRs, including eight PBDEs, six novel brominated FRs (NBFRs), two dechlorane plus variants (DPS), and 12 organophosphate FRs (OPFRs) were evaluated in the air of 10 large Chinese cities in 2018. OPFRs are the most prevalent FRs in China, exhibiting a wide range of 1-612 ng/m3, which is several orders of magnitude higher than PBDEs (1-1827 pg/m3) and NBFRs (1-1428 pg/m3). BDE 209 and DBDPE are the most abundant compounds in brominated FRs (>80%). The North China Plain (NCP, excluding Beijing), Guangzhou, and Lanzhou appear to be three hotspots, although with different FR patterns. From 2013/2014 to 2018, levels of PBDEs, NBFRs, and DPs have significantly decreased, while that of OPFRs has increased by 1 order of magnitude. Gas-particle partitioning analysis showed that FRs could have not reached equilibrium, and the steady-state model is better suited for FRs with a higher log KOA (>13). To facilitate a more accurate FR assessment in fine particles, we suggest that, in addition to the conventional volumetric concentration (pg/m3), the mass-normalized concentration (pg/g PM2.5) could also be used.

Biomass burning organic aerosols significantly influence the light absorption properties of polarity-dependent organic compounds in the Pearl River Delta Region, China.

Atmospheric brown carbon (BrC) is an important constituent of light-absorbing organic aerosols with many unclear issues. Here, the light-absorption properties of BrC with different polarity characteristics at a regional site of Pearl River Delta Region during 2016-2017, influenced by sources and molecular compositions, were revealed using radiocarbon analysis and Fourier transform ion cyclotron resonance mass spectrometry. Humic-like substance (HULIS), middle polar (MP), and low polar (LP) carbon fractions constitute 46 ± 17%, 30 ± 7%, and 7 ± 3% of total absorption coefficient from bulk extracts, respectively. Our results show that the absorption proportions of HULIS and MP to the total BrC absorption are higher than their mass proportions to organic carbon mass, indicating that HULIS and MP are the main light-absorbing components in water-soluble and water-insoluble organic carbon fractions, respectively. With decreases in non-fossil HULIS, MP, and LP carbon fractions (66 ± 2%, 52 ± 2%, and 36 ± 3%, respectively), the abundances of unsaturated compounds and mass absorption efficiency at 365 nm of three fractions decreased synchronously. Increases in both non-fossil carbon and levoglucosan in winter imply that the enhanced light-absorption could be attributed to elevated levels of biomass burning organic aerosols (BBOA), which increases the number of light-absorbing nitrogen-containing compounds. Moreover, the major type of potential BrC in HULIS and MP carbon fractions are oxidized BBOA, but the potential BrC chromophores in LP are mainly associated with primary BBOA. This study reveals that biomass burning has adverse effects on radiative forcing and air quality, and probably indicates the significant influences of atmospheric oxidation reactions on the forms of chromophores.

Light absorption and emissions inventory of humic-like substances from simulated rainforest biomass burning in Southeast Asia.

Humic-like substances (HULIS) are complex mixtures that are highly associated with brown carbon (BrC) and are important components of biomass burning (BB) emissions. In this study, we investigated the light absorption, emission factors (EFs), and amounts of HULIS emitted from the simulated burning of 27 types of regionally important rainforest biomass in Southeast Asia. We observed that HULIS had a high mass absorption efficiency at 365 nm (MAE365), with an average value of 2.6 ± 0.83 m2 g-1 C. HULIS emitted from BB accounted for 65% ± 13% of the amount of water-soluble organic carbon (WSOC) and 85% ± 10% of the light absorption of WSOC at 365 nm. The EFs of HULIS from BB averaged 2.3 ± 2.1 g kg-1 fuel, and the burning of the four vegetation subtypes (herbaceous plants, shrubs, evergreen trees, and deciduous trees) exhibited different characteristics. The differences in EFs among the subtypes were likely due to differences in lignin content in the vegetation, the burning conditions, or other factors. The light absorption characteristics of HULIS were strongly associated with the EFs. The annual emissions (minimum-maximum) of HULIS from BB in this region in 2016 were 200-371 Gg. Furthermore, the emissions from January to April accounted for 99% of the total annual emissions of HULIS, which is likely the result of the burning activities during this season. The most significant emission regions were Cambodia, Burma, Thailand, and Laos. This study, which evaluated emissions of HULIS by simulating open BB, contributes to a better understanding of the light-absorbing properties and regional budgets of BrC in this region.

Dual carbon isotopes (14C and 13C) and optical properties of WSOC and HULIS-C during winter in Guangzhou, China.

Water-soluble brown carbon (ws-BrC) exerts an important influence on climate change, but its emission sources and optical properties remain poorly understood. In this study, we isolated two ws-BrC proxies, water-soluble organic carbon (WSOC) and humic-like substance carbon (HULIS-C), from particulate matter collected in Guangzhou, China, during December 2012 for the measurement of dual carbon isotopes (14C and 13C) and light absorption. The mass absorption efficiencies of WSOC and HULIS-C at 365nm were 0.81±0.16 and 1.33±0.21m2g-1C, respectively. The 14C results showed that two-thirds of WSOC and HULIS-C were derived from non-fossil sources (e.g., biomass burning and biogenic emission), and the remaining third was derived from fossil sources. The δ13C values of WSOC and HULIS-C were -23.7±1.2‰ and -24.2±0.9‰, respectively, underlining the limited influences of C4 plants and natural gas on ws-BrC. Fitting the data to a multiple linear regression, we further concluded that approximately 80% and 10% of the light absorption at 365nm was due to non-fossil and fossil carbon, respectively. Non-fossil sources of ws-BrC, such as the burning of agricultural residue, were responsible for the light absorption recorded in Guangzhou.

Sources, compositions, and optical properties of humic-like substances in Beijing during the 2014 APEC summit: Results from dual carbon isotope and Fourier-transform ion cyclotron resonance mass spectrometry analyses.

Humic-like substances (HULIS) are a class of high molecular weight, light-absorbing compounds that are highly related to brown carbon (BrC). In this study, the sources and compositions of HULIS isolated from fine particles collected in Beijing, China during the 2014 Asia-Pacific Economic Cooperation (APEC) summit were characterized based on carbon isotope (13C and 14C) and Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analyses, respectively. HULIS were the main light-absorbing components of water-soluble organic carbon (WSOC), accounting for 80.2 ±â€¯6.1% of the WSOC absorption capacity at 365 nm. The carbon isotope data showed that HULIS had a lower non-fossil contribution (53 ±â€¯4%) and were less enriched with 13C (-24.2 ±â€¯0.6‰) relative to non-HULIS (62 ±â€¯8% and -20.8 ±â€¯0.3‰, respectively). The higher relative intensity fraction of sulfur-containing compounds in HULIS before and after APEC was attributed to higher sulfur dioxide levels emitted from fossil fuel combustion, whereas the higher fraction of nitrogen-containing compounds during APEC may have been due to the relatively greater contribution of non-fossil compounds or the influence of nitrate radical chemistry. The results of investigating the relationships among the sources, elemental compositions, and optical properties of HULIS demonstrated that the light absorption of HULIS appeared to increase with increasing unsaturation degree, but decrease with increasing oxidation level. The unsaturation of HULIS was affected by both sources and aging level.

Semivolatile Organic Compounds (SOCs) in Fine Particulate Matter (PM2.5) during Clear, Fog, and Haze Episodes in Winter in Beijing, China.

Few efforts have been made to elucidate the influence of weather conditions on the fate of semivolatile organic compounds (SOCs). Here, daily fine particulate matter (PM2.5) during clear, haze, and fog episodes collected in the winter in Beijing, China was analyzed for polycyclic aromatic hydrocarbons (PAHs), brominated flame retardants (BFRs), and organophosphate flame retardants (OPFRs). The total concentrations of PAHs, OPFRs, and BFRs had medians of 45.1 ng/m3 and 1347 and 46.7 pg/m3, respectively. The temporal pattern for PAH concentrations was largely dependent on coal combustion for residential heating. OPFR compositions that change during colder period were related to enhanced indoor emissions due to heating. The mean concentrations of SOCs during haze and fog days were 2-10 times higher than those during clear days. We found that BFRs with lower octanol and air partition coefficients tended to increase during haze and fog episodes, be removed from PM2.5 during clear episodes, or both. For PAHs and OPFRs, pollutants that are more recalcitrant to degradation were prone to accumulate during haze and fog days. The potential source contribution function (PSCF) model indicated that southern and eastern cities were major source regions of SOCs at this site.