Molecular characteristics of organic compositions in fresh and aged biomass burning aerosols

Characterization of biomass burning tracers in particulate matter at 12 sites in China: Significant increase of coal combustion emitted levoglucosan in northern China during winter

Biomass burning (BB) is the largest contributor to carbonaceous aerosols globally. Specific organic tracers can track BB particles and identify BB types. At present, there is limited information on the composition of BB tracers on a continental scale. In this study, we conducted year-round sampling of particulate matter (PM) at 12 sites in China. Nine BB tracers were measured in PM with aerodynamic diameters <1.1 μm (PM<1.1), in the range of 1.1-3.3 μm (PM1.1-3.3), and > 3.3 μm (PM>3.3). The annual average concentration of these nine BB tracers (∑9 BB tracers) in the total PM was 366 ng m-3 with the majority of levoglucosan (66 %). The concentration of ∑9 BB tracers was higher in northern China than in southern China, especially in winter. ∑9 BB tracers were most enriched in PM<1.1 (50-61 % in mass), followed by PM1.1-3.3 and PM>3.3. The highest concentrations of ∑9 BB tracers were observed in winter, while satellite-recorded fire spots were intensive in autumn and spring. The mismatch of seasonal trends between them indicated that the high levels of BB tracers in winter was not due to open BB. The composition of 4-hydroxybenzoic acid, syringic acid and vanillic acid suggested that the burning of crop residues and softwoods were the major BB types in China. The ratio of levoglucosan to mannosan could neither identify the major BB types in China nor distinguish between BB and coal combustion. Correlation analysis and the PMF model demonstrated that non-BB sources contributed 7 %-58 % to levoglucosan at the 12 sites, with coal combustion being the predominant non-BB source in China, especially in northern urban sites during winter. Our findings suggest that caution should be taken in application of these organic tracers to identify BB types and estimate BB aerosols.

Effects of photochemical aging on the molecular composition of organic aerosols derived from agricultural biomass burning in whole combustion process

Biomass burning organic aerosols (BBOA) are key components of atmospheric particulate matter, yet the effects of aging process on their chemical composition and related properties remain poorly understood. In this study, fresh smoke emissions from the combustion of three types of agricultural biomass residues (rice, maize, and wheat straws) were photochemically aged in an oxidation flow reactor. The changes in BBOA composition were characterized by offline analysis using ultrahigh performance liquid chromatography coupled with Orbitrap mass spectrometry. The BBOA molecular composition varied dramatically with biomass type and aging process. Fresh and aged BBOA were predominated by CHO and nitrogen-containing CHON, CHN, and CHONS species, while with very few CHOS and other non‑oxygen species. The signal peak area variations revealed that individual molecular species underwent dynamic changes, with 77-81 % of fresh species decreased or even disappeared and 33-46 % of aged species being newly formed. A notable increase was observed in the number and peak area of CxHyO≥6 compounds in aged BBOA, suggesting that photochemical process served as an important source of highly oxygenated species. Heterocyclic CxHyN2 compounds mostly dominated in fresh CHN species, whereas CxHyN1 were more abundant in aged ones. Fragmentation and homologs oxidation by addition of oxygen-containing functional groups were important pathways for the BBOA aging. The changes in BBOA composition with aging would have large impacts on particle optical properties and toxicity. This study highlights the significance of photochemical aging process in altering chemical composition and related properties of BBOA.

Laboratory study on the characteristics of fresh and aged PM1 emitted from typical forest vegetation combustion in Southwest China

The frequency and intensity of forest fires are amplified by climate change. Substantial quantities of PM1 emitted from forest fires can undergo gradual atmospheric dispersion and long-range transport, thus impacting air quality far from the source. However, the chemical composition and physical properties of PM emitted from forest fires and its changes during atmospheric transport remain uncertain. In this study, the evolution of organic carbon (OC), elemental carbon (EC), water-soluble ions, and water-soluble metals in the particulate phase of smoke emitted from the typical forest vegetation combustion in Southwest China before and after photo-oxidation was investigated in the laboratory. Two aging periods of 5 and 9 days were selected. The OC and TC mass concentrations tended to decrease after 9-days aged compared to fresh emissions. OP, OC2, and OC3 in PM1 are expected to be potential indicators of fresh smoke, while OC3 and OC4 may serve as suitable markers for identifying aged carbon sources from the typical forest vegetation combustion in Southwest China. K+ exhibited the highest abundant water-soluble ion in fresh PM1, whereas NO3- became the most abundant water-soluble ion in aged PM1. NH4NO3 emerged as the primary secondary inorganic aerosol emitted from typical forest vegetation combustion in Southwest China. Notably, a 5-day aging period proved insufficient for the complete formation of the secondary inorganic aerosols NH4NO3 and (NH4)2SO4. After aging, the mass concentration of the water-soluble metal Ni in PM1 from typical forest vegetation combustion in Southwest China decreased, while the mean mass concentrations of all other water-soluble metals increased in varying degrees. These findings provide valuable data support and theoretical guidance for studying the atmospheric evolution of forest fire aerosols, as well as contribute to policy formulation and management of atmospheric environment safety and human health.

Impact of Biomass Burning on Arctic Aerosol Composition

Emissions from biomass burning (BB) occurring at midlatitudes can reach the Arctic, where they influence the remote aerosol population. By using measurements of levoglucosan and black carbon, we identify seven BB events reaching Svalbard in 2020. We find that most of the BB events are significantly different to the rest of the year (nonevents) for most of the chemical and physical properties. Aerosol mass and number concentrations are enhanced by up to 1 order of magnitude during the BB events. During BB events, the submicrometer aerosol bulk composition changes from an organic- and sulfate-dominated regime to a clearly organic-dominated regime. This results in a significantly lower hygroscopicity parameter κ for BB aerosol (0.4 ± 0.2) compared to nonevents (0.5 ± 0.2), calculated from the nonrefractory aerosol composition. The organic fraction in the BB aerosol showed no significant difference for the O:C ratios (0.9 ± 0.3) compared to the year (0.9 ± 0.6). Accumulation mode particles were present during all BB events, while in the summer an additional Aitken mode was observed, indicating a mixture of the advected air mass with locally produced particles. BB tracers (vanillic, homovanillic, and hydroxybenzoic acid, nitrophenol, methylnitrophenol, and nitrocatechol) were significantly higher when air mass back trajectories passed over active fire regions in Eastern Europe, indicating agricultural and wildfires as sources. Our results suggest that the impact of BB on the Arctic aerosol depends on the season in which they occur, and agricultural and wildfires from Eastern Europe have the potential to disturb the background conditions the most.

Photochemical evolution of the molecular composition of dissolved organic carbon and dissolved brown carbon from wood smoldering

Recently, extreme wildfires occur frequently around the world and emit substantial brown carbon (BrC) into the atmosphere, whereas the molecular compositions and photochemical evolution of BrC remain poorly understood. In this work, primary smoke aerosols were generated from wood smoldering, and secondary smoke aerosols were formed by the OH radical photooxidation in an oxidation flow reactor, where both primary and secondary smoke samples were collected on filters. After solvent extraction of filter samples, the molecular composition of dissolved organic carbon (DOC) was determined by Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS). The molecular composition of dissolved BrC was obtained based on the constraints of DOC formulae. The proportion of dissolved BrC fractions accounted for approximately 1/3-1/2 molecular formulae of DOC. The molecular characteristics of dissolved BrC showed higher levels of carbon oxidation state, double bond equivalents, and modified aromaticity index than those of DOC, indicating that dissolved BrC fractions were a class of organic structures with relatively higher oxidation state, unsaturated and aromatic degree in DOC fractions. The comparative analysis suggested that aliphatic and olefinic structures dominated DOC fractions (contributing to 70.1%-76.9%), while olefinic, aromatic, and condensed aromatic structures dominated dissolved BrC fractions (contributing to 97.5%-99.9%). It is worth noting that dissolved BrC fractions only contained carboxylic-rich alicyclic molecules (CRAMs)-like structures, unsaturated hydrocarbons, aromatic structures, and highly oxygenated compounds. CRAMs-like structures were the most abundant species in both DOC and dissolved BrC fractions. Nevertheless, the specific molecular characteristics for DOC and dissolved BrC fractions varied with subgroups after aging. The results highlight the similarities and differences in the molecular compositions and characteristics of DOC and dissolved BrC fractions with aging. This work will provide insights into understanding the molecular composition of DOC and dissolved BrC in smoke.

Neutral saccharides and hemicellulose over two urban sites in Indo-Gangetic Plain and Central Europe during winter

Saccharides are ubiquitous organic compounds that are omnipresent in nature and are considered tracers of aerosol sources. Saccharides and hemicellulose were analyzed in the aerosols of two polluted regions (Allahabad, India and Sosnowiec, Poland). The chemical compositions of the compounds and their abundances were significantly different at the two sites. Levoglucosan was the most dominant saccharide present at both sites. Galactosan, anhydroglucofuranose, mannosan, glucose, arabitol, D-pinitol, sucrose, and trehalose were found in Allahabad samples in high abundance but were significantly lower than levoglucosan. Mannosan, galactosan, arabinose, glycerol, and sucrose were significant compounds in Sosnowiec after dominating levoglucosan. The major sources of saccharides present in the Allahabad aerosols are hardwood and agricultural waste-burning emissions, whereas those at Sosnowiec are attributed to the burning of softwood (mainly gymnosperm trees), pine needles, or sporadically grass during the winter. Further, the chemical characteristics of hemicellulose remnants present in ambient aerosol at the Indian and European sites were analyzed and discussed. At both locations, hemicellulose was found using methanolysis of the filter samples; however, its state of preservation was poor. We believe that the primary sources of hemicellulose remnants are incomplete wood burning, crop straw, grass burning, or plant debris. Relatively poor preservation is associated with partial hemicellulose degradation when exposed to elevated temperatures or due to the oxidation and microbial degradation of plant fragments.

Insight into the Primary and Secondary Particle-Bound Methoxyphenols and Nitroaromatic Compound Emissions from Solid Fuel Combustion and the Updated Source Tracers

Methoxyphenols and nitroaromatic compounds (NACs) have strong atmospheric radiative forcing effects and adverse effects on human health. They are emitted from the incomplete combustion of solid fuels and are secondarily formed through photochemical reactions. Here, an on-site study was conducted to determine the primary emission and secondary formation of particulate phase products from a variety of solid fuels through a potential aerosol mass-oxidation flow reactor. Emission factors for total quantified methoxyphenols and NACs (i.e., EF∑Methoxyphenols and EF∑NACs) varied by 2 orders of magnitude among different fuels, which were greatly influenced by volatile matter, incomplete combustibility, flame intensity, and combustion temperature. Guaiacol and 4-nitro-2-vinylphenol were used as tracers for primary organic aerosol due to the low aged-to-fresh ratios (0.21-0.97), while 4-methyl-guaiacol, 4-ethyl-guaiacol, eugenol, 4-methyl-syringol, isoeugenol, acetovanillone, syringaldehyde, homovanillin acid, vanillin acid, and syringic acid were identified as secondary organic aerosol (SOA) (aged-to-fresh ratios between 1.90 and 4.20). During simulated aging, the -CHO group reacted with the hydroxyl radical (•OH) to form the -COOH group, but there was no correlation between syringol and 4-nitrosyringol, implying that •OH is the main reactant rather than the nitriate radical (•NO3) in the atmospheric aging processes of methoxyphenols. Aging caused substantially different emission profiles due to variable photochemical reaction properties. The fresh EFs for guaiacol emitted from the biomass burning ranged from 3.80 ± 0.44 to 26.2 ± 5.40 mg·kg-1, which were much higher than those in coal combustions (of 0.03 ± 0.01 to 1.42 ± 0.28 mg·kg-1). However, the aged EFs (EFaged) for guaiacol was 1.02 ± 0.06 to 1.61 ± 0.11 mg·kg-1 in most biomass combustions, which were comparable with those of the bituminous chunk (1.20 ± 0.16 mg·kg-1). Therefore, guaiacol, a traditional biomass marker, is not an ideal tracer for aged PM2.5 emitted from biomass burning. Indeed, the syringol/guaiacol and syringol/4-nitrosyringol ratios were found to be more suitable and efficient to be used in source characterization.

Size distributions of molecular markers for biogenic secondary organic aerosol in urban Beijing

To understand the source, formation, and seasonality of biogenic secondary organic aerosol (BSOA), a nine-stage cascade impactor was utilized to collect size-segregated particulate samples from April 2017 to January 2018 in Beijing, China. BSOA tracers derived from isoprene, monoterpene, and sesquiterpene were measured with gas chromatography-mass spectrometry. Isoprene and monoterpene SOA tracers exhibited significant seasonal variations, with a summer maximum and a winter minimum. Dominance of 2-methyltetrols (isoprene SOA tracers) with a good correlation with levoglucosan (a biomass burning tracer), which was combined with the detection of methyltartaric acids (possible indicators for aged isoprene) in summer, implies possible biomass burning and long-range transport. In contrast, sesquiterpene SOA tracer (β-caryophyllinic acid) was dominant in winter and was probably associated with the local burning of biomass. Bimodal size distributions were observed for most isoprene SOA tracers, consistent with previous laboratory experiments and field studies showing that they can be formed not only in the aerosol phase but also in the gas phase. Monoterpene SOA tracers cis-pinonic acid and pinic acid showed a coarse-mode peak (5.8-9.0 μm) in four seasons due to their volatile nature. Sesquiterpene SOA tracer β-caryophyllinic acid showed a unimodal pattern with a major fine-mode peak (1.1-2.1 μm), which is linked to local biomass burning. The tracer-yield method was used to quantify the contributions of isoprene, monoterpene, and sesquiterpene to secondary organic carbon (SOC) and SOA. The highest isoprene SOC and SOA concentrations occurred in summer (2.00 μgC m^-3 and 4.93 μg m^-3, respectively), contributing to 1.61% of OC and 5.22% of PM_2.5, respectively. These results suggest that BSOA tracers are promising tracers for understanding the source, formation, and seasonality of BSOA.

Saccharides in atmospheric PM2.5 in tropical forest region of southwest China: Insights into impacts of biomass burning on organic carbon aerosols

Biomass burning (BB) in South and Southeast Asia has a strong impact on regional air quality, yet its impact on atmospheric PM_2.5 of tropical rainforest regions, a background region occupying a large area in South Asia, has rarely been investigated. In this work, we performed one-year PM_2.5 sampling during December 2018 to October 2019 at a tropical rainforest site in southwest China. PM_2.5 mass concentration, major chemical components, and ten saccharides were determined to study seasonal variations of PM_2.5 chemical composition, and further to understand possible impacts of BB to organic carbon (OC) aerosols at this background region. The concentration levels of PM_2.5, major PM_2.5 components, and total saccharides were significantly higher in dry season than in wet season. Besides, PM_2.5, OC, and total saccharides were highly correlated (R² > 0.64, p < 0.001) during the sampling period, suggesting they might share common sources. Source apportionment of saccharides revealed that BB was the main source in both seasons. Furthermore, the contributions of BB to OC (BB/OC) were estimated using levoglucosan as a molecular tracer while levoglucosan's chemical degradation was considered. It was found that over 80% of LG was degraded in both seasons, suggesting BB sources were largely from the transport of external air mass. The estimated BB/OC were over 50%, indicating BB was an important source of OC and likely of PM_2.5 in both seasons. The air-mass backward trajectory analysis and active fire spots data indicate intense BB emission sources were from South and Southeast Asia in dry season and the BB emissions in southern region of China could impact on the studied area in wet season.

Tracing the biomass burning emissions over the Arabian Sea in winter season: Implications from the molecular distributions and relative abundances of sugar compounds

The widespread haze pollution over South Asia typically occurs in winter, affecting the abundance of organic aerosols (OA) over the Arabian Sea due to prevailing meteorology. We determined the concentrations of biomass burning (BB) derived anhydrosugars (levoglucosan: Lev, galactosan: Gal, and mannosan: Man), sugars (glucose, fructose, sucrose, and trehalose) and sugar alcohols (arabitol, mannitol, erythritol, and inositol) over the Arabian Sea during a winter cruise (6-24 December 2018). Molecular distributions revealed predominance of levoglucosan or sucrose. Besides, levoglucosan strongly correlated with mannosan, galactosan, sugar alcohols and elemental carbon, emphasizing their BB-origin. Backward air mass trajectories intercepted by the satellite-based fire counts over the Indo-Gangetic Plain together with relationship between stable carbon isotopic composition of TC (δ¹³C_TC) and levoglucosan-C to organic carbon (%), confirmed the impact of BB-derived OA. A comparison of Lev/Man (av. 16.2) and Lev/K⁺ (av. 0.27) ratios over the Arabian Sea with the source-emissions revealed their origin from crop-residue burning. Rather high concentrations of Lev over the Arabian Sea compared to those documented over the Bay of Bengal, East China Sea, Sea of Japan and the western North Pacific further suggests a stronger impact of BB in the continental outflow over this marine basin. Besides, Lev/K⁺ ratios in marine aerosols exponentially decreased with an apparent increase in ambient relative humidity and temperature over the Arabian Sea during the South Asian outflow, implying a photochemical oxidation of BBOA. Such field-based relationship of Lev with the meteorological parameters can be useful for modelling the impact of BBOA on the surface Ocean. Besides, the aeolian input of sugar-C and water-soluble organic carbon (WSOC) accounted for 83 % and 92 % of that riverine supply to the Arabian Sea, respectively. This means atmospheric dry-deposition of sugars is an important external source of dissolved organic compounds to the surface water.

Clarifying winter clean heating importance: Insight chemical compositions and cytotoxicity exposure to primary and aged pollution emissions in China rural areas

Residential solid fuel combustion (RSFC) is an important source of PM_2.5. Here we investigate the cytotoxicity of primarily emitted and photochemically aged PM_2.5 to A549 cells. Owing to the formation of water-soluble ions and organics (e.g., oPAHs and nPAHs), emission factors of PM_2.5 were increased by 44.4% on average after 7-day equivalent photochemical aging, which greatly altered chemical profiles of freshly emitted PM_2.5. Consequently, the cytotoxicity varied with aging duration that 2-day and 7-day aged PM_2.5 induced 22.5% and 35.1%, respectively, higher levels of reactive oxygen species than primary emissions. Similar increases were also observed for multi-cytotoxicity. Correlation analysis and western blot results collectively confirmed HO-1/Nrf-2 signaling pathway dominated the cytotoxicity of aged PM_2.5 from RSFC, which was regulated by the enhanced o-PAHs and n-PAHs during photochemical aging. Thus, aged and secondary aerosol exposure needs to be paid more attention due to the enhanced cytotoxicity and the vast crowd involved.

Effect of photooxidation on size distribution, light absorption, and molecular compositions of smoke particles from rice straw combustion

Organic aerosol (OA) emitted from biomass burning (BB) impacts air quality and global radiation balance. However, the comprehensive characterization of OA remains poorly understood because of the complex evolutionary behavior of OA in atmospheric processes. In this work, smoke particles were generated from rice straw combustion. The effect of OH radicals photooxidation on size distribution, light absorption, and molecular compositions of smoke particles was systematically investigated. The results showed that the median diameters of smoke particles increased by a factor of approximately 1.2 after photooxidation. In the particle compositions, although both non-polar fractions (n-hexane-soluble organic carbon, HSOC) and polar fractions (water-soluble organic carbon, WSOC) underwent photobleaching after aging, the photobleaching properties of HSOC (1.87-2.19) was always higher than that of WSOC (1.52-1.33). Besides, the light-absorbing properties of HSOC were higher than that of WSOC, showing a factor of approximately 1.75 times for mass absorption efficiency at 365 nm (MAE₃₆₅). Consequently, the simple forcing efficiency (SFE) caused by absorption showed that HSOC has higher radiation effects than WSOC. After photooxidation, the concentration of 16 PAHs in HSOC fractions significantly decreased by 15.3%-72.5%. In WSOC fractions, the content of CHO, CHONS, and CHOS compounds decreased slightly, while the content of CHON compounds increased. Meantime, the variations in molecular properties supported the decrease in light absorption of WSOC fractions. These results reveal the aging behavior of smoke particles, then stress the importance of non-polar organic fractions in particles, providing new insights into understanding the atmospheric pollution caused by BB smoke particles.

Tracer-based characterization of fine carbonaceous aerosol in Beijing during a strict emission control period

Strict emission controls were implemented in Beijing and the surrounding regions in the North China Plain to guarantee good air quality during the 2014 Asia-Pacific Economic Cooperation (APEC) summit. Thus, the APEC period provides a good opportunity to study the sources and formation processes of atmospheric organic aerosol. Here, fine particles (PM_2.5, particulate matter with a diameter of 2.5 μm or less) collected in urban Beijing before and during the APEC period were analyzed for molecular tracers of primary and secondary organic aerosol (SOA). The primary organic carbon (POC) and secondary organic carbon (SOC) were also reconstructed using a tracer-based method. The concentrations of biogenic SOA tracers ranged from 1.09 to 34.5 ng m^-3 (mean 10.3 ± 8.51 ng m^-3). Monoterpene oxidation products were the largest contributor to biogenic SOA, followed by isoprene- and sesquiterpene-derived SOA. The concentrations of biogenic SOA tracers decreased by 50 % during the APEC, which was largely attributed to the implementation of emission controls by the Chinese government. The increasing mass fractions of biogenic SOA tracers from isoprene and sesquiterpene during the pollution episodes implied that their photooxidation processes contributed to the poor air quality in urban Beijing. The reconstructed biogenic and anthropogenic SOC and POC concentrations were 89.6 ± 96.8 ng m^-3, 570 ± 611 ng m^-3, and 2.49 ± 2.08 μg m^-3, respectively, accounting for 21.9 ± 11.4 % of OC in total. Biomass-burning derived OC was the largest contributor to carbonaceous aerosol over the North China Plain. By comparing the results before and during the APEC, the emission controls effectively mitigated about 34 % of the estimated OC and were more effective at reducing SOC than POC. This suggests that the reduction of the primary organic aerosol loading is harder than SOA over the North China Plain.

Tracers from Biomass Burning Emissions and Identification of Biomass Burning

The major organic compositions from biomass burning emissions are monosaccharide derivatives from the breakdown of cellulose, generally accompanied by small amounts of straight-chain, aliphatic, oxygenated compounds, and terpenoids from vegetation waxes, resins/gums, and other biopolymers. Levoglucosan from cellulose can be utilized as a specific or general indicator for biomass combustion emissions in aerosol samples. There are other important compounds, such as dehydroabietic acid, syringaldehyde, syringic acid, vanillic acid, vanillin, homovanillic acid, 4-hydroxybenzoic acid, and p-coumaric acid, which are additional key indicators of biomass burning. In this review, we will address these tracers from different types of biomass burning and the methods used to identify the sources in ambient aerosols. First, the methods of inferring biomass burning types by the ratio method are summarized, including levoglucosan/mannose, syringic acid/vanillic acid, levolgucosan/K+, vanillic acid/4-hydroxybenzoic acid, levoglucosan/OC, and levoglucosan/EC to infer the sources of biomass burning, such as crop residual burning, wheat burning, leaf burning, peatland fire, and forest fire in Asia. Second, we present the source tracer ratio methods that determine the biomass combustion types and their contributions. Finally, we introduce the PCA (Principal component analysis) and PMF (Positive matrix factor) methods to identify the type of biomass burning and its contributions according to emission factors of different species in various plants such as softwood, hardwood, and grass.

Spectral characteristics of dissolved organic carbon derived from biomass-pyrogenic smoke (SDOC) in the aqueous environment and its solubilization effect on hydrophobic organic pollutants

Dissolved organic carbon derived from biomass-pyrogenic smoke (SDOC) can be transported and deposited with atmospheric aerosols, enter aqueous environments, and possibly alter aqueous chemistry and quality. However, the characteristics of SDOC in aqueous environments and their effects on the fate of hydrophobic organic pollutants are poorly understood. In this study, we found that the emitted SDOC is 7.2∼19.6 wt.% of biochar retained in situ after biomass pyrolysis, and the emitted SDOC is approximately 1-3 orders of magnitude greater than dissolved organic carbon (DOC) released from biochar in a short term, which indicates that SDOC is a more important source of DOC in aqueous environments relative to biochar-released DOC after a biomass burning/pyrolysis event. The characteristics of SDOC in aqueous environments are dominated by the <1000 Da fraction, which accounts for >96 wt.% of bulk SDOC. In comparison with DOC in biochar, natural water, and soil, the S_275-295 value of SDOC (0.037-0.053) is significantly greater, further indicating that SDOC has a smaller molecular size. Moreover, fluorescence EEM suggests that a fluorescence component located at the Ex/Em of 205/310 nm and the combinational ranges of fluorescence index (1.28-2.28), humification index (0.07-0.80), and biological index (1.16-1.72) can be used to identify SDOC from DOC in other media. Solubilization experiments indicated that SDOC (20 mg/L) improved the solubility of hydrophobic pollutants (pyrene and triclocarban) by 2-6 folds in aqueous environments, which potentially enhances the mobility of pollutants and enlarges the potential risk region. This study indicates that SDOC may cause a severe harm to aqueous environments in addition to the atmosphere. The results have profound implications for comprehensive assessments of the environmental effects of SDOC while promoting its identification and elucidating its behavior in aqueous environments.

Organic compound source profiles of PM2.5 from traffic emissions, coal combustion, industrial processes and dust

Eighteen polycyclic aromatic hydrocarbons (PAHs), 24 n-alkanes, 7 hopanes, 2 cholestanes, inorganic ions, elements and carbon fractions were analyzed in real-world source samples of PM_2.5 (fine particulate matter) from traffic emissions (gasoline vehicles-TGV, diesel vehicles-TDV, diesel ship-TDS, and heavy oil ships-THOS), coal combustion (coal-fired industrial boilers-CIB, power plants-CPP, and residential stoves-CRS), industrial process emissions (cement industry-IPCI, and steel industry-IPSI), and dust (soil dust-DSD, road dust-DRD, and construction dust-DCD). High molecular weight (sum of five to seven rings) PAHs accounted for higher fractions for TGV (80%) and THS (61%) than for TDV, TDS and coal combustion sources (31%-47%). Hopane ratios (C29αβ/C30αβ) in coal related sources were mostly higher than 1, whereas that of traffic emissions was lower than 1. The homohopane index [S/(S + R)], which is a useful index for identifying the maturity of fuels, ranked as TGV > THS > TDV and TDS > coal combustion. For n-alkane profiles, coal related sources showed peaks at C16-C19, TDV, TDS and THS showed similar peaks at C17-C25, but peaks for DSD (C30-C32), DRD (C17-C20, C24-25 and C30-C31), CRS (C16-C18 and C28-C29) and TGV (C24-C26) are different. Organic markers were selected which can best differentiate the subtypes within source categories by considering the component levels and variations. Through a comprehensive review, we showed that it is inadvisable to directly use diagnostic ratios for source attribution, although their trends can assist in identifying influential sources.

Effects of hydrogen peroxide, sodium carbonate, and ethanol additives on the urea-based SNCR process

The issue of secondary pollutants represents a classic problem in the urea-based selective non-catalytic reduction (SNCR) process. Therefore, this study took to investigate the evolutions of secondary pollutants when including additives during the urea-based SNCR process. Results indicated that additives, namely hydrogen peroxide, sodium carbonate, and ethanol, clear improved denitration efficiency between 750 °C - 925 °C due to the increase of OH groups. Compared to rates without any additives, the "temperature window" width of hydrogen peroxide, sodium carbonate, and ethanol increased by 30%, 30%, and 52%, respectively. The temperature at the maximum denitration efficiency was decreased by 25 °C with the addition of ethanol. The addition of hydrogen peroxide, sodium carbonate, and ethanol decreased the amount of ammonia leakage at 725 °C - 900 °C. Besides, the emissions of HNCO and N₂O were decreased by adding sodium carbonate during 725 °C - 900 °C. Therefore, the addition of sodium carbonate proved to be beneficial for reducing the secondary pollutant emissions in SNCR. This study aims to provide a deeper understanding of the urea-based SNCR process in combustion.