Water-soluble Organic Carbon Research Articles

Organic aerosol formation and aging processes in Beijing constrained by size-resolved measurements of radiocarbon and stable isotopic 13C

This study investigates the sources and atmospheric processes of size-resolved carbonaceous aerosols in winter 2018 in urban Beijing, based on analysis of dual-carbon isotopes (i.e., radiocarbon and the stable isotope 13C). We found a size dependence of fossil source contributions to elemental carbon (EC), but no clear size dependence for organic carbon (OC). Comparable fossil source contributions to water-insoluble OC (WIOC; 55 ± 3%) and to water-soluble OC (WSOC; 54 ± 4%) highlight the importance of secondary aerosol formation, considering that fossil sources emit only small amounts of primary WSOC. OC concentrations increased during high PM2.5 pollution events, with increased fossil and non-fossil WSOC concentrating at larger particles (0.44–2.5 µm) than WIOC (0.25–2.5 µm), highlighting the aqueous-phase chemistry as an important pathway for OC production. The ratio of 13C/12C (expressed as δ13C) of total carbon (−27.0‰ to −23.3‰) fell in the range of anthropogenic aerosol, reflecting small biogenic influence. δ13C of OC increased with desorption temperature steps (200 °C, 350 °C and 650 °C). The strongly enriched δ13COC,650 (−26.9‰ to −20.3‰) and large mass fraction of OC650°C in total desorbed OC, both increasing with the increase of particle sizes, were caused by photochemical aging, especially during low and moderate PM2.5 pollution events, when regional, aged aerosol played an important role. During low pollution events, higher δ13COC,650 and WSOC/OC ratios reflect a larger contribution and more extensive chemical processing of aged aerosol. In contrast, relatively low δ13COC,200 (−27.2‰ to −25.7‰) suggests the influence of secondary OC formation on the more volatile OC desorbed at 200 °C. δ13COC,200 was similar for all particle sizes and for different pollution events, pointing to an internal mixture of local and aged regional OC. Our results show that the organic aerosol in Beijing arises from a mixture of various sources and complex formation processes, spanning local to regional scales. Particle sizes < 250 nm show strong contribution from local secondary OC formation, whereas refractory OC in particles around 1 µm shows strong evidence for regional aging processes. In summary, primary emission, secondary and aqueous-phase formation, and (photo-)chemical aging all need to be considered to understand organic aerosol in this region and their importance varies with particle size.

Elevated particulate methanesulfonate, oxalate and iron over Sydney Harbour in the austral summer of 2019-20 during unprecedented bushfire activity

In the austral summer period, Dec 7, 2019 to Mar 1, 2020, which included unprecedented bushfire activity, total suspended particulate concentrations of methanesulfonate (MSA), oxalate, labile iron, SO42−, Cl−, Na+, K+, NH4+, water soluble solids (WSS) and water soluble organic carbon (WSOC) were measured from weekly filter samples at Seaforth on the northern edge of Sydney Harbour. Particle number concentrations (PNC) and meteorological conditions were also measured at hourly intervals. These entities were previously measured in the spring-summer period, Sep 30, 2018 to Feb 24, 2019. Data analysis is focussed on inter-comparison between the summer of 2018–19 (S1) and 2019–20 (S2) spanning the period 7 Dec to 24 Feb. During S2 seasonally averaged MSA, oxalate, labile iron, K+, PNC (0.5–2.5 μm), and WSOC were elevated by 102%, 57%, 64%, 72%, 108%, and 1907%, respectively, by comparison to S1. Aqueous phase secondary formation of oxalate and a marine source of MSA were evident during S1; however, during S2 it was indicated that the bushfires created conditions where oxalate formation was shifted away from aqueous phase processing and MSA became associated with bushfire generated WSOC aerosol. Correlation changes at the a = 0.05 significance level between S1 and S2 for MSA, and for oxalate, are examined and discussed in relation to effects apparently caused by the bushfires. It is indicated that the biogeochemical cycling of sulfur and carbon, and particulate deposition of iron micronutrient to the South Pacific Ocean, may be altered by bushfires in Australia.

Spatial access and resource limitations control carbon mineralization in soils

Core-scale soil carbon fluxes are ultimately regulated by pore-scale dynamics of substrate availability and microbial access. These are constrained by physicochemical and biochemical phenomena (e.g. spatial access and hydrologic connectivity, physical occlusion, adsorption-desorption with mineral surfaces, nutrient and resource limitations). We conducted an experiment to determine how spatial access and resource limitations influence core-scale water-soluble SOM mineralization, and how these are regulated by antecedent moisture conditions. Intact soil cores were incubated at field-moist vs. drought conditions, after which they were saturated from above (to simulate precipitation) or below (to simulate groundwater recharge). Soluble C (acetate) and N (nitrate) forms were added to some cores during the rewetting process to alleviate potential nutrient limitations. Soil respiration was measured during the incubation, after which pore water was extracted from the saturated soils and analyzed for water soluble organic carbon concentrations and characterization. Our results showed that C amendments increased the cumulative CO2 evolved from the soil cores, suggesting that the soils were C-limited. Drought and rewetting increased soil respiration, and there was a greater abundance of complex aromatic molecules in pore waters sampled from these soils. This newly available substrate appeared to alleviate nutrient limitations on respiration, because there were no further respiration increases with subsequent C and N amendments. We had hypothesized that respiration would be influenced by wetting direction, as simulated precipitation would mobilize C from the surface. However, as a main effect, this response was seen only in the C-amended soils, indicating that surface-C may not have been bioavailable. At the pore scale (pore water samples), drought and the C, N amendments caused a net loss of identified molecules when the soils were rewet from below, whereas wetting from above caused a net increase in identified molecules, suggesting that fresh inputs stimulated the C-and N-limited microbial populations present deeper in the soil profile. Our experiment highlights the complex and interactive role of antecedent moisture conditions, wetting direction, and resource limitations in driving core-scale C fluxes.

Year‐Round Measurements of Dissolved Black Carbon in Coastal Southeast Asia Aerosols: Rethinking Its Atmospheric Deposition in the Ocean

AbstractDissolved black carbon (DBC) is an important recalcitrant fraction of marine dissolved organic matter. Riverine discharge is the largest known source of oceanic DBC; however, the significance of atmospheric deposition as a source of oceanic DBC remains poorly understood. In this study, year‐round aerosol sampling was carried out at a rural coastal site in Southeast Asia for DBC analysis using the benzene polycarboxylic acid (BPCA) method. The results revealed the uncertainty of an earlier estimate of the atmospheric deposition flux of DBC to the global ocean (FDBC), which assumed a linear correlation between DBC and water‐soluble organic carbon (WSOC). The correlation between DBC and WSOC depended on the sources of carbonaceous aerosols. The DBC/WSOC ratios were higher for the biomass burning aerosols. DBC was linearly correlated with black carbon (BC) for biomass or fossil fuel combustion aerosols. However, the DBC/BC ratios were higher for biomass burning aerosols (0.41 ± 0.22), whereas lower for fossil fuel combustion aerosols (0.04 ± 0.03). FDBC was revisited based on the relationship between DBC and BC. FDBC is primarily contributed by biomass burning aerosols and maybe previously underestimated. In this study, the DBC in aerosols had less condensed aromatic structures than the DBC present in the major rivers of the world, as shown by the BPCA compositions. This indicated that oceanic DBC sourced from atmospheric deposition was less likely to be removed by photodegradation and sedimentation, as compared to the DBC sourced from riverine discharge.

Chemical composition, optical properties, and oxidative potential of water- and methanol-soluble organic compounds emitted from the combustion of biomass materials and coal

Abstract. Biomass burning (BB) and coal combustion (CC) are important sources of brown carbon (BrC) in ambient aerosols. In this study, six biomass materials and five types of coal were combusted to generate fine smoke particles. The BrC fractions, including water-soluble organic carbon (WSOC), humic-like substance carbon (HULIS-C), and methanol-soluble organic carbon (MSOC), were subsequently fractionated, and their optical properties and chemical structures were then comprehensively investigated using UV–visible spectroscopy, proton nuclear magnetic resonance spectroscopy (1H NMR), and fluorescence excitation–emission matrix (EEM) spectroscopy combined with parallel factor (PARAFAC) analysis. In addition, the oxidative potential (OP) of BB and CC BrC was measured with the dithiothreitol (DTT) method. The results showed that WSOC, HULIS-C, and MSOC accounted for 2.3 %–22 %, 0.5 %–10 %, and 6.4 %–73 % of the total mass of combustion-derived smoke PM2.5, respectively, with MSOC extracting the highest concentrations of organic compounds. The MSOC fractions had the highest light absorption capacity (mass absorption efficiency at 365 nm (MAE365): 1.0–2.7 m2/gC) for both BB and CC smoke, indicating that MSOC contained more of the strong light-absorbing components. Therefore, MSOC may represent the total BrC better than the water-soluble fractions. Some significant differences were observed between the BrC fractions emitted from BB and CC with more water-soluble BrC fractions with higher MAE365 and lower absorption Ångström exponent values detected in smoke emitted from BB than from CC. EEM-PARAFAC identified four fluorophores: two protein-like, one humic-like, and one polyphenol-like fluorophores. The protein-like substances were the dominant components of WSOC (47 %–80 %), HULIS-C (44 %–87 %), and MSOC (42 %–70 %). The 1H-NMR results suggested that BB BrC contained more oxygenated aliphatic functional groups (H-C-O), whereas CC BrC contained more unsaturated fractions (H-C-C= and Ar−H). The DTT assays indicated that BB BrC generally had a stronger oxidative potential (DTTm, 2.6–85 pmol/min/µg) than CC BrC (DTTm, 0.4–11 pmol/min/µg), with MSOC having a stronger OP than WSOC and HULIS-C. In addition, HULIS-C contributed more than half of the DTT activity of WSOC (63.1 % ± 15.5 %), highlighting that HULIS was a major contributor of reactive oxygen species (ROS) production in WSOC. Furthermore, the principal component analysis and Pearson correlation coefficients indicated that highly oxygenated humic-like fluorophore C4 may be the important DTT active substances in BrC.

Seasonal changes in stable carbon isotopic composition in the bulk aerosol and gas phases at a suburban site in Prague

Isotope fractionation between the gas and aerosol phases is an important phenomenon for studying atmospheric processes. Here, for the first time, seasonally resolved stable carbon isotope ratio (δ13C) values are systematically used to study phase interactions in bulk aerosol and gaseous carbonaceous samples. Seasonal variations in the δ13C of total carbon (TC; δ13CTC) and water-soluble organic carbon (WSOC; δ13CWSOC) in fine aerosol particles (PM2.5) as well as in the total carbon of part of the gas phase (TCgas; δ13CTCgas) were studied at a suburban site in Prague, Czech Republic, Central Europe. Year-round samples were collected for the main and backup filters from 14 April 2016 to 1 May 2017 every 6 days with a 48 h sampling period (n = 66). During all seasons, the highest 13C enrichment was found in WSOC, followed by particulate TC, whereas the highest 13C depletion was found in gaseous TC. We observed a clear seasonal pattern for all δ13C, with the highest values in winter (avg. δ13CTC = −25.5 ± 0.8‰, δ13CWSOC = −25.0 ± 0.7‰, δ13CTCgas = −27.7 ± 0.5‰) and the lowest values in summer (avg. δ13CTC = −27.2 ± 0.5‰, δ13CWSOC = −26.4 ± 0.3‰, δ13CTCgas = −28.9 ± 0.3‰). This study supports the existence of different aerosol sources at the site during the year. Despite the different seasonal compositions of carbonaceous aerosols, the isotope difference (Δδ13C) between δ13CTC (aerosol) and δ13CTCgas (gas phase) was similar during the seasons (year avg. 1.97 ± 0.50‰). Moreover, Δδ13C between WSOC and TC in PM2.5 showed a difference between spring and winter, but in general, these values were also similar year-round (year avg. 0.71 ± 0.37‰). During the entire period, TCgas and WSOC were the most 13C-depleted and most 13C-enriched fractions, respectively, and although the resulting difference Δ(δ13CWSOC − δ13CTCgas) was significant, it was almost invariant throughout the year (2.67 ± 0.44‰). The present study suggests that the stable carbon isotopic fractionation between the bulk aerosol and gas phases is probably not entirely dependent on the chemical composition of individual carbonaceous compounds from different sources.

Heavy haze pollution during the COVID-19 lockdown in the Beijing-Tianjin-Hebei region, China

To investigate the characteristics of particulate matter with an aerodynamic diameter less than 2.5 μm (PM2.5) and its chemical compositions in the Beijing-Tianjin-Hebei (BTH) region of China during the novel coronavirus disease (COVID-19) lockdown, the ground-based data of PM2.5, trace gases, water-soluble inorganic ions, and organic and elemental carbon were analyzed in three typical cities (Beijing, Tianjin, and Baoding) in the BTH region of China from 5-15 February 2020. The PM2.5 source apportionment was established by combining the weather research and forecasting model and comprehensive air quality model with extensions (WRF-CAMx). The results showed that the maximum daily PM2.5 concentration reached the heavy pollution level (>150 μg/m3) in the above three cities. The sum concentration of SO42−, NO3− and NH4+ played a dominant position in PM2.5 chemical compositions of Beijing, Tianjin, and Baoding; secondary transformation of gaseous pollutants contributed significantly to PM2.5 generation, and the secondary transformation was enhanced as the increased PM2.5 concentrations. The results of WRF-CAMx showed obviously inter-transport of PM2.5 in the BTH region; the contribution of transportation source decreased significantly than previous reports in Beijing, Tianjin, and Baoding during the COVID-19 lockdown; but the contribution of industrial and residential emission sources increased significantly with the increase of PM2.5 concentration, and industry emission sources contributed the most to PM2.5 concentrations. Therefore, control policies should be devoted to reducing industrial emissions and regional joint control strategies to mitigate haze pollution.

Rapid mass growth and enhanced light extinction of atmospheric aerosols during the heating season haze episodes in Beijing revealed by aerosol–chemistry–radiation–boundary layer interaction

Abstract. Despite the numerous studies investigating haze formation mechanism in China, it is still puzzling that intensive haze episodes could form within hours directly following relatively clean periods. Haze has been suggested to be initiated by the variation of meteorological parameters and then to be substantially enhanced by aerosol–radiation–boundary layer feedback. However, knowledge on the detailed chemical processes and the driving factors for extensive aerosol mass accumulation during the feedback is still scarce. Here, the dependency of the aerosol number size distribution, mass concentration and chemical composition on the daytime mixing layer height (MLH) in urban Beijing is investigated. The size distribution and chemical composition-resolved dry aerosol light extinction is also explored. The results indicate that the aerosol mass concentration and fraction of nitrate increased dramatically when the MLH decreased from high to low conditions, corresponding to relatively clean and polluted conditions, respectively. Particles having their dry diameters in the size of ∼400–700 nm, and especially particle-phase ammonium nitrate and liquid water, contributed greatly to visibility degradation during the winter haze periods. The dependency of aerosol composition on the MLH revealed that ammonium nitrate and aerosol water content increased the most during low MLH conditions, which may have further triggered enhanced formation of sulfate and organic aerosol via heterogeneous reactions. As a result, more sulfate, nitrate and water-soluble organics were formed, leading to an enhanced water uptake ability and increased light extinction by the aerosols. The results of this study contribute towards a more detailed understanding of the aerosol–chemistry–radiation–boundary layer feedback that is likely to be responsible for explosive aerosol mass growth events in urban Beijing.

Spatiotemporal changes in aerosol properties by hygroscopic growth and impacts on radiative forcing and heating rates during DISCOVER-AQ 2011

Abstract. This work focuses on the characterization of vertically resolved aerosol hygroscopicity properties and their direct radiative effects through a unique combination of ground-based and airborne remote sensing measurements during the Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER-AQ) 2011 field campaign in the Baltimore–Washington DC metropolitan area. To that end, we combined aerosol measurements from a multiwavelength Raman lidar located at NASA Goddard Space Flight Center and the airborne NASA Langley High Spectral Resolution Lidar-1 (HSRL-1) lidar system. In situ measurements aboard the P-3B airplane and ground-based Aerosol Robotic Network – Distributed Regional Aerosol Gridded Observational Network (AERONET-DRAGON) served to validate and complement quantifications of aerosol hygroscopicity from lidar measurements and also to extend the study both temporally and spatially. The focus here is on 22 and 29 July 2011, which were very humid days and characterized by a stable atmosphere and increasing relative humidity with height in the planetary boundary layer (PBL). Combined lidar and radiosonde (temperature and water vapor mixing ratio) measurements allowed the retrieval of the Hänel hygroscopic growth factor which agreed with that obtained from airborne in situ measurements and also explained the significant increase of extinction and backscattering with height. Airborne measurements also confirmed aerosol hygroscopicity throughout the entire day in the PBL and identified sulfates and water-soluble organic carbon as the main species of aerosol particles. The combined Raman and HSRL-1 measurements permitted the inversion for aerosol microphysical properties revealing an increase of particle radius with altitude consistent with hygroscopic growth. Aerosol hygroscopicity pattern served as a possible explanation of aerosol optical depth increases during the day, particularly for fine-mode particles. Lidar measurements were used as input to the libRadtran radiative transfer code to obtain vertically resolved aerosol radiative effects and heating rates under dry and humid conditions, and the results reveal that aerosol hygroscopicity is responsible for larger cooling effects in the shortwave range (7–10 W m−2 depending on aerosol load) near the ground, while heating rates produced a warming of 0.12 K d−1 near the top of PBL where aerosol hygroscopic growth was highest.

Measurement report: Source characteristics of water-soluble organic carbon in PM&amp;lt;sub&amp;gt;2.5&amp;lt;/sub&amp;gt; at two sites in Japan, as assessed by long-term observation and stable carbon isotope ratio

Abstract. The sources and seasonal trends of water-soluble organic carbon (WSOC) in carbonaceous aerosols are of significant interest. From July 2017 to July 2019, we collected samples of PM2.5 (particulate matter, aerodynamic diameter&lt;2.5 µm) from one suburban and one rural site in Japan. The average δ13CWSOC was -25.2±1.1 ‰ and -24.6±2.4 ‰ at the suburban site and rural site, respectively. At the suburban site, the δ13CWSOC was consistent with the δ13C of burned C3 plants, and a high correlation was found between WSOC concentrations and non-sea-salt potassium concentrations; these results suggest that the main source of WSOC at this site was biomass burning of rice straw. At the rural site, the average δ13CWSOC was significantly heavier from autumn to spring (-23.9±2.1 ‰) than in summer (-27.4±0.7 ‰) (p&lt;0.01). The δ13CWSOC from autumn to spring was consistent with that of biomass burning of rice straw, whereas that in summer was considered to reflect mainly the formation of secondary organic aerosols from biogenic volatile organic compounds (VOCs). The heaviest δ13CWSOC (-21.3±1.9 ‰) was observed from February to April 2019, which may be explained by long-range transport of C4 plant burning such as corn from overseas. Thus, the present study indicates that δ13CWSOC is potentially useful for elucidating the sources and atmospheric processes that contribute to seasonal variations of WSOC concentration.

Changes in the concentration and composition of urban aerosols during the COVID-19 lockdown

This work investigates the impact of COVID-19 restrictive measures on the mass concentrations of PM1 and PM10, and their chemical components (water-soluble ions, organic and elemental carbon, and major and trace metals) at an urban site in the western Mediterranean. The evolution of gaseous pollutants (NOx, O3 and some volatile organic compounds) was also analyzed. The concentrations measured during the lockdown in 2020 were compared to those obtained during the same period over the preceding five years. The average decrease in the levels of NOx and traffic-related volatile organic compounds was higher than 50 %, while O3 concentrations did not exhibit significant variations during the study period. Our results show that temporal variations in PM1 and PM10 concentrations were strongly affected by the frequency of Saharan dust events. When these episodes were excluded from the analysis period, a 35 % decrease in PM1 and PM10 levels was observed. Traffic restrictions during the lockdown led to important reductions in the concentrations of elemental carbon and metals derived from road dust (e.g. Ca and Fe) and break wear (e.g. Cu). Regarding secondary inorganic aerosols, nitrate showed the largest reductions as a consequence of the drop in local emissions of NOx.

Leaching Char with Acidic Aqueous Phase from Biomass Pyrolysis: Removal of Alkali and Alkaline-Earth Metallic Species and Uptakes of Water-Soluble Organics

The removal of alkali and alkaline-earth metallic (AAEM) species from biomass and/or its pyrolysis-derived char is often required to mitigate ash-related issues during their combustion. Leaching of biomass with an acidic aqueous phase (AP) produced from its pyrolysis is a promising strategy but encounters several issues, including high moisture content in wet biomass after dewatering and loss of organic carbon from biomass. Here, we propose a new process that leaches char with pyrolytic AP for the removal of AAEM species from and the uptakes of water-soluble organics by char. The char and pyrolytic AP produced from the pyrolysis of wheat straw at 450 °C in an auger reactor were subjected to time-dependent leaching at a liquid-to-solid mass ratio of 20. The results demonstrate that the majority of K, Mg, and Ca are leached within the first hour. Nonacidic compounds in the pyrolytic AP slightly hinder the leaching of K but have no impacts on that of Mg and Ca. Except for acetol, the uptakes of other organic compounds (e.g., furfural and phenolic compounds) by char are rapid in the first hour, become slower in 1–2 h, and then reach equilibrium. The results from density functional theory (DFT) calculations suggest the presence of chemisorption for the interactions between these organic compounds and char. Repeated leaching runs at the optimized leaching time (1 h) suggest that the pyrolytic AP is sufficient for leaching the char from the same run, achieving removal rates of ∼63.7 wt % for K, ∼43.7 wt % for Mg, and ∼60.7 wt % for Ca. After repeated leaching, there are only four organic compounds, including 2,3-butanedione, acetol, 2(5H)-furanone, and the remaining acetic acid, left in the leachate, simplifying the compositions of the pyrolytic AP. Leaching the char, instead of wheat straw, with the pyrolytic AP offers significant advantages, including the reduced moisture content in the wet solid after dewatering, negligible loss of organic carbon, and enhanced capture of phenolic compounds.

Desiccation time and rainfall control gaseous carbon fluxes in an intermittent stream

Droughts are recognized to impact global biogeochemical cycles. However, the implication of desiccation on in-stream carbon (C) cycling is not well understood yet. We subjected sediments from a lowland, organic rich intermittent stream to experimental desiccation over a 9-week-period to investigate temporal changes in microbial functional traits in relation to their redox requirements, carbon dioxide (CO2) and methane (CH4) fluxes and water-soluble organic carbon (WSOC). Concurrently, the implications of rewetting by simulated short rainfalls (4 and 21 mm) on gaseous C fluxes were tested. Early desiccation triggered dynamic fluxes of CO2 and CH4 with peak values of 383 and 30 mg C m−2 h−1 (mean ± SD), respectively, likely in response to enhanced aerobic mineralization and accelerated evasion. At longer desiccation, CH4 dropped abruptly, likely because of reduced abundance of anaerobic microbial traits. The CO2 fluxes ceased later, suggesting aerobic activity was constrained only by extended desiccation over time. We found that rainfall boosted fluxes of CO2, which were modulated by rainfall size and the preceding desiccation time. Desiccation also reduced the amount of WSOC and the proportion of labile compounds leaching from sediment. It remains questionable to which extent changes of the sediment C pool are influenced by respiration processes, microbial C uptake and cell lysis due to drying-rewetting cycles. We highlight that the severity of the dry period, which is controlled by its duration and the presence of precipitation events, needs detailed consideration to estimate the impact of intermittent flow on global riverine C fluxes.

Approval Research for Carcinogen Humic-Like Substances (HULIS) Emitted from Residential Coal Combustion in High Lung Cancer Incidence Areas of China

The incidence and mortality rate of lung cancer is the highest in Xuanwei County, Yunnan Province, China. The mechanisms of the high lung incidence remain unclear, necessitating further study. However, the particle size distribution characteristics of HULIS emitted from residential coal combustion (RCC) have not been studied in Xuanwei. In this study, six kinds of residential coal were collected. Size-resolved particles emitted from the coal were sampled by using a burning system, which was simulated according to RCC made in our laboratory. Organic carbon (OC), elemental carbon (EC), water-soluble inorganic ion, water-soluble potentially toxic metals (WSPTMs), water-soluble organic carbon (WSOC), and HULIS-C (referred to as HULIS containing carbon contents) in the different size-segregated particulate matter (PM) samples were determined for health risk assessments by inhalation of PM. In our study, the ratio of HULIS-Cx to WSOCx values in RCC particles were 32.73–63.76% (average 53.85 ± 12.12%) for PM2.0 and 33.91–82.67% (average 57.06 ± 17.32%) for PM2.0~7.0, respectively. The carcinogenic risks of WSPTMs for both children and adults exceeded the acceptable level (1 × 10−6, indicating that we should pay more attention to these WSPTMs). Exploring the HULIS content and particle size distribution of the particulate matter produced by household coal combustion provides a new perspective and evidence for revealing the high incidence of lung cancer in Xuanwei, China.

Contributions of aerosol chemical composition and sources to light extinction during haze and non-haze days in Taiyuan, China

To better understand the causes of visibility degradation in Taiyuan, the concentrations of PM1.5 and main chemical compositions were analyzed during the period from July 28, 2014 to April 26, 2015. The average concentration of PM1.5 during the sampling period was 107.6 ± 51.0 μg/m3. The concentrations of secondary inorganic water-soluble ions (SIA, the sum of SO42−, NO3− and NH4+), OC and EC were 31.0 μg/m3, 14.6 μg/m3 and 6.0 μg/m3, accounting for 28.8%, 13.5% and 5.6% of PM1.5, respectively. Light extinction coefficients (bext) were estimated by the revised US Interagency Monitoring of Protected Visual Environments (IMPROVE) equation. (NH4)2SO4 (48.7%) was the largest contributor to bext in summer, while the contribution of organic matter (OM) to bext was the highest in spring (25.0%) and winter (42.0%). Compared with non-haze days in summer and winter, the contributions of (NH4)2SO4 and NH4NO3 to bext during haze days increased, while the contributions of OM, EC, fine soil and coarse matter (PM1.5-10) decreased. Air masses from the southern areas had the largest bext and contribution of (NH4)2SO4 in summer and winter. The results of source apportionment by positive matrix factorization model found that secondary sulfate, secondary nitrate, coal combustion, vehicle emission, fugitive dust, biomass burning were the main sources to bext in Taiyuan. Secondary sulfate (81.7%) and coal combustion (43.1%) were the largest contributors to the bext in summer and winter during haze days, respectively. The results of our study could improve the understanding of the major sources that affect visibility degradation in Taiyuan.

Influence of pollution reduction interventions on atmospheric PM2.5: A case study from the 2017 Xiamen

To investigate the influence of pollution control on particulate matter with a diameter ≤2.5 μm (PM2.5), 40 samples were collected before and during the 2017 BRICS summit (BRICS) in an urban and a suburban area of the city of Xiamen, China. The average urban and suburban area PM2.5 concentrations during the BRICS were 26.3% and 35.9% lower than those before the summit, respectively. Chemical characteristics of PM2.5, such as water-soluble ions (WSIIs), organic and elemental carbon (OC and EC), macro elements and trace elements (inorganic elements), were measured. WSIIs and organic matter accounted for the highest proportions in PM2.5. During the BRICS, concentrations of WSIIs, OC, EC and inorganic elements decreased by 17.6%, 39.0%, 42.9%, 44.1% in urban areas and decreased by 0.9%, 35.1%, 53.8%, 79.4% in suburban areas. The influence of primary sources on WSIIs and carbon aerosol decreased and secondary formation increased. High O3 concentrations played an important role in the formation of secondary aerosols. However, the contribution of inorganic element sources did not noticeably change according to Pb–Sr-Nd isotope analysis. Pollution control during the BRICS was effective but not sufficient to reduce health risk from heavy metals in PM2.5, and carcinogenic risks from Cr, Cd, and As exceeded the safety value (10−6).

Distribution of organic carbon fractions in soil aggregates in Chinese fir plantations with different stand ages

BackgroundRevealing the variations in soil aggregate-related organic carbon (OC) and labile organic carbon (LOC) fractions in a chronosequence of Chinese fir plantations plays an important role in better understanding the impact of soil carbon sink or source on the Chinese fir plantation ecosystem. In this study, soil samples in a depth of 0–20 cm were collected from Chinese fir plantations at different stand ages (0, 9, 17, and 26 years old) in Guangxi, China. With the optimal moisture sieving method adopted, the soil aggregates of 4 different sizes were obtained, including > 2-mm, 2–1-mm, 1–0.25-mm, and < 0.25-mm aggregates. Soil OC and LOC fractions were measured in the aggregates of different sizes. The LOC fractions included readily oxidizable carbon (ROC), particulate organic carbon (POC), microbial biomass carbon (MBC), water-soluble organic carbon (WOC), and mineralized organic carbon (MOC).ResultsSoil aggregate stability, as indicated by the mean weight diameter (MWD), was the highest in the 17-year-old Chinese fir plantations and was significantly positively related (p < 0.05) to the concentrations of OC and LOC fractions (except for the ROC and MOC), with the POC in particular. As for all stand ages of Chinese fir plantations, the concentrations of soil OC and LOC fractions were significantly increased as the aggregate size decreased. Consequently, there were more OC and LOC fractions distributed in the < 0.25-mm aggregates. During the stand development, the concentrations of soil OC and LOC fractions first increased and then decreased, with the highest levels detected in the 17-year-old Chinese fir plantations, indicating that the 17-year-old Chinese fir plantations were conducive to the accumulation of soil OC and LOC fractions.ConclusionAfter 17 years of planting, promoted soil carbon (especially for the POC) accumulation contributes significantly to enhancing soil aggregate stability for the Chinese fir plantations in Guangxi, China.

Temporal trends of the concentration and sources of secondary organic aerosols in PM2.5 in Shanghai during 2012 and 2018

Based on the concentrations of the carbonaceous components and the typical organic tracers in 682 p.m.2.5 samples collected in Shanghai from 2012 to 2018, the temporal trends of the concentrations and potential sources of the secondary organic aerosols in PM2.5 in Shanghai were investigated. The annual average concentrations of organic carbon (OC), elemental carbon (EC) and water-soluble organic carbon (WSOC) all showed a decreasing trend along with the PM2.5 concentration. The annual concentration of total carbon (TC) in 2018 (4.3 μg m−3) was about 34% of that in 2012. Compared with that in 2013, the concentrations of isoprene and sesquiterpene SOA tracers in 2018 decreased by 48% and 43%. Meanwhile, the concentration of monoterpene SOA tracers kept stable in 2 ng m−3 to 3 ng m−3, and the concentration of toluene SOA tracer decreased slightly from 1.3 ng m−3 in 2013 to 1.0 ng m−3 in 2018. Correlation analysis with levoglucosan suggested that biomass burning should be an important source of sesquitertene in Shanghai. It was found that the 2-MGA/2-MTLs ratio of the isoprene tracers was more strongly affected by the ambient temperature but not NOx in Shanghai. The concentration of secondary organic carbon (SOC) estimated with OC/EC-based, WSOC-based and tracer-based methods showed a decreasing trend during the study period, but the contribution of SOC to OC was increasing. Anthropogenic aromatic volatile organic compounds was the increasingly important contributor to the SOC in PM2.5, and should be the key pollutants to be controlled to further improve the air quality in Shanghai.

Secondary Organic Aerosols in PM2.5 in Bengbu, a Typical City in Central China: Concentration, Seasonal Variation and Sources

To investigate the concentration, seasonal variation, and sources of secondary organic aerosols (SOAs) in the inland areas of central China, 244 seasonal PM2.5 samples were collected from January to October 2019 at one urban site and one suburban site simultaneously in Bengbu of Anhui Province. Concentrations of organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC), and typical organic tracers, including saccharides, tracers of SOAs from isoprene, terpenes, and toluene, were measured. Results showed that Bengbu has high pollution levels of organic aerosols, with annual average OC concentrations of about 9.5 μg m−3. About 60% of the OC in PM2.5 in Bengbu was water soluble. Different seasonal trends were found for the SOA tracers of isoprene, monoterpene, seisquiterpene, and toluene. The highest seasonal average concentration of the isoprene SOA tracers was observed in summer and of the monoterpene and seisquiterpene SOA tracers in autumn. A stronger correlation was found between the 2-methylglyceric acid-to-2-methyltetrol ratio (MGA/MTL) and ambient temperature than that between MGA/MTLs and NOX concentration, suggesting that temperature has an important impact on the MGA/MTL ratio besides NOX concentration. The OC/EC-based method, WSOC-based method, tracer yield method, and positive matrix factorization (PMF)-based method were used to estimate the concentration and sources of secondary organic carbon (SOC), and the PMF-based method was believed to be able to give reasonable results. SOC was the main contributor of WSOC in PM2.5 in Bengbu, while biomass burning made an important contribution to WSOC in autumn and winter (~40%). SOC was mainly associated with SOA tracers in summer and mainly associated with secondary ions in spring and winter, suggesting different formation mechanisms in different seasons.

Comparative analysis of the chemical characteristics and sources of fine atmospheric particulate matter (PM2.5) at two sites in Changzhou, China

In this study, PM2.5 and its chemical components were compared at an industrial site and a suburban site in Changzhou, China, during the winter of 2016. The average PM2.5 concentration was higher at the industrial site (113.06 ± 64.74 μg/m3) than that at the suburban site (84.75 ± 41.76 μg/m3), which suggests that severe pollution with higher emissions occurred in the industrial region. The ion balance indicated that PM2.5 was weakly acidic and neutral at the suburban and industrial sites, respectively. Water-soluble inorganic ions (WSIIs) were the largest contributor to PM2.5 (suburban 49.8% vs. industrial 36.0%), and carbonaceous components comprised a significant fraction (approximately 30%) of ambient PM2.5. Correlations between water-soluble organic carbon (WSOC) and eight carbon fractions showed secondary formation, and biomass burning had a significant impact on the carbonaceous species. The nitrogen and sulfur oxidation ratios exceeded 0.10, which further implied the likelihood of secondary transformation. Thirteen elements comprised ~3.0% of the PM2.5 mass at both sites.Soot-particle aerosol mass spectrometry (SP-AMS) coupling positive matrix factorization (PMF) was used to characterize the chemical composition and evaluate the sources of water-soluble organic aerosols (WSOA). The results showed that the WSOA originated from three sources. The PMF model identified six sources of PM2.5, including secondary aerosols, biomass burning, traffic, soil dust, coal combustion, and road dust (industrial emissions), with mass contributions of 45.1% (38.3%), 18.7% (14.0%), 6.4% (15.9%), 13.8% (8.7%), 7.3% (13.3%), and 8.7% (9.6%) at the suburban (industrial) site. To the best of our knowledge, this is the first study to comprehensively study the chemical characteristics and source apportionment of PM2.5 in suburban/industrial regions.