Significant Contribution of Primary Sources to Water-Soluble Organic Carbon During Spring in Beijing, China

Seasonal Characterization of Primary and Secondary Sources of Fine PM-Bound Water-Soluble Organic Carbon in Central Los Angeles

Understanding the sources and formation processes of fine particulate matter (PM2.5) is crucial for improving urban air quality and public health. This study provides a real-time analysis of PM2.5-bound water-soluble organic carbon (WSOC) and related carbonaceous species during winter, spring, and summer periods in 2023-2024, aiming to identify their major sources in central Los Angeles. Using advanced online monitoring equipment, including a Sunset Laboratory EC/OC analyzer and a custom-developed setup including a total organic carbon (TOC) analyzer coupled with a particle collection system, we obtained hourly measurements of organic carbon (OC), its fractions (OC1-OC4, based on volatility), elemental carbon (EC), and WSOC. Positive matrix factorization (PMF) identified three principal PM2.5 sources: vehicular emissions, secondary organic carbon (SOC) formation influenced by nighttime aqueous-phase chemical processes, and SOC formation driven by daytime photochemical reactions. Vehicular emissions dominated EC levels, accounting for 86-95% across seasons. This factor also had high contributions from nitrogen oxides (NOₓ) (75-82%), vehicle counts (approximately 85%), and OC1 (51-83%), reflecting the persistent influence of traffic emissions. Nighttime SOC formation was significant in winter, with WSOC and OC4 contributing 58% and 40% to this factor. In contrast, daytime photochemical SOC formation was prominent in summer, with WSOC and OC4 contributing 63% and 47%, and ozone loading up to 89%, reflecting increased photochemical activity. Spring exhibited a mix of aqueous and photochemical SOC formation, with similar contributions from WSOC (38-35%) and OC4 (35-33%), reflecting the transitional season's mixed SOC formation mechanisms. Diurnal profiles revealed that primary emissions peaked during morning rush hours, while secondary formation processes elevated OC levels at night in winter and during afternoons in summer. The EC tracer method corroborated these findings by estimating primary and secondary organic carbon levels, highlighting significant seasonal and diurnal variations in carbonaceous aerosols. These results emphasize the need for targeted strategies addressing both primary emissions and the precursors of secondary aerosol formation, to improve air quality in Los Angeles.

Revealing the composition and optical properties of marine carbonaceous aerosols: A case of the eastern China marginal seas

Marine aerosols are major components of atmospheric aerosols, playing substantial roles in influencing the regional and global environment and climate. Marine aerosols are not only produced by seawater directly, but also by indirect processes such as atmospheric oxidation of marine bioactive gases as well as terrestrial transport. Over the Eastern China Marginal Seas (ECMS), marine aerosols are strongly affected by marine emission and transport of terrestrial aerosols. However, only few studies have paid attention to the optical properties across three marginal seas. In this study, marine aerosol samples were collected from the entire ECMS in spring 2023 to explore the composition and properties of carbonaceous species. Due to the significant influence of terrestrial transport on Bohai Sea, the average concentration of total suspended particles (TSP) is as high as (359.65 ± 150.45) μg m-3, while the average concentrations of organic carbon (OC) and element carbon (EC) can be up to (17.99 ± 7.71) μg m-3 and (3.28 ± 1.23) μg m-3, respectively. Besides, intense solar radiation may be a potential factor leading to an increase in the solubility of OC in aerosols over southern Yellow Sea. The light-absorbing capacity (MAE365) of water-soluble organic carbon (WSOC) is higher in northern sea region, being (0.58 ± 0.11) m2 g-1 in Bohai Sea, (0.40 ± 0.12) m2 g-1 in Yellow Sea and (0.29 ± 0.11) m2 g-1 in East China Sea. The current results show that humic-like and protein-like substances are the main fluorescent components in water-soluble organic matter. Terrestrial sources enhance the warming effect of aerosols over ECMS by about 1.5-2 times more than marine sources. This study suggests that future research should focus on the impact of terrestrial sources on the northern region of ECMS and the impact of marine sources on the southern region of ECMS.

Dynamics of residential indoor gas- and particle-phase water-soluble organic carbon: measurements during the CASA experiment

Previous time-integrated (2 h to 4 h) measurements show that total gas-phase water-soluble organic carbon (WSOCg) is 10 to 20 times higher inside homes compared to outside. However, concentration dynamics of WSOCg and total particle phase WSOC (WSOCp)-are not well understood. During the Chemical Assessment of Surfaces and Air (CASA) experiment, we measured concentration dynamics of WSOCg and WSOCp inside a residential test facility in the house background and during scripted activities. A total organic carbon (TOC) analyzer pulled alternately from a particle-into-liquid sampler (PILS) or a mist chamber (MC). WSOCg concentrations (215 ± 29 μg-C m-3) were generally 36× higher than WSOCp (6 ± 3 μg-C m-3) and 20× higher than outdoor levels. A building-specific emission factor (Ef) of 31 mg-C h-1 maintained the relatively high house WSOCg background, which was dominated by ethanol (46 μg-C m-3 to 82 μg-C m-3). When we opened the windows, WSOCg decayed slower (2.8 h-1) than the air change rate (21.2 h-1) and Ef increased (243 mg-C h-1). The response (increased Ef) suggests WSOCg concentrations are regulated by large near surface reservoirs rather than diffusion through surface materials. Cooking and ozone addition had a small impact on WSOC, whereas surface cleaning, volatile organic compound (VOC) additions, or wood smoke injections had significant impacts on WSOC concentrations. WSOCg concentration decay rates from these activities (0.4 h-1 to 4.0 h-1) were greater than the normal operating 0.24 h-1 air change rate, which is consistent with an important role for surface removal.

Characterization and apportionment of carbonaceous aerosol emission factors from light-duty and heavy-duty vehicle fleets in Maharashtra, India

This study aims to investigate the characteristics of carbonaceous aerosols and estimate emission factor (EF) based on roadway tunnel measurements, from two distinct vehicular fleets: an all light-duty vehicle (LDV) fleet, and a mixed fleet of 80% LDV and 20% heavy-duty vehicle (HDV). Carbonaceous content (organic carbon: OC and elemental carbon: EC) in total fine particles (PM2.5) accounted for 41% ± 6.8% in LDV fleet and 48% ± 7.2% in mixed fleet. While higher volatile OC dominated in the LDV fleet emissions, in mixed fleet, lower volatile OC and EC emissions dominated due to the presence of higher HDV and super-emitter (SE) fractions which led to significantly higher optically active absorbing aerosols. Reconstructed HDV fleet EF was higher than LDV fleet by 36 times (PM2.5), 19 times (OC) and 51 times (EC). Our findings emphasize the significance of implementing vehicle inspection and maintenance programs, coupled with decarbonization of HDVs to mitigate on-road vehicular emissions in India.

Acidity and oxidative potential of atmospheric aerosols over a remote mangrove ecosystem during the advection of anthropogenic plumes

To investigate the acidity and the water-soluble oxidative potential of PM10, during the continental biomass-burning plume transport, a three-year (2018-2020) winter-time campaign was conducted over a pristine island (21.35°N, 88.32°E) of Sundarban mangrove ecosystem situated at the shore of Bay of Bengal. The average PM10 concentration over Sundarban was found to be 98.3 ± 22.2 μg m-3 for the entire study period with a high fraction of non-sea-salt- SO42- and water-soluble organic carbons (WSOC) that originated from the regional solid fuel burning. The thermodynamic E-AIM(IV) model had estimated that the winter-time aerosols over Sundarban were acidic (pH:2.4 ± 0.6) and mainly governed by non-sea-salt-SO42-. The volume and mass normalized oxidative potential of PM10 was found to be 1.81 ± 0.40 nmol DTT min-1 m-3 and 18.4 ± 6.1 pmol DTT min-1 μg-1 respectively which are surprisingly higher than several urban atmospheres across the world including IGP. The acid-digested water-soluble transition metals (Cu, Mn) show higher influences in the oxidative potential (under high aerosol acidity) compared to the WSOC. The study revealed that the advection of regional solid fuel burning plume and associated non-sea-salt-SO42- is enhancing aerosol acidity and oxidative stress that in turn alters the intrinsic properties of aerosols over such marine ecosystems rich in ecology and bio-geochemistry.

Development and performance evaluation of online monitors for near real-time measurement of total and water-soluble organic carbon in fine and coarse ambient PM

In this study, we developed two online monitors for total organic carbon (TOC) and water-soluble organic carbon (WSOC) measurements in fine (dp < 2.5μm) and coarse (2.5μm < dp < 10μm) particulate matter (PM), respectively. Their performance has been evaluated in laboratory and field tests to demonstrate the feasibility of using these monitors to measure near real-time concentrations, with consideration of their potential for being employed in long-term measurements. The fine PM collection setup was equipped with a versatile aerosol concentration enrichment system (VACES) connected to an aerosol-into-liquid-sampler (AILS), whereas two virtual impactors (VIs) in tandem with a modified BioSampler were used to collect coarse PM. These particle collection setups were in tandem with a Sievers M9 TOC analyzer to read TOC and WSOC concentrations in aqueous samples hourly. The average hourly TOC concentration measured by our developed monitors in fine and coarse PM were 5.17 ± 2.41 and 0.92 ± 0.29 μg/m3, respectively. In addition, our TOC readings showed good agreement and were comparable with those quantified using Sunset Lab EC/OC analyzer operating in parallel as a reference. Furthermore, we conducted field tests to produce diurnal profiles of fine PM-bound WSOC, which can show the effects of ambient temperature on maximum values in the nighttime chemistry of the winter, as well as on increased photochemical activities in afternoon peaks during the summer. According to our experimental campaign, WSOC mean values during the study period (3.07 μg/m3 for the winter and 2.7 μg/m3 for the summer) were in a comparable range with those of earlier studies in Los Angeles. Overall, our results corroborate the performance of our developed monitors in near real-time measurements of TOC and WSOC, which can be employed for future source apportionment studies in Los Angeles and other areas, aiding in understanding the health impacts of different pollution sources.

Research progress on the characteristics, sources, and environmental and potential health effects of water-soluble organic compounds in atmospheric particulate matter

Water-soluble organic compounds (WSOCs) have received extensive attention due to their indistinct chemical components, complex sources, negative environmental impact, and potential health effects. To the best of our knowledge, until now, there has been no comprehensive review focused on the research progress of WSOCs. This paper reviewed the studies on chemical constituent and characterization, distribution condition, sources, environmental impact, as well as the potential health effects of WSOCs in the past 13 years. Moreover, the main existing challenges and directions for the future research on WSOCs were discussed from several aspects. Because of the complex composition of WSOCs and many unknown individual components that have not been detected, there is still a need for the identification and quantification of WSOCs. As modern people spend more time in indoor environments, it is meaningful to fill the gaps in the component characteristics and sources of indoor WSOCs. In addition, although in vitro cell experiments have shown that WSOCs could induce cellular oxidative stress and trigger the inflammatory response, the corresponding mechanisms of action need to be further explored. The current population epidemiology research of WSOCs is missing. Prospectively, we propose to conduct a comprehensive and simultaneous analysis strategy for concentration screening, source apportionment, potential health effects, and action mechanisms of WSOCs based on high throughput omics coupled with machine learning simulation and prediction.