Vehicle -emitted fine particulate matter (PM 2.5 ) has been associated with significant health outcomes and environmental risks. This study estimates the contribution of traffic -related exhaust emissions (TREE) to observed PM 2.5 using a novel factorization framework. Specifically, co -measured nitrogen oxides (NO x ) concentrations served as a marker of vehicle -tailpipe emissions and were integrated into the optimization of a Non -negative Matrix Factorization (NMF) analysis to guide the factor extraction. The novel TREE-NMF approach was applied to long-term (2012 - 2019) PM 2.5 observations from air quality monitoring (AQM) stations in two urban areas. The extracted TREE factor was evaluated against co -measured black carbon (BC) and PM 2.5 species to which the TREE-NMF optimization was blind. The contribution of the TREE factor to the observed PM 2.5 concentrations at an AQM station from the first location showed close agreement ( R 2 = 0 .79) with monitored BC data. In the second location, a comparison of the extracted TREE factor with measurements at a nearby Surface PARTiculate mAtter Network (SPARTAN) station revealed moderate correlations with PM 2.5 species commonly associated with fuel combustion, and a good linear regression fit with measured equivalent BC concentrations. The estimated concentrations of the TREE factor at the second location accounted for 7 - 11 % of the observed PM 2.5 in the AQM stations. Moreover, analysis of specific days known to be characterized by little traffic emissions suggested that approximately 60 - 78 % of the traffic -related PM 2.5 concentrations could be attributed to particulate traffic -exhaust emissions. The methodology applied in this study holds great potential in areas with limited monitoring of PM 2.5 speciation, in particular BC, and its results could be valuable for both future environmental health research, regional radiative forcing estimates, and promulgation of tailored regulations for traffic -related air pollution abatement.

Carbonaceous aerosols play an important role in radiative forcing in the remote and climate-sensitive Tibetan Plateau (TP). However, the sources of carbonaceous aerosols to the TP remain poorly defined, in part due to the lack of regionally relevant data about the sources of carbonaceous aerosols. To address this knowledge gap, we present the first comprehensive analysis of the delta C-13 signatures of carbonaceous aerosol endmembers local to the TP, encompassing total carbon, water-insoluble particle carbon, and elemental carbon originating from fossil fuel combustion, biomass combustion, and topsoil. The delta C-13 signatures of these local carbonaceous endmembers differ from components collected in other regions of the world. For instance, fossil fuel-derived aerosols from the TP were C-13-depleted relative to fossil fuel-derived aerosols reported in other regions, while biomass fuel-derived aerosols from the TP were C-13-enriched relative to biomass fuel-derived aerosols reported in other regions. The delta C-13 values of fine-particle topsoil in the TP were related to regional variations in vegetation type. These findings enhance our understanding of the unique features of carbonaceous aerosols in the TP and aid in accurate source apportionment and environmental assessments of carbonaceous aerosols in this climate-sensitive region.

To elucidate the molecular composition and sources of organic aerosols in Central Asia, carbonaceous compounds, major ions, and 15 organic molecular tracers of total suspended particulates (TSP) were analyzed from September 2018 to August 2019 in Dushanbe, Tajikistan. Extremely high TSP concentrations (annual mean +/- std: 211 +/- 131 mu gm(-3)) were observed, particularly during summer (seasonal mean +/- std: 333 +/- 183 mu g m(- 3)). Organic carbon (OC: 11.9 +/- 7.0 mu gm(-3)) and elemental carbon (EC: 5.1 +/- 2.2 mu gm(-3)) exhibited distinct seasonal variations from TSP, with the highest values occurring in winter. A high concentration of Ca2+ was observed (11.9 +/- 9.2 mu g m(-3)), accounting for 50.8% of the total ions and reflecting the considerable influence of dust on aerosols. Among the measured organic molecular tracers, levoglucosan was the predominant compound (632 +/- 770 ng m(-3)), and its concentration correlated significantly with OC and EC during the study period. These findings highlight biomass burning (BB) as an important contributor to the particulate air pollution in Dushanbe. High ratios of levoglucosan to mannosan, and syringic acid to vanillic acid suggest that mixed hardwood and herbaceous plants were the main burning materials in the area, with softwood being a minor one. According to the diagnostic tracer ratio, OC derived from BB constituted a large fraction of the primary OC (POC) in ambient aerosols, accounting for an annual mean of nearly 30% and reaching 63% in winter. The annual contribution of fungal spores to POC was 10%, with a maximum of 16% in spring. Measurements of plant debris, accounting for 3% of POC, divulged that these have the same variation as fungal spores.

Light-absorbing carbonaceous aerosols primarily comprise black carbon (BC) and brown carbon (BrC), and they play a key role in atmospheric radiative forcing and global climate. Here, we present the light absorption, potential sources, and health risks of BC and BrC during the prescribed burning season at an urban background site in Brisbane based on the measurements with a seven-wavelength aethalometer. The enhancements in light absorption at 880 nm were potentially governed by the transport of prescribed burning emissions. Source apportionment results revealed that fossil-fuel (FF) combustion contributed more to the total equivalent BC (eBC) (67%) over the entire measurement period as compared to biomass burning (BB). The percentages of secondary BrC to BrC for BB- and FF-dominated periods were 60% and 21%, respectively, indicating the greater potential of BB emissions to form secondary BrC compared to FF emissions. The diurnal trend showed that the peaks of secondary BrC occurred at nighttime with high relative humidity, implying that the formation of secondary BrC was potentially associated with aqueous reactions. Potential source contribution function (PSCF) results suggested that air masses originating from southern and northern Brisbane were the potential pollution sources, where BB and traffic emissions were dominant. In addition, the health risks of eBC (based on equivalent numbers of passively smoked cigarettes) remarkably increased for periods with elevated eBC emissions, potentially originating from prescribed burns. These findings contribute to our understanding of the impact of BB on the light absorption properties of BC and BrC and could serve as a reference for government officials when performing prescribed burns with reduced environmental and health effects.

Carbonaceous aerosols play an important role in radiative forcing in the remote and climate-sensitive Tibetan Plateau (TP). However, the sources of carbonaceous aerosols to the TP remain poorly defined, in part due to the lack of regionally relevant data about the sources of carbonaceous aerosols. To address this knowledge gap, we present the first comprehensive analysis of the delta C-13 signatures of carbonaceous aerosol endmembers local to the TP, encompassing total carbon, water-insoluble particle carbon, and elemental carbon originating from fossil fuel combustion, biomass combustion, and topsoil. The delta C-13 signatures of these local carbonaceous endmembers differ from components collected in other regions of the world. For instance, fossil fuel-derived aerosols from the TP were C-13-depleted relative to fossil fuel-derived aerosols reported in other regions, while biomass fuel-derived aerosols from the TP were C-13-enriched relative to biomass fuel-derived aerosols reported in other regions. The delta C-13 values of fine-particle topsoil in the TP were related to regional variations in vegetation type. These findings enhance our understanding of the unique features of carbonaceous aerosols in the TP and aid in accurate source apportionment and environmental assessments of carbonaceous aerosols in this climate-sensitive region.

The Indo-Gangetic Plain (IGP) is a major regional and global emitter of atmospheric pollutants, which adversely affect surrounding areas such as the Himalayas. We present a comprehensive dataset on carbonaceous aerosol (CA) composition, radiocarbon (D14C) -based source apportionment, and light absorption of total suspended particle (TSP) samples collected over a 3--year period from high-altitude Jomsom in the central Himalayas. The 3-year mean TSP, organic carbon (OC), and elemental carbon (EC) concentrations were 92.0 +/- 28.6, 9.74 +/- 6.31, and 2.02 +/- 1.35 lg m-3, respectively, with the highest concentrations observed during the pre-monsoon season, followed by the post-monsoon, winter, and monsoon seasons. The D14C analysis revealed that the contribution of fossil fuel combustion (ffossil) to EC was 47.9% +/- 11.5%, which is consistent with observations in urban and remote regions in South Asia and attests that EC likely arrives in Jomsom from upwind IGP sources via long-range transport. In addition, the lowest ffossil (38.7% +/- 13.3%) was observed in winter, indicating large contributions in this season from local biomass burning. The mass absorption cross- of EC (MACEC: 8.27 +/- 1.76 m2/g) and watersoluble organic carbon (MACWSOC: 0.98 +/- 0.45 m2/g) were slightly higher and lower than those reported in urban regions, respectively, indicating that CA undergo an aging process. Organic aerosol coating during transport and variation of biomass burning probably led to the seasonal variation in MAC of two components. Overall, WSOC contributed considerably to the light absorption (11.1% +/- 4.23%) of EC. The findings suggest that to protect glaciers of the Himalayas from pollution-related melting, it is essential to mitigate emissions from the IGP.(c) 2022 China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).

Analyses of black carbon (BC) data from three different environments in India -Delhi megacity, Srinagar metropolitan and Gulmarg hill station, showed that Delhi had the highest annual average BC concentration (12.3 +/- 10.2 mu g m- 3), followed by Srinagar (4.3 +/- 5 mu g m-3) and Gulmarg (2.4 +/- 2 mu g m-3). The inflow of aerosols from the neighboring agricultural regions, notably during Winter, causes Delhi to have the highest seasonal average BC (16.8 mu g m- 3). Srinagar had the highest average seasonal BC during autumn (6.3 mu g m- 3) due to the burning of horticulture residue and hardwood for charcoal making and residential heating. At Gulmarg, on the other hand, the winter season's high BC (2.2 mu g m- 3) is due to the increased emissions from the tourist traffic, snowmobile/ATVs and wood burning for residential heating. BC concentrations in Delhi and Srinagar were roughly in line with their population size. However, compared to sites with the similar population, BC at Gul-marg was roughly twice higher than the other sites. There was a higher contribution to BC from fossil fuels than biomass burning at all three sites, which indicates that cars are the primary source of BC. Overall, values of BC aerosol optical properties in Delhi are much higher than those in Srinagar and Gulmarg. During the cold season, continental air masses transport BC from the neighboring areas to Delhi and westerlies enhance the local BC loading at Srinagar and Gulmarg. The predominant presence of absorbing aerosols, particularly BC, during late autumn and winter at all three sites leads to an increase in aerosol optical depth (AOD), a reduction in single scattering albedo (SSA) and an increase in asymmetry parameter (AP). As a result, there is a significant increase in the radiative forcing of the atmosphere (RFATM), with the highest values observed in January in Delhi (+71.5 W m-2) and Srinagar (+56.05 W m-2), and in November at Gulmarg (+18.5 W m-2). These findings suggest that small rural towns that are affected by seasonal emissions, low planetary boundary layers, and frequent tem-perature inversions, can contribute to a substantial amount of radiative forcing. This study provides a larger perspective on increasing BC in Delhi, and urban-rural fringe areas in the Indian Himalayas, which is crucial for identifying what actions must be taken to control BC emissions to reduce impacts on cryosphere, human health and other sectors.

Fluorescence spectroscopy is a commonly used technique to analyze dissolved organic matter in aquatic environments. Given the high sensitivity and non-destructive analysis, fluorescence has recently been used to study water-soluble organic carbon (WSOC) in atmospheric aerosols, which have substantial abundance, various sources and play an important role in climate change. Yet, current research on WSOC characterization is rather sparse and limited to a few isolated sites, making it challenging to draw fundamental and mechanistic conclusions. Here we presented a review of the fluorescence properties of atmospheric WSOC reported in various field and laboratory studies, to discuss the current advances and limitations of fluorescence applications. We highlighted that photochemical reactions and relevant aging processes have profound impacts on fluorescence properties of atmospheric WSOC, which were previously unnoticed for organic matter in aquatic environments. Furthermore, we discussed the differences in sources and chemical compositions of fluorescent components between the atmosphere and hydrosphere. We concluded that the commonly used fluorescence characteristics derived from aquatic environments may not be applicable as references for atmospheric WSOC. We emphasized that there is a need for more systematic studies on the fluorescence properties of atmospheric WSOC and to establish a more robust reference and dataset for fluorescence studies in atmosphere based on extensive source specific experiments. (C) 2020 Elsevier Ltd. All rights reserved.

The characteristics of black carbon (BC) aerosols, their sources, and their impact on atmospheric radiative forcing were extensively studied during the COVID-19 lockdown (28th March-31st May 2020) at a high-altitude rural site over the Western Ghats in southwest India. BC concentration and the contribution of BC originating from biomass burning (BCbb) estimated from the aethalometer model during the lockdown period were compared with the same periods in 2017 and 2018 and with the pre-lockdown period (1st February to March 20, 2020). BC concentrations were 44, 19, and 17% lower during the lockdown period compared with the prelockdown periods of 2020 and similar periods (28th March to 31st May) of 2017 and 2018, respectively. BCbb contributed similar to 50% to total BC during the lockdown period of 2020 and compensated for the decrease in BC concentration due to lower traffic emissions. The characteristics of light-absorbing organic carbon (brown carbon; BrC) absorption at 370 nm were evaluated during the lockdown and the pre-lockdown periods of 2020, 2017, and 2018. The BrC was estimated to be the highest during the lockdown period of 2020. Finally, atmospheric radiative forcing was calculated using the mean BC concentration during the pre-lockdown, lockdown, and similar periods (28th March to 31st May) of 2017 and 2018.

To alleviate air pollution in western China, experiencing rapid economic growth following national western development strategies, an accurate and compressive assessment of PM2.5 sources is critical. Here, we firstly investigated the spatiotemporal variation in PM2.5 and analyzed its association with weather conditions and emission changes. Then, WRF-Chem simulations were conducted for an entire year to obtain various emission sectors' contributions to the PM2.5 mass by a hybrid method, which considers both the proportions of various components as well as each sector contributing to these components. The results showed that residential emissions had the largest contribution to PM2.5 because of its dominating contribution for primary components of PM2.5 (BC and POA), which can explain > 70% of PM2.5. Seasonally, the residential contributions to PM2.5 were higher in the non-monsoon period than in the monsoon period because of the higher contribution ratios to primary components. Regionally, as an essential source of the gaseous precursors, the industrial and transportation sectors were the second-largest contributors to PM2.5 in the highly populated urban (HP) and remote background (RM) regions, respectively. Further assessment of emission reduction measures indicated that eliminating 50% of residential emissions induced a 29.4% and 33.1% decrease in the annual PM2.5 mass of the HP and RM regions, respectively, with higher decrease proportions in non-monsoon. By comparison, eliminating 50% of industrial emissions caused a significantly lower decrease in PM2.5 for both HP (10%) and RM (4.6%). Eliminating 50% of transportation emissions led to PM2.5 concentrations to decline by 9.3% in RM, which was greater than the 4.6% reduction caused by eliminating 50% of industrial emissions. Therefore, in addition to focusing on the residential sector, especially in non-monsoon in western China, the transportation sector should be a focus to alleviate PM2.5 pollution on the Tibetan Plateau. The outcome of this study provides valuable information for policy-makers to make strategies to mitigate air pollution in western China.