We report measurements of the optical properties of methanol-soluble organic carbon (MSOC) and water-soluble organic carbon (WSOC) in the metropolitan city of Mumbai (19.01(degrees) N, 72.92(degrees) E), India. The MSOC and WSOC extracts were analysed using UV-visible spectroscopy. The study covered a period of nine months from September 2017 to May 2018. On average, MSOC constituted 30% and WSOC constituted 24% of the PM2.5 mass for the sampling period with peak concentration observed in the winter season. The absorption coefficients of MSOC were on average 1.57 times higher than WSOC for the sampling period. The absorption coefficients of MSOC and WSOC were correlated with the brown carbon absorption coefficients. Mass absorption cross- (MAC) was calculated by normalizing the absorption coefficients with its concentration, and the absorption angstrom exponent (AAE) was calculated by exponential fitting of the absorption coefficients. The MAC values for WSOC were estimated to be 1.03 +/- 0.39 m(2) g(-1), while for MSOC, it was 1.41 +/- 0.76 m(2) g(-1). The relative radiative forcing compared to black carbon was estimated at 10.1 +/- 5.2% and 6.3 +/- 3.8% for MSOC and WSOC, respectively.

Black carbon (BC) is one of the short-lived air pollutants that contributes significantly to aerosol radiative forcing and global climate change. It is emitted by the incomplete combustion of fossil fuels, biofue Is, and biomass. Urban environments are quite complex and thus, the use of mobile jointly with fixed monitoring provides a better understanding of the dynamics of BC distribution in such areas. The present study addresses the measurement of BC concentration using real-time mobile and ambient monitoring in Barranquilla, an industrialized urban area of the Colombian Caribbean. A microaethalometer (MA200) and an aethalometer (AE33) were used for measuring the BC concentration. The absorption Angstrom exponent (AAE) values were determined for the study area, for identifying the BC emission sources. The results of the ambient sampling show that vehicle traffic emissions prevail; however, the influence of biomass burning was also observed. The mean ambient BC concentration was found to be 1.04 +/- 1.03 mu g/m(3) and varied between 0.5 and 4.0 mu g/m(3). From the mobile measurements obtained in real traffic conditions on the road, a much higher average value of 16.1 +/- 16.5 mu g/m(3 )was measured. Many parts of the city showed BC concentrations higher than 20 mu g/m(3). The spatial distribution of BC concentration shows that vehicle emissions and traffic jams, a consequence of road and transport infrastructure, are the factors that most affect the BC concentration. A comparison of results obtained from two aethalometers indicates that the concentrations measured by MA200 are 9% lower than those measured by AE33. The ME obtained was found to vary between 1.1 and 1.6, indicating vehicular emissions as the most crucial source. In addition, it was observed that the BC concentration on working days was 25 times higher than on the weekends in the case of mobile monitoring and 1.5 times higher in the case of ambient monitoring. (C) 2021 China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V.

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

Brown carbon (BrC) aerosols have important warming effects on Earth's radiative forcing. However, information on the evolution of the light-absorption properties of BrC aerosols in the Asian outflow region is limited. In this study, we evaluated the light-absorption properties of BrC using in-situ filter measurements and sky radiometer observations of the ground-based remote sensing network SKYradiometer NETwork (SKYNET) made on Fukue Island, western Japan in 2018. The light-absorption coefficient of BrC obtained from filter measurements had a temporal trend similar to that of the ambient concentration of black carbon (BC), indicating that BrC and BC have common combustion sources. The absorption Angstrom exponent in the wavelength range of 340-870 nm derived from the SKYNET observations was 15% higher in spring (1.81 +/- 0.30) than through the whole year (1.53 +/- 0.50), suggesting that the Asian outflow carries light-absorbing aerosols to Fukue Island and the western North Pacific. After eliminating the contributions of BC, the absorption Angstrom exponent of BrC alone obtained from filter observations had a positive Spearman correlation (r(s) = 0.77, p < 0.1) with that derived from SKYNET observations but 33% higher values, indicating that the light-absorption properties of BrC were suc-cessfully captured using the two methods. Using the atmospheric transport model FLEXPART and fire hotspots obtained from the Visible Infrared Imaging Radiometer Suite product, we identified a high-BrC event related to an air mass originating from regions with consistent fossil fuel combustion and sporadic open biomass burning in central East China. The results of the study may help to clarify the dynamics and climatic effects of BrC aerosols in East Asia. (C) 2021 Elsevier B.V. All rights reserved.

The evolution of aerosol absorption and the contribution of absorbing species under different severities of particulate pollution are poorly understood, though absorption is key in aerosol radiative forcing. To resolve the problems, aerosol absorbing properties from low to high particulate pollution were investigated by using intensive observations of aerosol optical properties in the winter of 2019-2020 in Lanzhou, Northwest China. The aerosol scattering coefficient increased linearly with increasing particulate matter <2.5 mu m in diameter (PM2.5) and the absorption coefficient increased more rapidly under higher particulate pollution, leading to rapid decline in single scattering albedo (SSA) and sharp increase in mass absorption efficiency of PM2.5 (MAEPM(2.5)). The SSA (MAEPM(2.5)) decreased (increased) from 0.87 (0.76) in the lowest PM2.5 bin to 0.82 (1.11) in the highest PM2.5 bin. The linear relationship between the scattering coefficient and PM2.5 was attributed to decreasing aerosol hygroscopicity with increasing PM2.5. Elemental carbon (EC), fine soils (FS), and organic carbon (OC) accounted for 77.4%, 16.6%, and 6.0% of the total aerosol absorption, respectively. From low to high particulate pollution levels, the contribution of EC absorption increased from 68.3% to 80.5% while that of FS decreased from 25.5% to 13.9%. The aerosol radiative forcing efficiency was strongly correlated with SSA. Our results show a unique rapid increase in aerosol absorption under high particulate pollution during winter in Lanzhou, which is opposite to the trends observed in eastern Chinese cities, where SSA increases with increasing PM2.5.

Knowledge of aerosol size and composition is very important for investigating the radiative forcing impacts of aerosols, distinguishing aerosol sources, and identifying harmful particulate types in air quality monitoring. The ability to identify aerosol type synoptically would greatly contribute to the knowledge of aerosol type distribution at both regional and global scales, especially where there are no data on chemical composition. In this study, aerosol classification techniques were based on aerosol optical properties from remotely-observed data from the Ozone Monitoring Instrument (OMI) and Aerosol Robotic Network (AERONET) over Saudi Arabia for the period 2004-2016 and validated using data from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO). For this purpose, the OMI-based Aerosol Absorption Optical Depth (AAOD) and UltraViolet Aerosol Index (UVAI), and AERONET-based AAOD, Angstrom Exponent (AE), Absorption Angstrom Exponent (AAE), Fine Mode Fraction (FMF), and Single Scattering Albedo (SSA) were obtained. Spatial analysis of the satellite-based OMI-AAOD showed the dominance of absorbing aerosols over the study area, but with high seasonal variability. The study found significant underestimation by OMI AAOD suggesting that the OMAERUV product may need improvement over bright desert surfaces such as the study area. Aerosols were classified into (i) Dust, (ii) Black Carbon (BC), and (iii) Mixed (BC and Dust) based on the relationships technique, between the aerosol absorption properties (AAE, SSA, and UVAI) and size parameters (AE and FMF). Additionally, the AE vs. UVAI and FMF vs. UVAI relationships misclassified the aerosol types over the study area, and the FMF vs. AE, FMF vs. AAE and FMF vs. SSA relationships were found to be robust. As expected, the dust aerosol type was dominant both annually and seasonally due to frequent dust storm events. Also, fine particulates such as BC and Mixed (BC and Dust) were observed, likely due to industrial activities (cement, petrochemical, fertilizer), water desalination plants, and electric energy generation. This is the first study to classify aerosol types over Saudi Arabia using several different aerosol property relationships, as well as over more than one site, and using data over a much longer time-period than previous studies. This enables classification and recognition of specific aerosol types over the Arabian Peninsula and similar desert regions.

Light absorption by brown carbon (BrC) is dynamic due to atmospheric aging processes, leading to complex and poorly constrained effects on photochemistry and climate. In this study, a smog chamber was used to simulate the heterogeneous ozone (O-3) aging of soot particles. Twelve aging times and seven O-3 concentrations were set to investigate the effects of aging degree on BrC light absorption. The results showed that light absorption by BrC was enhanced after O-3 aging, but followed a non-monotonic trend with an initial increase and subsequent decrease. An aging time of 60 min and O-3 concentration of 1.2 ppm were optimal for enhancing BrC absorption, where the contribution of BrC to total absorption and the contribution of BrC relative to black carbon absorption at 370 nm of ozonized soot were 23.0 +/- 1.8% and 30.0 +/- 3.0%, respectively, much greater than those of fresh soot (8.1 +/- 1.1% and 8.8 +/- 1.3%, respectively). The absorption Angstrom exponent (AAE) and delta C (Delta C) of ozonized soot at 60 min ranged from 1.18 +/- 0.01 to 1.31 +/- 0.03 and from 13.5 +/- 7.0 to 24.3 +/- 13.5 mu g m(-3), respectively, and were greater than those of fresh soot (1.12 +/- 0.02 and 8.0 +/- 0.8 mu g m(-3)), but also showed non-monotonic trends, suggesting the formation of BrC during O-3 aging. Comparative results indicated that AAE might be a better BrC indicator for soot than Delta C. The non-monotonic trend was tentatively explained by changes in organic carbon, oxygenated functional groups and conjugated structures, as well as polycyclic aromatic hydrocarbon (PAH) degradation and oxygenated PAH formation. The relative intensities of oxidative formation and degradation of chromophores may determine BrC evolution during O-3 aging. This study will be useful for clarifying BrC evolution in the atmosphere and estimating its radiative forcing. (C) 2020 Elsevier Ltd. All rights reserved.

Under typical Chinese wintry rural conditions, dominating individual coal heating would emit lots of the fine fraction of ambient aerosol exclusively including carbonaceous particulate matter. In this study, a specified drop tube furnace system is employed to simulate experimentally particle matter emitted during individual coal combustion. Emphatically, the effects of coal types, oxygen concentration and combustion ambient on the formation characteristics of carbonaceous aerosols in the flue gas were discussed. It was found that the fraction of organic carbon (OC) and elemental carbon (EC) in the flue gas produced by bituminous coal combustion was lower than that of lignite. Meanwhile, with the increase of oxygen concentration, the production of OC and EC decreased, but the sensitivity of EC to oxygen concentration was higher than that of OC, which indicated that the formation mechanism of OC and EC is extremely different. Noticeable, the Absorption Angstrom Exponent (AAE) of methanol-soluble organic carbon (MSOC) is higher than that of water-soluble organic carbon (WSOC), which indicates that a large amount of methanol-soluble but water-insoluble brown carbon has strong light absorption capacity between 330 nm and 550 nm, and its light absorption capacity tends to be in the short-wave region. The mass absorption efficiency (MAE) of brown carbon produced by coal combustion (0.1-1 m(2)/gC) is similar to that of atmospheric aerosol (0.3-1.8 m(2)/gC), which indicates that the contribution of brown carbon emitted from coal combustion to the light absorption capacity of atmospheric aerosol should not be underestimated.

Atmospheric PM1 (particulate matter with aerodynamic diameter <= 1 mu m) samples have been collected during foggy (n = 17) and non-foggy nights (n = 19) in wintertime at Kanpur in central Indo-Gangetic Plain (IGP) to assess light absorption characteristics and direct radiative forcing of water-extractable brown carbon (BrC). We have observed a significant enhancement (two-tailed t-test: t = 2.2; at significance level: p < 0.05) in the absorption coefficient of water-extractable BrC at 365 nm (b(abs-BrC-365)) from non-foggy (Avg.: 53.5 Mm(-1)) to foggy episodes (69.3 Mm(-1)). Enhancement in mass absorption efficiency (MAE) of BrC (1.8 m(2)/g C) during foggy episodes is consistent with that of b(abs-BrC-365). Absorption Angstrom exponent (AAE) remained similar (2.8) during foggy and non-foggy episodes. Significantly lower value of AAE (2.8) at Kanpur compared to other places in IGP ( similar to 5) highlights more light absorbing potential of atmospheric BrC over central IGP. Furthermore, MAE of EC at 660 nm during foggy period (8.5 m(2)/g) is relatively high as compared to that during the non-foggy episode (7.0 m(2)/g). The MAE of BrC and EC exhibited enhancement by similar to 15% and 20%, respectively during foggy events. These observations are also reflected by an increase (t = 11.1; p < 0.05) in direct radiative forcing of water-extractable BrC (relative to EC) in the atmosphere: from 23.7 +/- 10.8% during non-foggy to 54.3 +/- 16.5% during foggy episodes. Differences in chemical composition, loading, absorption properties and direct radiative forcing (DRF) of carbonaceous aerosols during non-foggy and foggy episodes indicate predominant influence of fog-processing.

Light-absorbing components of atmospheric aerosols have gained particular attention in recent years due to their climatic and environmental effects. Based on two-year measurements of aerosol absorption at seven wavelengths, aerosol absorption properties and black carbon (BC) were investigated in the North China Plain (NCP), one of the most densely populated and polluted regions in the world. Aerosol absorption was stronger in fall and the heating season (from November to March) than in spring and summer at all seven wavelengths. Similar spectral dependence of aerosol absorption was observed in non-heating seasons despite substantially strong absorption in fall. With an average absorption Angstrom exponent (alpha) of 1.36 in non-heating seasons, freshly emitted BC from local fossil fuel burning was thought to be the major component of light-absorbing aerosols. In the heating season, strong ultraviolet absorption led to an average alpha of 1.81, clearly indicating the importance of non-BC light-absorbing components, which were possibly from coal burning for domestic heating and aging processes on a regional scale. Diurnally, the variation of BC mass concentrations experienced a double-peak pattern with a higher level at night throughout the year. However, the diurnal cycle of alpha in the heating season was distinctly different from that in non-heating seasons. a peaked in the late afternoon in non-heating seasons with concomitantly observed low valley in BC mass concentrations. In contrast, alpha peaked around the midnight in the heating season and lowered down during the daytime. The relationship of aerosol absorption and winds in non-heating seasons also differed from that in the heating season. BC mass concentrations declined while alpha increased with increasing wind speed in non-heating seasons, which suggested elevated non-BC light absorbers in transported aged aerosols. No apparent dependence of alpha on wind speed was found in the heating season, probably due to well mixed regional pollution. Pollution episodes were mostly encountered under low winds and had a low level of alpha, implying aerosol absorption should be largely attributed to freshly emitted BC from local sources under such conditions. Extensive field campaigns and long-term chemical and optical measurements of light-absorbing aerosols are needed in the future to further advance our understanding on optical properties of light-absorbing aerosols and their radiative forcing in this region. (C) 2016 The Authors. Published by Elsevier Ltd.