The Black carbon (BC) and Brown carbon (BrC) concentration has been measured over Srinagar (Garhwal) in central Himalayas during October 2020 to September 2021 periods. The average BC mass was 2.59 +/- 1.96 mu g m- 3 and its absorption coefficients were abundant at shorter wavelength. BC seasonal variation exhibited a significant variability, with highest during winter (4.54 +/- 2.64 mu g m- 3) followed by pre-monsoon (2.69 +/- 2.04 mu g m- 3) and post-monsoon (1.93 +/- 0.91 mu g m- 3) while lowest was observed in the monsoon (1.05 +/- 0.54 mu g m- 3). Relatively high contribution of total spectral light absorption coefficient (Abs lambda) was observed (75.94 Mm-1) at 370 nm than longer wavelength (16.86 Mm-1) at 950 nm. The BrC contribution was higher at 370 nm (32.50 Mm-1) to the total babs (lambda), while at higher wavelengths it has extensively decreased (2.54 Mm-1 at 660 nm). Seasonally, the absorption coefficient of BC and BrC was greater in winter (83.99 and 68.37 Mm-1) while lowest in monsoon (19.38 and 9.27 Mm-1), respectively. The babs BrC/babs (t) ratio revealed higher contribution of BrC in winters. The secondary brown carbon (BrCsec) and primary brown carbon (BrCpri) contributed 43.16 % and 56.88 % towards the total BrC Abs (lambda) at 370 nm with higher in winter and lowest in monsoon, respectively. BrCsec and BrCprim has shown higher contribution in evening (18.00-20.00 h) and in morning (09.00-11.00 h) hours. The average radiative forcing (RF) of BC was 36.11 +/- 6.99 Wm-2, 2.19 +/- 1.22 Wm-2 and -33.92 +/- 5.96 Wm-2 at the atmosphere (ATM), Top of the Atmosphere (TOA), and at the Surface (SUR), respectively.

Aerosol optical properties, including absorption and scattering coefficients (B-abs, and B-scat), extinction coefficient (B-ext), single scattering albedo (SSA), and so forth, are critical metrics to estimate the radiative balance of the atmosphere. However, their ground measurements are sparsely distributed in the world, where Central Asia is void in these measurements. We had been performing the measurements of AOPs and BC with a photoacoustic extinctiometer (PAX) in Jimunai, a border town of China neighboring Kazakhstan, Central Asia, from Aug 2016 to Apr 2019. This three-year study first reported statistically significant trends of B-abs, B-scat, B-ext, SSA, and derived concentrations of BC (Mann-Kendall trend test, p-value 0.05) in the Central-Asian area. B-abs and B-scat show increasing trends and SSA was decreasing determined by the greater increasing pace of B-abs than B-scat. Seasonal and diurnal variations of the AOPs were associated with climate shift and residents' commute activity, respectively. The difference in the magnitudes and trends of AOPs between the measurements and satellites' observations advise that more care should be invested when choosing remote-sensing data to represent the AOPs at a specific site. The increasing trend of derived BC concentrations is reflected in the deposition record of BC in a snowpit of the nearby Muz Taw glacier. We suppose that the dramatically increasing BC particles emitted from Jimunai are significant factors triggering the melting of the adjacent mountain glaciers. The outflow of dust from the neighboring Gurbantiinggiit Desert could occasionally invade into Jimunai and deteriorate the local air quality, as evidenced by a probable dust event captured by the PAX on Feb 15, 2018. Finally, we outlook the future perspectives of measurements in Jimunai as a long-standing station.

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.

Biomass burning (BB) is an important source of brown carbon (BrC) and black carbon (BC), which are two key highly absorbent substances in atmospheric particles and can have a substantial positive impact on the climate radiative forcing. This study presents the light absorption properties of BC and BrC in PM2.5 during the winter in Beijing, with a discussion on the regional transportation of the light absorption of BC and BrC. Relatively high levels of the light absorption coefficient (Abs lambda) of BC, BrC, and the chemical compounds were found during haze episodes. The average AbsBC at lambda = 880 and AbsBrC at lambda = 370 during the haze period were as high as 4.4 and 2.9 times higher than those during the clean periods. The biomass burning tracer levoglucosan was significantly correlated with AbsBC880 (R2 = 0.53, P < 0.001), AbsBrC370 (R2 = 0.47, P < 0.001) and AbsBC(BB) (R2 = 0.69, P < 0.001). The average contributions of biomass burning to organic carbon (OC) and AbsBC were 33% and 48%, respectively, indicating that biomass burning was an important source of light-absorbing substances in the atmosphere. Concentration-weighted trajectory (CWT) analyses using TrajStat software also demonstrated that regional transport of biomass burning emissions from the northwestern and southwestern areas, which cover the intense fire spots from VIIRS, had a considerable influence on the light absorption properties of PM2.5 and even haze formation in Beijing during the winter.

Coal consumed in domestic cooking and heating in rural areas of China is considered as a major source of air pollution. To efficiently represent the emission of coal burnt for residential living at various combustion regimes, four coal samples are selected for combustion experiments in the simulated air state at three different temperatures in a drop-tube furnace system in this study. Size-segregated particulate matter in flue gas from combustion of the four coal samples at different temperatures were collected by a TISCH-type Andersen eight-stage impact sampler operating synchronously with the furnace system. The emission factors of the particulate matter samples show that OC2 and OC3 are the main carbonaceous products of bituminous coal and lignite combustion. It is also found that the particulate matter from lignite flue gas contains EC1 in a large proportion and a small amount of highly-refractory EC2 and EC3 from bituminous coals. Meanwhile, in order to evaluate the light-absorption of organic carbon in particulate matter, the mass absorption cross efficiency (alpha/rho) is investigated. The clear-sky radiative transfer model shows that BrC emitted from low-temperature burning leads to even positive top-ofatmosphere radiative forcing at surfaces with an albedo of 0.19. In the 300-700 nm spectral band, the simple forcing efficiency (SFE) of particulate matter sampled significantly decreases as combustion temperature and coal maturity increase. The particulate matter presents a high SFE in the range of 0.4-1.1 mu m in terms of particle size.

The rapid changes in the pattern of atmospheric warming as well as the degradation of glaciers in the Himalayas point to the inevitability of accurate source characterization and quantification of the impact of aerosols. In this regard, optical and chemical properties of aerosols, and their role in radiative effects are examined over a remote high-altitude site Lachung (27.4 degrees N, 88.4 degrees E, 2700 m a.s.l.) in the eastern Himalayas during August-2018 to February-2020. It is found that the sulphate (SO42- ) and carbonaceous aerosols (both organic carbon - OC and elemental carbon - EC) significantly contribute to the total aerosol mass loading in winter (DJF) and spring (MAM), resulting in high values of scattering and absorption coefficients. Aerosol single scattering albedo (SSA) is relatively higher in winter ( 0.85) due to a significantly higher amount of OC (OC/EC > 8). However, SSA 0.8 in spring despite of higher SO42- concentrations (SO42- /EC > 4.0 and SO42-/OC - 1.0) than winter. A reverse pattern is seen in summer-monsoon (JJAS) having lower SO42-/EC < 2 and SO42- /OC < 0.5, resulting in SSA as low as -0.64. The seasonal values of aerosol direct radiative forcing in the top of the atmosphere (DRFTOA) are as high as -2.9 +/- 1.2 Wm- 2 during the period of abundant OC in winter and -2.8 +/- 0.5 Wm- 2 during the period of abundant SO42- in spring. The combined effect of carbonaceous and SO42- aerosols on the surface cooling is highest in spring (-16.7 +/- 4.9 Wm- 2). DRF in the atmosphere is also - 34% higher in spring (13.8 +/- 4.5 Wm- 2, which translates to an atmospheric heating rate of - 0.39 K day-1), than in winter. The seasonal pattern of forcing influenced by the heterogeneous sources and chemical composition of aerosols over the eastern Himalayan site is significantly influenced by the transport of aerosols from the Indo-Gangetic Plains of India.

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.

Household cookstove emissions are an important source of carbonaceous aerosols globally. The light-absorbing organic carbon (OC), also termed brown carbon (BrC), from cookstove emissions can impact the Earth's radiative balance, but is rarely investigated. In this work, PM2.5 filter samples were collected during combustion experiments with red oak wood, charcoal, and kerosene in a variety of cookstoves mainly at two water boiling test phases (cold start CS, hot start HS). Samples were extracted in methanol and extracts were examined using spectrophotometry. The mass absorption coefficients (MAC(lambda), m(2) g(-1)) at five wavelengths (365, 400, 450, 500, and 550 nm) were mostly inter-correlated and were used as a measurement proxy for BrC. The MAC(365) for red oak combustion during the CS phase correlated strongly to the elemental carbon (EC)/OC mass ratio, indicating a dependency of BrC absorption on burn conditions. The emissions from cookstoves burning red oak have an average MAC(lambda) 2-6 times greater than those burning charcoal and kerosene, and around 3-4 times greater than that from biomass burning measured in previous studies. These results suggest that residential cookstove emissions could contribute largely to ambient BrC, and the simulation of BrC radiative forcing in climate models for biofuel combustion in cookstoves should be treated specifically and separated from open biomass burning. (C) 2018 Elsevier Ltd. All rights reserved.

Aerosol scattering and absorption characteristics were investigated at an urban megacity Delhi in the western Indo-Gangetic Basin (IGB) during the period from October 2011 to September 2012 using different in-situ measurements. The scattering coefficient (sigma(sp) at 550 nm) varied between 71 and 3014 Mm(-1) (mean similar to 710 +/- 615 Mm(-1)) during the entire study period, which was about ten times higher than the absorption coefficient (sigma(abs) at 550 nm similar to 67 +/- 40 Mm(-1)). Seasonally, sigma(sp) and sigma(abs) were substantially higher during the winter/post-monsoon periods, which also gave rise to single scattering albedo (SSA) by similar to 5%. The magnitude of SSA (at 550 nm) varied between 0.81 and 0.94 (mean: 0.89 +/- 0.05). Further, the magnitude of scattering Angstrom exponent (SAE) and back-scattering Angstrom exponent (BAE) showed a wide range from -1.20 to 1.57 and -1.13 to 0.87, respectively which suggests large variability in aerosol sizes and emission sources. Relatively higher aerosol backscatter fraction (b at 550 nm) during the monsoon (0.25 +/- 0.10) suggests more inhomogeneous scattering, associated with the coarser dust particles. However, lower value of b during winter (0.13 +/- 0.02) is associated with more isotropic scattering due to dominance of smaller size particles. This is further confirmed with the estimated asymmetry parameter (AP at 550 nm), which exhibits opposite trend with b. The aerosol optical parameters were used in a radiative transfer model to estimate aerosol radiative forcing. A mean radiative forcing of -61 +/- 22 Wm(-2) (ranging from -111 to -40 Wm(-2)) was observed at the surface and 42 24 Wm(-2) (ranging from 18 to 87 Wm(-2)) into the atmosphere, which can give rise to the mean atmospheric heating rate of 1.18 K day(-1).