This study investigates the inter-annual variability of carbonaceous aerosols (CA) over Kolkata, a megacity in eastern India, using dual carbon isotopes (C-14 and C-13) alongside measurements of the optical properties of brown carbon (BrC). Sampling was conducted during the post-monsoon, winter, and spring seasons over two consecutive years (2020-21 and 2021-22). The analysis reveals that PM2.5 and CA concentrations were higher in 2020-21 (194 +/- 40 and 54 +/- 15 mu g m(-3), respectively) compared to 2021-22 (141 +/- 31 and 44 +/- 21 mu g m(-3)), likely due to higher precipitation in 2021-22. The contribution of biomass burning and biogenic sources to CA (f(bio_TC)) was slightly higher in 2020-21 (70 +/- 3 %) than in 2021-22 (68 +/- 3 %), with both years exhibiting a consistent decreasing trend from post-monsoon to spring. Observed lower values for oxidised CA proxies, such as the WSOC/OC ratio (0.41 +/- 0.08) and AMS-derived f(44) (0.13 +/- 0.02), throughout the study period suggest that surface CA over Kolkata primarily originates from local sources rather than long-range transport. The relative radiative forcing (RRF) also showed a clear reduction in the subsequent year; however, on average, the RRF of methanol-soluble BrC (16 +/- 6 %) was approximately three times higher than that of the water-soluble fraction (5.5 +/- 2.2 %), highlighting the substantial role of BrC in influencing regional radiative forcing. These findings underscore the substantial impact of local emissions over transported pollutants on Kolkata's ground-level air quality.

Light-absorbing impurities (LAIs), such as mineral dust (MD), organic carbon (OC), and black carbon (BC), deposited in snow, can reduce snow albedo and accelerate snowmelt. The Ili Basin, influenced by its unique geography and westerly atmospheric circulation, is a critical region for LAI deposition. However, quantitative assessments on the impact of LAIs on snow in this region remain limited. This study investigated the spatial distribution of LAIs in snow and provided a quantitative evaluation of the effects of MD and BC on snow albedo, radiative forcing, and snowmelt duration through sampling analysis and model simulations. The results revealed that the Kunes River Basin in the eastern Ili Basin exhibited relatively high concentrations of MD. In contrast, the southwestern Tekes River Basin showed relatively high concentrations of OC and BC. Among the impurities, MD plays a dominant role in the reduction of snow albedo and has a greater effect on the absorption of solar radiation by snow than BC, while MD is the most important light-absorbing impurity responsible for the reduction in the number of snow-melting days in the Ili Basin. Under the combined influence of MD and BC, the snowmelt period in the Ili Basin was reduced by 2.19 +/- 1.43 to 7.31 +/- 4.76 days. This study provides an initial understanding of the characteristics of LAIs in snow and their effects on snowmelt within the Ili Basin, offering essential basic data for future research on the influence of LAIs on snowmelt runoff and hydrological processes in this region.

Aerosol absorption and scattering notably influence the atmospheric radiative balance. Significant uncertainties persist regarding the impact of aerosol models on aerosol radiative forcing (ARF) under distinct atmospheric conditions. The effects of various aerosol models on ARF under clear and haze conditions are analyzed utilizing MODIS data, combined with observations from Beijing, and the 6S (Second Simulation of the Satellite Signal in the Solar Spectrum) for simulations. Results showed that ARF at the surface (ARF-SFC) and top of the atmosphere (ARF-TOA) registered negative values on clear and hazy days. On hazy days, the desert model demonstrated enhanced cooling at TOA, while the urban model showed intensified surface cooling. Hazy conditions amplified ARF-TOA by 57%, 54%, and 61% for desert, urban, and continental models respectively, relative to clear days, with corresponding ARF-SFC increases of 57%, 54%, and 56%. Aerosol radiative forcing efficiency at TOA generally exhibited greater values in winter than in summer. Black carbon (BC) radiative forcing simulations using the three-component method showed positive values at TOA and negative values at the surface. During hazy days, BC intensified upper-atmosphere heating and surface cooling effects. This research will lay the scientific foundation for reducing uncertainty in ARF estimates and developing effective environmental strategies.

Brown carbon (BrC) is the ubiquitous part of the atmospheric organic carbon. It absorbs solar lights and greatly impacts the Earth's radiative balance. This study examines the spectral characteristics of BrC and its radiative effect in the Dhaka South (DS) site and Dhaka North (DN) site from July 2023 to January 2024 with a high-volume particulate matter sampler on quartz filters. Spectral characteristics such as absorption coefficient (babe,), mass absorption efficiency (MAE), absorption angstrom exponent (AAE), and refractive index (Kabs-x) were determined by using a UV -visible spectrophotometer, and fluorescence emission spectra were analyzed in different pH by the fluorescent spectrophotometer. The concentrations of BrC and black carbon (BC) were determined by an aethalometer. The mean concentrations of BrC and BC in Dhaka city were 18.63 +/- 3.84 mu g 111-3 and 17.93 +/- 3.82 pg M-3, respectively. The AAE values lie in the range of 3.20-4.01 (DN) and 3.27-4.53 (DS), and the radiative forcing efficiency of BrC was obtained at 4.43 +/- 1.02 W g-1 in DN and 3.93 +/- 0.74 W g-1 in DS, indicating the presence of highly light-absorbing BrC in these locations. Average MAE and Kabs_k values were 1.55 +/- 0.45 m2g1 and 0.044 + 0.013, respectively, in DS, alternatively 1.84 +/- 0.59 m2g1 and 0.052 +/- 0.016 in DN. The fluorescence excitation-emission spectra confirmed the presence of a polyconjugate cyclic ring with multifunctional groups in the structure of BrC. Light absorption properties and fluorescence emission spectra were varied with the change of pH. As the pH increased (2-8), the AAE value decreased and MAEB,c_365 increased due to protonation or deprotonation. This study highlights that the BrC has a significant impact on the air quality as well as the Earth's radiative balance, emphasizing its strong light-absorbing properties and variability with environmental factors.

Aerosol optical properties and radiative forcing critically influence Earth's climate, particularly in semi-arid regions. This study investigates these properties in Yinchuan, Northwest China, focusing on aerosol optical depth (AOD), single-scattering albedo (SSA), & Aring;ngstr & ouml;m Index, and direct radiative forcing (DRF) using 2023 CE-318 sun photometer data, HYSPLIT trajectory analysis, and the SBDART model. Spring AOD peaks at 0.58 +/- 0.15 (500 nm) due to desert dust, with coarse-mode particles dominating, while summer SSA reaches 0.94, driven by fine-mode aerosols. Internal mixing of dust and anthropogenic aerosols significantly alters DRF through enhanced absorption, with spring surface DRF at -101 +/- 22W m-2 indicating strong cooling and internal mixing increasing atmospheric DRF to 52.25W m-2. These findings elucidate dust-anthropogenic interactions' impact on optical properties and radiative forcing, offering critical observations for semi-arid climate research.

Air pollution is a global health issue, and events like forest fires, agricultural burning, dust storms, and fireworks can significantly worsen it. Festivals involving fireworks and wood-log fires, such as Diwali and Holi, are key examples of events that impact local air quality. During Holi, the ritual of Holika involves burning of biomass that releases large amounts of aerosols and other pollutants. To assess the impact of Holika burning, observations were conducted from March 5th to March 18th, 2017. On March 12th, 2017, around 1.8 million kg of wood and biomass were openly burned in about 2250 units of Holika, located in and around the Varanasi city (25.23 N, 82.97 E, similar to 82.20 m amsl). As the Holika burning event began the impact on the Black Carbon (BC), particulate matter 10 & 2.5 (PM10 and PM2.5), sulphur dioxide (SO2), oxides of nitrogen (NOx), ozone (O-3) and carbon monoxide (CO) concentration were observed. Thorough optical investigations have been conducted to better comprehend the radiative effects of aerosols produced due to Holika burning on the environment. The measured AOD at 500 nm values were 0.315 +/- 0.072, 0.392, and 0.329 +/- 0.037, while the BC mass was 7.09 +/- 1.78, 9.95, and 7.18 +/- 0.27 mu g/m(3) for the pre-Holika, Holika, and post-Holika periods. Aerosol radiative forcing at the top of the atmosphere (ARF-TOA), at the surface (ARF-SUR), and in the atmosphere (ARF-ATM) are 2.46 +/- 4.15, -40.22 +/- 2.35, and 42.68 +/- 4.12 W/m(2) for pre-Holika, 6.34, -53.45, and 59.80 W/m(2) for Holika, and 5.50 +/- 0.97, -47.11 +/- 5.20, and 52.61 +/- 6.17 W/m(2) for post-Holika burning. These intense observation and analysis revealed that Holika burning adversely impacts AQI, BC concentration and effects climate in terms of ARF and heating rate.

Aerosols emitted from biomass burning affect human health and climate, both regionally and globally. The magnitude of these impacts is altered by the biomass burning plume injection height (BB-PIH). However, these alterations are not well-understood on a global scale. We present the novel implementation of BB-PIH in global simulations with an atmospheric chemistry model (GEOS-Chem) coupled with detailed TwO-Moment Aerosol Sectional (TOMAS) microphysics. We conduct BB-PIH simulations under three scenarios: (a) All smoke is well-mixed into the boundary layer, and (b) and (c) smoke injection height is based on Global Fire Assimilation System (GFAS) plume heights. Elevating BB-PIH increases the simulated global-mean aerosol optical depth (10%) despite a global-mean decrease (1%) in near-surface PM2.5. Increasing the tropospheric column mass yields enhanced cooling by the global-mean clear-sky biomass burning direct radiative effect. However, increasing BB-PIH places more smoke above clouds in some regions; thus, the all-sky biomass burning direct radiative effect has weaker cooling in these regions as a result of increasing the BB-PIH. Elevating the BB-PIH increases the simulated global-mean cloud condensation nuclei concentrations at low-cloud altitudes, strengthening the global-mean cooling of the biomass burning aerosol indirect effect with a more than doubling over marine areas. Elevating BB-PIH also generally improves model agreement with the satellite-retrieved total and smoke extinction coefficient profiles. Our 2-year global simulations with new BB-PIH capability enable understanding of the global-scale impacts of BB-PIH modeling on simulated air-quality and radiative effects, going beyond the current understanding limited to specific biomass burning regions and seasons. Plain Language Summary Biomass burning includes wildfires, prescribed burns, and agricultural burns; and is an important source of aerosol particles in the atmosphere. These aerosol particles are important for climate and human health. Our work contributes to understanding the global and interannual impacts of changing the height of these particles in the atmosphere. We ran multiple global atmospheric chemistry model simulations with each simulation having different heights for aerosol particles from biomass burning. Simulations with a higher average emission height had more smoke aerosol particles in the entire atmosphere, resulting in an increase in the cooling radiative impact of biomass burning compared to simulations with a lower average emission height. We found that simulations with a higher average emission height for biomass burning aerosols had slightly better agreement with satellite observations relative to lower heights. This study shows the importance of biomass burning aerosol emission height on Earth's global air quality and climate.

Objective Xinjiang, recognized as a crucial coal resource area and strategic reserve in China, possesses abundant coal resources. The Zhundong coalfield, a large-scale open-pit mining area within this region, significantly contributes to increased concentrations of light-absorbing aerosols due to its coal production activities and associated industrial processes. These activities also produce substantial amounts of black carbon (BC), which, through atmospheric transport, mixes with snow and ice, influencing glacier ablation in the Tianshan Mountains. While previous studies on the Zhundong coalfield have predominantly concentrated on the ecological pollution resulting from mining activities, they have overlooked the implications for climate and radiative forcing in the area. In this context, it is crucial to employ satellite remote sensing technology to analyze and assess the optical properties and radiative forcing effects of light-absorbing aerosols in the Zhundong coalfield region. Such an approach is significant for understanding the regional environmental and climatic impacts associated with the development of open-pit coal resources in the arid regions of western China. Methods We investigate the temporal and spatial characteristics of aerosol optical depth (AOD) in the Zhundong coalfield by utilizing MODIS aerosol product (MOD04_L2) data spanning from 2005 to 2020. To simulate aerosol particle size information, a Mie scattering model is employed under the core-shell assumption. An uncertainty interval of 0.03 is selected to estimate the possible range of particle sizes within each grid, constrained by maximum and minimum values. The inter of these constraints is then used to calculate the optical parameters for various particle size combinations. Additionally, the influence of sand and dust aerosols is considered by setting the single scattering albedo (SSA) range for these aerosols between 0.93 and 0.96. The simulated extinction coefficient (sigma(ext)) is used as a threshold value; any portion smaller than this threshold is excluded to quantify the concentration of local BC columns. Finally, the radiative forcing effect of light-absorbing aerosols in the Zhundong coalfield over the past decade is evaluated using the SBDART radiative transfer model. Results and Discussions The AOD in the Zhundong coalfield exhibited pronounced spatial heterogeneity from 2005 to 2020, with high AOD values predominantly concentrated in the mining area and its surrounding regions (Fig. 2). Seasonal variations reveal the highest concentrations in spring and winter, followed by fall, with the lowest levels observed in summer. During spring and winter, AOD values generally exceed 0.15, except in certain desert areas. Interannual fluctuations in AOD are frequent, marked by significant turning points in 2010, 2012, and 2017 (Fig. 3), which indicates that coal production, energy restructuring, and capacity reduction policies have a significant effect on air quality in mining regions. The inter-monthly variation displays a distinct U pattern (Fig. 3), with AOD peaking at 0.27 in February, which highlights the substantial influence of anthropogenic activities on regional air quality. Dusty weather in spring emerges as a dominant factor. Overall, the temporal variation in AOD in the Zhundong coalfield reflects the combined effects of natural factors and human activities. In the Wucaiwan and Dajing mining areas, the range of BC number density is (1?3)x10(18) grid(-1) (Fig. 6). In 2012, against the backdrop of China's coal economic performance, open-pit mining was less affected by the decline in production growth due to its larger production capacity and lower costs, influenced by mining methods, climatic conditions, and economic activities. In contrast, shaft mining is more heavily affected by safety risks and environmental constraints, which may lead to production limitations, especially under strengthened policy and regulatory measures. As a result, there are greater fluctuations in BC number density in the Dajing mining area (Fig. 6). The range of BC number density is 20?40 kg/grid, with seasonal variations largely consistent, although peak months differed. This suggests that BC mass concentration is closely related to particle aging and size (Fig. 7). Radiative forcing values at the top of the atmosphere, at the surface, and within the atmosphere showed varying degrees of decrease between 2011 and 2017, followed by a gradual increase. This suggests that reducing emissions of light-absorbing aerosols from mining sites can effectively lower regional radiative forcing values in the context of reduced coal production (Fig. 10). Radiative forcing values are higher in March and April during spring, when BC is aged and mixed with other aerosol components through mutual encapsulation, which results in more complex microphysical-chemical properties. This process enhances the absorption capacity of BC for both short- and long-wave radiations (Fig. 10). Conclusions We analyze the overall change in AOD in the Zhundong coalfield from 2005 to 2020 using the MODIS aerosol dataset. By integrating a meter scattering model to simulate optical parameters under various particle size combinations and constraining these simulations with single scattering albedo (SSA) observations from MODIS, this approach allows us to determine the eligible particle size information and optical parameters, enabling the calculation of BC mass concentration within the atmospheric column of the Zhundong coalfield. Subsequently, the area's radiative forcing is estimated using the SBDART radiative transfer model. The findings reveal several key insights. 1) The changes in AOD are closely linked to policy implementation and economic activities within the coal mining area. Interannual variations indicate that AOD peaked in 2012 and subsequently declined, which suggests that policies and economic activities significantly affect AOD levels. Seasonally, AOD is higher in spring and winter and lower in summer. The unique topographic and meteorological conditions facilitate the transport of BC from the mining area to other regions, which highlights the combined effects of seasonal meteorological conditions and human activities. 2) The column concentration of light-absorbing aerosols in the coal mine area is affected by both anthropogenic activities and meteorological conditions, particularly during sandy and dusty weather. A comparison of column concentrations between the Wucaiwan and Dajing mines shows that open-pit mining adapts more effectively in 2012, given the context of China's coal economic operations, whereas shaft mining may face greater challenges. 3) By examining the changes in AOD and light-absorbing aerosols, it is evident that reducing emissions of light-absorbing aerosols from coal mining areas can effectively decrease regional radiative forcing values in the short term. Inter-monthly variations reveal that atmospheric radiative forcing trends differ from those at the surface and the top of the atmosphere, with the latter two being closely related to the optical properties of light-absorbing aerosols. In spring, the frequent occurrence of sand and dust facilitates the mixing of BC with other substances, forming light-absorbing aerosols with a core-shell structure. This significantly enhances the light-absorbing capacity of BC, thereby increasing radiative forcing.

Estimating Top-of-Atmosphere (TOA) flux and radiance is essential for understanding Earth's radiation budget and climate dynamics. This study utilized polar nephelometer measurements of aerosol scattering coefficients at 17 angles (9-170 degrees), enabling the experimental determination of aerosol phase functions and the calculation of Legendre moments. These moments were then used to estimate TOA flux and radiance. Conducted at a tropical coastal site in India, the study observed significant seasonal and diurnal variations in angular scattering patterns, with the highest scattering during winter and the lowest during the monsoon. Notably, a prominent secondary scattering mode, with varying magnitude across different seasons, was observed in the 20-30 degrees angular range, highlighting the influence of different air masses and aerosol sources. Chemical analysis of size-segregated aerosols revealed that fine-mode aerosols were dominated by anthropogenic species, such as sulfate, nitrate, and ammonium, throughout all seasons. In contrast, coarse-mode aerosols showed a clear presence of sea-salt aerosols during the monsoon and mineral dust during the pre-monsoon periods. The presence of very large coarse-mode non-spherical aerosols caused increased oscillations in the phase function beyond 60 degrees during the pre-monsoon and monsoon seasons. This also led to a weak association between the phase function derived from angular scattering measurements and those predicted by the Henyey-Greenstein approximation. As a result, TOA fluxes and radiances derived using the Henyey-Greenstein approximation (with the asymmetry parameter as input in the radiative transfer model) showed a significant difference- up to 24% in seasons with substantial coarse-mode aerosol presence- compared to those derived using the Legendre moments of the phase function. Therefore, TOA flux and radiance estimates using Legendre moments are generally more accurate in the presence of complex aerosol scattering characteristics, particularly for non-spherical or coarse-mode aerosols, while the Henyey-Greenstein phase function may yield less accurate results due to its simplified representation of scattering behavior.

This study investigates aerosol characteristics using ground-based measurements at two distinct regions, MohalKullu (31.9 degrees N, 77.12 degrees E; 1154 m amsl) and Kosi-Katarmal (29.64 degrees N, 79.62 degrees E; 1225 m amsl), from July 2019 to June 2022. The average Black Carbon (BC) concentrations were 1.5 f 1.0 mu g m- 3 at Mohal and 1.1 f 1.4 mu g m-3 at Katarmal. BC showed strong seasonal variability, with maxima during post-monsoon (2.6 f 1.0 mu g m- 3) and pre-monsoon (1.8 f 0.5 mu g m-3) seasons. The diurnal variation displayed distinct morning and evening peaks in all the seasons. High pre-monsoon AOD500 (0.30 f 0.06 to 0.54 f 0.08) and low values of & Aring;ngstrom exponent (0.67 f 0.10 to 0.95 f 0.30) indicated dominance of large particles, whereas lower AOD500 (0.21 f 0.07 to 0.25 f 0.03) in post-monsoon and winter, along with larger & Aring;ngstrom exponent (1.05 f 0.74 to 1.13 f 0.11), indicated smaller particles. Satellite-derived (OMI and MAIAC) AOD500 showed weak to moderate correlation with ground-based measurements at Mohal (R = 0.4639 for MAIAC, R = 0.1402 for OMI) and Katarmal (R = 0.3976 for MAIAC, R = 0.2980 for OMI). Using optical properties of aerosols and clouds (OPAC) and Santa Barbara discrete ordinate radiative transfer (SBDART) models, the short-wave aerosol radiative forcing (SWARF) was found negative at the surface and top of the atmosphere but positive in the atmosphere, suggesting significant surface cooling and atmospheric warming leading to high heating rates, respectively. Annual mean atmospheric radiative forcing was 27.36 f 6.00 Wm- 2 at Mohal and 21.87 f 7.26 Wm- 2 at Katarmal. These findings may have consequences for planning air pollution strategies and understanding the effects of regional climate change.