This study assesses the physical and optical properties and estimated the radiative forcing of aerosol at Agra over the Indo-Gangetic Basin (IGB) during July 2016-December 2019 using black carbon (BC) mass concentration (AE-33 aethalometer), data sets from satellite and model simulations. The optical properties of aerosol and radiative forcing have been measured by the Optical and Physical Properties of Aerosols and Clouds (OPAC) and Santa Barbara Discrete Ordinate Radiative Transfer Atmospheric Radiative Transfer (SBDART) model. The high BC mass concentration has been observed in November and lowest in August. An adverse meteorological condition due to a combination of temperature and low wind speed results in poor dispersion in the wintertime is a common factor for high concentration level pollutants over Agra. The diurnal and temporal cycle of BC mass concentration exhibits a high concentration at nighttime due to the lower atmospheric boundary layer. The seasonal variation of absorption coefficient (& beta;abs) and Absorption Angstrom Exponent (AAE) is found to be higher during post-monsoon and lowest in monsoon season. This suggests that black carbon concentration over Agra is mainly generated from crop burning, waste burning, automobile exhaust and long-range transport from Punjab and Haryana as the present site is downwind. OPAC-derived aerosol optical depth (AOD), single-scattering albedo (SSA), Angstrom Exponent (AE) and asymmetry parameter (AsyP) were estimated to be 0.57 & PLUSMN; 0.07, 0.78 & PLUSMN; 0.16, 0.99 & PLUSMN; 0.21 and 0.81 & PLUSMN; 0.15, respectively. AOD and AE from the OPAC and the moderate resolution imaging spectroradiometer (MODIS) have shown the consistent relationship. The mean radiative forcing is 18.3 & PLUSMN; 2.1 W m-2 at the top of the atmosphere while, at the surface, net radiative forcing is -42.4 & PLUSMN; 7.2 and 59.1 & PLUSMN; 6.5 W m-2 at the atmosphere during the study period. Vertical profiles were estimated using the observations from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite and the change in heating rate from the SBDART model over Agra. First-time short-lived climate forcer black carbon mass concentration along with optical properties of aerosols has been reported, and quantification of radiative forcing has been done at the Agra region.The radiative forcing due to black carbon has been found to be high highlighting the heat risk over this region.image

This study reports black carbon (BC) characteristics and climate effects for a 22-month period during 2018-2020 at a receptor location in the eastern Indo-Gangetic Plains (IGP). The overall averaged BC mass concentration was 7.8 & PLUSMN; 4.7 & mu;g m- 3, and the nighttime average (9.1 & PLUSMN; 6.1 & mu;g m- 3) was nearly double that of the daytime (5.8 & PLUSMN; 3.5 & mu;g m- 3). BC was most enhanced during winter, with mean concentration (14.3 & PLUSMN; 3.8 & mu;g m- 3) higher by 4 times as compared to summer. A two-component mixing model, frequency distribution of the Angstrom exponent, and a simultaneous increase in brown carbon (BrC) absorption coefficient suggested that this enhancement was mostly due to the biomass burning (BB) fraction of BC. CALIPSO-derived products showed that the extinction coefficient was highest at 0.62 & PLUSMN; 0.31 km-1 in winter and lowest at 0.12 & PLUSMN; 0.05 km-1 in summer. Backscatter plots and particle depolarization ratios indicated presence of spherical dust particles during summer and smoke plumes during post-monsoon and winter. Concentration-weighted trajectories (CWTs) helped in quantifying significant contributions of the IGP outflow to BC, BC-BB and BrC absorption. Finally, a large direct radiative forcing of the atmosphere by BC (37 & PLUSMN; 22 W m- 2) was estimated via the radiative transfer model SBDART, with an associated atmospheric heating rate of 1.02 K d-1.

Mineral dust aerosols over the Himalayas are assessed using polarization-resolved observations of Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) onboard Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite over 11 years (2006-2018). The extinction coefficient due to dust aerosols is retrieved using observations of the depolarization ratio which gives the relative contribution of dust aerosols in the scattering volume. Dust extinction coefficients show significant regional and seasonal variation over the Himalayas. High dust loading is observed during the pre-monsoon season (March-May) whereas dust loading is low during the summer monsoon season (June-September). This is due to the reduced dust transport associated with the weak westerlies that prevailed over the Himalayas. Regionally, the mid-Himalayas is characterized by the highest dust extinction coefficient with a 10-fold increase as the season changes from winter (December-February) to pre-monsoon (March-May). Polluted dust (dust combined with anthropogenic aerosols) contributes to 64-74% of total aerosols over the Himalayas. Dry deposition causes a substantial amount of dust aerosols (1-31 mg m(-2) day(-1)) to be deposited over the Himalayas, reducing the albedo by 0.3% on fresh snow and up to 2.7% on aged snow, causing a radiative forcing of 0.38-23.7 Wm(-2) at the top of the atmosphere. The Himalayan cryosphere may therefore experience large warming leading to snow melting and enhanced reduction in snow cover.

Atmospheric aerosols affect human health, alter cloud optical properties, influence the climate and radiative balance, and contribute to the cooling of the atmosphere. Aerosol climatology based on aerosol robotic network (AERONET) and ozone monitoring instrument (OMI) data from two locations (Urban Dhaka and coastal Bhola Island) over Bangladesh was conducted for 8 years (2012- 2019), focusing on two characterization schemes. Four aerosol parameters, such as extinction angstrom exponent (EAE), absorption AE (AAE), single scattering albedo (SSA), and real refractive index (RRI), were exclusively discussed to determine the types of aerosol. In addition, the light absorption properties of aerosol were inspected tagging the association between size parameters similar to fine mode fraction (FMF), AE, and absorption parameters (SSA and AAE). Results of aerosol absorption optical depth (AAOD) were validated with the satellite-borne cloud-aerosol lidar and infrared pathfinder satellite observation (CALIPSO) aerosol subtype profiles. The overall average values of AAOD for Dhaka and Bhola were (0.110 +/- 0.002) [0.106, 0.114] and (0.075 +/- 0.001) [0.073, 0.078], respectively. The values derived by OMI were the similar (0.024 +/- 0.001 [0.023, 0.025] for Dhaka, and 0.023 +/- 0.001 [0.023, 0.024] for Bhola). Two types of aerosols were potentially identified, for example, biomass burning and urban/industrial types over Bangladesh with insignificant contribution from the dust aerosol. Black carbon (BC) was the prominent absorbing aerosol (45.9%-89.1%) in all seasons with negligible contributions from mixed BC and/or dust and dust alone. Correlations between FMF and SSA confirmed that BC was the dominant aerosol type over Dhaka and Bhola. CALIPSO's vertical information was consistent with the AERONET column information. The results of aerosol parameters will have a substantial impact on the aerosol radiative forcing, and climate modeling as well as air quality management in Southeast Asia's heavily polluted territories.

Black carbon (BC), dust, and organic carbon (OC) aerosols, when deposited onto the surface of glaciers, can absorb light and decrease the snow albedo. These impurities in snow are referred to as ILAIs (i.e., insoluble light absorbing impurities). Atmospheric chemical models have been extensively used to simulate the transport and deposition of atmospheric aerosols in glacierized areas. However, systematic investigations of ILAIs in snowpack of glaciers on the Tibetan Plateau (TP) are rare. In this study, observations of ILAIs in snow and simulations of ILAIs of atmospheric aerosol at surface over four glaciers on the TP have been analyzed. Strong correlation between BC and dust was found in surface aged-snow, and their correlation significantly varied with snowpit depth. BC and OC concentrations in snowpit tended to decrease with depth. Significant differences of ILAI concentrations among depth intervals reflect their diverse hydrophilicities, physiochemical properties and postdepositional processes in snowpit, offering important observational constraints on the related processes. Monthly variation of atmospheric ILAIs at surface over glaciers is characterized by distinct spatial heterogeneity. The statistical results show higher ILAI concentrations in the summer of 2015 than 2014, which is in qualitative agreement with CALIPSO observations, likely reflecting the effects of inter-annual variation of summer monsoon on snow ILAI loadings. Optical attenuation (ATN) of BC is gradually decreased with depth of snowpit, whereas the trend of mass absorption cross- (MAC) of BC throughout the profile of snowpit is opposite to that of ATN. The scanning electron microscopy (SEM) imaging demonstrates that calcium and silicon rich particles dominate over biological, quartz and flying ash particles in the cryoconite, providing additional constraints on the sources of dust-in-snow and can facilitate better understanding of the physicochemical properties and climatic effects of particles in the glacial cryoconite.

The tropospheric NO2 concentration from OMI AURA always shows high concentrations of NO2 at a few locations in India, one of the high concentrations of NO2 hotspots is associated with the locations of seven coal-fired Thermal Power plants (TPPs) in Singrauli. Emissions from TPPs are among the major sources of black carbon (BC) soot in the atmosphere. Knowledge of BC emissions from TPPs is important in characterizing regional carbonaceous particulate emissions, understanding the fog/haze/smog formation, evaluating regional climate forcing, modeling aerosol optical parameters and concentrations of black carbon, and evaluating human health. Furthermore, elevated BC concentrations, over the Indo-Gangetic Plain (IGP) and the Himalayan foothills, have emerged as an important subject to estimate the effects of deposition and atmospheric warming of BC on the accelerated melting of snow and glaciers in the Himalaya. For the first time, this study reports BC concentrations and aerosol optical parameters near dense coal-fired power plants and open cast coal mining adjacent to the east IGP. In-situ measurements were carried out in Singrauli (located in south-east IGP) at a fixed site about 10 km from power plants and in transit measurements in close proximity to the plants, for few days in the month of January and March 2013. At the fixed site, BC concentration up to the 95 mu gm(-3) is observed with strong diurnal variations. BC concentration shows two maxima peaks during early morning and evening hours. High BC concentrations are observed in close proximity to the coal-fired TPPs (>200 mu gm(-3)), compared to the outside domain of our study region. Co-located ground-based sunphotometer measurements of aerosol optical depth (AOD) show strong spatial variability at the fixed site, with AOD in the range 0.38-0.58, and the highest AOD in the range 0.7-0.95 near the TPPs in transit measurements (similar to the peak of BC concentrations). Additionally, the Angstrom exponent was found to be in the range 0.4-1.0 (maximum in the morning time) and highest in the proximity of TPPs (similar to 1.0), suggesting abundance of fine particulates, whereas there was low Angstrom exponent over the surrounding coal mining areas. Low Angstrom exponent is characterized by dust from the unpaved roads and nearby coal mining areas. MODIS derived daily AOD shows a good match with the MICROTOPS AOD. The CALIPSO derived subtypes of the aerosol plot shows that the aerosols over Singrauli region are mainly dust, polluted dust, and elevated smoke. The preliminary study for few days provides information about the BC concentrations and aerosol optical properties from Singrauli (one of the NO2 hotspot locations in India). This preliminary study suggests that long-term continuous monitoring of BC is needed to understand the BC concentrations and aerosol optical properties for better quantification and the estimation of the emission to evaluate radiative forcing in the region.

Winter-specific characteristics of airborne particulates over middle Indo-Gangetic Plain (IGP) were evaluated in terms of aerosol chemical and micro-physical properties under three-dimensional domain. Emphases were made for the first time to identify intra-seasonal variations of aerosols sources, horizontal and vertical transport, effects of regional meteorology and estimating composite aerosol short-wave radiative forcing over an urban region (25 degrees 10'-25 degrees 19'N; 82 degrees 54'-83 degrees 4'E) at middle-IGP. Space-borne passive (Aqua and Terra MODIS, Aura OMI) and active sensor (CALIPSO-CALIOP) based observations were concurrently used with ground based aerosol mass measurement for entire winter and pre-summer months (December, 1, 2014 to March, 31, 2015). Exceptionally high aerosol mass loading was recorded for both PK (267.6 +/- 107.0 mu g m(-3)) and PM2.5 (150.2 +/- 89.4 mu g m(-3)) typically exceeding national standard. Aerosol type was mostly dominated by fine particulates (particulate ratio: 0.61) during pre to mid-winter episodes before being converted to mixed aerosol types (ratio: 0.41-0.53). Time series analysis of aerosols mass typically identified three dissimilar aerosol loading episodes with varying attributes, well resemble to that of previous year's observation representing its persisting nature. Black carbon (9.4 +/- 3.7 mu g m(-3)) was found to constitute significant proportion of fine particulates (2-27%) with a strong diurnal profile. Secondary inorganic ions also accounted a fraction of particulates (PM2.5: 22.5%; PM10: 26.9%) having SO4-2, NO3- and NH4+ constituting major proportion. Satellite retrieved MODIS-AOD (0.01-2.30) and fine mode fractions (FMF: 0.01-1.00) identified intra-seasonal variation with transport of aerosols from upper to middle-IGP through continental westerly. Varying statistical association of columnar and surface aerosol loading both in terms of fine (r; PM2.5: MODIS-AOD: 0.51) and coarse particulates (PM10: MODIS-AOD: 0.53) was found influenced by local meteorology (boundary layer and humidity) and aerosol vertical profile. A gradual increase in aerosol vertical profile (surface to 4.9 km) was evident with dominance of polluted continental, polluted dust and smoke at lower altitude. Presence of mineral dusts in higher altitude during later phase was linked with its transboundary transport, originating from western dry regions. Conclusively, winter-specific short-wave aerosol radiative forcing revealed an ATM warming effect (31-47 W m(-2)) while cooling both at TOA (-20 to -32 W m(-2)) and SUF (-51 to -80 W m(-2)) with significant level of intra-seasonal variations in heating rates (0.86-132 K day(-1)). (C) 2016 Elsevier B.V. All rights reserved.