In this study, we investigated the aerosol radiative forcing (ARF) using ground-based measurements of PM2.5 and black carbon aerosols at a semi-arid, rain shadow location, Solapur in peninsular India. It is observed that aerosols caused a net cooling effect at top of the atmosphere (TOP) indicating that the aerosols reflect more solar radiation back to space than they absorb. At the surface, the aerosols caused a net cooling effect indicating more presence of scattering type aerosols. The resulting ARF of the aerosols was found to be ranging from +38 Wm-2 in monsoon to +53 Wm-2 in pre-monsoon indicating trapping of energy which resulted in a warming of the atmosphere. However, BC -only forcing indicated a significant warming effect at TOP as well as in the atmosphere which showed the potential of the absorbing carbonaceous aerosols. Overall, BC was responsible for 44% and 32% of the composite ARF, even though it formed only 7% and 2% of composite aerosol in the dry and wet periods, respectively. The warming impact of BC aerosols was also manifested in terms of their contribution to aerosol radiative forcing efficiency (ARFE) which was about four times more for BC-only than that for composite aerosols. More atmospheric heating rates were observed during dry periods for composite and BC-only aerosols than during wet period. These findings have important implications for aerosol-cloud-precipitation studies as well as the atmospheric thermodynamics and hydrological cycle over this semi-arid region where the total aerosol load is not significant and rainfall amount is scarce.

The properties of the atmospheric aerosols depend on the source region and on the modifications that occur during their transport in the air. We have studied physical and chemical properties of aerosols along with their sink mechanism over two locations in southwest India, an urban site (Pune) and well-established climate observatory at Sinhagad (SINH), which represents rural and high altitude site. The ground-based measurements of aerosols, together with their radiative properties in this study have provided means to understand the observed variability and the impact on the aerosol radiative properties effectively over this region. The annual mean elemental carbon concentration (3.4 mu g m(- 3)) at Pune was observed about three times higher compared to SINH (1.3 mu g m(- 3)), indicating strong emissions of carbon-rich aerosols at the urban location. Aerosol optical properties were derived using the OPAC model which were used to compute the Aerosol radiative forcing (ARF) over both stations calculated using SBDART (Santa Barbara DISORT Atmospheric Radiative Transfer) model shows pronounced seasonal variations due to changes in aerosol optical depth and single scattering albedo at both locations. The year-round ARF was 4-5 times higher over Pune (31.4 +/- 3.5 Wm(- 2)) compared to SINH (7.2 +/- 1.1 Wm(- 2)). The atmospheric heating rate due to aerosols shows a similar pattern as ARF for these locations. The heating was higher in the wintertime, similar to 0.9-1.6 K day(- 1) at Pune, and similar to 0.3-0.6 K day(- 1) at SINH. The estimated scavenging ratio was found high for NO3- and Ca.(2+). The wet deposition fluxes of Cl-, SO42-, Na+, Mg2+ were observed higher for SINH as compared to Pune, due to the high amount of rain received at SINH.

In the present study, we estimated the aerosol radiative forcing and heating rates near Yala Glacier, Nepal (28.21 degrees N, 85.61 degrees E; 4900 masl), using in situ black carbon (BC) mass concentration measurements, satellite data sets, and model simulations. The real-time ambient BC mass concentration was continuously measured using an Aethalometer (AE-33) from October 2016 to May 2017. The Optical Properties of Aerosols and Clouds (OPAC) model was used to simulate the aerosol optical properties in conjunction with the in situ measurements and satellite data sets. Outputs from OPAC and the satellite data sets were used as inputs for the Santa Barbara Discrete Ordinate Radiative Transfer Atmospheric Radiative Transfer (SBDART) model to estimate the radiative forcing. The in situ measurements showed that the BC mass concentration peaked during the pre-monsoon season (707.9 +/- 541.8 ng m(-3)), which was corroborated by the higher aerosol optical depth (AOD) values during this season (0.058 +/- 0.002). The diurnal cycle of the BC mass concentration exhibited a night-time low and afternoon high, which were influenced by the boundary layer dynamics and valley wind flow pattern. The Concentration Weighted Trajectory (CWT) analysis indicated diverse source regions, including northern Asia, the Indo-Gangetic Plain (IGP), and parts of Nepal and Bangladesh. The Moderate Resolution Imaging Spectroradiometer (MODIS)-derived AOD and Angstrom exponent (AE), and the OPAC-simulated single-scattering albedo (SSA) and asymmetry parameter (AP) over the study site were estimated to be 0.048 +/- 0.009 and 1.32 +/- 0.01, and 0.938 +/- 0.019 and 0.710 +/- 0.042, respectively, during the study period. The mean radiative forcing during the study period for the top of the atmosphere, surface and atmosphere were 3.4, -0.5 and 3.9 W m(-2), respectively. Higher atmospheric forcing was observed in the pre-monsoon season, leading to changes in the heating rates.

Observations on black carbon (BC) aerosols over an urban site (Pune) and a rural, high altitude site (Sinhagad) during summer and winter seasons over the period of 2009-2013 are reported. Apart from the temporal variation of BC over both the sites, its mass fraction to total suspended particulates (TSP) is studied. Finally, using the chemical composition of TSP and BC in the OPAC model, season-wise optical properties of aerosols are obtained which are further used in the SBDART model to derive the aerosol radiative forcing (ARF) at surface and top of the atmosphere and thereby the atmospheric forcing and heating rates in each season over both the sites. BC mass concentration and its mass fraction to TSP (Mf BC) were higher at Pune than at Sinhagad, indicating impact of more anthropogenic sources. At both the sites winter season witnessed higher BC concentrations than summer as well as higher Mf BC which is due to the prevailing favorable meteorological conditions in winter. Diurnal variation of BC showed different patterns at Pune and Sinhagad in terms of strength and occurrence of high and low values that could be attributed to varying local boundary layer conditions and source activities at both the sites. Negative ARF indicated cooling at top of the atmosphere and at surface leading to warming of the atmosphere at both the sites. However, surface cooling and atmospheric warming was more dominant at Pune leading to higher atmospheric heating rates, underlining the impact of absorbing BC aerosols which were about three times more at Pune than Sinhagad. (C) 2015 Elsevier Ltd. All rights reserved.

This article reports observational evidence of Black Carbon (BC) induced cloud burning effect (Semi direct effect) for the first time over a mountainous location in North east India. Simultaneous aircraft observations of Black Carbon (BC) mass concentrations and cloud microphysical parameters were carried out over Guwahati, in Northeast India during Cloud Aerosol Interactions and Precipitation Enhancement Experiment (CAIPEEX) Phase-I in 2009. Elevated pollution layers of BC (concentration exceeding 1 mu g m(-3)) were observed over the site up to 7 km on different experimental days (August 30, September 4 and 6 in 2009) in the cloud regime. The vertical heating rate and radiative forcing induced by elevated BC layers in the cloud regime were estimated using an optical model along with a radiative transfer model. The instantaneous vertical heating rate induced by BC in cloud layers is found to be as high as 2.65 K/day. The instantaneous vertical heating by BC is found to be inducing a significant reduction in the measured cloud liquid water content (LWC) over the site. Subsequently, the BC stimulated heating has been found to be reducing the cloud fraction (CFR) and thus inducing a cloud burning effect (Semi direct effect), over the region. The estimated instantaneous BC induced radiative forcing in the cloud regime is found to be +12.7-+45.1 W m(-2) during the experimental periods. This large warming and reduction in cloudiness can decrease the precipitation over the region. However, more simultaneous BC-cloud observations and further research are necessary to establish a stable semi-direct effect over the region. (C) 2014 Elsevier Ltd. All rights reserved.