Analyses of black carbon (BC) data from three different environments in India -Delhi megacity, Srinagar metropolitan and Gulmarg hill station, showed that Delhi had the highest annual average BC concentration (12.3 +/- 10.2 mu g m- 3), followed by Srinagar (4.3 +/- 5 mu g m-3) and Gulmarg (2.4 +/- 2 mu g m-3). The inflow of aerosols from the neighboring agricultural regions, notably during Winter, causes Delhi to have the highest seasonal average BC (16.8 mu g m- 3). Srinagar had the highest average seasonal BC during autumn (6.3 mu g m- 3) due to the burning of horticulture residue and hardwood for charcoal making and residential heating. At Gulmarg, on the other hand, the winter season's high BC (2.2 mu g m- 3) is due to the increased emissions from the tourist traffic, snowmobile/ATVs and wood burning for residential heating. BC concentrations in Delhi and Srinagar were roughly in line with their population size. However, compared to sites with the similar population, BC at Gul-marg was roughly twice higher than the other sites. There was a higher contribution to BC from fossil fuels than biomass burning at all three sites, which indicates that cars are the primary source of BC. Overall, values of BC aerosol optical properties in Delhi are much higher than those in Srinagar and Gulmarg. During the cold season, continental air masses transport BC from the neighboring areas to Delhi and westerlies enhance the local BC loading at Srinagar and Gulmarg. The predominant presence of absorbing aerosols, particularly BC, during late autumn and winter at all three sites leads to an increase in aerosol optical depth (AOD), a reduction in single scattering albedo (SSA) and an increase in asymmetry parameter (AP). As a result, there is a significant increase in the radiative forcing of the atmosphere (RFATM), with the highest values observed in January in Delhi (+71.5 W m-2) and Srinagar (+56.05 W m-2), and in November at Gulmarg (+18.5 W m-2). These findings suggest that small rural towns that are affected by seasonal emissions, low planetary boundary layers, and frequent tem-perature inversions, can contribute to a substantial amount of radiative forcing. This study provides a larger perspective on increasing BC in Delhi, and urban-rural fringe areas in the Indian Himalayas, which is crucial for identifying what actions must be taken to control BC emissions to reduce impacts on cryosphere, human health and other sectors.

Changes in aerosol characteristics (spectral aerosol optical depth, AOD and composition) are examined during the transition from 'relatively clean' to 'extreme' aerosol days in the summer of 2012 at Delhi National Capital Region (NCR), India. AOD smaller than 054 (i.e. 12-year mean AOD - 1 sigma) represents 'relatively clean' days in Delhi during the summer. 'Extreme' days are defined by the condition when AOD(0.5) exceeds 12-year mean AOD + 1 standard deviation (sigma). Mean (+/- 1 sigma) AOD increases to 1.2 +/- 0.12 along with a decrease of Angstrom Exponent from 0.54 +/- 0.09 to 022 +/- 0.12 during the 'extreme' days. Aerosol composition is inferred by fixing the number concentrations of various individual species through iterative tweaking when simulated (following Mie theory) AOD spectrum matches with the measured one. Contribution of coarse mode dust to aerosol mass increased from 763% (relatively clean) to 96.8% (extreme events), while the corresponding contributions to AOD(0.5) increased from 35.0% to 70.8%. Spectrally increasing single scattering albedo (SSA) and CALIPSO aerosol sub-type information support the dominant presence of dust during the 'extreme' aerosol days. Aerosol direct radiative forcing (ADRF) at the Lop-of-the-atmosphere increases from 212 W m(-2) (relatively clean) to 56.6 W m(-2) (extreme), while the corresponding change in surface ADRF is from -995 W m(-2) to 153.5 W m(-2). Coarse mode dust contributes 603% of the observed surface ADRF during the 'extreme' days. On the contrary, 0.4% mass fraction of black carbon (BC) translates into 13.1% contribution to AOD(0.5) and 33.5% to surface ADRF during the 'extreme' days. The atmospheric heating rate increased by 75.1% from 1.7 K/day to 2.96 K/day during the 'extreme' days. (C) 2016 Elsevier B.V. All rights reserved.

Particulate matter (PM2.5) samples were collected over Delhi, India during January to December 2012 and analysed for carbonaceous aerosols and inorganic ions (SO42 -and NO3-) in order to examine variations in atmospheric chemistry, combustion sources and influence of long-range transport. The PM2.5 samples are measured (offline) via medium volume air samplers and analysed gravimetrically for carbonaceous (organic carbon, OC; elemental carbon, EC) aerosols and inorganic ions (SO42 -and NO3-). Furthermore, continuous (online) measurements of PM2.5 (via Beta-attenuation analyser), black carbon (BC) mass concentration (via Magee scientific Aethalometer) and carbon monoxide (via CO-analyser) are carried out. PM2.5 (online) range from 18.2 to 500.6 mu gm(-3) (annual mean of 124.6 +/- 87.9 mu gm(-3)) exhibiting higher night-time (129.4 mu gm(-3)) than daytime (103.8 mu g m(-3)) concentrations. The online concentrations are 38% and 28% lower than the offline during night and day, respectively. In general, larger night-time concentrations are found for the BC, OC, NO3- and SO42-, which are seasonally dependent with larger differences during late post-monsoon and winter. The high correlation (R-2=0.74) between OC and EC along with the OC/EC of 7.09 (day time) and 4.55 (night-time), suggest significant influence of biomass-burning emissions (burning of wood and agricultural waste) as well as secondary organic aerosol formation during daytime. Concentrated weighted trajectory (CWT) analysis reveals that the potential sources for the carbonaceous aerosols and pollutants are local emissions within the urban environment and transported smoke from agricultural burning in northwest India during post-monsoon. BC radiative forcing estimates result in very high atmospheric heating rates (similar to 1.8-2.0 K day(-1)) due to agricultural burning effects during the 2012 post-monsoon season. (C) 2015 Elsevier B.V. All rights reserved.