The current study compares black carbon radiative effects at the densely populated plain station, Varanasi and the lesser populated plateau station Ranchi with large forest cover but with numerous open coal mines. While the measured average black carbon mass density (BC) reduces from February to March at Ranchi following an increase in convective mixing, it is observed to increase by 150% from February to March in Varanasi, as transport from northeast forest fires increases. It is observed that absorption due to black carbon of non-fossil fuel origin is prevalent throughout the day, in Varanasi, while this contribution is most significant during post sunset hours in Ranchi. Radiative forcing, estimated hourly using chemical model (to derive BC-aod) and radiative transfer model, indicates that at least 5% of the incoming radiation is always cutoff during any time of the day in Varanasi while this is about 4% in Ranchi. BC effectively causes an apparent delayed sunrise by reducing the incoming radiation on the plains of Indo Gangetic Basin (IGB) by up to 25% at the daybreak. An estimate of crop loss due to cut off in radiation, using an empirical formula for crop yield as a function of radiation, indicates a possible loss of more than a quintal per hectare considering anthesis (February) and maturity (March) periods for the winter wheat in both the IGB stations with consistently higher losses in Varanasi.

Aerosol physiochemical properties over a varied mining plateau region at the eastern end of a monsoon trough are reported for the first time and analyzed at different time scales. Aerosol optical depth (single scattering albedo, SSA) is found to be 0.49 (0.9) in pre-monsoon, 0.4 (0.94) in monsoon, 0.46 (0.92) in post-monsoon, and 0.36 (0.89) in winter, with an annual mean of 0.43 (0.91). The volume-size distribution is tri-modal, with 0.02 (ultra-fine), 0.2 (accumulation) and 7 (coarse) µm, but with seasonal signatures. The angstrom exponent (AE) varies along with the AOD, especially in winter, although they are inversely related to each other during monsoons; the increase in size may be due to the effect of humidity. AODbc varies between 13.4

Composite and carbonaceous aerosol radiative forcing (RF) over Ranchi (23.5 degrees N, 85.3 degrees E) in eastern India at monthly and seasonal scales during February 2011 to January 2012 is derived from mean optical properties obtained from Sun-sky radiometer and a radiative transfer model. Ranchi is located on the Chotanagpur plateau at 650 m above mean sea level; the region is unique with dense open active mines, a source of mineral aerosols with opposing optical properties such as coal and limestone. Diurnal mean composite aerosol RF at the surface, in the spectral band 0.3-3.0 mu m increases from winter (December, January, February) to premonsoon (March, April, May) with maximum (-65 Wm(-2)) aerosol RF in March that is associated with highest black carbon (BC) aerosol optical depth (AOD), 0.05. Minimum surface aerosol RF occurs in July with minimum values of AOD and AOD(BC). Aerosol RF at top of the atmosphere is maximum (-17 Wm(-2)) in April, and is positive (+1.2 Wm(-2)) in March. On an average, carbonaceous aerosols (BC) contribute similar to 8.8% to total AOD and about 60% to total atmospheric absorption. A rapid increase of BC is seen in the postmonsoon with 1.0 mu g m(-3) in September to 3.0 mu g m(-3) in October. Aerosol-induced solar dimming is about 9.4% (premonsoon), 7.0% (monsoon), 10.6% (postmonsoon), and 10.2% (winter) of the surface radiation. Seasonal mean aerosol heating rate is observed to be maximum in premonsoon (similar to 1.15 degrees K/d(-1)), followed by postmonsoon, while winter and monsoon experience minimum (similar to 0.45 degrees K/d(-1)) heating, assuming typical aerosol profiles of the model.

Aerosol radiative forcing (ARE) over intense mining area in Indian monsoon trough region, computed based on the aerosol optical properties obtained through Prede (POM-1L) sky radiometer and radiative transfer model, are analysed for the year 2011 based on 21 clear sky days spread through seasons. Due to active mining and varied minerals ARF is expected to be significantly modulated by single scattering albedo (SSA). Our studies show that radiative forcing normalized by aerosol optical depth (ADD) is highly correlated with SSA (0.96) while ARF at the surface with AOD by 0.92. Our results indicate that for a given AOD, limits or range of ARF are determined by SSA, hence endorses the need to obtain SSA accurately, preferably derived through observations concurrent with AOD. Noticeably, ARE at the top-of the atmosphere is well connected to SSA (r = 0.77) than AOD (r = 0.6). Relation between observed black carbon and SSA are investigated. A possible over estimation of SSA by the inversion algorithm, SKYRAD.pack 4.2, used in the current study is also discussed. Choice of atmospheric profiles deviating from tropical to mid altitude summer or winter does not appear to be sensitive in ARE calculation by SBDART. Based on the 21 clear sky days, a multiple linear regression equation is obtained for ARF(bot) as a function of AOD and SSA with a bias of +/- 2.7 Wm(-2). This equation is verified with an independent data set of seasonal mean AOD and SSA to calculate seasonal ARF that compares well with the modeled ARE within +/- 4 Wm(-2). (C) 2013 Elsevier Ltd. All rights reserved.

Atmospheric aerosols are important component in the radiation budget and generally tend to decrease the amount of solar radiation falling on earth. Some aerosols like BC are absorbing in the nature and affect the climate by increasing AOD and warming the climate. Its direct and indirect effect on environment and human health is partially known but more studies are needed to understand it properly. That is why it is important to do its Quantitative and qualitative analysis and study its impact on climate etc. Ranchi is comes under northern region which is most polluted region among India where many pollutants including BC are high in concentration, So this study of BC over Ranchi can help to know its concentration of BC is found to vary on a diurnal as well as seasonal basis. The role of atmospheric boundary layer is very important in the variation of BC concentration. The present study aims to find the relation of BC with the boundary layer and understand its variation. Further its impact on AOD and global radiation will also study. This research may form a small step towards a comprehensive study of black carbon aerosol in the atmosphere in the northern city Ranchi of India.

Continuous and near-real-time measurements of the mass concentration of Aerosol Black Carbon (BC) were carried out 1st to 31st July 2010 of rainy season and compare with data of July-2010 to March-2011 using an Aethalometer (model AE-31 of Magee Scientific, USA). The principle of the Aethalometer is to measure the attenuation of a beam of light transmitted through a filter, while the filter is continuously collecting an aero-sol sample. This measurement is made at successive regular intervals of a time base period has been. the BC mass concentration is estimated by measuring the change in the transmittance of a quartz filter tape, on to which the particles impinge. The instrument was operated at a time base of 5 min, round the clock with a flow rate of 4-liter min–¹, to study the impact of rainy season on black carbon concentrations over a typical urban environment namely Ranchi, India. BC concentrations were high during morning (0600 to 0900 h) and evening hours (1900 to 2300 h) compared to afternoon hours. During early morning hours, high values of BC are attributed to the turbulence set-in by the solar heating which breaks the night-time stable layer and aero-sols in the nocturnal residual layer are mixed up with those near the surface.