Large spatial extent of biomass burning occurs in northeast region of India during annual dry season for shifting cultivation purposes. Characterization of optical properties of resultant biomass burning aerosols is important for the study of atmospheric radiative process and for remote sensing of both Surface and atmospheric properties in these regions. In the present study, physical and optical properties of biomass burning aerosols in Arunachal Pradesh, North Eastern Region of India have been studied for the first time using ground based measurements using a MICROTOPS-II sunphotometer, an Aethalometer, a quartz crystal microbalance impactor (QCM), SO2 analyser, and an UV meter. Aerosol size distribution suggested dominance of accumulation mode particle loading during burning days compared to normal days. The slope of data points between simultaneous measurements of AOD (500 nm) and UVery suggested that every 0.1 increase in aerosol optical depth (AOD) causes 0.1 minimal erythermal dose (MED h(-1)) reduction during normal day and reduction of 0.36 MED h(-1) in ground reaching UVery during biomass burning periods. Diurnal variations of black carbon aerosol (BC) concentrations increased by a factor of similar to 2 during morning and evening hours compared to afternoon hours during biomass burning period. Daily average black carbon aerosol loading and SO2 concentrations were found to be high during burning day compared to background values. The proportion of BC to total aerosol mass concentration was observed to be similar to 5% during normal days and similar to 14% during burning days. The changes in black carbon mass concentration values have implications for estimating radiative forcing due to aerosols over the region. (C) 2008 Elsevier B.V. All rights reserved.

Black carbon (BC) has become the subject of interest in the recent years for a variety of reasons. BC aerosol may cause environmental as well as harmful health effects in densely inhabited regions. BC is a strong absorber of radiation in the visible and near-infrared part of the spectrum, where most of the solar energy is distributed. Black carbon is emitted into the atmosphere as a byproduct of all combustion processes, viz., vegetation burning, industrial effluents, motor vehicle exhausts, etc. In this paper, we present results from our measurements on BC aerosols, total aerosol mass concentration, and aerosol optical depth over an urban environment; namely Hyderabad during January-May, 2003. Diurnal variations of BC suggest. that high BC concentrations are observed during 6:00-9:00 h and 19:00-23:00 h. Weekday variations, of BC suggest that the day,average BC concentrations increases gradually from Monday to Wednesday and gradually decreases from Thursday to, Sunday. Fraction of BC to total mass concentration has been observed to be 7%. BC showed positive correlation with total mass concentration and aerosol, optical depth at 500 nm. Radiative transfer calculations suggest that during January-May, diurnal averaged aerosol forcing at the. surface was calculated to be -33 WM-2 and at the top of the atmosphere (TOA) it is to be +9Wm(-2). (C) 2004 Elsevier Ltd. All rights reserved.