Impact of Chemical Fire Accident on Spectral Solar Irradiance over Urban Environment-A Case Study

Abstract

Varying levels of atmospheric pollution presently plague many large cities in the world and long-term effect of urban aerosol layer on thermal climate received little attention. Aerosols are important in local and regional climatology through direct and indirect atmospheric processes. The present study deals with the impact of anthropogenic activity associated with chemical factory accident over an urban environment namely Hyderabad, India. Ground based measurements of solar irradiance and aerosol optical depth have been measured by using Multi Filter Rotating Shadow band Radiometer(MFRSR), Multi Wavelength Radiometer(MWR), Quartz Crystal Microbalance(QCM) Impactor and MICROTOPS-II sunphotometer respectively. Spatial variation of Aerosol optical depth (AOD) has been showed distinct increase on the accident day and subsequent days compared to normal days. Aerosol size measurements suggest the dominance of accumulation mode particles at distances ~100km away from accident site. Spectral measurements of solar irradiance exhibited variations based on polluted urban atmospheric conditions. We have made an attempt to quantify the percentage attenuation of solar irradiance due to chemical fire accident. In the highly polluted case, relative attenuations of global solar irradiance has been found to be ~8% and attenuation of direct normal irradiance is ~18% compared to normal days. An enhancement of about ~35% diffuse solar radiation has been observed due to fire accident. The diffuse-to-direct ratio of solar irradiance has been found to depend strongly on the atmospheric conditions. The statistical analysis between columnar aerosol optical depth and direct normal solar irradiance showed negative correlation with 83 W / m 2 reduction in solar irradiance for 0.1increase in aerosol optical depth at 500nm. The results of the study suggested that the effect of chemical fire accident persisted up to 3 days.