Spectral dependency of aerosol optical depth and derived aerosol size distribution over Delhi: An implication to pollution source
Sustain. Environ. Res., 23(2), 113-128 (2013)
Amit Kumar Mishra, Arun Srivastava and Vinod Kumar Jain
Air pollution, aerosol optical depth (AOD), Angstrom parameters, aerosol size distribution, coarse mode fraction (CMF), fine mode fraction (FMF)
A measurement campaign of spectral dependency of aerosol optical depth (AOD) using MICROTOP-II Sunphotometer has been carried out during two phases (first one during transition from winter to spring and second one in full flagged summer) at three different sites [Jawaharlal Nehru University (JNU), Mukherjee Nagar (MN) and Patel Nagar (PN)] in Delhi. The MICROTOP measurements coupled with Aerosol Robotic Network (AERONET)-derived AOD observations have been used extensively to study aerosol behavior during the pre-monsoon season. Comparison of daily averaged AOD from Moderate Resolution Imaging Spectroradiometer (MODIS) and AERONET showed good agreement with MICROTOP observations with significant correlation coefficients of 0.89 ± 0.01 and 0.92 ± 0.01, respectively. The monthly averaged AERONET-derived AOD500 showed relatively higher value in May (0.77 ± 0.23) as compared to March (0.52 ± 0.19) and April (0.50 ± 0.14) during the pre-monsoon season. Daily mean values of AOD500 were found maximum at MN (0.67-0.98) and PN (0.66-0.92) as compared to JNU site (0.32-0.77). The diurnal variation of AOD and Angstrom exponent (AE) over JNU was found to be associated with traffic rush hours and revealed vehicular emissions as a main source of pollution. Daily mean columnar aerosol size distribution shows power law size distribution i.e., Junge size distribution at all observed sites. Total number of fine and coarse mode particles coupled with volume size distribution showed dominance of fine mode aerosol particles over the studied area. The influence of dust particles over the region (observed by Sunphotometer) was well corroborated with satellite (OMI, MODIS) and other ground based (AERONET) remote sensors. Aerosol index, AOD and AE were found to be 1-7-3.5, 0.5-0.9 and < 0.5 during the dusty condition, respectively. The results presented in this study depend on specific observation period and instrumentation used.