Aerosol climatology over an urban site, Tirupati (India) derived from columnar and surface measurements: first time results obtained from a 30-day campaign

Abstract

In the present study, collocated and simultaneous data on spectral aerosol optical depth (AOD), mass concentration and size distribution of near-surface composite aerosols and black carbon aerosol mass concentrations were obtained from Microtops-II Sunphotometer, Quartz Crystal Microbalance (QCM) and Aethalometer, respectively, over an urban location, Tirupati (India) in the month of May 2009. The mean AOD at 500 nm and Ångström parameters (α, β) during this period were obtained as 0.64±0.13 and 0.89±0.24, 0.36±0.10, respectively. The total surface aerosol mass concentration varied from 13 to 60 μg m⁻³ out of which coarse mode dominated by 39%. The mean value of total mass concentration of aerosols was 23.80±0.25 μg m⁻³. The Ångström wavelength exponent (α) showed a positive correlation of 0.60 with the near-surface fine-mode fraction. The total mass concentration showed positive and negative correlations of 0.72 and 0.68 with air temperature and relative humidity, respectively. Along with this, the diurnal variation of black carbon aerosol concentration varied from 2 to 14 μg m⁻³ and observed prominently a sharp fumigation peak at around 07:00–09:00 h and the nocturnal peak between 20:00 and 22:00 h with a low value in afternoon hours (15:00 h) with a mean BC mass concentration of 3.76±0.23 μg m⁻³. A scatter plot between BC mass concentration (M_b) and total surface mass concentration (M_t) showed significant positive correlation of 0.73 and was used to estimate mean mass fraction (F_BC) for the study period, which was found to be 8.1±0.5%.