The present study examines the aerosol characteristics over two locations in the northwest region of India (Dehradun and Patiala) during premonsoon season of 2013. The average mass concentrations of particulates (PM10; PM2.5; PM1) were found to be118±36,34±11, and19±10 µgm−3and140±48,30±13, and14±06 µgm−3over Dehradun and Patiala, respectively. The average aerosol optical depth (AOD500 nm) is observed to be0.62±0.11over Dehradun and0.56±0.21over Patiala. Ångström exponent and fine mode fraction show higher values over Dehradun as compared to Patiala. The average mass concentration of black carbon was found to be3343±546 ngm−3and6335±760 ngm−3over Dehradun and Patiala, respectively. The diurnal pattern of BC is mainly controlled by boundary layer dynamics and local anthropogenic activities over both the stations. The average single scattering albedo (SSA500 nm) exhibited low value over Patiala (0.83±0.01) in comparison to Dehradun (0.90±0.01), suggesting the abundance of absorbing type aerosols over Patiala. The average atmospheric aerosol radiative forcing is +37.34 Wm−2and +54.81 Wm−2over Dehradun and Patiala, respectively, leading to atmospheric heating rate of 1.0 K day−1over Dehradun and 1.5 K day−1over Patiala.

Climatological aerosol optical depths (AOD) over Tropical coastal city Machilipatnam, India have been examined to bring out the temporal heterogeneity in columnar aerosol characteristics. AOD values at 388 nm derived from the Ozone Monitoring Instrument (OMI) sensor EOS-AURA satellite, for the period of 2005–2013 have been analyzed for the purpose. AOD trends exhibited seasonal annual mean variations. Frequency distributions of the AOD values are examined to infer the monthly mean values. Monthly and seasonal variations of AOD are investigated in the light of regional synoptic meteorology. AODs>0.6 showed maximum occurrence in monsoon months. The mean AOD values increased towards summer reaching ~0.69 ± 0.34 and attained peak in monsoon season with a value of ~0.74 ± 0.33 and decreased during post-monsoon reaching as low as ~0.73 ± 0.3. Positive slope ~0.016 observed for inter annual distribution trend line. Factors like synoptic scale circulation patterns which are causing modulations of AOD apart from local sources were discussed.

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