Inter and Intra-Annual Variability in Aerosol Characteristics over Northwestern Indo-Gangetic Plain

ABSTRACT

This study reports the temporal characteristics of aerosols mass concentration (PM₁₀, PM_2.5, PM₁), size distribution and optical depth from December 2011 to November 2013 over Patiala (30.33°N, 76.4°E, 249 a.s.l.), a site located in Indo-Gangetic Plain (IGP) in northwestern India, a region with the highest population density in the world. PM₁₀, PM_2.5, and PM₁ varied from 71 to 221, 27 to 92, and 17 to 75 µg/m³, respectively, with the highest concentration of PM₁₀ during summer of 2012, and PM_2.5 and PM₁ during autumn of 2013. These mass concentrations were significantly higher than National Ambient Air Quality (NAAQ) standards (PM₁₀ = 60 and PM_2.5 = 40 µg/m³), suggesting poor quality of air over IGP. Both natural and anthropogenic sources were found to be responsible for poor air quality of IGP with more contribution from the latter source as inferred from Ångström exponent (α_380–870) and fine mode fraction (FMF: PM_2.5/PM₁₀) of aerosols, which have shown large temporal variability. The particle size distribution is skewed towards particles with size less than 1.00 µm and very few particles are having the size greater than 6.25 µm. Aerosol optical depth at 500 nm (AOD₅₀₀) ranged from 0.36 to 0.64 and shows the highest value during summer of 2012 (0.64 ± 0.09) and autumn of 2013 (0.64 ± 0.25) and minimum (0.36 ± 0.05) in spring of 2013, further reflecting the different effects of aerosols on climate during different seasons. The relation between AOD₅₀₀ and PM mass has also been investigated, which has exhibited significant seasonality and AOD₅₀₀ is more sensitive towards the concentration of PM₁ rather than PM_2.5 and PM₁₀. These results give insight to the relative contribution of natural as well as anthropogenic aerosol sources to their total atmospheric abundances and their possible effect on ambient air quality and Earth’s radiation balance.