Measurements of Volatile Organic Compounds at a rural site in India: Variability and sources during the seasonal transition.

Volatile Organic Compounds (VOCs) play a vital role in tropospheric ozone formation that controls the oxidative capacity of the troposphere. A total of 31 potential ozone precursor VOCs have been measured at a tropical rural site, Gadanki (13.5°N, 79.2°E) in Southern peninsular India. This study provides the primary information about different VOCs, their chemical classification and potential sources. There is a strong seasonal and diurnal variability among the VOC composition. n-Decane and n-dodecane dominate the other VOCs and contribute to a large fraction (>50 %) of the concentration of total VOCs (TVOCs) in winter and summer, monsoon is dominated by n-dodecane and post monsoon season has been dominated by ethane emissions. The source apportionment using interspecies correlation and Positive Matrix Factorisation (PMF) analysis resulted in four potential emission source factors namely biogenic, biomass burning/biofuel, fossil fuel and natural gas emissions. Winter and summer seasons have been dominated by VOCs originating from biomass burning/biofuel factors, monsoon has been dominated by biogenic emissions and post-monsoon season has been dominated by natural gas emissions. Even though it is a rural site, there are significant finger prints of anthropogenic emissions in the form of fossil fuel and natural gas most probably due to an adjacent national highway and long range transport. However, for the overall period, the VOCs emitted from biogenic and biomass burning together dominate the other two factors, indicating the expected source factor behaviour of a rural atmosphere.