How the Atmosphere over Eastern Himalaya, India is Polluted with Carbonyl Compounds? Temporal Variability and Identification of Sources

A study was conducted on atmospheric carbonyl compounds for the first time over a Himalayan atmosphere in India. Samples were collected from a high altitude hill station, Darjeeling (27.01 degrees N, 88.15 degrees E, 2200 masl) during June 2012 to May 2013. Temporal variation, meteorological influence, source apportionment and ozone formation potential etc were studied for acetaldehyde, formaldehyde, acetone, butanaldehyde, propanaldehyde, benzaldehyde, crotonaldehyde, valeraldehyde, isovaleraldehyde, hexanaldehyde, p-tolualdehyde and o-tolualdehyde. High concentration of Acetone (81.6 +/- 63.5 mu g m(-3)) was observed which could be due to the higher photochemical production from its precursor volatile organic compounds emitted from tea plants and tea processing units. The concentration of acetaldehyde (20.7 +/- 47.6 mu g m(-3)) and formaldehyde (11.6 +/- 16.3 mu g m(-3)) were found to be comparable with metro cities of India and world. The average annual concentration of total carbonyl compounds was 174.2 +/- 184.6 mu g m(-3) with maximum during postmonsoon (456.9 +/- 199.5 mu g m(-3)) and minimum during winter season (72.2 +/- 42.9 mu g m(-3)). Meteorological parameters like temperature and surface reaching solar radiative flux played the major roles for the seasonal variation of the carbonyl concentration over the hill station. The average ratio of formaldehyde to acetaldehyde over Darjeeling was found to be 1.64 +/- 1.43 well representing a typical urban atmosphere at this part of Himalaya. Positive matrix factorization model showed that the biogenic emissions from tea plants and vehicular emissions were the major sources of carbonyl compounds over the hill station.