Atmospheric Polycyclic Aromatic Hydrocarbons (PAH) in Manipur of the Northeast India: Monitoring on Urban, Rural, and Mountain Sites

A passive air sampling was conducted to measure polycyclic aromatic hydrocarbon (PAH) in ambient air of Imphal (urban), Thoubal (rural), and Waithou (mountain) of Manipur, Northeast India from January 2009 to December 2009. The mean PAH concentrations of urban air (235.6ng/m(3)) were high compared to rural (206.3ng/m(3)) and mountain (202.1ng/m(3)). PAH compounds with 2- to 3-aromatic rings were predominant. Monthly variation of PAH concentration showed seasonal dependence exhibiting higher concentration during autumn and winter compared to spring and summer. Diagnostic ratio of specific PAH compounds suggests emission from diesel-powered vehicles and gasoline-powered vehicles could be major sources of contamination while coal burning emits high PAH in rural Manipur. Principal component analysis confirmed low molecular weight and medium molecular weight PAH are primary factor responsible for bringing variations in PAH concentrations. The back trajectory analysis revealed long-range transport of PAH to study area. A high level of PAH at the present site is a result of both local emission as well as long range transport from other part of southern Indian cities including Indian coastal regions and from Bangladesh.