Aerosol-associated non-polar organic compounds (NPOCs) at Jammu, India, in the North-Western Himalayan Region: seasonal variations in sources and processes

Fine particulate (PM₂.₅) bound non-polar organic compounds (NPOCs) and associated diagnostic parameters were studied at Jammu, an urban location in the foothills of North-Western Himalayan Region. PM₂.₅ was collected daily (24 h, once a week) over a year to assess monthly and seasonal variations in NPOC concentration and their source(s) activity. Samples were analyzed on thermal desorption-gas chromatography mass spectrometry to identify and quantify source-specific organic markers. Homologous series of n-alkanes, polycyclic aromatic hydrocarbons (PAHs), isoprenoid hydrocarbons and nicotine were investigated to understand the sources of aerosols in the region. The annual mean concentration of PM₂.₅ during the sampling period was found higher than the permissible limit of India’s National Ambient Air Quality Standards (NAAQS) and World Health Organisation (WHO) guidelines. The rise of concentration for PM₂.₅ and associated NPOCs in summer season was attributed to enhanced emission. The n-alkane-based diagnostic parameters indicated mixed contributions of NPOCs from anthropogenic sources like fossil fuel-related combustion with significant inputs from biogenic emission. Moreover, high influence of petrogenic contribution was observed in summer (monsoon) months. The quantifiable amounts of isoprenoid hydrocarbons further confirmed this observation. Total PAH concentration also followed an increasing trend from March to June, and June onwards a sharp decrease was observed. The higher concentration of environmental tobacco smoke marker nicotine in winter months was plausibly due to lower air temperature and conditions unfavourable to photo-degradation. A clear dominance of low molecular weight PAHs was noticed with rare presence of toxic PAHs in the ambient atmosphere of Jammu. PAH-based diagnostic parameters suggested substantial contribution from low temperature pyrolysis processes like biomass/crop-residue burning, wood and coal fire in the region. Specific wood burning markers further confirmed this observation.