Characterization of aerosol associated non-polar organic compounds using TD-GC-MS: A four year study from Delhi, India

Abstract

Aerosol associated Non-Polar Organic Compounds (NPOCs) – 25 n-alkanes, 17 Polycyclic Aromatic Hydrocarbons (PAHs), and 3 Isoprenoid hydrocarbons – have been identified and quantified in PM10 samples collected over four years in time sequence (2006–2009), using Thermal Desorption Gas Chromatography Mass Spectrometry, in Delhi region. Established organic markers, associated diagnostic parameters, and molecular diagnostic ratios were used to assess and discern the contributing biogenic, petrogenic and pyrogenic sources to NPOCs. Analysis show that anthropogenic contributions to NPOCs exhibit increase from 2006 to 2009. Distribution profiles of NPOCs were significantly affected by change in season. Lower concentrations of NPOCs during summer months, and higher during winter, once scaled to Planetary Boundary Layer height, suggests that contributing sources were most active during summer months. During monsoon season high mass fractions of Total n-alkanes (ppm), Total PAHs (ppm), and Black carbon (BC) % alludes at the role of differential washout process involving hydrophilic and hydrophobic fractions of ambient aerosols. Significantly high, four year average concentrations of TPAH and BC signify the dominance of pyrogenic source contributions to PM10. High correlation between monthly mean concentrations of TPAH and BC (R2=0.75) suggests that besides common emission source, they are also contributed, individually, by exclusive independent sources.