Monthly and Seasonal Variations in Aerosol Associated n-alkane Profiles in Relation to Meteorological Parameters in New Delhi, India

A one-year extensive investigation to assess monthly and seasonal variations in the PM10 associated homologous series of n-alkane (C-11-C-35) profiles was carried out in New Delhi, India. Quantitative estimation of n-alkanes, involving 3-4 PM10 samples/month, was done by using thermal desorption gas chromatography mass spectrometry (TD-GC-MS). Significant seasonal variations were observed, both in mass concentrations (annual mean: 517 +/- 256 ng/m(3)) and mass fractions (annual mean: 4368 +/- 2067 ppm) of total n-alkanes (C-11-C-35). The impact of the Planetary Boundary Layer (PBL) on the n-alkane profiles was the most significant among all the meteorological parameters considered. A strong positive correlation (r = 0.84) between PM10 load (mu g/m(3)) and mass concentrations of total n-alkanes (ng/m(3)) was observed; whereas a negative correlation (r = -0.72) was seen between the PM10 load and mass fractions of total n-alkanes (ppm). Annual mean values of the Carbon Preference Index (CPI) and Wax n-alkanes percentage (WNA%) stood at 2.2 +/- 0.6 and 39 +/- 10%, respectively. Established diagnostic tools indicated that during autumn, the dominant inputs of aerosol associated n-alkanes came from petrogenic (vehicular and industrial) emissions (72 +/- 7%), with lesser contributions from biogenic activities (28 +/- 7%). In other seasons, although petrogenic sources remained a dominant contributor (53 +/- 6%-59 +/- 14%), the contributions from biological sources were also comparable (41 +/- 14%-47 +/- 6%). Emissions of total n-alkanes from both petrogenic and biogenic sources were maximum during spring. In the rest of the months, small variations were observed in the emissions of total n-alkanes from petrogenic sources, whereas large variations were noted in the emissions from biogenic sources.