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

Abstract

A one-year extensive investigation to assess monthly and seasonal variations in the PM 10 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 PM 10 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 PM 10 load (μg/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 PM 10 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.

Profile of particulate-bound organic compounds in ambient environment of Srinagar: a high-altitude urban location in the North-Western Himalayas

“…On an average, 92-100 % recovery of the samples and SRM standards through thermal desorption was obtained. Reproducibility of the standard mix and selected samples was ascertained by processing them in quintuplicate; analytical precision of better than 5 % was obtained (Yadav et al 2013b). The protocol was optimized for 92-100 % recovery and analytical precision of 5 %.…”

Biomass Combustion a Dominant Source of Carbonaceous Aerosols in the Ambient Environment of Western Himalayas

“…The significant increase in the aerosol load and CA fraction during winter implied higher emissions of CA from biomass combustion; biomass burning requirements during this season increase significantly (Rawat et al, 2009). Further, increase in the ambient aerosol load is also assisted by the lowering of the planetary boundary layer (PBL) height during winter (Yadav et al, 2013). A decline in biomass combustion activity and increase in the PBL height during summer results in the observed decrease in the ambient aerosol load; overall, a sharp decline in the aerosol concentration during monsoon is induced through rain assisted washout (Yadav et al, 2013).…”

“…The average PBL height during summer and monsoon varied between 500-1500 m, whereas it was below 500 m during winter season. The large variation in PBL height from winter to summer accompanies a corresponding change in the mixing volume, which amplifies the ambient aerosol load in winter and their decrease in summer (Yadav et al, 2013). Calm wind condition during winter season and the lowering of ventilation coefficient further ensures the persistence of aerosol in the ambient environment.…”

“…Further, increase in the ambient aerosol load is also assisted by the lowering of the planetary boundary layer (PBL) height during winter (Yadav et al, 2013). A decline in biomass combustion activity and increase in the PBL height during summer results in the observed decrease in the ambient aerosol load; overall, a sharp decline in the aerosol concentration during monsoon is induced through rain assisted washout (Yadav et al, 2013).…”

“…In summer the traditional biomass combustion declines as its usage is limited only for cooking, consequently its presence in aerosol load is also low; whereas during monsoon, high humidity and frequent rain washout could play a role in the decline of Char-EC and Soot-EC; nevertheless the possibility of washout of Char-EC is higher due to its bigger size. The high concentration of Char-EC in winter also is favored by meteorological conditions; low wind speed and low planetary boundary layer height reduce the mixing volume and cause increase in aerosol concentration (Yadav et al, 2013).…”