Assessment of carbon fractions of aerosols collected under gravity settling at two different heights in the Delhi region

To understand height, location and season-specific variability in the composition and amount of different carbon fractions present in aerosols, samples were collected under gravity settling at two different heights (5 feet and 30 feet) from ground at nine different locations in the Delhi region, over the time span of 1 year. Sample collection height, not only determined the mass of different carbon fractions present but also their distribution (TC:OC:EC). Carbon forms estimated in aerosol samples carry signatures of location-specific characteristic of activity, particularly when the samples are collected close to ground. The EC fractions in aerosol samples collected at 30 feet height suggested no location-specificity whereas the OC fractions detected in the aerosol samples manifested variability with location, change of season, and the height at which the samples were collected. The analysis of the estimated OC/EC ratios suggested that the some fraction of OC may have arisen from the process of secondary organic carbon (SOC) formation in the atmosphere. Fractal dimensions of carbonaceous aggregates present in aerosols were also determined for different seasons, during summer and winter months it varies from 1.5 to 2.0 ± 0.05. The average diameters of the primary particles were also measured, constituting the aggregates, ranged between 24 and 57 nm.