Measurement and Distribution Pattern of n-alkanes in Size-Segregated Aerosols During Diwali Festival in Delhi, India

The loading of particulate matter (PM) and levels of particle-bound n-alkanes (C21-C33) in size-segregated aerosols were studied in Delhi on the occasion of Diwali during 3-5 November 2021. Three sets of samples were collected, i.e., Before Diwali (BD), Diwali Day (DD), and After Diwali (AD), in different size ranges. The mass loading was the highest in all size fractions in the DD sample. In the BD sample, the coarse fraction contributed the maximum (49%) to the total mass loading, whereas in DD and AD samples, submicron fractions contributed the most (50% and 46%, respectively). Local meteorology (low temperature, high RH, and low wind speed) played a significant role in the high buildup of pollutants in the atmosphere. Total n-alkanes concentration in the size-segregated PM was several times higher in DD (similar to 11-37 times) and AD (similar to 9-14 times) samples than in BD samples. Lower n-alkanes (C <= 25) with maxima at C25 indicated emissions from increased vehicular activities due to extra movement of people for shopping and meeting friends and relatives during the occasion. The higher n-alkanes (C > 25) with odd-even predominance and maxima at C29 indicated biogenic emissions mainly from candles/oil lamps, wood, and refuse burning during Diwali. CWT analysis of total n-alkanes showed the contribution of local emissions during the Diwali festival. To the best of authors' knowledge, the levels of n-alkanes (C21-C33) in size-segregated PM were studied for the first time during the Diwali festival in Delhi.