Investigating daytime and night-time differences with the seasonal trend and sources of inorganic fine aerosols in Indo-Gangetic plain

This study investigates the seasonal distribution of inorganic aerosols in Central New Delhi and identifies their potential source regions using concentration weighted trajectories (CWTs). Secondary inorganic aerosols (NO3-, SO42-, NH4+) are the largest contributors to fine particulate matter in New Delhi, India. The concentrations of secondary inorganic aerosols showed very distinct seasonal patterns with higher concentrations in winter and post-monsoon seasons. Inorganic ions Ca2+, Mg2+ and K+ were also examined to understand their temporal trends. The primary aerosols were found to have smaller diurnal differences than secondary aerosols. The higher coefficient of divergence for secondary aerosols indicated a significant difference in their chemistry and/or meteorology during daytime and night-time, respectively. The backward trajectory analysis revealed the advection of ionic species from distant sources responsible for their significant seasonality. The highest concentrations of K+ during the post-monsoon season were mainly influenced by air masses arriving from Punjab and Haryana regions resulting from the prominent agricultural crop residue burning in these areas. CWT also identified the Thar Desert and Punjab as potential regions for enhanced levels of Ca2+ and K+, respectively. Also, the brick kilns located in western UP were observed as the major potential sources for NO3- and SO42-.