Characterization of Aerosol Properties in the Delhi Region During the Biomass Burning and Subsequent Hudhud Cyclone

Abstract

The physicochemical and optical attributes of aerosols (PM₁₀) in the Delhi, National Physical Laboratory (NPL) [28.70°N; 77.10°E] region were examined during Biomass Burning (BB) and Subsequent Hudhud Cyclone (HC) in October 2014. Advanced offline characterization techniques, including Scanning Electron Microscope coupled with Energy Dispersive X-ray spectroscopy (SEM–EDS) and Wavelength Dispersive X-ray Fluorescence Spectroscopy (WD-XRF), were employed to probe particle morphology and chemical composition. Vertical profile data was obtained utilizing a dual-polarized micro-pulse lidar (MPL) system stationed at NPL. SEM–EDS analysis revealed the prevalence of carbon-rich spherical/core–shell aerosol particles attributed to the long-range transportation from BB activities in Punjab and Haryana. Frequency distribution analysis of the Aspect Ratio (AR), indicative of particle non-sphericity, shows that the majority of particles (~ 65%) fell within the AR range of 1.0–1.2, confirming the predominance of spherical/smooth particles during BB. During the HC, these particles transformed into non-spherical shapes upon mingling with moisture-laden sea aerosol spray particles predominantly composed of sea salts, exhibiting frequency distributions with peaks at AR range > 1.2–1.4 and > 1.6–1.8, and demonstrating a higher LDR value of ~ 4.7% (relative to ~ 3.7% during BB). WD-XRF analysis corroborated these findings, revealing an increase in Na and Cl element concentrations (avg.) from 6.54 to 7.52% and 0.63 to 1.03%, respectively, during the HC. Aerosol backscatter coefficient (ABC) values at 1.5 km (relative to that of lower altitudes i.e., 1 and 0.5 km) altitude during the HC were observed to be increased i.e., 0.052 km⁻¹sr⁻¹ owing to the predominance of particles with sea origins.