Investigation of optical and physical properties of aerosol over different sub-zones of Ahmedabad, India

This study investigates the impact of local environmental conditions on aerosol optical and physical properties in Ahmedabad city, India, using continuous in-situ measurements from September 2020 to March 2022. Aerosol Optical Thickness (AOT), Angstrom Exponent (a) and second derivative of Angstrom Exponent (α′) were analyzed across four distinct environments: rural, mix, traffic, and industry. AOT500 Average value for different location are 0.489,0.465,0.498,0.493 respectively. The results revealed significant temporal and spatial variations in aerosol loading and characteristics. AOT exhibited a clear seasonal pattern, with higher values during dry conditions and reduced values in post-monsoon. Notably, the industry location consistently displayed elevated AOT levels. An intriguing anomaly in November 2020, attributed to Diwali celebrations restrictions due to COVID-19, led to remarkably low AOT values. The presence of fine mode aerosols dominated in November, while coarse mode particles prevailed in March, as indicated by α values. The Angstrom parameters using least square method is not found appropriate for size distribution as it’s only valid for uni model aerosols which follows Junge’s size distribution law. The second derivative of α highlighted shifts in aerosol size distribution with wavelength, with peaks suggesting fine aerosol dominance during events like increased industrial activity.