Polar Integrating Nephelometer Inversion of Air Quality over a Rural Station in North India

Jain S, Devara PCS, Khan AA, Bhoyar PD and Sasso ND

Published on: 2022-12-08

Abstract

Nephelometers measure light scattering and therefore are the perfect tool to study the regional/global climate change directly and air quality through inversion indirectly. An Ecotech Model Aurora 4000 three-wavelength integrating polar Nephelometer has been in round-the-clock operation at Amity University Haryana (AUH), Gurugram for the past over three years. This cutting-edge technology-based instrument determines real-time total scattering coefficient (σsp), of the light due to aerosol particles in the atmosphere at three wavelengths (450nm (Blue), σspb; 525nm (Green) σspg; and 635nm (Red) σspr). Data for each measurement cycle from 10o through 90o at a total of 17 different positions are recorded.  All the three wavelengths produce differential scattering and are affected differently by particles of different sizes, shape, and composition. Parameters such as angular distribution of total scattering coefficient (from 0 to 90 degrees), σsp, asymmetry parameter, size index, turbidity coefficient and linear visibility are computed. Besides the day-to-day variation in the particle total scattering during the lockdown period, special observations carried out on two typical experimental days on 21st and 23rd March 2020 have also been presented in this paper. The results reveal that the initial higher values of (σsp) prior to lockdown declined drastically during the lockdown period. The particle size distributions, retrieved from wavelength dependence of σsp, indicate abundance of smaller particles which corroborate with in-situ measurements made at the same location but with different sensing techniques. The low σsp values observed during the situations like Coronavirus COVID-19 pandemic etc. are attributed to the reduced human activity and associated reduction in emissions from transport, industrial and construction activities. Moreover, the significant fluctuations in scattering coefficient (signatures of pollution level) observed during the period of lockdown are attributed to local meteorology (especially wind and rainfall) and indoor pollution (domestic cooking of various types etc.) in and around the study area.