Assessment of nighttime air quality over an urban location in Indo-Gangetic plain using remote sensing observations

Abstract

Nocturnal inversion can trap atmospheric pollutants in the lower atmosphere and can significantly impact human health and reduce visibility, particularly in mega-cities. Therefore, nighttime monitoring of atmospheric aerosols and gases is very important. In this paper, we have selected an urban location of Kanpur located in a highly polluted region of Indo-Gangetic Plains (IGP) to study the variability in nighttime aerosols in response to trace gases and meteorological parameters. For this purpose, we have analyzed all the available data of aerosol optical depth at 500 nm (AOD), Angstrom Exponent (440–870) (AE) from AERONET's newly developed direct moon algorithm. We also examined nighttime data of temperature, relative humidity, methane, ozone, and carbon monoxide from AIRS (Atmospheric Infrared Sounder). The average values of nighttime AOD, AE, and precipitable water (PW) were observed to be 0.65 ± 0.04, 1.06 ± 0.21, and 2.86 ± 1.71, respectively. The highest value (0.90 ± 0.05) of lunar AOD is found in November with a corresponding AE value of 1.28 representing the dominance of fine-mode aerosols in Kanpur. In summer, AOD exhibited a slight decreasing trend (slope = −0.008) while AE exhibited an increasing trend (slope = 0.029) indicating that the aerosol burden is decreasing but the contribution of fine mode aerosols is increasing. Urban aerosols were the most abundant type (62.75 %) in the atmosphere of Kanpur during nighttime. Average values of methane, carbon monoxide, and ozone were found to be 1876.30 ± 21.79 ppbv, 127.40 ± 15.12 ppbv, and 40.76 ± 4.55 ppbv, respectively. HYSPLIT cluster analysis on high AOD day indicate the transportation of desert dust and biomass burning aerosols from western and north western regions of India. WTC between AOD and temperature posits a positive correlation in the medium-term period. AOD and carbon monoxide showed an anti-phase association.