Remote sensing of nighttime air quality over the megacity of Lahore, Pakistan

In recent years, air quality is deteriorating which causes severe impacts on the climate system, and human health, particularly in the mega-cities of Pakistan. As we enter an era of more health related issues, poor air quality and rapid climate change, therefore the implications for nighttime air quality need to be better understood for air quality improvement. In this paper, for the first time, the nighttime air quality of Lahore was assessed using data from Aerosol Robotic Network (AERONET), Atmospheric Infrared Sounder (AIRS) and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) over Lahore during the period April 2021-August 2022. The highest mean monthly Aerosol Optical Depth (AOD) and Water Vapour Content (WVC) of 1.29 and 5.3 cm were observed in July 2022, respectively, whereas the highest Angstrom Exponent (AE) value of 1.5 occurred in August 2022. Moreover, the nighttime aerosol classification using the association between AOD and AE reveals the dominance of Background Conditions (BC), Urban Industrial/Biomass Burning aerosols (UI/BB), Desert Dust (DD) and Mixed Type (MT) aerosols. Over a couple of previous years, Lahore has witnessed worse air quality mainly due to biomass burning, dust aerosols, industrial pollutants and fuel combustion. Therefore, our main focus was on DD and UI/BB aerosols along with their source regions. We have also used the HYSPLIT model to understand the transport of nighttime aerosols. Moreover, nighttime high concentrations of mean monthly Carbon Monoxide (CO) and Ozone (O3) were observed in March and May 2022, respectively.

Automated summary

In recent years, air quality in the mega-cities of Pakistan, particularly Lahore, has been deteriorating, causing severe impacts on the climate system and human health. This paper assesses the nighttime air quality of Lahore using data from various satellite observations. The study reveals high aerosol concentrations, especially from biomass burning and dust aerosols, and high levels of carbon monoxide and ozone during specific months.