Assessment of air quality variations in Punjab, Pakistan, using Sentinel-5P during COVID-19 lockdowns

Air pollution is an increasing global concern and the World Health Organization has designated it as a major environmental threat. It is a significant research area; that is why spatiotemporal analysis of five air quality pollutants, nitrogen dioxide (NO₂), carbon monoxide (CO), sulfur dioxide (SO₂), and formaldehyde (HCHO) concentration is monitored using Sentinel-5-precursor in Punjab, Pakistan. Punjab province's rapid growth in agriculture, urbanization, transport, and power generation contributes to increasing air pollution, making the region critical for air quality monitoring. The objective of this study is to assess the variation in air quality pollutant concentration across Punjab in COVID-19-associated lockdowns. Lockdowns imposed by the government consist of different phases, such as before lockdown period, complete lockdown period, smart lockdown period, and after lockdown period. This study employs Google Earth Engine (GEE) to analyze pollutant concentration variations, addressing the challenge of spatially understanding pollutant variations across the study area for effective air quality monitoring to support public health and environmental management. The study results highlight the positive impact of the COVID-19 lockdown on air quality as NO₂ concentrations decrease between 2020-2021 and 2023-2024 (0.00023 to 0.00016 mol/m²). Concentrations of CO and HCHO increased noticeably while SO₂ showed a mixed trend, such as decreasing during lockdowns and increasing afterwards. These findings emphasize the essential need to target specific pollutants in order to improve air quality and public health. The results give critical information to the Ministry of Climate Change, policymakers, and researchers, allowing them to make well-informed decisions and implement effective strategies to reduce the environmental and health impacts of air pollution in the Punjab province.