Using Multiple Platforms to Investigate the Impacts of COVID-19 Measures on Air Quality in South Africa

Abstract:

The Highveld region of South Africa includes the megacity conurbation of Johannesburg-Tshwane-Ekurhuleni within Gauteng Province, as well as highly industrialized areas that include 14 of the country’s coal-fired power stations. The ground-level pollution levels in the Highveld often exceed National Ambient Air Quality Standards, and the area is known as a global “hot-spot” for NO₂ pollution from satellite measurements. There is moderate spatial coverage of ground-based measurements in the region, with many situated in low-income settlements. Despite regulatory efforts targeting large industrial sources in this region, air pollution has not improved substantially in the past decade. Air quality management is challenging due to the complexity of sources, as well as the spatial and temporal heterogeneity of emissions and resultant concentrations. Thus, analyzing the impact of COVID-19 measures provides an opportunity to improve the quantification of the linkages between policy interventions, changes in emissions, and resultant air quality, that can be applied by government after the pandemic for sustained improvement in air quality. In order to give health facilities time to prepare, the South African government imposed a sudden and strict lockdown early in the pandemic starting 27 March 2020 until 1 May, before slowly relaxing the measures. This initial lockdown, in particular, had an impact on many large sources of emissions including power generation, industries, and vehicles. For the Highveld region, this occurred in the transition from the rainy season (in summer) to the dry winter. The winters of the Highveld are marked by very stable meteorological conditions with strong inversions that lead to increases in ground-level air pollution. This study uses measurements from TROPOMI and ground-based stations together with a 3D chemical transport model (CAMx) to investigate the linkages between COVID-19 measures and air quality in the industrialized Highveld. This multiple platform approach is necessary due to the moderate spatial coverage of ground-based measurements. Initial results show decreases in NO₂ in April, with levels increasing from May. These results will be presented together with CAMx simulations of BAU and emission perturbation experiments to unravel the drivers of pollution.