Concentrations of air pollutants over South Africa decreased during the national lockdown (imposed to try and counter the Covid-19 pandemic), preliminary analysis of satellite data indicated. The study focused on nitrogen dioxide (NO₂) and sulphur dioxide (SO₂).

The research was being carried out by researchers from South Africa’s Council for Scientific and Industrial Research (CSIR) and the UK’s University of Leicester. It was aimed at understanding the effects of the lockdown on air pollution in South Africa.

Data sourced from the TROPOMI instrument on the Sentinel-5P satellite provided information on pollutants in the atmosphere. This was supplemented by data from ground-based sensors, which recorded the levels of the pollutants at the level at which people breathe.

(Sentinel-5P is a European Space Agency satellite, the suffix -P standing for Precursor, as it preceded the Sentinel-5 satellite. Sentinel-5P was launched in October 2017 and Sentinel-5 should be launched next year. TROPOMI stands for Tropospheric Monitoring Instrument.)

The preliminary data show that, over the Highveld, there had been a 23% decrease in NO₂ concentrations over the period of March 27 to April 20, in comparison to the pre-lockdown period of March 10 to March 26. The fall in SO₂ concentrations was even greater, coming to 47%, for the period March 27 to April 17 (again, in contrast to the March 10 to March 26 period).

In spatial terms, there was a greater decrease in NO₂ in and around Gauteng province, because of the reduction in vehicle traffic. There was also a sizeable fall over the Highveld’s industrialised region. 

“It would be premature to attribute this change solely to the decreases in emissions from the lockdown,” cautioned CSIR principal researcher Professor Rebecca Garland. “Confirmation with additional surface observations and a model are required. This work is on-going.”

“This change will likely be temporary as many of the emissions reductions due to the lockdown will reverse when we go back to our normal day-to-day activities that make large contributions to air pollution,” pointed out University of Leicester Associate Professor in Earth Observations Eloise Marais. “This period does provide us with a unique opportunity to learn about the influence of different sources on air quality, whether natural or anthropogenic. This information is crucial for developing effective air quality policies.”