How Covid-19 lockdowns and car-free days affected air pollution in Rwanda’s capital
Rising levels of vehicle traffic, industrial activity and urban sprawl are contributing to rising levels of air pollution across the global south. This is particularly the case in cities where urbanisation is progressing fastest.
In Kigali, the capital of Rwanda, the population has surged from less than 500,000 in 2000 to more than one million today. It is set to increase to nearly two million by 2030. At the same time, vehicle numbers in the city have increased from just 55,000 in 1999 to more than 200,000 in 2019.
Air pollution is the fourth-highest risk factor for premature mortality worldwide. And there is growing recognition that even at relatively low levels air pollution can cause significant health impacts, such as heart attacks and strokes.
Fine particulate matter (PM2.5) – such as dust, dirt, soot, or smoke – is 70 times smaller than human hair and is one of the most significant contributors to urban air pollution. In Kigali, the amount of PM2.5 in the air is approximately double the level deemed permissible by the World Health Organisation. This emphasizes the need for action and the scale of the potential benefit to be achieved. A challenge, however, lies in a lack of analysis on the sources of air pollution and the opportunities for action.
We found that PM2.5 was reduced by 15% on car-free days. We also found that the Covid-19 lockdown in 2020 – which reduced travel activity by over 80% – reduced air pollution by around 33%. A consequent partial lockdown, which allowed cars but not motorcycles, reduced travel activity by 41% and air pollution by around 21%.
Results from these analyses help us to understand both the causes of air pollution and the opportunities for policy action to address it.
Starting in 2016, on car-free days major roads are blocked off to provide space for collective exercise sessions to promote healthy living. Initially run once a month in 2018, the car-free days were made fortnightly and extended to secondary cities across Rwanda.
We found that, after controlling for the weather and seasonal variability, car-free days reduced PM2.5 by about 15%. This led to a 3.7% reduction in total PM2.5 pollution in the city every year.