Air pollution in fast-growing African cities presents a risk of premature death

Ten more African cities have signed on to the C40 Clean Air Cities Declaration to improve air quality. C40 is an international group of mayors collaborating to make cities more environmentally sustainable.

In May 2022, Abidjan, Accra, Addis Ababa, Dakar, Ekurhuleni, Freetown, Johannesburg, Lagos, Nairobi and Tshwane joined Durban, the first African city to sign the declaration.

As part of the C40 pledge, city leaders have committed to actions to tackle air pollution and slow human-caused changes in climate. These include actions such as setting targets that follow the World Health Organisation’s clean air guidelines.

This is a welcome commitment, as air pollution is a leading burden on global health. More than 6.5 million people die prematurely from exposure to air pollution each year worldwide. And air quality is worsening in African cities during a period of rapid growth and development. African cities are forecast to grow by 3 – 31% annually from now until the end of the century. This is far steeper than growth rates in Indian cities, at about 1 – 3% per year.

A major challenge in combating air pollution in Africa’s cities is the scarcity of data. Air quality is not monitored in most cities and resources to compile inventories of the types and sizes of sources contributing to air pollution are lacking. All these efforts are costly and require sustained, long-term funding.

Publicly available data from satellite observations provide a picture of multiple air pollutants. In our recent study, we sampled these data over fast-growing cities in the tropics, including 26 in Africa. Our investigation covered a 14-year period between 2005 and 2018.

We determined that the quality of air is declining at unprecedented rates. We found that the cause is a shift from rural to urban sources and that combined worsening air quality and population growth is linked to 180,000 additional premature deaths.

Such harmful effects will persist without bold air quality policies.

Shift in pollution

For centuries, air pollution in Africa has been dominated by open burning of biomass. This is a common practice by farmers in the dry season to clear land and to prepare for the next sowing season. The smoke produced is full of pollutants, bad for people and the environment.

This is now changing, in cities at least.

In our analysis, we identified that urban pollution sources have surpassed rural biomass burning as the main cause for worsening air pollution in cities. Satellite observations are too coarse (~10 km) to pinpoint the exact sources, but we can speculate that these include road traffic, burning of waste, and household use of fuels like charcoal and wood.

Our study focused on the fastest growing cities in the tropics. Amongst these are Lagos (population 15.4 million people growing at 3.5% per year) in Nigeria, Dar es Salaam (population 7.4 million people, 5.1% per year) in Tanzania, and Kinshasa (population 15.6 million people, 4.4% per year) in the Democratic Republic of the Congo.

The air quality indicators we tracked were fine particulate matter pollution (PM2.5) and the gas-phase compounds nitrogen dioxide (NO2), ammonia (NH3), and volatile organic compounds (VOCs). These either directly impact health (PM2.5, NO2) or form air pollutants that do (VOCs, NH3). These can all be produced from traffic, and burning of household waste and fuel.

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