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Pollution

Air pollution kills 780,000 people in Africa each year

Modeling study from NASA suggests Saharan dust storms account for much of the burden

by Katherine Bourzac
April 23, 2019 | APPEARED IN VOLUME 97, ISSUE 17

09717-leadcon-dust.jpg
Credit: Jeff Schmaltz/NASA
Dust storms in the Sahara Desert degrade air quality and are a major cause of mortality in Africa.

Air pollution causes about 780,000 premature deaths per year in Africa, according to a modeling study by researchers at NASA (JGR Atmospheres 2019, DOI: 10.1029/2018JD029336).

The extent of air pollution across the continent, and how it affects people’s health, has been difficult to quantify. In the new study, researchers used satellite data and models of atmospheric chemistry and health to fill in some of the data gaps. Surprisingly, they found that a majority of deaths due to poor air quality are caused by particulate matter carried by Sahara Desert dust storms.

The negative health effects of air pollution are well known. Exposures to ozone and particulate matter, for example, cause respiratory and cardiovascular disease. But most countries in Africa lack the infrastructure needed to map in detail the levels of pollutants people are exposed to and how those pollutants affect public health, says Susanne Bauer, an atmospheric modeler at the NASA/Goddard Institute for Space Studies who led the study.

“All Sub-Saharan African countries suffer from lack of continuous air quality monitoring and also lack of well-maintained and easily accessible data on health indicators—perhaps with the exception of countries such as South Africa,” says Kiros Berhane, an epidemiologist at the University of Southern California Keck School of Medicine who was not involved with the NASA study.

Without such a monitoring framework, few studies have considered the impacts of a variety of sources of air pollution outside urban areas in Africa, Bauer says, and the studies that have been published have given widely varying estimates, from tens of thousands to hundreds of thousands of deaths annually.

In the NASA study, Bauer’s group focused on three major sources of outdoor air pollution in Africa: industrialization, which includes sources such as cars and factories; fires, primarily agricultural burning; and natural sources, which are dominated by mineral dust. The team used satellite observations of aerosol particles in the atmosphere above Africa to estimate emissions, and atmospheric and climate modeling to predict the extent and transport of particulate matter, ozone, carbon monoxide, and sulfur dioxide. Then they used epidemiological models to predict the health impacts of the pollution in 2016.

The strong influence of dust storms on public health surprised Bauer. According to her models, exposure to natural emissions, primarily fine particulate matter in dust, caused 556,475 premature deaths on the continent in 2016 with about 43,489 of those occurring in West Africa. Industrial emissions caused 182,398 deaths and biomass burning caused 43,374. Overall, African mortality resulting from poor air quality is similar in scale to HIV/AIDS mortality in the region, Bauer says. However, she cautions, it’s difficult to make a hard and fast comparison because infectious disease deaths are likely undercounted.

Berhane says Bauer’s study is welcome in a region where there is far too little pollution data. He is also surprised by the impact of dust, and says it’s worth further study, especially as the continent continues to industrialize. Over time, the relative contributions from natural versus anthropogenic emissions are likely to change, he says.

Rebecca Garland, who works on air quality and climate modeling at the Council for Scientific and Industrial Research in Pretoria, says the NASA group did a good job using satellite data to estimate how much pollution was close enough to the ground to cause health effects—something that’s tricky but necessary to do in the absence of ground-level measurements. However, she says the modeling study is too coarse to guide regional policy decisions—for that, governments need local pollution data.

But there are hurdles to collecting those data. In many countries in sub-Saharan Africa, public health budgets are already strained as governments try to ameliorate infectious disease and child malnutrition while also building infrastructure to deliver clean water and improve sanitation, says University of Cape Coast epidemiologist A. Kofi Amegah. Pollution data are “nonexistent because of the very limited number of researchers on the continent working on air pollution health effects, coupled with the lack of funding,” Amegah says. Conventional air pollution sensors are expensive. In his country, Ghana, ground-based monitoring is limited to the capital city of Accra, despite the fact that other areas in the country are increasingly urbanized, he says. He echos Garland’s call for local data, adding that without the data, governments in the region are not likely to act on air quality. Amegah’s research group is implementing networks of low-cost air pollution sensors to address the data gap.

Meanwhile, Garland is part of a team that’s trying to bring together atmospheric scientists across the continent. She hopes the scientists banding together in the African Group on Atmospheric Sciences or ANGA, which means “atmosphere” in Kiswahili, will bring more sustained attention to the problem of air pollution in the region, and encourage the development of local solutions.

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