LAGOS, Nigeria – Fast-growing countries often see sharp increases in air pollution as their populations and economies expand. But a new study on air quality in Africa, published on Monday, found the opposite: one of the continent’s most vibrant regions is becoming less polluted.
The study, published in Proceedings of the National Academy of Sciences, found that levels of dangerous nitrogen oxides, a by-product of combustion, in northern Sub-Saharan Africa have declined dramatically as wealth and population in the area have increased.
“The traditional paradigm is that as middle and low-income countries grow, we often see more emissions, and seeing a different kind of trajectory is very interesting,” said Jonathan Hickman, a researcher at NASA’s Goddard Institute for Space Studies. who was the lead author of the study. “It is good to see a decline occurring when you would expect to see pollution increasing.”
The reason, according to the researchers, is that an increase in pollution from industry and transportation in the area studied – from Senegal and Côte d’Ivoire in the west to South Sudan, Uganda and Kenya in the east – appears to have been offset by a decline in the number of fires caused by farmers.
Although not a major industrial polluter like Asia and North America, Africa has long been the site of widespread biomass burning during the dry season.
Burning vegetation is considered an inexpensive and efficient method of clearing the land in preparation for the planting season, and burning has the advantage of retaining mineral nutrients in the soil. But the consequences for human health and global warming are potentially serious. Fires for soil management can combine with urban pollution to produce toxic air. And fires emit carbon dioxide, which warms the planet, into the atmosphere.
Brush fires tend to evoke images of out-of-control fires in places like Australia or the western United States, but northern Equatorial Africa is the region with the largest biomass fire area in the world, according to researchers, with about 70 percent of the total land burned.
The new study used NASA satellite data and images to measure dangerous gases present in the region’s air and determine fire trends between 2005, when NASA records began, and 2017. At peak fire seasons, dioxide levels nitrogen, or NO2, a harmful element the gas produced by road traffic and the combustion of other fossil fuels and linked to respiratory problems such as asthma decreased by 4.5% in the lower atmosphere.
That drop was so significant, said Dr. Hickman, that it resulted in a net reduction of the pollutant in the region.
The discovery is important because Africa’s growing population, currently 1.2 billion, but expected to reach 2 billion by 2040, is rapidly urbanizing. Pollution has overtaken AIDS as the main cause of death on the continent. But governments often prioritize economic growth over the environment, which means that there is little emphasis on collecting data on air quality or implementing clean air policies.
The new study “provides an important tool to fill some of these data gaps in Africa, where there is a shortage of air pollution studies at various levels,” said Andriannah Mbandi, a Kenya-based environmental researcher and affiliated with the Stockholm Environmental Institute. . “It would be great if the follow-up work on this document quantified these levels for health and economic indicators, which is useful for policy makers.”
Although fires may be subsiding, pollution is still growing.
Emissions from burning fossil fuels are expected to increase considerably in Africa. Despite the African Union’s commitment to green energy in 2015, 80 percent of the energy generated on the continent comes from coal or other fossil fuels. More and more used cars are being imported, which increases transport emissions.
This could trigger a reversal of the positive trend identified in Monday’s study, especially in populous and wealthy countries like Nigeria.
“As you increase GDP, you see a decrease in the amount of NO2, but it just followed that pattern to some extent,” said Hickman, describing the analysis the team carried out, adjusting the levels of wealth and pollution within the model .
“At the highest levels of this GDP metric, air pollution levels have almost returned to the levels when we started,” he said. “What this suggests is that this decline that we are seeing is likely to slow down and can be reversed as a consequence of the increased use of fossils.”