Whether fine dust, nitrogen oxides or other pollutants – the air is thick in many metropolises around the world. Two studies now show what effects particulate matter and nitrogen oxides in particular have on health and how many people die prematurely as a result of this exposure. According to this, 86 percent of all city dwellers worldwide are exposed to unhealthy concentrations of fine dust. This resulted in 1.8 million additional deaths in 2019. In addition, the researchers attribute almost two million asthma illnesses in children to increased nitric oxide levels in the city air.
The emissions from traffic, households and industry are important sources of air pollution – and can make you sick. Especially fine dust below 2.5 micrometers particle size (PM2.5) and nitrogen oxides are considered to be the cause of respiratory and lung diseases, but also of asthma and cardiovascular diseases. In addition, there is increasing evidence that the ultra-fine dust penetrates into the brain and can promote Alzheimer’s, Parkinson’s and other neurodegenerative diseases there. Studies suggest that even exposure below the official limit values increases mortality from secondary diseases.
Limits for fine dust pollution far exceeded
Two research teams headed by Susan Anenberg from George Washington University in Washington DC have now investigated what air pollution means for the residents of the often heavily polluted cities. “In view of the fact that the majority of the world’s population lives in urban areas, it is important to know the exposure to air pollutants and their consequences,” explain the scientists. So far, however, this has only been recorded in some of the cities worldwide, often only for the megacities. That is why Anenberg and her colleagues have now evaluated air measurements and health data from more than 13,100 urban centers worldwide from the period 2000 to 2019. In one study, they focused on the increased mortality from fine dust with a particle size of PM2.5; in the second study, the focus was on childhood asthma due to nitric oxide exposure.
For particulate matter pollution, the team determined that around 86 percent of city dwellers worldwide – 2.5 billion people – were exposed to high levels of particulate matter in 2019. On average, the pollution was 35 micrograms of fine dust per cubic meter of air and thus exceeded the current limit values of the World Health Organization (WHO) of five micrograms per cubic meter on an annual average by a factor of seven. The limit of ten micrograms per cubic meter, which was still valid in 2019, was also significantly exceeded, as the researchers report. According to her, this increased exposure caused around 1.8 million additional deaths in 2019 alone. “61 out of 100,000 deaths in urban areas were due to fine dust pollution,” said Anenberg and her colleagues.
The pollution and the number of additional deaths is particularly high in the metropolitan areas of Southeast Asia, where there were also the highest increases in air pollution. In Europe and on the American continent, however, fine dust pollution in cities fell by 21 and 29 percent respectively between 2000 and 2019. “Nevertheless, a large part of the world’s urban population still lives in areas with unhealthy particulate matter levels,” says Anenberg’s colleague Veronica Southerland.
8.5 percent of annual asthma cases are caused by nitrogen oxides
In the second study, the scientists focused on the link between nitric oxides and asthma in children. To do this, they evaluated satellite data on land use and nitrogen oxide concentrations and compared them with on-site measurements. With the help of a model, they then compared the nitrogen oxide pollution and asthma cases for 13,189 urban areas worldwide for the period from 2000 to 2019. On the basis of epidemiological data, they then determined which concentration had what effect on the risk of asthma. The analyzes showed that in 2019, 1.85 million new cases of asthma occurred in children due to the increased nitric oxide exposure – this corresponds to 8.5 percent of all new cases of childhood asthma this year. “Our study shows that nitric oxide increases the risk of asthma in children and that this problem is particularly acute in cities,” says Anenberg.
After all, there was a downward trend in nitric oxide-related asthma cases: In 2000, 176 out of 100,000 childhood asthma cases were due to excessively high nitric oxide levels, in 2019 it was 165 per 100,000. “In places that have an efficient air quality management program, nitrogen dioxide levels have been falling for decades – with corresponding benefits for children’s health,” says Anenberg. “But even with these measures, the current nitric oxide levels still contribute to childhood asthma. This demonstrates that combating air pollution is a crucial element for children’s health. “
Source: Susan Anenberg (George Washington University, Washington DC) et al., The Lancet Planetary Health, doi: 10.1016 / S2542-5196 (21) 00350-8; doi: 10.1016 / S2542-5196 (21) 00255-2