90% of the world's urban population breathes polluted air

A new study concludes that 86% of the world's city dwellers (2.5 billion people) are exposed to annual average levels of fine particles that exceed the World Health Organization (WHO) guideline since 2005. And a second study concludes that almost two million cases of childhood asthma are related to nitrogen dioxide air pollution caused by traffic and that two out of three occur in cities.

Population breathes polluted air

Both studies are published in The Lancet Planetary Health journal and highlight the continuing need for strategies to improve air pollution and reduce exposure to harmful emissions, particularly among children and the elderly.

In the first modeling study, the researchers analyzed PM2.5 ( fine particles with a diameter equal to or less than 2.5 micrometers ), the main environmental risk factor for disease. Inhaling is known to increase the risk of premature death from conditions such as cardiovascular disease, respiratory disease, lung cancer, and lower respiratory tract infections.

Despite the fact that more than half (55%) of the world's population lives in cities, little research has been done to date comparing the burden of disease caused by PM2.5 in urban areas around the world, and most assessments look at PM2.5 only in megacities. This new study examines PM2.5 concentrations and associated mortality trends in more than 13,000 cities around the world between 2000 and 2019.

The population-weighted average PM2.5 concentration in all urban areas globally was 35 micrograms per cubic meter in 2019, unchanged from 2000. This is equal to seven times 2021 WHO guideline for the annual average of PM2.5 (five micrograms per cubic meter). The authors estimate that 61 of every 100,000 deaths in urban areas were attributable to PM2.5 in 2019.

Although the global mean concentrations of PM2.5 in urban areas were constant during this period, there were large variations by region. Globally, approximately 86% of urban dwellers (2.5 billion people) lived in areas that exceeded the 2005 WHO guideline for mean annual exposure to PM2.5 (10 micrograms per cubic meter) in 2019, which caused an excess of 1.8 million deaths.

Nitrogen oxides

In the second study, the researchers looked at NO2 (nitrogen dioxide gas), an air pollutant emitted primarily from vehicles, power plants, industrial manufacturing, and agriculture.

Previous research has shown that transport-related air pollution, for which NO2 serves as a marker, is associated with both exacerbations of asthma and new cases of asthma in children. However, to date, there have been no studies specifically looking at trends in the burden of transport-related NO2 pollution in the incidence of pediatric asthma in urban areas.

The study analyzes health and pollution trends in 13,000 cities around the world In this research, global NO2 concentrations were calculated with a resolution of one kilometer by combining satellite data with data sets on different types of land use, such as roads and green spaces. NO2 concentrations were applied to population and reference asthma rates to estimate the incidence of pediatric asthma attributable to NO2 between 2000-2019 in 13,189 urban areas worldwide.

The study revealed that in 2019 there were 1.85 million new cases of pediatric asthma associated with NO2; 8.5% of all new pediatric asthma cases registered that year. About two out of three of these pediatric asthma cases attributable to NO2 occurred in the 13,189 urban areas included in the study. In urban areas, NO2 was responsible for 16% of all new pediatric asthma cases in 2019.

Levels of NO2 contribute

In both 2000 and 2019, 1.2 million cases of pediatric asthma in urban areas could be attributed to NO2 contamination, however, the rate per 100,000 children decreased by 11%, from 176 to 156 per 100,000 children, since the urban population grew 14%.

"Our results demonstrate the significant influence of combustion-related air pollution on the health of children in cities around the world," says Dr. Susan Anenberg of George Washington University, who is the corresponding author of both studies.

"In places with effective air quality management programs, NO2 concentrations have been on a downward trend for decades, with benefits for children's respiratory health," he adds. Even with these improvements, current levels of NO2 contribute substantially to the incidence of pediatric asthma, which shows that the mitigation of air pollution should be a fundamental element of children's public health strategies ”.

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