Particulate matter is one of the greatest risk factors for damage to health and premature deaths worldwide. Using a combination of different methods, a study has now mapped daily fine dust pollution worldwide for the first time. The result: Only 0.18 percent of the global land area and 0.0001 percent of the world's population is exposed to particulate matter pollution below the limit values set by the World Health Organization (WHO). While levels in Europe and North America fell between 2000 and 2019, the study finds rising levels in many other parts of the world.
According to studies, particulate air pollution caused 6.67 million premature deaths in 2019 alone. The tiny particles with an average particle size of just 2.5 micrometers (PM 2.5) can reach the air sacs in the lungs and cause serious damage, including diseases of the lungs and cardiovascular system. According to current knowledge, there is no safe threshold below which exposure does not cause damage. Since even low levels of particulate matter pollution can lead to health problems and premature deaths, the WHO lowered the limit values for particulate matter in 2021 from ten micrograms per cubic meter of outdoor air to five micrograms per cubic meter for average annual pollution. For daily exposure, the limit was lowered from 25 to 15 micrograms per cubic meter.
Particulate matter pollution mapped globally
Many countries around the world are now monitoring particulate matter pollution and have set up measuring stations. "However, the often sparse and inconsistent distribution of the measuring stations makes it difficult to determine the global PM2.5 pollution precisely," explains a team led by Wenhua Yu from Monash University in Melbourne, Australia. In order to obtain comparable data at local, regional, national and global levels, the researchers combined data from 5446 measuring stations in 65 countries with satellite-based meteorological data and geographical information.
"Using an innovative machine learning approach, we integrated this information to map daily fine particle concentrations on a global scale with a high spatial resolution of ten by ten kilometers for the period from 2000 to 2019," describes Yu's colleague Yuming Guo. The result: "According to our calculations, the population-weighted fine dust concentration worldwide during this period was 32.8 micrograms per cubic meter," according to the research team. That exceeds the WHO annual exposure limit by more than six times.
Limit values exceeded worldwide
East Asia was by far the hardest hit, with annual levels of 50 micrograms per cubic meter, ten times the limit. Even in Australia and New Zealand, which according to the study have the lowest particulate matter pollution, the annual pollution was above the limit at 8.5 micrograms per cubic meter. In addition, Yu and his team found an increasing trend in these regions between 2000 and 2019, as well as in South Asia, Latin America and the Caribbean. In Europe and North America, on the other hand, the values fell slightly between 2000 and 2019.
Only 0.18 percent of the world's land area and 0.0001 percent of the world's population were exposed to particulate matter pollution below five micrograms per cubic meter on an annual average. The researchers also found that the limit values were clearly exceeded in relation to the daily values. On more than 70 percent of the days, the global average fine dust pollution was above 15 micrograms per cubic meter, in South and East Asia even on more than 90 percent of the days. The frontrunner in daily particulate matter pollution was Singapore, where the limit value was exceeded on 361 out of 365 days in 2019, closely followed by Qatar and Pakistan with 360 days each. Based on the annual average pollution, China was at the top.
basis for future research
Depending on the region, the research team found different seasonal patterns of particulate matter concentrations: "Northeast China and northern India were hardest hit in the winter months of December, January and February, while eastern areas of North America experienced the highest PM2.5 levels in the summer months of June, July and August." values,” reports Guo. Further studies could shed more light on what factors contribute to these seasonal variations.
Yu and his team point out that the results should be interpreted with caution, especially in regions with few measuring stations, since they are estimates based on machine learning. However, for regions with a good coverage of measuring stations, the team has proven that the model determines reliable values. The study can therefore be an important source of information for future scientific investigations into the effects of air pollution and for political decisions. "Our results are important for global strategies to reduce air pollution and for assessing the short- and long-term health effects of global PM2.5 pollution," the research team said.
Source: Wenhua Yu (Monash University, Melbourne, Australia) et al., The Lancet Planetary Health, doi: 10.1016/S2542-5196(23)00008-6