Almost no area of land on Earth has levels of air pollution deemed safe by the World Health Organisation, a new study has found.
Australian Monash University used machine learning to bring together perhaps the most comprehensive set of readings of daily ambient fine particulate matter, known as PM2.5, across the globe.
Researchers found only 0.18 per cent of the global land area and 0.001 per cent of the global population are exposed to concentrations of PM2.5 below levels of safety recommended by World Health Organisation.
PM2.5 can be caused by a range of factors, including industrial processes, transport and even weather events such as dust storms.
Owing to its tiny size, PM2.5 can penetrate the thoracic region of the respiratory system, leading to increased risk of death from respiratory and cardiovascular conditions such as asthma and lung cancer.
Despite a slight decrease in high PM2.5 exposed days globally, by 2019 more than 70 per cent of days still had PM2.5 concentrations higher than 15 μg/m³. The WHO recommends annual average concentrations of PM2.5 should not exceed 5 µg/m3.
Globally, the annual average PM2.5 from 2000 to 2019 was 32.8 µg/m3.
The study, published in Lancet Planetary Health, recorded drops in daily levels of fine particulate matter in Europe and North America in the two decades to 2019. But increases were seen in Southern Asia, Australia, New Zealand, Latin America and the Caribbean.
Levels of PM2.5 also vary according to season. High levels were detected in areas including north-east China and north India during their winter months of December, January, and February, “whereas eastern areas in northern America had high PM2.5 in summer months (June, July, and August)”, said Prof Yuming Guo from the Monash University School of Public Health and Preventive Medicine in Melbourne.
“We also recorded relatively high PM2.5 air pollution in August and September in South America and from June to September in sub-Saharan Africa.”
Prof Guo said the study should help with future decision-making on air quality.
“It provides a deep understanding of the current state of outdoor air pollution and its impacts on human health”, he said.
“With this information, policymakers, public health officials, and researchers can better assess the short-term and long-term health effects of air pollution and develop air pollution mitigation strategies.”