Researchers have identified the specific components of PM2.5 most strongly linked to asthma hospitalisations, finding that nickel, vanadium and sulfate particles are among the most dangerous compounds in the PM2.5 mixture, alongside nitrate, bromine and ammonium.
Together, these pollutants were found to drive a significant portion of hospitalisations among asthma patients exposed to long-term air pollution.
Senior author Joel Schwartz, professor of environmental epidemiology at the Harvard T.H. Chan School of Public Health, said: ‘We know that PM2.5 increases the risk of asthma attacks and hospitalisations, but those particles are made of many compounds and we haven’t known which are most harmful. Our study teases out which specific compounds in the PM2.5 mixture necessitate the strongest control efforts in order to improve asthma outcomes.’
The study, published in the American Journal of Respiratory and Critical Care Medicine, analysed 469,005 asthma hospitalisations recorded in 11 U.S. states between 2002 and 2016.
Using machine learning models, the team estimated annual levels of 15 compounds that make up PM2.5, including metals and organic components, at ‘zip code’ level. They then applied a statistical method to measure how each compound contributed to asthma hospitalisations.
They found that for each decile increase in the pollutant mixture, asthma hospitalisations rose 10.6% among children and 8% among adults aged 19 to 64, with nickel, vanadium and sulfate consistently emerging as the strongest contributors.
Schwartz said the results point directly to pollution sources that could be regulated more effectively: ‘If we want to reduce asthma hospitalisations, these are the sources that need to be better controlled – which we know how to do.
‘Nickel and vanadium, for example, are produced from burning fuel oil, such as heating oil and heavier oils used by larger buildings. Sulfates come from coal burning. We can put scrubbers on coal combustion plants or replace coal with less polluting fuels, and we can remove metal contaminants from fuel oil.’
While the study focused on long-term exposure, the authors noted that more research is needed to understand how short-term spikes in specific PM2.5 components affect asthma.
The full research can be accessed here.