The chemical composition of air pollution in the United States has changed over time, a new study has found.
The report, published in the journal Atmospheric Environment by the University of North Carolina at Chapel Hill, found that fine particulate matter (PM2.5), had significantly reduced in the United States, but also that its chemical composition completely changed between 2006 to 2020.
The conclusion was reached by analyzing space and time trends for PM2.5. The findings will prove useful to track the changes in air pollution against targets implemented by authorities, the study authors said.
PM2.5 is a pollutant found in the air. It's composed of multiple chemicals and has previously been linked to some serious health problems in humans. It is pumped into the atmosphere through emissions created by diesel fuel, gasoline and oil.
If there is too much PM2.5 in the air it can increase the risk of conditions such as heart disease and asthma. It is essential to keep levels of the pollutant down, as it could save human lives.
The Environmental Protection Agency (EPA) updated its "health standard for PM2.5" just earlier this month.
To improve the air quality in the U.S., the agency is reducing the air quality standard for the pollutant from 12 micrograms per cubic meter to 9 micrograms per cubic meter. This means there are stricter thresholds for how much of this pollutant is considered unhealthy.
For this reason, the results of this report are particularly timely, Saravanan Arunachalam, senior author of the study and deputy director of the UNC Institute for the Environment, said in a statement.
"States with monitors that are exceeding the new standard for PM2.5 will be looking to understand the chemical constituents of PM2.5, and how they have changed over time, and this will be key to developing emissions reductions policies to address potential future non-attainment designations," Arunachalam continued.
In the new study, researchers found that the largest improvements to air quality during the 15 years studied, were found in areas with the "worst baseline air quality." This included The Ohio Valley and states to the southeast, all of which had "regulations on emissions sources such as coal-burning power plants and industry."
There was a particular spike in poor air quality in the West in 2020, due to forest fires.
"Different chemical constituents of PM2.5 are linked to various emissions sources, thus, the development of future emissions control strategies to reduce PM2.5 concentrations should be based on the comprehensive analysis of spatiotemporal trends of PM2.5 chemical composition and deep understanding of the relationships between changes in emissions and ambient concentrations," Bin Cheng, a co-author and research associate at the Institute, said in a summary
U.S. sulfate and ammonium levels have declined, but the researchers still suggest that policy makers look at other ways to decrease carbon, considering how it is contributing to the overall PM2.5.
They also advise adopting different methods of carbon reduction depending on different regions.
"The results from this study will also contribute to future epidemiological studies to identify specific PM2.5 components that affect human health more than others," Arunachalam said in a summary of the findings.
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