Researchers from the University of York have discovered why, in some emerging economies, reducing particle pollution actually increases surface ozone pollution, negatively impacting health, ecosystems, and agriculture. According to the researchers, the findings, published in Nature Geoscience, call into question established methods for combating air pollution.

According to research, addressing particle pollution causes an increase in photochemical smog.
Smog in New Delhi. Image credit: Jacqueline Hamilton, University of York.

The main component of “smog” is surface ozone, which is produced by chemical reactions between nitrogen oxides (NOx) and volatile organic compounds (VOC). When pollutants emitted by automobiles, power plants, industrial boilers, refineries, chemical plants, and other sources react in the presence of sunlight, this occurs.

When countries such as China improved air quality by reducing particle pollution emitted from coal-burning, steel production, vehicles, and fires over the last decade, the scientific community was surprised to see ozone pollution rise. 

The study has now shed new light on the connection between these two pollutants. Historically, policymakers thought of ozone and particles as separate issues, but researchers have shown that they are closely linked in some areas. Some short-lived ozone-forming components (peroxy radicals) adhere to particle pollution, preventing them from forming ozone. As the particle count decreases, more peroxy radicals become available for reactions, and ozone levels rise.

The study modeled the effects of reducing particle pollution and discovered that it could cause a 20-30% increase in ozone in some densely populated areas of India and China. This would have a significant negative impact on ecosystems and crop yield if left unmanaged. 

The researchers are calling for new strategies that take into account the interaction of pollutants. The problem can be solved by reducing a broader range of pollutants, specifically (VOCs) from chemicals and fuels and NOx from combustion.”Particle pollution and ozone pollution have been viewed by policymakers around the world as separate issues, but our study emphasizes the need to look at them together,” said co-lead author Professor Mathew Evans from the Department of Chemistry at the University of York. 

For 40 years, we assumed that ozone was solely dependent on volatile organic compounds and nitrogen oxides, and it is only now that we are piecing the puzzle together and seeing this relationship with particle pollution. 

The policy must now be updated to reflect this new information.”Particulate matter in the atmosphere is a legitimate priority due to the serious threat it poses to human health. However, this study emphasizes the difficult choices that governments must make when it comes to investing in air pollution management. Solutions are not always obvious, and there may be hidden links between different pollutants.”

The WHO estimates that outdoor air pollution causes 4.2 million premature deaths each year. Developing countries such as India, China, and Africa are particularly hard hit. According to the modeling study, significant reductions in particle pollution in these areas would necessitate dramatic reductions in NOx and VOC emissions – up to 50% in order to keep ozone pollution under control.

Professor Alastair Lewis of the National Centre for Atmospheric Science, a co-lead author of the study, added “This study demonstrates the dangers of focusing too narrowly on a single pollutant. Particle pollution in China has improved dramatically in recent years, but focusing solely on particles can have unintended consequences. 

Accelerating the reduction of NOx and VOC emissions is now critical.”An aerosol-inhibited photochemical ozone regime suppresses surface ozone, according to a study published in Nature Geoscience.

Source: Materials provided by University of York

 DOI: 10.1038/s41561-022-00972-9

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