A recent study has revealed that severe wintertime ozone (O3) pollution may be driven by alkene emissions from local petrochemical industries, posing a significant threat to human health. Researchers from the Hong Kong Polytechnic University focused on winter O3 pollution in Lanzhou, China, and found alarming levels of ozone even during cold January days in 2018. Ozone levels exceeded 100 parts per billion by volume (ppbv), reaching a peak of 121 ppbv.
Contrary to the usual belief that O3 pollution is mainly associated with warm weather and strong solar radiation, the researchers discovered that O3 concentrations in Lanzhou were exceptionally high in winter. They used an advanced photochemical box model, a tool for simulating photochemical smog in urban areas, to investigate the phenomenon.
The study revealed that alkene ozonolysis, a chemical reaction occurring without sunlight, was the dominant driver of O3 formation. This reaction produces Criegee intermediates, which rapidly generate reactive radicals such as hydroxide (OH), hydroperoxyl radical (HO2), and organic peroxy radical (RO2), significantly accelerating O3 production. Alkene emissions contributed to nearly 90 percent of the O3 levels during these episodes.
The study highlights trans/cis-2-butene and propene as major alkene contributors to this unusual pollution. Based on these findings, the researchers suggested actionable mitigation strategies, such as reducing alkene levels by 28.6 percent or nitrogen oxides by 27.7 percent during early afternoon hours to significantly lower O3 levels.
This research challenges previous assumptions about O3 pollution and demonstrates that intense ozone formation can also occur under cold, low-light conditions. The authors emphasize the need for targeted actions in industrial regions to curb alkene emissions and improve air quality.
Long-term exposure to ozone pollution can have detrimental effects on respiratory health, causing inflammation, irritation, coughing, chest tightness, and exacerbating asthma symptoms.
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