Winter Ozone Pollution: A Surprising Puzzle Solved

Researchers have identified a surprising phenomenon: severe winter ozone (O₃) pollution in Lanzhou, China, primarily caused by alkene emissions from local petrochemical industries. Typically linked to warm weather and strong sunlight, hourly O₃ levels surpassed 100 ppbv during cold January days in 2018, reaching a peak of 121 ppbv.

Alkene Ozonolysis Key to Ozone Formation

Using an advanced photochemical box model, the study identified alkene ozonolysis as the dominant driver of O₃ formation, rather than the traditional radical sources initiated by photolysis. This chemical reaction occurs without sunlight and produces Criegee intermediates that rapidly generate reactive radicals (OH, HO₂, and RO₂), which then accelerate O₃ production. Ultimately, alkenes contributed to nearly 90% of the O₃ during the episodes.

‘Wait, #ozonepollution in winter? You might think it's a summer problem, but ozone can still form in colder months. #environmentalhealth’

The research highlights key alkene species-trans/cis-2-butene and propene-as major contributors to this unusual pollution. Importantly, the study proposes actionable mitigation strategies: reducing alkene levels by 28.6% or nitrogen oxides by 27.7% during early afternoon hours could significantly reduce O₃ levels.

"This study updates how we understand O₃ pollution, proving that intense O₃ formation can occur in cold, low-light conditions," said the authors Jin Yang and Yangzong Zeren. "Our findings complement conventional views and call for targeted action in industrial regions."

Source: Eurekalert