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A groundbreaking study has revealed that severe wintertime ozone (O3) pollution, traditionally associated with summer heat and sunlight, is significantly driven by alkene emissions from local petrochemical industries. Researchers from the Hong Kong Polytechnic University focused their investigation on Lanzhou, China, where alarming ozone levels were recorded during cold winter days in January 2018.
Published in the journal Environmental Science and Ecotechnology, the study challenges conventional wisdom about ozone formation. Researchers noted hourly O3 concentrations exceeding 100 parts per billion by volume (ppbv), peaking at a concerning 121 ppbv, despite the absence of strong solar radiation.
The study employed an advanced photochemical box model to simulate urban photochemical smog. Unlike the traditional understanding that sunlight-driven photolysis initiates ozone formation, the team identified alkene ozonolysis as the dominant process. This chemical reaction occurs without sunlight, producing Criegee intermediates that rapidly generate reactive radicals such as hydroxide (OH), hydroperoxyl radical (HO2), and organic peroxy radical (RO2). These radicals then accelerate ozone production.
The research highlighted specific alkene compounds, including trans/cis-2-butene and propene, as the primary contributors to this unusual winter pollution. Alkenes were found to be responsible for nearly 90 percent of the ozone formed during the episodes.
Mitigation strategies proposed by the researchers suggest that reducing alkene emissions by 28.6 percent or nitrogen oxides (NOx) by 27.7 percent during early afternoon hours could substantially decrease ozone levels.
“This study updates how we understand O3 pollution, proving that intense ozone formation can occur in cold, low-light conditions,” stated researchers Jin Yang and Yangzong Zeren. They emphasized the need for “targeted action in industrial regions” to address the problem.
The findings underline the serious health risks posed by prolonged exposure to ozone pollution, which can damage respiratory tissues, cause inflammation, and worsen conditions like asthma. The study serves as a critical call to action for policymakers and industries to implement effective measures to mitigate this overlooked wintertime pollution phenomenon.
