Study finds petrochemical industries behind winter ozone pollution

• BILKULONLINE
  SUNDAY Special

New Delhi, Jan 12: Severe wintertime ozone (O3) pollution may be driven by alkene emissions from local petrochemical industries, and can be detrimental to human health, finds a study.

Researchers from the Hong Kong Polytechnic University focussed on wintertime O3 pollution in Lanzhou, China. Traditionally associated with warm weather and strong solar radiation, hourly O3 levels exceeding 100 parts per billion by volume (ppbv) were recorded during cold January days in 2018, peaking at an alarming 121 ppbv.

In the paper, published in the journal Environmental Science and Ecotechnology, the researchers noted that they found that “O3 concentrations in Lanzhou were extremely high in winter”. This is “contrary to the consensus that O3 pollution mainly occurs in warm weather with strong solar radiation,” said the researchers. For the study, the team used an advanced photochemical box model, which is a numerical model that simulates photochemical smog at the urban scale.

The team 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 (hydroxide (OH), hydroperoxyl radical (HO2), and organic peroxy radical (RO2)), which then accelerate O3 production. Ultimately, alkenes contributed to nearly 90 per cent of the O3 during the episodes.

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 per cent or nitrogen oxides by 27.7 per cent 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. They called “for targeted action in industrial regions”. Long-term exposure to ozone pollution can damage the tissues of the respiratory tract, causing inflammation and irritation. It can also lead to coughing, chest tightness, and worsening of asthma symptoms.