Futurity · Climate & nature

Scientists Directly Observe Key Smog-Forming Reaction

Researchers have directly observed a fleeting chemical reaction that creates a key ingredient in urban smog, offering new insights into pollution formation and potentially improving air quality forecasts.

The study tracked short-lived Criegee intermediates formed when ozone reacted with isoprene, a gas abundant from plants. These molecules drive atmospheric chemistry affecting pollution and particle formation, previously understood mainly through indirect evidence.

Isoprene, emitted by trees, reacts with ozone to create secondary organic aerosols, which form urban haze and can be inhaled. While trees are a major source of isoprene, the findings emphasize controlling ground-level ozone, its precursor.

To observe these elusive molecules, scientists used ultrasensitive cavity ring-down spectroscopy. This technique detects compounds that exist briefly and in low concentrations by observing them where they are created.

The team measured Criegee intermediates from the isoprene-ozone reaction, determining reaction rates and testing atmospheric models with direct observations, a significant advancement from relying on stable end products.

This builds on prior work observing Criegee intermediates in simpler reactions. Isoprene, with its complex structure and atmospheric importance, presented a greater challenge.

Improved measurements of these early reactions can enhance atmospheric models for predicting pollution events and understanding fine-particle formation. The study, conducted in a lab, provides a foundation for examining complex real-world atmospheric reactions.

Future research will apply similar techniques to pinenes, another class of compounds emitted by trees, to understand their reactions with ozone and contribution to air pollution.

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