This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Scientists have directly observed a fleeting chemical reaction that creates a key ingredient in urban smog. The research offers insight into the earliest stages of pollution formation and could help improve air quality forecasting models.
The researchers directly tracked short-lived molecules called Criegee intermediates as they formed when ozone reacted with isoprene, a gas released in large quantities by trees and other plants. These highly reactive molecules help drive atmospheric chemistry that can ultimately affect air pollution and particle formation, but scientists had previously understood them mainly through indirect evidence. The study, published in Nature Communications, was conducted by UC Riverside chemist and first author Lei Yang, corresponding author Jingsong Zhang, a UCR chemistry professor, and several doctoral students.
Though unfamiliar to most people, isoprene is one of the most abundant chemicals released into the atmosphere. Trees and other plants emit hundreds of millions of tons of this gas every year, making natural vegetation one of the largest sources of reactive gases in the atmosphere. Isoprene itself poses little direct harm.
It belongs to a family of compounds called alkenes, which react with ozone in the atmosphere. When that happens, they launch a chain of chemical reactions that create particles called secondary organic aerosols, which make up much of the haze hanging over cities, scatter sunlight and can travel deep into the lungs. Although trees produce most of the world's isoprene, the findings do not suggest forests are driving air pollution.
Instead, they highlight the importance of controlling ground-level ozone, which fuels these reactions. "We can't do anything about the alkenes or isoprene from trees," Zhang said. "If you want to solve the air quality problem, you have to reduce ozone in the air.
Ozone is the main driver. In practice, this means reducing emissions of its chemical precursors, especially nitrogen oxides and volatile organic compounds." Scientists have known for decades that ozone reacts with isoprene and other alkenes, but the first moments of that reaction have remained largely invisible. The chemistry unfolds within hundredths of a second, creating unstable molecules called Criegee intermediates that disappear almost as soon as they form.
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