Ozone production and the circadian rhythm of plants

A team that includes NCAR scientists Anne Boynard and Alex Guenther has found that the rate at which plant canopies emit isoprene, a volatile organic compound, is influenced by circadian rhythms. The discovery has the potential to lead to more accurate predictions of ground-level ozone, which is harmful to human health.

For the study, the researchers made measurements of isoprene in Malaysia above both tropical rain forest and oil palm plantations. They observed for the first time ever a circadian (24-hour) rhythm operating in concert across the entire tree canopy, especially in the palm plantation.

The finding changes how scientists estimate isoprene emissions from plants, as both the palm plantations and rain forest emit less isoprene than shown by computer models of emissions. This has implications for ground-level ozone, which forms when volatile organic compounds such as isoprene react with nitrogen oxides from automobiles and industry.

The researchers incorporated the circadian pattern into the NCAR Model of Emissions of Gases and Aerosols from Nature (MEGAN) model to estimate isoprene emissions for input to ozone models. They then compared simulated ground-level ozone to observed ozone measurements from 290 monitoring sites in the United States. They found that model accuracy was significantly improved. Accounting for circadian impacts on isoprene emissions could especially improve ozone predictions in isoprene-sensitive regions of the world, which include the United States, Mediterranean, Middle East, Japan, and parts of Southeast Asia.

The research was published in Nature Geoscience in September.

C. N. Hewitt, K. Ashworth, A. Boynard, A. Guenther, B. Langford, A. R. MacKenzie, P. K. Misztal, E. Nemitz, S. M. Owen, M. Possell, T. A. M. Pugh, A. C. Ryan, O. Wild, “Ground-level ozone influenced by circadian control of isoprene emissions,” Nature Geoscience, 2011; DOI: 10.1038/ngeo1271


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