Australian native plants contribute to smog

Researchers in Australia have found that their native plants emit chemical compounds that can interact with man-made air pollutants and exacerbate smog formation over cities.

The research into Australian grasses and eucalypt trees by scientists from the Commonwealth Scientific and Industrial Research Organisation (CSIRO) has revealed that plants release hydrocarbons that can significantly add to photochemical smog problems. “It’s not just cars and industry that cause air pollution,” said Ian Galbally, from CSIRO Atmospheric Research.

“The blue haze you often see over the Dandenong Ranges in Victoria and in the Blue Mountains near Sydney is caused in part by the gases released by vegetation,” said Galbally. “We found that grasses, particularly when cut, are potent emitters of reactive hydrocarbons.

The research was carried out using mature naturally grown plants, rather than single leaves of cultivated plants in controlled conditions of temperature and radiation as in previous studies. “We deliberately sought trees that hadn’t been grown under controlled conditions, but were ‘real world’ specimens,” said Dr Peter Nelson, Senior Research Scientist with CSIRO Energy Technology.

Vegetation was enclosed in flexible Teflon film containers ventilated with ambient air to control temperatures to near ambient conditions, enabling the monitoring of concentrations of carbon dioxide, nitric oxide, nitrogen dioxide, ozone and non-methane volatile hydrocarbons. Gas samples were also periodically collected for high-resolution gas chromatographic analysis of volatiles such as isoprene and other hydrocarbons. Temperature, total light intensity and photosynthetically-active radiation were also measured.

According to Nelson, plants release the chemicals into the atmosphere in large quantities. “One of the things we have found already is a close relationship between the amount of the sun’s radiation, of the type that is important for photosynthesis and the plant’s growth, and the level of hydrocarbons they emit. Emission rates are highest during the day and drop off towards evening,” said Nelson.

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