High temperatures make air pollution worse. A new study has found that during heat waves, plants reduce their ozone absorption which lead to high levels of the gas remaining in the environment.
Ozone is a gas that exists both at stratosphere and troposphere and can be beneficial or toxic depending on its location. When close to the ground, the gas is known to increase asthma risk in children and damage crops and tress. Ozone is the major ingredient in the urban smog.
Ozone levels range from 0 parts per billion (ppb) to 300 ppb depending on the level of pollution. A related study had recently reported that ozone levels increase risk of burst appendix in people.
Heat waves that swept through the U.K. and parts of Europe in July 2006, broke all records which led to premature deaths of many people. Currently the U.K. is facing another heat wave similar to the ones that occurred in 2006 and 2009 and is showing no signs of cooling.
The present study was conducted by researchers from Stockholm Environment Institute (SEI) at the University of York along with their colleagues at King's College, London.
During heat waves, plants tend to close their stomata to reduce loss of water through leaves. But, it could also lead to excess ozone in the atmosphere, explained Dr Lisa Emberson, lead author of the study.
In the present study, researchers looked at the atmospheric conditions during the drought that occurred in the summer of 2006 in the U.K. The team used computer models to study the ozone effect in two different scenarios; one with perfect ozone uptake by plants and in the other where plants absorbed minimum amount of the gas.
They found that the worst case scenario for the heat wave was when the plants were absorbing minimum ozone. They also discovered that the difference between perfect and minimum absorption was equivalent to two weeks of high ozone level in the atmosphere that led to premature deaths in the U.K.
About 970 deaths occurred during the heat wave when there was minimum uptake of ozone by the plants, scientists estimated. Of these 970 people, 400 could be saved if the plants absorbed ozone at normal rate.
"Vegetation can absorb as much as 20 per cent of the global atmospheric ozone production, so the potential impact on air quality is substantial. What we set out to do in this study was to quantify that impact in terms of increased ozone levels and the toll on human life," said Dr Emberson, a senior lecturer in the Environment Department at the University of York and director of SEI's York Centre, according to a news release.
"The most vulnerable people to ozone pollution are those with existing respiratory and cardiovascular diseases," added Dr Emberson. "For example, ground-level ozone can lead to lung inflammation, decreased lung function, and an increase in asthma attacks. That is why, during high ozone episodes, especially in urban areas, people are generally advised not to do physical activity."
The study is published in the journal Atmospheric Chemistry and Physics.