Plants are less able to absorb increased levels of ozone pollution during hot weather, according to a study funded by the UK government
Ozone pollution rises during hot weather while plantsâ€™ ability to absorb ozone is reduced, according to Defra-funded research.
With more ozone pollution in the air from reduced absorption from plants, the study by the Stockholm Environment Institute (SEI)â€™s York Centre estimates that this cost the lives of 460 people in the UK during the hot summer of 2006.
The research found that ozone pollution from traffic fumes, industrial processes and other sources is at its worst during extreme heat but vegetation is also less effective at reducing pollution than it is at lower temperatures.
According to lead author Lisa Emberson, this is because during heat waves when the ground is especially dry, plants become stressed and shut their stomata (small pores on their leaves) to conserve water.
Dr Emberson, University of York lecturer and SEIâ€™s York Centre director, explained that this natural protective mechanism makes them more resilient to extreme heat and high ozone levels, but it also stops them from absorbing ozone and other pollutants.
She said: â€œVegetation can absorb as much as 20% 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.â€
She also said that the hot weather currently being experience in the UK was likely to curtail vegetationâ€™s ability to absorb ozone, depending on how dry the soil is.
The research team, which also included scientists at Kingâ€™s College London, focused on the summer of 2006, when a heat wave and drought occurred across the UK and much of Europe. They combined two models used for human health and ecosystem risk assessment to compare two scenarios, one with perfect ozone uptake by plants, and one with minimal ozone absorption.
The difference between perfect and minimal uptake was equivalent to 16 days of ozone levels above the threshold for human safety across the entire UK â€“ and as many as 20 days in the East Midlands and eastern UK.
Using these same scenarios, the team also estimated that 970 premature deaths due to ozone would have occurred under minimal plant ozone uptake conditions over the June to July period; of these 460 could have been avoided if plants had been absorbing ozone at full capacity. All estimated premature deaths are in addition to human health and mortality impacts from the heat itself.
Ground-level ozone pollution can lead to lung inflammation decreased lung function, and an increase in asthma attacks. As a result, Ms Emberson said, vulnerable people in both urban and rural areas with respiratory problems are advised against physical activity during episodes of high ozone pollution.
The York lecturer said she hoped the study would lead on to more research on the effects of heat and drought on air pollution.
She said: â€œThe more we know, the better we will be able to judge how successful our emission reduction efforts have been so far, and whether we need additional efforts â€“ in the UK, across Europe and beyond, since we know that pollutants such as ozone and its precursors can carried around the globe.â€
The study, â€˜Scorched Earth: How will changes in the strength of the vegetation sink to ozone deposition affect human health and ecosystems?â€™, was published last week (July 18) in the journal Atmospheric Chemistry and Physics. The research was financed by the UK Department for Environment, Food and Rural Affairs (Defra).