Why heat waves produce pollution

With extreme heat events becoming more and more common during Australian summers, there has been much national and international attention on the effect of heat waves on health. Heat waves are associated with increased illness and death, as well as increased ozone pollution which can trigger a range of breathing problems. However, there are still many large gaps in knowledge. Why do heat waves cause pollution? And given they are so dangerous to our health, what can we do about it?

By conducting a range of air quality measurement and modelling campaigns in the Sydney region, our research has explained the causes of extra air pollution – stemming from stressed vegetation and the speeding up of chemical reactions in the atmosphere. At the moment, air quality warnings are mainly issued at times of fires. However, our research shows the need to broaden these warnings, to allow for people with respiratory difficulties to take preventative measures. When policy makers and agencies such as the NSW Government Office of Environment and Heritage (OEH) adopt this knowledge, it will help to better prepare our communities from adverse health effects during heat waves.

During the air quality measurement campaign in Wollongong (2012-2013), Sydney recorded some of its highest temperatures ever, with temperatures exceeding 40 degrees Celsius. These high temperatures were associated with high ozone pollution in the area, and by using an air quality model we were able to understand why. This required us to first check that the model could simulate high ozone events, and then turn off some of the model processes to test which process was responsible for the high levels of pollution.

Our analysis showed two factors to be equally responsible for the high levels of ozone pollution: extreme emissions of various compounds (biogenic volatile organic compounds, or VOCs) from plants, caused by the extreme heat, and changes in the chemistry of the atmosphere, also caused by the extreme heat. Given that there was no industrial pollution involved in these events, there is little we can do to reduce the problem. We can however, include air quality warnings along with heat stress alerts to reduce the serious health implications of such days in future.

In order to get a comprehensive understanding of extreme heat events in the Sydney region, our research incorporated a combination of air quality measurements and modelling: routine measurements made by the OEH and the Environmental Protection Authority (EPA); a detailed measurement campaign involving researchers from CSIRO, the University of Wollongong and other partner universities; and modelling from CAUL Hub researchers at the University of Melbourne. This collaboration was critical, as it meant data was easily attainable and ensured results were reliable.

Featured image: Steven Utembe’s paper, Hot Summers: Effect of Extreme Temperatures on Ozone in Sydney, Australia on the cover of Atmosphere

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