Hot Summers: Effect of Extreme Temperatures on Ozone in Sydney, Australia

Steven Utembe,Yvonne Scorgie,Peter Rayner,Elise-Andree Guérette,Martin Cope,Hiep Duc,Jeremy Silver,Clare Paton-Walsh,Alan Griffiths,Jenny Fisher,Kathryn Emmerson,Khalia Monk

doi:10.3390/atmos9120466

Abstract

Poor air quality is often associated with hot weather, but the quantitative attribution of high temperatures on air quality remains unclear. In this study, the effect of elevated temperatures on air quality is investigated in Greater Sydney using January 2013, a period of extreme heat during which temperatures at times exceeded 40 °C, as a case study. Using observations from 17 measurement sites and the Weather Research and Forecasting Chemistry (WRF-Chem) model, we analyse the effect of elevated temperatures on ozone in Sydney by running a number of sensitivity studies in which: (1) the model is run with biogenic emissions generated by MEGAN and separately run with monthly average Model of Emissions of Gases and Aerosols from Nature ( MEGAN) biogenic emissions (for January 2013); (2) the model results from the standard run are compared with those in which average temperatures (for January 2013) are only applied to the chemistry; (3) the model is run using both averaged biogenic emissions and temperatures; and (4 and 5) the model is run with half and zero biogenic emissions. The results show that the impact on simulated ozone through the effect of temperature on reaction rates is similar to the impact via the effect of temperature on biogenic emissions and the relative impacts are largely additive when compared to the run in which both are averaged. When averaged across 17 sites in Greater Sydney, the differences between ozone simulated under standard and averaged model conditions are as high as 16 ppbv. Removing biogenic emissions in the model has the effect of removing all simulated ozone episodes during extreme heat periods, highlighting the important role of biogenic emissions in Australia, where Eucalypts are a key biogenic source.

Highlights

It is estimated that poor air quality is responsible for millions of premature deaths per year around the globe [1]
Since accurate simulation of temperature, wind speed and wind direction is critical for the accurate simulation of surface ozone and other trace gases, it is instructive to evaluate model performance of meteorology
The Australian Bureau of Meteorology (BoM) weather station at Sydney Observatory Hill showed an average recorded temperature of 27.6 ◦ C for January, which was 1.8 ◦ C warmer than the historical average for this location in this month. This was a result of prolonged and widespread extreme heat periods that affected most parts of Australia during January 2013 so that higher temperatures were recorded across the whole southeast of Australia

Summary

Introduction

It is estimated that poor air quality is responsible for millions of premature deaths per year around the globe [1]. Many studies have shown the negative implications of global warming for future air quality and its implications for increased mortality. The air quality in Australia is relatively good compared to the Northern Hemisphere [7,8], the study by Silva et al [6] showed an increased risk under climate change conditions. Broome et al [10] calculated that modest reductions in air pollution in Sydney had substantial health benefits. They found that only a 10% reduction in PM2.5 exposure (using 2007 exposure data) would result in 650 fewer premature deaths over a period of 10 years

Methods

Results

Conclusion