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

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.

Occurrence and Coupling of Heat and Ozone Events and Their Relation to Mortality Rates in Berlin, Germany, between 2000 and 2014

“…For HE, we could show that the more intense these events are, the higher the probability is to be accompanied with elevated ozone concentrations. This relationship is well investigated, as high air temperatures promote the formation of high ozone concentrations through precursors [35][36][37]67,68]. This effect may be time-dependent, as we could show for Berlin, that heat events lasting over more multiple days, occurred in combination with elevated ozone concentrations.…”

Skill-Testing Chemical Transport Models across Contrasting Atmospheric Mixing States Using Radon-222

“…Generally, good model skill was reported with the exception of transitional conditions (periods of substantial synoptic non-stationarity or in the presence of mesoscale motions). Likewise, Utembe et al [29] evaluated W-UM2 performance in January 2013 using eight BoM-approved sites and reported better model skill than shown here in Sections 3.2-3.4. Details regarding the more extensive meteorological evaluations of the models discussed here are given in Monk et al [25].…”

“…Given the complexity of the Westmead site, and the benchmark µMB for temperature of around ±1 °C provided by Monk et al [25], all models performed acceptably. By comparison, for January 2013 Utembe et al [29] reported a temperature µMB of 0.2 °C for W-UM2 averaging over 17 sites in the Sydney region. (b) For O-CTM, simulated temperatures were occasionally noisy and the composite diurnal mean bias (T MOD -T OBS ) was consistently positive (Figure 2b).…”

“…W-UM2 is based on version 3.7.1 of WRF-Chem operated by the University of Melbourne. As discussed in Utembe et al [29], WRF-Chem is an online coupled model, here run in nudged mode, using the Advanced Research WRF (ARW) dynamic core. The model has 33 levels, with increased vertical resolution in the boundary layer.…”

“…This will result in less than optimum comparisons between observed and simulated meteorological quantities. Detailed evaluations at more appropriate sites are the subject of separate investigations (e.g., [25,26,[29][30][31]).…”