Keywords

1 Introduction

Previous research indicates that human mortality is impacted by both meteorological conditions and atmospheric pollutant levels, such as the high temperatures and high levels of ozone experienced during the 2003 heat wave that had a substantial effect on human health (Vautard et al. 2005). Stedman (2004) suggests that between 21 and 38% of the excess deaths observed during the summer 2003 European heat wave were attributed to ozone and PM10 pollutants. In this study, the chemical transport model (CTM) CHIMERE (Vautard et al. 2001) has been coupled to the climate simulations.

Three different simulations were considered as following: (i) 4 years with ERA-INTERIM driven experiment (2005–2008), (ii) current climate (1990–1999), and (iii) future climate (2046–2055), following the A1B scenario. For all the simulations, the same emissions from TNO/GEMS (2004) were used (Visschedijck et al. 2007). This will allow us to verify if the changes in climate conditions will actually lead to a change in ozone concentration, especially during heat wave events.

To validate the skills of our ALARO-CHIMERE system, the simulations for the time period 2005–2008 have been validated using observational data (PM10 and O3) from IRCELINE. In Delcloo et al. (2014a), it has already been shown that the use of the Town Energy Balance parameterization in the land surface scheme of ALARO have significantly improved the modelling of PM10 and ozone in the urban areas. When comparing the time series of observed and modelled PM10 data for the station of Uccle during the time period 2005–2008, a correlation coefficient (R) of 0.72 and a bias of 1.7 μg/m3 are found. The intercomparison statistics for ozone show a negative bias of −9.3 µg/m3 with a correlation of 0.86, which elucidates that the model underestimates some of the observed ozone peaks. Since the station of Uccle is situated in a suburban area, the observed ozone time series show more elevated maximum ozone concentrations during ozone peaks, due to less influence by titration by NO. This chemical reaction favors the destruction of ozone and happens typically on locations which are much more exposed to traffic emissions (Beekmann and Vautard 2010).

2 Results and Discussion

2.1 Urban Micro-climate

From previous work it is shown that while the Brussels Capital Region warms substantially for the 2050s horizon, climate change will have a neutral impact on the annual mean urban heat island (UHI) intensity. The biggest and statistically significant change of nocturnal (daytime) UHI is noted during winter (summer) season with an increase (decrease) of +0.2 °C (−0.1 °C). During summer, the decrease in daytime UHI is directly connected to soil drying over rural areas, while the increase in nocturnal UHI during the winter can be explained by the projected decrease of wind speed (Hamdi et al. 2014).

The projected climate change under scenario A1B for 2050 leads to an increase of the number and duration of heat waves. More specifically, for rural (urban) areas, climate change increases the intensity of heat waves more during the day (night).

2.2 Air Quality

For the policy maker, it is interesting to know how these changes in heat wave intensity/events will have an impact on air quality by looking at how the number of exceedances will evolve in the future climate scenarios. To evaluate these changes, we have verified the number of days in which ozone concentrations exceed the warning thresholds of 180 μg/m3 during a heat wave event in the present and future climate simulations.

Table 30.1 shows results for some stations, which clearly indicate an increase in exceeding the warning threshold for ozone in the future climate. It is important for the interpretation of these results to take into account that the emissions that have been used are more representative for the first half of the time period 2000–2010 instead of the 90s. A strong reduction in NOx and NMVOCs has been observed since then (Wilson et al. 2012). From the results in Table 30.1 we can deduce that for the city climate, the increase is higher when compared with the results from stations, located in a more rural area. However, we also observe that for stations, located in more forested area (Vezin, Offagne), the increase in ozone concentrations is even more elevated.

Table 30.1 The relative change in number of days in which ozone concentrations exceed the warning threshold of 180 µg/m3 for the future climate simulations compared to the present climate simulations for some stations under consideration
Full size table

3 Conclusions

The projected climate change simulations under scenario A1B for 2050 show that this will lead to an increase of the number and duration of heat waves. More specifically, for rural (urban) areas, climate change increases the intensity of heat waves more during the day (night).

The effects of these changes on air quality elucidate that in the future climate more exceedances of the warning threshold for ozone will take place. Especially for the suburban and more forested regions this seems to be the case. Since the intensity of the heat waves will increase for the future climate, a significant impact on the ozone burden is to be expected.