A new method to estimate air-quality levels using a synoptic-regression approach. Part II: Future O3 concentrations

Using the synoptic-regression based approach developed in Part I of this research, this study estimates future maximum 8 hourly mean O3 levels (m8hO3) using three future SRES (Special Report on Emission) scenarios for a rural background area situated in The Netherlands. The statistical downscaling tool was used to downscale the Atmospheric–Ocean Coupled General Circulation Model (AOGCM) ECHAM5-MPI/OM for the present-day 20 Century (20C) control run (1991–2000) and the future SRES scenarios A2, A1B and B1 for two periods (2051–2060 and 2091–2100). First, the statistical downscaling tool is evaluated in terms of downscaled m8hO3 levels for the present-day climate, using a long record of observed m8hO3 concentrations. It was found that a bias correction is needed and this bias correction is then further used to estimate future m8hO3 concentrations. Under the various SRES scenarios, the overall mean m8hO3 increases with 2.5–6.5 and 6.1–10.9 μg m−3, for the 2051–2060 and 2091–2100 period respectively, which is about 20% of the present-day 10-year average. This effect is enhanced when considering the summer season only, with a range of increase between the different future scenarios of 5.4–12.5 μg m−3 and 13.4–26 μg m−3 (for 2051–2060 and 2091–2100 respectively) against a present-day summer average of 73.5 μg m−3. An increase in maximum temperature and shortwave radiation, associated with a decrease in cloud cover under the various future scenarios are the main drivers of ozone increase. A comparison with August 2003 shows the physical plausibility of our results and reflects that the extreme summer of 2003 might show a close resemblance to future European summers in terms of m8hO3 and meteorological characteristics.