a decrease in PBL height in both the Northwest and Southwest, all of which are in contrast to the work presented here. We point out these differences to illustrate that although the work presented here is generally consistent with other similar studies, it does represent only a single realization of a future climate, and the use of different models, number of years simulated, and assumptions about future emissions will all result in a different future climate realization. Ozone and Climate It is well known that elevated ozone in polluted environments is closely linked to temperature34,35. Although the exact mechanism relating temperature and elevated ozone may vary by region, it is likely due to a combination of the following: temperature-dependent chemical rate constants, the relationship between stagnation events and temperature, changes in meteorological parameters associated with elevated temperatures (e.g., insolation and water vapor), and temperature-dependent emissions (e.g., biogenic emissions). Figure 5 depicts the observed and modeled relationship between summertime (June, July, August) daily maximum temperature and daily maximum ozone at 72 rural sites within the Clean Air Status and Trends Network (CASTNET; ). Observations are from 1998-2002 and model results are from the two summers representing the warmest and coldest simulated summers from the current decade (CD_Base case). Observations beyond 2002 are not considered because the large reduction in power plant NOX emissions in the eastern U.S. that occurred around 2002 is not reflected in the NEI2002 emission inventory. In general, the modeled ozone and temperature fall within the range of observed values in each region. However, the modeled results do not show the same variability as seen in the observations. This is not unexpected since five years of observations are used compared to two modeled years, and because the model results are averaged over a 36-km grid-cell whereas the observations represent measurements at a single point. The average ozone-temperature relationship can be represented by the slope of the linear best-fit. The slopes of the modeled and observed linear best-fit for each region are within approximately +/- 15% of each other, except for in the Central and Southeast regions. These two regions show only minor ozone correlation to temperature, suggesting that temperature is either not the main driver for peak ozone at the
a decrease in PBL height in both the Northwest and Southwest, all of which are in contrast to the work presented here. We point out these differences to illustrate that although the work presented here is generally consistent with other similar studies, it does represent only a single realization of a future climate, and the use of different models, number of years simulated, and assumptions about future emissions will all result in a different future climate realization. Ozone and Climate It is well known that elevated ozone in polluted environments is closely linked to temperature34,35. Although the exact mechanism relating temperature and elevated ozone may vary by region, it is likely due to a combination of the following: temperature-dependent chemical rate constants, the relationship between stagnation events and temperature, changes in meteorological parameters associated with elevated temperatures (e.g., insolation and water vapor), and temperature-dependent emissions (e.g., biogenic emissions). Figure 5 depicts the observed and modeled relationship between summertime (June, July, August) daily maximum temperature and daily maximum ozone at 72 rural sites within the Clean Air Status and Trends Network (CASTNET; ). Observations are from 1998-2002 and model results are from the two summers representing the warmest and coldest simulated summers from the current decade (CD_Base case). Observations beyond 2002 are not considered because the large reduction in power plant NOX emissions in the eastern U.S. that occurred around 2002 is not reflected in the NEI2002 emission inventory. In general, the modeled ozone and temperature fall within the range of observed values in each region. However, the modeled results do not show the same variability as seen in the observations. This is not unexpected since five years of observations are used compared to two modeled years, and because the model results are averaged over a 36-km grid-cell whereas the observations represent measurements at a single point. The average ozone-temperature relationship can be represented by the slope of the linear best-fit. The slopes of the modeled and observed linear best-fit for each region are within approximately +/- 15% of each other, except for in the Central and Southeast regions. These two regions show only minor ozone correlation to temperature, suggesting that temperature is either not the main driver for peak ozone at the