The impact of emissions and climate change on future ozone concentrations in the USA

The potential impacts of climate change and future anthropogenic emissions on ozone levels in the USA are examined by linking global climate models to regional meteorological and air quality models during 3-year summer periods over the nine climate regions of the continental United States for three cases: (1) using 2016 meteorology and emissions (CTRL), (2) using 2050 meteorology and 2016 emissions (CASE1), and (3) using 2050 meteorology and 2050 emissions (CASE2). As climate change alone is expected to worsen ozone pollution and emission reductions are expected to reduce ozone concentrations, in this paper, the non-linear response of future ozone levels to both meteorological conditions and emissions was studied. The results show the well-known positive ozone correlation with surface temperature and negative ozone correlation with humidity in all regions. Climate change alone will increase future MDA8 ozone in the USA by 3.6 ppb. With climate change and policy intervention based on RCP 8.5, ozone levels will decrease 7.2 ppb on average for all climate regions in the USA. Furthermore, while climate change alone will double the number of stations violating the current National Ambient Air Quality Standard (NAAQS) for ozone in 2050, when policies are in effect, this number was reduced to 21 stations. The number of high-ozone days will also increase in climate change only case in all regions with an average of 5.7 extra high-ozone days which confirms previous studies. The results show that even with high-ozone precursor reductions, the ozone levels will still violate the current national ozone standard. Therefore, in order to meet the current ozone standard by 2050, more stringent climate and air pollution control policies for most regions in the USA are needed.