The effects of transport, climate, and emissions on ozone pollution in the U.S.
Date
2020
Authors
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Journal ISSN
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Publisher
University of Delaware
Abstract
This research is composed of three main topics. First, the importance of transport to ozone pollution in the U.S. Mid-Atlantic. Second, the impact of emissions and climate change on future ozone concentrations in the U.S.. Third, the effects of future emission reduction scenarios on ozone pollution in the U.S. ☐ Ozone is a secondary pollutant which forms in the presence of it's precursors (NOx and VOC) and solar radiation. High levels of ozone are positively associated with asthma incidence and daily non-accidental mortality rate. In 2016, 90% of non-compliance to the national ambient air quality standards (NAAQS) was due to ozone whereas only 10% was due to particulate matter and other regulated pollutants. Climate change, through creating atmospheric conditions favoring ozone formation, has been and will continue to increase ozone concentrations in many parts of world including the U.S. ☐ First study focuses on ozone transport in the U.S. Mid-Atlantic region where high levels of ozone are due to high emissions and transport of ozone precursors from upwind states. Therefore, local emission reductions are not the most effective way to reach attainment in these areas. In this study we used two air quality models with source apportionment methods to study the extent of ozone precursor transport in the Mid-Atlantic and the efficacy of emission-reduction strategies, with a focus on Delaware. We found that in Delaware reducing local emissions of NOx and VOC by 20% is minimally effective, and the same emission reduction in each of five upwind states individually lowers ozone but not sufficiently to reach attainment. Only a consorted effort by the five upwind states together can lower Delaware ozone significantly. The emission reduction needed by the five states together is approximately 10%, half that of each individual state. This suggests that coordinated efforts and long-term, multi-state strategies are necessary to protect air quality in the Mid-Atlantic. ☐ In the second study, the non-linear response of future ozone levels to both meteorological conditions and emissions are studied by linking global climate models to regional meteorological and air quality models. The regional climate in 2016 and in 2050 under the Representative Concentration Pathway 8.5 (RCP 8.5) is simulated using the Weather Research and Forecasting (WRF) model to downscale 3-year summer time slices from the Community Earth System Model (CESM). The downscaled meteorology is then used with the Comprehensive Air Quality Model with Extensions (CAMx) to simulate air quality during each of these 3-year summer periods over the nine climate regions of the continental U.S.. We considered three cases for this study. The control case with 2016 meteorology and 2016 emissions is compared against two future scenarios. The first future scenario includes only the meteorological effects of climate change, without any additional emission reductions, thus with the same emissions as today. The second future scenario includes the effects of both climate change and emission reductions, although with no explicit climate policy (i.e., RCP 8.5). The results show the well-known positive ozone correlation with surface temperature and negative ozone correlation with humidity in all regions. Climate change alone would increase future ozone levels by 3.6 ppb, but, with climate change and emission reductions based on RCP 8.5, ozone levels will actually decrease by 7.2 ppb on average for all climate regions in the U.S.. Even with large reductions in the emissions of pollutants that favor ozone formation (-45.2%, -49.5%, and -69.8% for NOx, VOC, and CO, respectively), future ozone levels will still violate the current ozone standard in most regions of the U.S. ☐ The third study is focused on the role of future emissions of the energy and transportation sector on the ozone levels in the U.S. under the RCP8.5. In this study we used the same modeling framework that we used in the second study. The control case with 2016 emissions and 2050 meteorology is compared to two emission reduction cases. The first emission reduction case includes only the effects of reducing U.S. energy sector emissions. In this case, we assumed 25% coal plant shutdown and projected the gas plants to increase by 50% to fulfill the energy needs in 2050. The second future case, includes the effects of reducing emissions in both U.S. energy and transportation sector. We considered a case in which 40% of future onroad sector will be electrified with net zero emissions. The results showed that for the first case, the Central region where the most coal shutdowns took place, ozone levels decreased by 0.7 ppb, but when both energy and transportation sector emission reduced, ozone levels decreased by 3.7 ppb in North East region.
Description
Keywords
Air quality, Emissions, Ozone pollution