Future changes in global climate and in ozone-precursor emissions over the coming century resulting from human-related activities are likely to continue to have important consequences on surface ozone pollution over the contiguous United States. Factors affecting U.S. surface ozone include global and regional climate, domestic anthropogenic/natural precursor emissions, and anthropogenic/natural precursor emissions outside the U.S. associated with the pollutant transport. Given the adverse effects of ozone on human health, agriculture and ecosystems, it is critical to understand the potential effects of these factors on ozone. However, large uncertainties exist in evaluating future ozone changes due to the uncertainties in climate change and in emissions. Uncertainties in the economic/population growth, technological/societal development and natural climatic variation challenge our ability to evaluate future levels of ozone.
In this presentation, I will analyze some of our results regarding the projections of U.S. ozone changes from the present (1996–2000) to the mid (2048–2052) and late (2095–2099) 21st century. Included in this analysis will be an evaluation of the individual and combined effects of climate change, resulting changes in biogenic precursor emissions, and changes in anthropogenic precursor emissions within and outside the contiguous U.S. territory. In order to evaluate the uncertainties in ozone projections, two cases of potential changes in climate and precursor emissions are considered, following the A1fi (high emissions) and B1 (low emissions) scenarios from the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emissions Scenarios (SRES). The two scenarios were chosen as representative of the current understanding of the upper and lower ends of potential climate changes over the coming century. The analyses for future ozone projections are based on results from the global chemistry-transport model, Model for OZone And Related chemical Tracers version 2.4 (MOZART-2.4), driven by meteorological fields from a state-of-the-art climate model, namely the Parallel Climate Model (PCM). In addition to its capability of simulating the pollutant chemistry and transport within the continental U.S., the global model also accounts for the effects of long-range transport and chemical interactions affecting the U.S. from outside the U.S.