The effects of global changes upon regional ozone pollution in the United States J. Chen1,*, J. Avise1,**, B. Lamb1, E. Salathé2, C. Mass2, A. Guenther3, C. Wiedinmyer3, J.-F. Lamarque3, S. O'Neill4, D. McKenzie5, and N. Larkin5 1Washington State University, Pullman, WA, USA 2University of Washington, Seattle, WA, USA 3National Center for Atmospheric Research, Boulder, CO, USA 4United States Dept. of Agriculture, Natural Resources Conservation Service, Portland, OR, USA 5United States Dept. of Agriculture, Forest Service, Seattle, WA, USA *now at: National Research Council Canada, Ottawa, ON, Canada **now at: California Air Resources Board, Sacramento, CA, USA
Abstract. A comprehensive numerical modeling framework was developed to estimate the
effects of collective global changes upon ozone pollution in the US in 2050.
The framework consists of the global climate and chemistry models, PCM
(Parallel Climate Model) and MOZART-2 (Model for Ozone and Related Chemical
Tracers v.2), coupled with regional meteorology and chemistry models, MM5
(Mesoscale Meteorological model) and CMAQ (Community Multi-scale Air Quality
model). The modeling system was applied for two 10-year simulations:
1990–1999 as a present-day base case and 2045–2054 as a future case. For
the current decade, the daily maximum 8-h moving average (DM8H) ozone mixing
ratio distributions for spring, summer and fall showed good agreement with
observations. The future case simulation followed the Intergovernmental Panel
on Climate Change (IPCC) A2 scenario together with business-as-usual US
emission projections and projected alterations in land use, land cover (LULC)
due to urban expansion and changes in vegetation. For these projections, US
anthropogenic NOx (NO+NO2) and VOC (volatile organic carbon)
emissions increased by approximately 6% and 50%, respectively, while
biogenic VOC emissions decreased, in spite of warmer temperatures, due to
decreases in forested lands and expansion of croplands, grasslands and urban
areas. A stochastic model for wildfire emissions was applied that projected
25% higher VOC emissions in the future. For the global and US emission
projection used here, regional ozone pollution becomes worse in the
2045–2054 period for all months. Annually, the mean DM8H ozone was projected
to increase by 9.6 ppbv (22%). The changes were higher in the spring and
winter (25%) and smaller in the summer (17%). The area affected by elevated
ozone within the US continent was projected to increase; areas with levels
exceeding the 75 ppbv ozone standard at least once a year increased by 38%.
In addition, the length of the ozone season was projected to increase with
more pollution episodes in the spring and fall. For selected urban areas, the
system projected a higher number of pollution events per year and these
events had more consecutive days when DM8H ozone exceed 75 ppbv.
Citation: Chen, J., Avise, J., Lamb, B., Salathé, E., Mass, C., Guenther, A., Wiedinmyer, C., Lamarque, J.-F., O'Neill, S., McKenzie, D., and Larkin, N.: The effects of global changes upon regional ozone pollution in the United States, Atmos. Chem. Phys., 9, 1125-1141, doi:10.5194/acp-9-1125-2009, 2009.