Why do models overestimate surface ozone in the Southeast United States?

Authors

Katherine R. Travis, Harvard University
Daniel J. Jacob, Harvard University
Jenny A. Fisher, University of WollongongFollow
Patrick S. Kim, Harvard University
Eloise A. Marais, Harvard University
Lei Zhu, Harvard University
Karen Yu, Harvard University
Christopher C. Miller, Harvard University
Robert M. Yantosca, Harvard University
Melissa P. Sulprizio, Harvard University
Anne M. Thompson, NASA Goddard Space Flight Center
Paul O. Wennberg, California Institute of TechnologyFollow
John D. Crounse, California Institute of Technology
Jason M. St. Clair, California Institute of Technology
Ronald C. Cohen, University of California
Joshua L. Laughner, University of California, Berkeley
Jack E. Dibb, University of New Hampshire
Samuel R. Hall, National Center for Atmospheric Research
Kirk Ullmann, National Center For Atmospheric Research, Boulder, United States
Glenn M. Wolfe, NASA Goddard Space Flight Center, University of Maryland
Illana B. Pollack, Colorado State University
Jeff Peischl, National Oceanic and Atmospheric Administration, University of Colorado
Jonathan A. Neuman, University of Colorado, National Oceanic and Atmospheric Administration
Xianliang Zhou, New York State Department Of Health, State University of New York Albany

RIS ID

110184

Publication Details

Travis, K. R., Jacob, D. J., Fisher, J. A., Kim, P. S., Marais, E. A., Zhu, L., Yu, K., Miller, C. C., Yantosca, R. M., Sulprizio, M. P., Thompson, A. M., Wennberg, P. O., Crounse, J. D., St. Clair, J. M., Cohen, R. C., Laughner, J. L., Dibb, J. E., Hall, S. R., Ullmann, K., Wolfe, G. M., Pollack, I. B., Peischl, J., Neuman, J. A. & Zhou, X. (2016). Why do models overestimate surface ozone in the Southeast United States?. Atmospheric Chemistry and Physics, 16 (21), 13561-13577.

Abstract

Ozone pollution in the Southeast US involves complex chemistry driven by emissions of anthropogenic nitrogen oxide radicals (NO_x  ≡  NO + NO₂) and biogenic isoprene. Model estimates of surface ozone concentrations tend to be biased high in the region and this is of concern for designing effective emission control strategies to meet air quality standards. We use detailed chemical observations from the SEAC⁴RS aircraft campaign in August and September 2013, interpreted with the GEOS-Chem chemical transport model at 0.25°  x  0.3125° horizontal resolution, to better understand the factors controlling surface ozone in the Southeast US. We find that the National Emission Inventory (NEI) for NO_x from the US Environmental Protection Agency (EPA) is too high. This finding is based on SEAC⁴RS observations of NO_x and its oxidation products, surface network observations of nitrate wet deposition fluxes, and OMI satellite observations of tropospheric NO₂ columns. Our results indicate that NEI NO_x emissions from mobile and industrial sources must be reduced by 30-60 %, dependent on the assumption of the contribution by soil NO_x emissions. Upper-tropospheric NO₂ from lightning makes a large contribution to satellite observations of tropospheric NO₂ that must be accounted for when using these data to estimate surface NO_x emissions. We find that only half of isoprene oxidation proceeds by the high-NO_x pathway to produce ozone; this fraction is only moderately sensitive to changes in NO_x emissions because isoprene and NO_x emissions are spatially segregated. GEOS-Chem with reduced NO_x emissions provides an unbiased simulation of ozone observations from the aircraft and reproduces the observed ozone production efficiency in the boundary layer as derived from a regression of ozone and NO_x oxidation products. However, the model is still biased high by 6 ± 14 ppb relative to observed surface ozone in the Southeast US. Ozonesondes launched during midday hours show a 7 ppb ozone decrease from 1.5 km to the surface that GEOS-Chem does not capture. This bias may reflect a combination of excessive vertical mixing and net ozone production in the model boundary layer.