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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 103, NO. D11, PAGES 13,435–13,450, 1998

Seasonal budgets of reactive nitrogen species and ozone over the United States, and export fluxes to the global atmosphere

Jinyou Liang

Department of Earth and Planetary Sciences and Division of Engineering and Applied Sciences Harvard University Cambridge, MA

Larry W. Horowitz

Department of Earth and Planetary Sciences and Division of Engineering and Applied Sciences Harvard University Cambridge, MA

Daniel J. Jacob

Department of Earth and Planetary Sciences and Division of Engineering and Applied Sciences Harvard University Cambridge, MA

Yuhang Wang

Department of Earth and Planetary Sciences and Division of Engineering and Applied Sciences Harvard University Cambridge, MA

Arlene M. Fiore

Department of Earth and Planetary Sciences and Division of Engineering and Applied Sciences Harvard University Cambridge, MA

Jennifer A. Logan

Department of Earth and Planetary Sciences and Division of Engineering and Applied Sciences Harvard University Cambridge, MA

Geraldine M. Gardner

Department of Earth and Planetary Sciences and Division of Engineering and Applied Sciences Harvard University Cambridge, MA

J. William Munger

Department of Earth and Planetary Sciences and Division of Engineering and Applied Sciences Harvard University Cambridge, MA

Abstract

A three-dimensional, continental-scale photochemical model is used to investigate seasonal budgets of O₃ and NO _y species (including NO _x and its oxidation products) in the boundary layer over the United States and to estimate the export of these species from the U.S. boundary layer to the global atmosphere. Model results are evaluated with year-round observations for O₃, CO, and NO _y species at nonurban sites. A seasonal transition from NO _x to hydrocarbon-limited conditions for O₃ production over the eastern United States is found to take place in the fall, with the reverse transition taking place in the spring. The mean NO _x /NO _y molar ratio in the U.S. boundary layer in the model ranges from 0.2 in summer to 0.6 in winter, in accord with observations, and reflecting largely the seasonal variation in the chemical lifetime of NO _x . Formation of hydroxy organic nitrates during oxidation of isoprene, followed by decomposition of these nitrates to HNO₃, is estimated to account for 30% of the chemical sink of NO _x in the U.S. boundary layer in summer. Model results indicate that peroxyacylnitrates (PANs) are most abundant in the U.S. boundary layer in spring (25% of total NO _y .), reflecting a combination of active photochemistry and low temperatures. About 20% of the NO _x emitted from fossil fuel combustion in the United States in the model is exported out of the U.S. boundary layer as NO _x or PANs (15% in summer, 25% in winter). This export responds less than proportionally to changes in NO _x emissions in summer, but more than proportionally in winter. The annual mean export of NO _x and PANs from the U.S. boundary layer is estimated to be 1.4 Tg N yr⁻¹, representing an important source of NO _x on the scale of the northern hemisphere troposphere. The eventual O₃ production in the global troposphere due to the exported NO _x and PANs is estimated to be twice as large, on an annual basis, as the direct export of O₃ pollution from the U.S. boundary layer. Fossil fuel combustion in the United States is estimated to account for about 10% of the total source of O₃ in the northern hemisphere troposphere on an annual basis.

Received 26 March 1997; accepted 29 October 1997.

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Citation: Liang, J., L. W. Horowitz, D. J. Jacob, Y. Wang, A. M. Fiore, J. A. Logan, G. M. Gardner, and J. W. Munger (1998), Seasonal budgets of reactive nitrogen species and ozone over the United States, and export fluxes to the global atmosphere, J. Geophys. Res., 103(D11), 13,435–13,450.

Copyright 1998 by the American Geophysical Union.