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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 102, NO. D19, PAGES 23,363–23,373, 1997

Photochemical oxidant formation over southern Switzerland. 2. Model results

T. Staffelbach

Swiss Federal Research Station for Agroecology and Agriculture, Institute of Environmental Protection and Agriculture, Bern-Liebefeld

A. Neftel

Swiss Federal Research Station for Agroecology and Agriculture, Institute of Environmental Protection and Agriculture, Bern-Liebefeld

L. W. Horowitz

Harvard University, Cambridge, Massachusetts

Abstract

Measurements of photooxidants made during summer 1994 in the southern part of Switzerland are compared with results of a one-dimensional Lagrangian model. The agreement between modeled and measured ozone concentrations is good. Concentrations of highly soluble species such as H₂O₂ and HNO₃ are overestimated by the model. The model underestimates concentrations of isoprene, HCHO, and HONO. The impact of this discrepancy on the question of NO_x versus VOC limitation of the ozone production is discussed. According to the model, reduction of the NO_x emissions is more effective in reducing O₃ than reduction of the VOC emissions for a large fraction of the area under investigation. This finding is in accordance with what we concluded from the data. The southern part of Switzerland is often impacted by a plume originating from Milan, which leads to additional ozone at the measuring site. We used the model to simulate the influence of this plume on the chemical regime. The plume emissions are picked up by the model at two different times. Both cases deliver the same concentrations for the end point of the calculations. If the emissions are picked up early in the morning, the ozone production becomes VOC sensitive for a few hours before switching back to being NO_x sensitive. If the emissions are picked up later, the O₃ production stays NO_x sensitive all the time. Forcing the model to reproduce measured concentrations of HONO and isoprene shifts the O₃ production toward being more NO_x sensitive.

Received 30 October 1996; accepted 21 March 1997.

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Citation: Staffelbach, T., A. Neftel, and L. W. Horowitz (1997), Photochemical oxidant formation over southern Switzerland. 2. Model results, J. Geophys. Res., 102(D19), 23,363–23,373.

Copyright 1997 by the American Geophysical Union.