Author(s)

S. Andreani-Aksoyoglu, J. Keller, A.S.H.Prévôt & P. Builtjes

Abstract

It is very important for ozone control strategies to know whether ozone production is sensitive to NOx or VOC emissions to avoid unwished effects due to the nonlinearity of the photochemistry. Indicator species derived from measurements can be useful to assess the sensitivity. However, indicator values can vary under certain circumstances. In an earlier model study, we showed that the thresholds of indicators are affected by the wind fields and emissions. In this work, we studied the variability of indicator thresholds further by model simulations. A 3-day episode in July 1993 in Switzerland was modelled using the meteorological model SAIMM and the photochemical model CAMx. The studied indicators are NOy, HCHO/NOy, O3/NOz and H2O2/HNO3. The effects of some factors such as the definition of sensitivity, boundary concentrations and degree of emission reductions are discussed. 1 Introduction The relation between ozone and its main precursors NOx (NO + NO2) and VOC (volatile organic compounds) is very important for environmental policy because of the adverse impacts of ozone on human health and on crops and forests (NRC [l]). Some researchers proposed the use of observable species as indicators for ozone production sensitivity to changes in the precursor emissions. Milford et al. [2] proposed NO, as indicator and Sillman [3] expanded the concept of indicator species to include several others such as O3/NOz, H2O2/HNO3, HCHO/NOy. Indicators have been used over different areas by various numerical models (e.g.

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