Steady states and transport processes in urban ozone balances

Abstract Core chemical theory is combined with transport processes and local emissions to study the validity of commonly made assumptions regarding steady states to interpret urban and regional ozone data. It is shown that photo-stationary states of NO and NO2 cannot exist in urban areas or polluted regions in addition to the lack of such a state for ozone. Calculations in published papers, which make the assumption of a photo-stationary state for NO and NO2, or ozone, are likely to be inaccurate by unacceptable amounts. The Leighton Ratio is re-interpreted to show how it incorporates both the peroxy radical and transport effects on ozone, separating local chemical production from its transport. To illustrate the concepts and test the assumptions, hourly observations of ozone and its precursors from Yanbu in Saudi Arabia are analyzed. The major role of local transport processes and a large import of ozone at night, probably from aloft, are uncovered as a by-product.