OZONE-PRECURSOR RELATIONSHIPS - A MODELING STUDY OF SEMIEMPIRICAL RELATIONSHIPS

The functional relationships of maximum ozone levels to non-methane organic gases (NMOG) and NO(x) concentrations (and emissions), which are relevant to urban ozone issues, have been investigated using data generated by a single-cell trajectory model as well as outdoor smog chamber data. A general relationship is shown to exist, at least approximately, for outdoor smog chamber simulations with initial precursors and for air masses which have initial input and continuous emissions of precursors and are diluted. When diurnally varying sunlight intensity and temperature are fixed, the relationship expresses maximum ozone concentrations as a product of the square root of effective NO(x) concentrations (initial input and continuous emissions) and a function of effective NMOG/NO(x) ratios (R). The function of R can be approximated as a simple function involving an exponential function. The present model holds for the entire domain of effective precursor concentrations and for NMOG mixtures as well as single NMOG species. The present model (with a temperature-dependent function) represents outdoor smog chamber data reasonably well. The temperature dependence of maximum ozone levels is shown to be larger for outdoor smog chamber data than predicted by current photochemical models.