Ozone-precursor relationships: a modeling study of semiempirical relationships

Abstract

The functional relationships of maximum ozone levels to non-methane organic gases (NMOG) and NO* 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* concentrations (initial input and continuous emissions) and a function of effective NMOG/ NO* 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.

Assessing Ozone-Precursor Relationships Based on a Smog Production Model and Ambient Data

“…6 Both SPM versions are applied to routine ambient data from numerous monitoring sites in several metropolitan U.S. areas. …”

“…10 Incorporating these features, a semi-empirical model relating ozone maximum concentrations to precursor emissions was derived using outdoor smog chamber data and the results of air quality model simulations. 6 In the NO x -limited regime, the following relationship was obtained: (15) where (NO X E) represents NO X emissions that have been received by the air mass and expressed as an effective concentration at the time of ozone maximum. With the outdoor smog chamber data on Los Angeles air, 11 y = 1.03 was obtained.…”

“…With the outdoor smog chamber data on Los Angeles air, 11 y = 1.03 was obtained. 6 A further evaluation of parameter y has been made using a single-cell trajectory air quality model with typical simulation conditions. 12 Including dry depositions of O 3 and NO y species, y~ 0.9 was obtained for low-and high-dilution (17) where (NO^)^ is given by Equation 9.…”

“…Another critical assumption in SPM is Equation 6. The loss processes of NO y from the gas phase during days conducive to ozone formation are dry deposition, secondary organic aerosol formation, and inorganic nitrate formation (mainly NH 4 NO 3 ).…”

The strategic gap in air-quality management

“…This varies greatly from one authority to another and leads to inconsistency in the monitoring of similar phenomena in different areas (Cannibal, 1998;Hadfield and Cannibal, 1996). As a consequence, locally oriented monitoring is poorly equipped to provide the information which is necessary to establish the relationship between tropospheric ozone and its precursors in any one area (Allen and Foley, 1993;Chang and Rudy, 1993;Bower and Stevenson, 1994). This situation is compounded by two additional factors.…”