A regional model study of the ozone budget in the eastern United States

Abstract

In order to better understand the photochemical and meteorological processes controlling regional scale air quality problems such as ozone formation, we have developed a three‐dimensional Eulerian model and applied this model to a high‐pressure period (July 4 to July 7, 1986) over the eastern United States. Meteorological and physical variables from a three‐dimensional primitive‐equation model are used to drive the transport parameters over a grid with 60×60 km2 horizontal resolution, and 15 unequally spaced vertical layers extending from the ground to roughly 15 km. The treatment and incorporation of the dynamic model, the transport model, surface deposition, emission of anthropogenic and natural O3 precursors, the chemical mechanism for 35 individual species, solar radiation and the numerical methods are discussed in detail. Model performance is tested by comparing model predicted O3 concentrations with observations from the U.S. Environmental Protection Agency ozone‐monitoring network. Although a significant correlation between model and observed O3 is found, systematic discrepancies also exist and are discussed in relation to the basic model formulation, and variability in the observed O3. Additionally, a comparison of time‐averaged NOx and anthropogenic nonmethane hydrocarbon (NMHC) concentrations to relatively long term observations provides a qualitative assessment of the model's ability to simulate certain aspects of these O3 precursors from the few available observations. The model is used as a diagnostic tool to analyze various aspects of regional scale O3 formation and the budgets of the primary O3 precursors. Ozone formation over much of the continental model domain is shown to be NOx. limited. On the other hand, for midday NOx levels greater than about 4 or 5 ppbv, O3 formation is generally suppressed because of the low NMHC to NOx ratios (1 to 7) that are characteristic of the emissions inventory. Regional‐scale budget analyses show that very Hide NOx or NMHC is transported to the free troposphere for the high‐pressure conditions of this study and in the absence of a significant subgrid‐scale vertical mixing process (i.e., efficient cumulus transport). We calculate a net turnover time of about 1.5 days for continental O3 below 1800 m with in situ photochemical formation being balanced by photochemical loss and transport off the American continent. The results of this work are intended to serve as a baseline for further model development.

Estimation of the ground-level ozone lifetime under rural conditions

“…All these factors determine the obtained ozone lifetime at two rural stations (Preila and Rūgšteliškis) having different values during the same season ( Table 1). The estimated ozone lifetimes are consistent with the results found in other works [22][23][24][25]. The comparison of the estimated ozone lifetime under different rural conditions, e. g., with prevalence of different underlying surfaces, shows that ozone lifetimes differ from 1.3 up to 1.6 times.…”

Findings on NOy as an indicator for ozone sensitivity based on different numerical simulations

“…Ozone formation in the troposphere shows a nonlinear dependence on the availability of the precursors nitrogen oxides (NOx -NO + NO2) and volatile organic compounds (VOCs). In the real atmosphere, physical processes such as advection, turbulent diffusion, and dry deposition make the situation even more complex [McKeen et al, 1991a]. Temperature, humidity, and radiation, the latter determining the photolysis rate coefficient, have a direct influence on ozone chemistry [Cardelino and Chameides, 1990; Sillman and Samson, 1995; Vogel et al, 1995].…”

Photochemical modelling in the Po basin with focus on formaldehyde and ozone

“…Parameterization of the vertical transport of chemical tracers in connection with convective plumes and the compensating sinking motion was introduced by Flatøy and Hov (1995). Dry deposition rates are computed as a function of latitude, time of day, time of year, land type, vegetation type, and meteorological conditions according to McKeen et al (1991) and Hass (1991). The wet deposition is calculated based on the rate of precipitation at the ground, on the rainout rate from the individual vertical layers, and on the wet scavenging coefficients for individual species.…”