Abstract
The concentrations of O3 and its precursors over North America are simulated for three summer months with a three‐dimensional, continental‐scale photochemical model using meteorological input from the Goddard Institute for Space Studies (GISS) general circulation model (GCM). The model has 4°×5° grid resolution and represents non linear chemistry in urban and industrial plumes with a subgrid nested scheme. Simulated median afternoon O3 concentrations at rural U.S. sites are within 5 ppb of observations in most cases, except in the south central United States where concentrations are overpredicted by 15–20 ppb. The model captures successfully the development of regional high‐O3 episodes over the northeastern United States on the back side of weak, warm, stagnant anticyclones. Simulated concentrations of CO and nonmethane hydrocarbons are generally in good agreement with observations, concentrations of NOx are underpredicted by 10–30%, and concentrations of peroxyacylnitrates (PANs) are overpredicted by a factor of 2 to 3. The overprediction of PANs is attributed to flaws in the photochemical mechanism, including excessive production from oxidation of isoprene, and may also reflect an underestimate of PANs deposition. Subgrid nonlinear chemistry as captured by the nested plumes scheme decreases the net O3 production computed in the United States boundary layer by 8% on average.
Highlights
The grid is 4ølatitude regulating03 over the United Statesin summerand to determine x 5ø longitudew, ith ninelayersin theverticaldefinedby a sigma the exportsof 0 3 and its precursorsfrom the United Statesto the coordinate,replicatingthe grid of a general global atmosphere.We focus here on model descriptionand circulationmodel (GCM) developedat the GoddardInstitutefor evaluation.The objectivesare addressedin the companionpaper SpaceStudies(GISS)
Hours, with rural air entrained into the plume by cross-flow occupiedby theseplumesis diffusion: 4
HereA' is the areaof the old box U1, computedat the previous timestepfromequation(C1); Wois thewindspeedattheprevious time step;E is an entrainmenftactorfor rural air into theplumes (AT- Au- Ap)(1-e-A*/&')
Summary
This paper is the first of two presentinga three-dimensional, continental-scalesimulation of 03 over North America for three Framework summer months. 1984;Changet al., 1987;Carmichaelet al., 1991;McKeenet al., day averagesof other meteorologicalvariables These models all use fine grid humidity,cloudreflectivities). They are designedto simulatehigh-O3 Table liststhechemicaltracerstransporteidn themodel: odd episodesoccurringover spatialscalesof a few hundredkm and oxygen (O,,), NO,,, peroxyacylnitrates(PANs), CO, a lumped temporalscalesof a few days. Anthropogenicemissionsin polynomialsof 11 independenvtariablesdefiningthe chemical Central and South America are estimated from national data for environment (Table 3). Yields of CO from the oxidationof HC1, HC2, and Isopreneemissionis a functionof vegetationtype, surfaceair methane(1.7 ppm)aretakenas60%, 30%, and90%, respectively temperature,and insolation(AppendixB) It is computedwith [Lurmann et al, 1986]. The andJodD),which arecomputedin turnaspolynomialsof seven maximumover thesouthcentralUnitedStatesin Figure reflects independentvariablesparameterizingresults from the radiative a combination of dense deciduous forest cover and high
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