A numerical study of tropospheric photochemistry using a one-dimensional model

Abstract. A photochemical box model with CO-CH4-NOy-H20 chemistry is used to calculate the diurnally averaged net photochemical rate of change of ozone (hereinafter called the chemical ozone tendency) in the troposphere for different values of parameters: NO x and ozone concentration, temperature, humidity, CO concentration, and surface albedo. To understand the dependency of the chemical ozone tendency on the input parameters, a detailed sensitivity study is performed. Subsequently, the expected variations of the ozone tendencies with altitude, latitude, and season are analyzed. The magnitude of the tendency decreases rapidly with height mostly as a result of lower absolute humidity and temperature. In the upper troposphere (at 190 mbar) the maximum tendencies are below 2 parts per billion by volume/day. Lower temperature and specific humidity cause a shift of the value of NO x at which the ozone production balances the destruction of ozone (balance point) to lower NO x values; these two parameters are also, to a large extent, responsible for lower magnitudes of the tendency at higher latitudes and in winter. In the upper troposphere we find that the net tendency is at least as sensitive to variations in H20 concentration as to NO x. This suggests a possible synergism between direct NO x pollution by aircraft and the indirect modification of H20 by climate change. In the second part of the paper the box model calculated rates are used as ozone's chemical tendency terms during a simulation conducted with the three-dimensional global chemistry transport model (GCTM). The box model is used to calculate the tendencies as a function of NO x and ozone at all tropospheric levels of the GCTM, at nine latitudes and for four seasons using zonally and monthly averaged data: water vapor and temperature from observations and model CO. These tables together with the NO x fields obtained in an earlier GCTM simulation are used in the GCTM simulation of 0 3 if nonmethane hydrocarbon levels are low. The global monthly averaged chemical ozone tendency fields saved during the simulation are presented and analyzed for the present-day and preindustrial conditions. The chemical tendency fields show a strong correlation with the NO x fields. In contrast with the lower and middle troposphere where the tendencies are negative in remote regions over the oceans, in the upper troposphere, where NO x is generally greater than 50 parts per trillion by volume and the balance point is low, the tendencies are generally small but positive. The GCTM simulations of the preindustrial ozone show that in the upper troposphere the presentday ozone tendencies are greater than the simulated preindustrial tendencies. In the boundary layer and in the midtroposphere the present-day tendencies are greater near anthropogenic NO x sources and smaller (generally more negative), due to higher ozone levels, in regions not affected by these sources.

Section: ;mentioning

confidence: 99%

Tropospheric chemical ozone tendencies in CO‐CH₄‐NO_y‐H₂O system: Their sensitivity to variations in environmental parameters and their application to a global chemistry transport model study

Klonecki¹,

Levy²

1997

“…This possibility has been advocated by . Fishman and Crutzen (1977) and Fishman et al (1979), suggesting as ozone sources in the troposphere the oxidation of CO, CN,,, and other hydrocarbons in the presence of NO and NO2. ..ring hi p rao , ac r ...hang .minimum t a bout day 120.…”

Section: Introductionmentioning

confidence: 99%

Equatorial ozone characteristics as measured at Natal (5.9°S, 35.2°W)

Kirchhoff¹,

Hilsenrath²,

Motta³

et al. 1983

Ozone density profiles obtained with ECC balloon sondes during the first 3 years of a joint INPE/NASA long‐term program of measurements at Natal have been analyzed. Ozone variations with time, as expected, are small. A correlation analysis of ozone and temperature profiles taken concurrently indicates a small correlation coefficient in the troposphere, a positive and increasing correlation between the tropopause and the ozone peak, turning negative above it. Outstanding features of the data are tropospheric densities substantially higher than those measured at other low latitude stations and also a total ozone content that is higher than that given by satellite measurements.

“…Naturally, their results are strong functions of the modelers assumptions regarding OH and NOx concentrations and wet and dry removal parameters. Fishman and Crutzen [1977] used a one-dimensional model to estimate the ratio at 0 and 6 km, with and without heterogeneous removal. The heterogeneous removal parameteri-zation used in their study might be described as a slow, continuous rainout.…”

Section: Introductionmentioning

confidence: 99%

Measurements of the nitric acid to NO_x ratio in the troposphere

Huebert¹,

Vanbramer²,

Lebel³

et al. 1990

Nitric acid concentrations, measured by both teflon/nylon filter packs (FP) and the tungstic oxide denuder (DEN), are compared with the average NOx concentrations from laserinduced fluorescent and chemiluminescent methods. The HNO3/NOx ratio based on filter packs ranged from 0.8 to 10.4, with a mean of 3.4. The DEN nitric acid concentrations produced ratios ranging from <0.3 to 9.8, with a mean of 2.6. Average marine ratios were larger than those from continental regions, in part due to continental anthropogenic sources of NOx. Although we collected very few boundary layer samples, their average ratios were smaller than those in the free troposphere, apparently because of the effect of dry surface removal of nitric acid. The nitric acid to NOx ratio was greatest when the NOx/NOy ratio was smallest, such that the nitrogen photochemistry was nearing completion.