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

Abstract

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.

The governing processes and timescales of stratosphere-to-troposphere transport and its contribution to ozone in the Arctic troposphere

“…During this time, NO x mixing ratios in the Arctic free troposphere increase from the ∼10-20 pptv to ∼30 pptv (Stroud et al, 2003). Near the lower end of the critical range (10-20 pptv), production of ozone is slow and net destruction dominates (Klonecki and Levy, 1997). As NO x increases to 150 pptv, production of ozone increases and the chemical ozone tendency first changes from negative to positive and then increases rapidly with a linear dependence on NO x concentrations (Klonecki and Levy, 1997;Jaeglé et al, 1999).…”

“…(e.g., Danielsen and Mohnen, 1977;Oltmans, 1981;Levy et al, 1985;Logan, 1985Logan, , 1999Wang et al, 1998;Stohl et al, 2003) and active photochemical production (e.g., Liu et al, 1987;Wang et al, 1998;Yienger et al, 1999). Surface measurements of radioactive debris ( 90 Sr) and Beryllium-7 ( 7 Be) also show a spring maximum associated with the seasonal cycle of stratosphere-troposphere exchange (STE) (e.g.…”

An evaluation of chemistry's role in the winter‐spring ozone maximum found in the northern midlatitude free troposphere

“…With CH 4 being specified for each hemisphere, the seven parameters are tropospheric pressure, latitude, month, albedo, 03, NOx, CO, and H20. The tables are constructed for the GCTM tropospheric pressure levels, 17 latitude bands, every other month, both land and sea albedos, and for a range of 0 3, NOx, CO, and H20 mixing ratios corresponding to values observed in the troposphere [see Klonecki and Levy, 1997]. In these photochemical calculations, H2CO , H202, and CH302H are assumed to be in photochemical diurnal steady state, HNO 3 is specified at observed levels, and the very small direct contribution to ozone production from the peroxyacetyl radical is not considered.…”

Analysis of Ground Level Ozone and Nitrogen Oxides in the City of Dar es Salaam and the Rural Area of Bagamoyo, Tanzania

“…Kenya found a similar diurnal cycle. This was explained by the photochemical destruction of ozone in the free troposphere under low NO x conditions, which are likely far cleaner in east African areas, but this may also be due to dry surface deposition [32]- [33]. Mwetemo, a small village with small scale farming, surrounded by forest about 45 km from the coastal town of Bagamoyo, had low NO x concentrations (below 12 ppb; see Table 3).…”

“…Bagamoyo is more remote and NO x concentrations were very low. Ozone might also be photochemically destroyed in the free troposphere under low NO x conditions [33]. Being 45 km from the sea, clean air from the Indian Ocean travels to the Mwetemo village.…”