Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
D8 2015 3.0 Included Sulfate microphysics with SO 2 gas-to-particle
D9 2050 2.0 Included SA0
conversion of 100%
The following heterogeneous reactions were identified in DeMore et al. (1997) as possible reactions on sulfate or PSC. Most models assume that the rate constant is in
the form gvA/4, where g is the reaction probability, v is the thermal velocity of the reactant, and A is the surface area of the sulfate or PSC.
N 2 O 5 + H 2 O 2HNO 3
ClONO 2 + H 2 O HNO 3 +
HOCl
BrONO2 + H2O HNO3 +
HOBr
ClONO 2 + HCl HNO 3 + Cl 2
HOCl + HCl Cl 2 + H 2 O
HOBr + HCl BrCl + H 2 O
These reactions occur on the surface of particles (sulfate or PSC). In addition, all but two of the nine models (LLNL and UNIVAQ) include the reaction N2O5 + HCl '
HNO3 + ClNO2 on PSC. In most cases, H2O and HCl molecules are adsorbed or dissolved in the particles, and the reaction proceeds as the other reactant collides
with the particle. There are slight variations in the temperature dependence of g for reactions on sulfate particles used in the various models. Previous analyses
(Murphy and Ravishankara, 1994; Borrmann et al., 1997; Michelsen et al., 1999) have shown that g is very sensitive to temperature for some reactions. As the air
parcel goes around the globe, it experiences temperatures that are both lower and higher than the zonal mean temperature. Ignoring zonal asymmetry in temperature
by using zonal mean values in calculations may underestimate the O3 impact from HSCT (Pitari et al., 1993; Considine et al., 1994; Grooß et al. 1994; Weisenstein et
al., 1998). Because the sulfate surface area is specified in the calculations, the temperature-dependence comes from g and v. Some models compute an effective gv
based on a temperature-weighted g and v from zonal-mean temperature, whereas other models compute a temperature-weighted product of gv. Some of the listed
reactions also occur on type I PSCs (assumed to be nitric acid trihydrate (NAT)) or type II PSCs (assumed to be "ice"). Exact treatments in each model vary; see the
Technical Report on Supersonic Aircraft Effects for details.
4.3.2. Definition of Scenarios
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