Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
concentrations measured in the plume are used to infer OH concentrations or emission indices for OH using known reaction parameters for OH + NO (Tremmel et al.,
1998).
Another pair of heterogeneous reactions occurring on soot have been shown to be of importance in the troposphere (Brouwer et al., 1986):
N 2 O 5 + H 2 O + [soot] 2HNO 3 + [soot] (20a)
N 2 O 5 + [soot] NO 2 , NO + [soot . O] (20b)
[soot.O] CO, CO 2 (19b)
Reaction 20a is a hydrolysis reaction for which soot is the support material, whereas reaction 20b corresponds to a reduction-oxidation reaction in which soot is the
reducing agent. The primary oxidation product [soot.O] of reaction 20b has not been identified, but it releases CO and CO 2 upon heating (reaction 19b), similar to the
oxidation of soot by NO 2 in reaction 19a. The heterogeneous reaction of the NO x reservoir HNO 3 on soot also corresponds to a reduction-oxidation reaction analogous
to the examples listed above (Rogaski et al., 1997):
2HNO 3 + 2[soot] NO 2 , NO + 2[soot . O] + H 2 O(ads) and/or [soot . OH] (21)
Finally, ozone reacts heterogeneously with soot in a redox reaction in which soot is the reducing agent (Stephens et al., 1986; Fendel et al., 1995; Rogaski et al.,
1997):
O 3 + [soot] O 2 + [soot . O] (22)
[soot.O] CO, CO 2 (19b)
It is important to note that reaction 22 does not correspond to a catalytic reaction because for every ozone molecule reacted, CO and CO 2 are formed according to
reaction 19b. Therefore, soot is consumed as shown in the mass balance involving carbon (Stephens et al., 1986). Thus, in all of the above reactions-with the possible
exception of reaction 19d-soot appears to act as a reducing agent that is consumed in the course of the reduction-oxidation reaction.
Heterogeneous reactions of other potentially important reservoir and active compounds on soot are virtually unexplored. Examples may include reactions of HNO4 ,
H2O2 , HOx , XNO2 , and XONO2 , with X=Cl, Br. HNO2 does not, however, seem to undergo heterogeneous interaction on soot to any significant extent (Gerecke et al.,
1998).
http://www.ipcc.ch/ipccreports/sres/aviation/024.htm (3 von 8)08.05.2008 02:41:40