Health Assessment Document for Diesel Emissions - NSCEP | US ...

1
2
3
4
5
6
7
8
9
10
11
12
with
k 2 [N0 2 ]
[0] = ---
3 k 1 [NO]
where k 1 and k 2 are the rate constants for Reactions 1 and 2, respectively, and brackets signify
concentrations. This photostationary state is strongly affected by NO-to-N0 2 conversions caused
by reactions involving organic compounds.
The important atmospheric reactions ofN0 2 also include formation ofN03 radicals and
N0 2 + 0 3 .... N0 3 + 0 2
M
: N20s
24 with N 2 0 5 being in equilibrium with N0 2 and N03 radicals.
25 The other important atmospheric reactions of NO and N0 2 include nitrous and nitric acid
26 formation, respectively, by reaction with OH radicals:
27 NO + OH .... HN0 2
28 N0 2 + OH .... HN0 3
29
30 2.4.2.1.2. Reactions of sulfur dioxide. Reaction with OH radical is the dominant S0 2
31 atmospheric gas-phase reaction process (Stockwell and Calvert, 1983):
32 S0 2 + OH .... HS0 3
33 followed by the formation ofH0 2 radicals and H 2S0 4 :
34 HS03 + 0 2 .... H0 2 + S03
35 H 20
36 H 2S0 4
37
38 Because S0 2 is soluble in water, it undergoes scavenging by fog, cloud water, and
39 raindrops. In aqueous systems; S0 2 is readily oxidized to sulfate (Calvert and Stockwell, 1983).
2/1198 2-31 DRAFT --DO NOT CITE OR QUOTE