CRC Report No. A-34 - Coordinating Research Council

April 2005
Comparison of Source Contributions at Diamond Bar in
Experiments 12 (no chemical decay) and 11 (with chemical decay)
350
300
Expt 11 (with chemical decay) - ppbC
250
200
150
100
Gasoline - day
Gasoline - night
(Biogenics) x 10 - day
(Biogenics) X 10 - night
(CNG/aged + LPG) x 10 - day
(CNG/aged + LPG) x 10 - night
1:1
50
0
0 50 100 150 200 250 300 350
Expt 12 (no chemical decay) - ppbC
Figure 4-8. The effects of chemical reaction on concentrations of high, medium and low
reactivity source categories at a mid-basin receptor (Diamond Bar).
Figure 4-9 shows the effects of chemical reaction on simulated ambient concentrations at a
downwind site, Crestline. As for Diamond Bar, the most heavily depleted source category is
biogenic emissions, which are almost completely removed at night. However, biogenic
emissions are less depleted at Crestline than Diamond Bar during the day because there are
stronger local sources of biogenic emissions at Crestline. The gasoline and CNG/aged
categories are more depleted by reaction at Crestline than Diamond Bar indicating that at
Crestline these emissions are being transported from far upwind which allows time for even a
low reactivity category such as CNG/aged (ethane) to lose about 10% to chemical reaction. The
differences in the amount of chemical processing of emissions between Diamond Bar and
Crestline and day vs. night show that it will be difficult to adjust a receptor model to account for
chemical reactions.
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