N2O5 lifetime

Table 3 shows the atmospheric lifetime for eleven PAH with respect to gas-phase reaction with OH and NO3 radicals, O3 and N2O5. This was calculated from the estimated and calculated rate constants. It is evident that most of the nitroarenes formed under ambient atmospheric conditions were produced by reaction of PAH with OH. The PAH reaction with NO3 radical was also considered as an important step because it resulted in the formation of nitroarenes from the N2O5 reaction with gas-phase PAH. 

A useful quantity with which to compare this with is the reciprocal of the lifetime calculated from the sum of the first order loss processes involving NO3 and N2O5... 

The atmospheric lifetimes of N2O5 at room temperature and atmospheric pressure is calculated from the above formula as about 10 s, and during this lifetime N2O5 is converted to HONO2 either by homogeneous reaction with H2O molecule. 

Conversion of N2O5 and CIONO2 on aerosols is rather uncertain as the reaction probability per collision, yy, is not well known. The lifetime tpx of a gaseous molecule against collision with aerosols in the background atmosphere at 17 km is 10" s and thus the reaction time becomes /ac/Y- To make /a one month, y = 2 X 10 is required, which is much larger than y measured [14] for concentrated sulphuric acid at 300 K. 

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