An upper limit on the production of N 2 O from the reaction of O(¹D) With CO 2 in the presence of N 2

While the major sources and sinks of N 2 O are known, there is debate concerning additional processes. A new source of N 2 O was proposed, reaction of N 2 with excited CO 3 *, formed from O(¹D) and CO 2 . Mixtures of O 3 , CO 2 , N 2 , and O 2 at total pressures of 1 atm were photolyzed at 254 nm to form O(¹D). The decrease in O 3 and a search for N 2 O formation were carried out using FTIR at 298 K and ∼264 K. N 2 O was not detected at either temperature. Upper limits were derived for the rate constant of the reaction CO 3 * + N 2 → N 2 O + CO 2 , k≤5.5×10 −13 cm³ molecule −1 s −1 at 298 K and k≤4.2×10 −13 cm³ molecule −1 s −1 at 264 K. Applying the rate constant at 264 K to typical stratospheric conditions at the spring equinox, 17 km and 40°N, the N 2 O formation rate was calculated to be ≤1 molecule cm −3 s −1 . These experiments did not use isotopically heavy reactants and therefore may underestimate the N 2 O yield. It is assumed that the results of these studies are applicable to stratospheric conditions. It is also assumed that N 2 O is not destroyed as it is formed by unrecognized secondary reactions. However, within these constraints, the upper limit suggests that this reaction is not a significant source of N 2 O.