An upper limit on the production of N2O from the reaction of O(¹D) With CO2 in the presence of N2

While the major sources and sinks of N2O are known, there is debate concerning additional processes. A new source of N2O was proposed, reaction of N2 with excited CO3*, formed from O(¹D) and CO2. Mixtures of O3, CO2, N2, and O2 at total pressures of 1 atm were photolyzed at 254 nm to form O(¹D). The decrease in O3 and a search for N2O formation were carried out using FTIR at 298 K and ∼264 K. N2O was not detected at either temperature. Upper limits were derived for the rate constant of the reaction CO3* + N2 → N2O + CO2, 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 N2O 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 N2O yield. It is assumed that the results of these studies are applicable to stratospheric conditions. It is also assumed that N2O 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 N2O.