Decomposition of N 2 O over particulate matter

Nitrous oxide is shown to undergo both a thermal and a photochemical decomposition at 296 K when it is adsorbed on various dry sands. The photochemical process occurs with light of wavelengths greater than 280 nm where gaseous N 2 O does not absorb. At low pressures (<0.1 torr) the half‐life for the thermal decomposition of nitrous oxide to nitrogen when placed in contact with ∼5 gms of heat treated Tunisian sand in a one‐liter vessel was 350 ± 35 days. Under certain photolytic conditions this half‐life was reduced. The efficiency of the photolytic process for a particular sand depends on the pressure (fraction of surface covered) and on the wave‐length of light. For Tunisian sand at 1.1 torr and with the full mercury arc (>280 nm), the destruction efficiency is ∼2 × 10 −5 molecules/incident photon. These results indicate that particulate matter in the troposphere may be responsible for the decomposition of nitrous oxide and hence act as an atmospheric sink for N 2 O. However, moisture causes a drastic reduction in the number of molecules dissociated per incident photon.