Reactive uptake of HONO on aluminium oxide surface

Kinetics and products of the interaction of HONO with solid films of Al 2 O 3 were investigated under dark and UV irradiation conditions using a low pressure flow reactor (1–10 Torr) combined with a modulated molecular beam mass spectrometer for monitoring of the gaseous species involved. The reactive uptake of HONO to Al 2 O 3 was studied as a function of HONO concentration ([HONO] 0 = (0.6–3.5) × 10 12 molecule cm −3 ), relative humidity (RH = 1.4 × 10 −4 to 35.4%), temperature ( T = 275–320 K) and UV irradiation intensity ( J NO 2 = 0.002 – 0.012 s − 1 ). The measured reactive uptake coefficient was independent of the HONO concentration and temperature. In contrast, the relative humidity (RH) was found to have a strong impact on the uptake coefficient: γ = 4.8 × 10 −6 (RH) −0.61 and γ = 1.7 × 10 −5 (RH) −0.44 under dark conditions and on irradiated surface ( J NO 2 = 0.012 s − 1 ), respectively ( γ calculated with BET surface area, 30% conservative uncertainty). NO 2 and NO were observed as products of the HONO reaction with Al 2 O 3 surface with yields of 40 ± 6 and 60 ± 9%, respectively, independent of relative humidity, temperature, concentration of HONO and UV irradiation intensity under experimental conditions used. The HONO uptake on mineral aerosol (calculated with uptake data for HONO on Al 2 O 3 surface) appears to be of minor importance compared with other HONO loss processes in the boundary layer of the earth atmosphere.