Reactive uptake of HONO on aluminium oxide surface

Kinetics and products of the interaction of HONO with solid films of Al2O3 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 Al2O3 was studied as a function of HONO concentration ([HONO]0 = (0.6–3.5) × 1012 molecule cm−3), relative humidity (RH = 1.4 × 10−4 to 35.4%), temperature (T = 275–320 K) and UV irradiation intensity (JNO2=0.002–0.012 s−1JNO2=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 (JNO2=0.012 s−1JNO2=0.012 s−1), respectively (γ calculated with BET surface area, 30% conservative uncertainty). NO2 and NO were observed as products of the HONO reaction with Al2O3 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 Al2O3 surface) appears to be of minor importance compared with other HONO loss processes in the boundary layer of the earth atmosphere.

Graphical abstractKinetics and products of the interaction of HONO with solid films of Al2O3 were investigated under dark and UV irradiation conditions.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Uptake of HONO to Al2O3 surface was studied under dark and UV irradiation conditions. ► Uptake coefficient was measured as function of temperature and relative humidity. ► NO2 and NO were observed as reaction products with 60 and 40% yields, respectively. ► HONO loss on mineral aerosol is of minor importance in the atmosphere.