Laboratory Studies of Heterogeneous Reactions of HO2 Radical with Inorganic Aerosol Particles under the Ambient Conditions

The HO2 uptake coefficient for aerosol particles ((NH4)2SO4 and NaCl) under ambient conditions (760Torr and 296K) was measured using an aerosol flow tube(AFT) coupled with a chemical conversion/laser-induced fluorescence(CC/LIF) technique. The CC/LIF technique enabled experiments to be performed at almost the same HO2 radical concentration as that in the atmosphere(~108 molecules cm-3). HO2 radicals were injected into the AFT through a vertically movable Pyrex tube. Injector position dependent profiles of LIF intensity were measured as a function of aerosol concentration at various relative humilities(RH). The uptake coefficients of dry aerosol (NaCl and (NH4)2SO4) particles were < 0.05, while the uptake coefficients of wet particles of NaCl and (NH4)2SO4 were estimated to be 0.10 and 0.15, respectively, which suggested that heterogeneous loss was enhanced by the particle containing water. To estimate the contribution of heterogeneous loss of HO2 by aerosol, the diurnal variation of HO2 using a box-model calculation was demonstrated. As a result, the daytime maximum concentrations of HO2 were changed to 95 and 70 %, relative to an absence of heterogeneous loss for marine and urban areas, respectively.