Investigation of HO2 uptake mechanisms onto multiple-component ambient aerosols collected in summer and winter time in Yokohama, Japan

The heterogeneous loss of HO2 radicals onto ambient aerosols plays an important role in tropospheric chemistry. However, sparse investigation of the dominating parameters con-trolling the HO2 uptake coefficients onto ambient aerosols ( gamma HO2) has largely hindered the application of the measured gamma HO2 to the global spatial prediction. Here we induced an of-fline method using LFP-LIF technique to measure the kinetics of HO2 uptake onto ambi-ent aerosols collected in summertime and wintertime in Yokohama city, a regional urban site near Tokyo, Japan. By controlling the dominating parameters which influence gamma HO2, we were able to investigate the detailed HO2 uptake mechanism. We characterized the chemi-cal composition of the collected ambient aerosols, including organics, inorganics, transition metals ions, etc. and modeled gamma HO2 using different mechanisms. Results show that gamma HO2 increased with the increase in RH, and the aerosol states ("dry" or wet/aqueous) have large effects on gamma HO2. With fixed RH and aerosol chemical composition, gamma HO2was highly dependent on pH and inversely correlated with [HO2]0. By combing the measured gamma HO2 values with the modeled ones, we found that both the HO2 self-reaction and transition metal-catalyzed reactions should be accounted for to yield a single parameterization to predict gamma HO2, and different chemical compositions may have collective effects on gamma HO2. Results may serve for extending the gamma HO2 values measured at one observation site to different environmental conditions, which will help us to achieve more accurate modeling results concerning secondary pollutant formation (i.e., ozone).(c) 2023 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.