Data for: Real-time quantification of the total HO2 reactivity of ambient air and HO2 uptake kinetics onto ambient aerosols in Kyoto (Japan)
HO2 radicals play important roles in tropospheric chemistry. The large discrepancies between field measurements and sophisticated model predictions for the overall HO2 concentrations may due to the not yet been properly quantified HO2 uptake coefficients onto ambient aerosols (γ). This study presents the first on-line measurement of the total HO2 reactivity caused by the ambient gas phase (k_g^') and aerosol phase (k_a^') in summer 2018 in Kyoto, Japan, using a combination technique of laser-flash photolysis and laser-induced fluorescence (LFP–LIF), coupled with a versatile aerosol concentration enrichment system (VACES) that enriches ambient aerosols by ~10 times to compensate its relative low concentration. Results show k_g^' ranged from 0.1 s−1 (25th percentile) to 0.32 s−1 (75th percentile) with the average value of 0.22 ± 0.16 s−1 (1), which matches well with the modeling results from the HO2 reaction with NO2. With the application of VACES and the auto-switching aerosol filter, k_a^' ranged from 0.004 s−1 (25th percentile) to 0.028 s−1 (75th percentile) with an average value of 0.017 ± 0.015 s−1, which, when converted to ambient conditions (by dividing the enrichment factor), is ~10 times higher than the HO2 reactivity caused by its self-reaction under ambient concentration levels (~ 5 ppt) at 298 K. The related γ ranged from 0.08 (25th percentile) to 0.36 (75th percentile) with the average value of 0.24, which is comparable with the values used in previous modeling studies (around 0.2) but with a large variation of ±0.20 (1) within the measurement time, suggests large bias may exist for the estimation of HO2 concentrations when using a constant γ value. Ambient air backward trajectories analysis indicates the predominant NO2 emission sources came from the mainland of Japan, but no significant differences regarding HO2 uptake coefficients when air masses came through the mainland or from the coastal direction. This study provides more reliable γ which could promote the accuracy of the modeling of heterogeneous processes in tropospheric chemistry.