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.

氧自由基（HO2）在平流层化学中扮演着至关重要的角色。由于尚未对环境气溶胶上HO2的吸收系数（γ）进行恰当的量化，因此，在总体HO2浓度方面，现场测量值与复杂模型预测值之间存在较大差异。本研究首次在2018年夏季于日本京都，利用激光闪光光解和激光诱导荧光（LFP–LIF）相结合的技术，对由环境气体相（k_g^'）和气溶胶相（k_a^'）引起的总HO2反应活性进行了在线测量。该技术辅以多功能的气溶胶浓度富集系统（VACES），通过将环境气溶胶浓度提高约10倍，以补偿其相对较低的浓度。结果显示，k_g^'的值介于0.1 s−1（第25百分位数）至0.32 s−1（第75百分位数），平均值为0.22 ± 0.16 s−1（1），这与HO2与NO2反应的模型结果吻合良好。在应用VACES和自动切换气溶胶过滤器后，k_a^'的值介于0.004 s−1（第25百分位数）至0.028 s−1（第75百分位数），平均值为0.017 ± 0.015 s−1，将此值转换为环境条件（通过除以富集因子）后，约为在298 K温度下，由自身反应引起的HO2反应活性的10倍。相关的γ值介于0.08（第25百分位数）至0.36（第75百分位数），平均值为0.24，与先前建模研究中使用的值（约为0.2）相当，但在测量时间内存在±0.20（1）的大幅波动，表明在使用恒定γ值估算HO2浓度时可能存在较大偏差。环境空气反向轨迹分析表明，主要NO2排放源来自日本本土，但空气团通过本土或沿海方向通过时，在HO2吸收系数方面没有显著差异。本研究提供了更可靠的γ值，这将有助于提高对平流层化学中非均相过程建模的准确性。