Real-time quantification of the total HO2 reactivity of ambient air and HO2 uptake kinetics onto ambient aerosols in Kyoto (Japan)
Real-time quantification of the total HO2 reactivity of ambient air and HO2 uptake kinetics onto ambient aerosols in Kyoto (Japan)
复制标题
DOI：
10.1016/j.atmosenv.2019.117189
复制
发表时间：
2020-02
影响因子：
5
通讯作者：
Jun Zhou;K. Murano;N. Kohno;Y. Sakamoto;Y. Kajii
中科院分区：
文献类型：
--
作者：
Jun Zhou;K. Murano;N. Kohno;Y. Sakamoto;Y. Kajii
HO 2自由基在对流层化学中起着重要的作用。大气气溶胶对HO 2的吸收系数（γ）还没有得到很好的量化，这是导致现场测量结果与复杂模式预测结果之间存在较大差异的原因。这项研究提出了2018年夏天在日本京都首次在线测量由环境气相（k g '）和气溶胶相（k a'）引起的总HO 2反应性，使用组合激光闪光光解和激光诱导荧光（LFP-LIF）技术与多功能气溶胶浓度富集系统（VACES）相结合，富集环境气溶胶。结果表明，k g '的范围为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（1σ），这可以主要由HO 2与NO 2的反应来解释。使用VACES和自动切换气溶胶过滤器时，ka '的范围为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。当将ka '转换为环境条件（除以富集因子）时，该结果比在298 K环境浓度水平（~ 5 ppt）下由其自身反应引起的HO 2反应性高~ 10倍。相关γ的范围为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0.2）相当;然而，在测量时间内，其存在±0.20（1σ）的较大变化。这表明，当使用恒定的γ值时，HO 2浓度的估计可能存在很大的偏差。此外，我们建议在模拟研究中应根据环境条件采用不同的γ值;由于可能的气溶胶相态变化，本文获得的γ值可作为城市地区夏季的上限值。环境空气后向轨迹分析表明，NO2的主要排放源来自日本本土。然而，没有显着的差异，关于HO 2吸收系数观察时，空气质量来自大陆或沿海方向。该研究提供了相当可靠的γ，这可以提高对流层化学非均匀过程的模拟精度。然而，结合在线和离线方法似乎更适合于解决γ的变化和模型差异，在进一步的研究。
HO 2 radicals play important roles in tropospheric chemistry. The large discrepancies among field measurements and sophisticated model predictions for the overall HO 2 concentrations can be attributed to the HO 2 uptake coefficients onto ambient aerosols (γ) have not yet been properly quantified. This study presents the first online measurement of the total HO 2 reactivity caused by the ambient gas phase (k g') and aerosol phase (k a') in the summer of 2018 in Kyoto, Japan, using a combined laser-flash photolysis and laser-induced fluorescence (LFP–LIF) technique coupled with a versatile aerosol concentration enrichment system (VACES) that enriches ambient aerosols. The results denote that k g'ranged from 0.1 s− 1 (25 th percentile) to 0.32 s− 1 (75 th percentile) with an average value of 0.22±0.16 s− 1 (1σ), which can be primarily explained by the reaction of HO 2 with NO 2. With the application of VACES and the auto-switching aerosol filter, k a'ranged from 0.004 s− 1 (25 th percentile) to 0.028 s− 1 (75 th percentile) with an average value of 0.017±0.015 s− 1. When converted k a'to ambient conditions (by dividing with the enrichment factor), this result was~ 10 times higher than the HO 2 reactivity caused by its self-reaction under ambient concentration levels (~ 5 ppt) at 298 K. The related γ ranged from 0.08 (25 th percentile) to 0.36 (75 th percentile), with an average value of 0.24, which is comparable with the values used in previous modeling studies (~ 0.2); however, it presents a large variation of±0.20 (1σ) within the measurement time. This indicates that a large bias may exist with respect to the estimation of HO 2 concentrations when using a constant γ value. Further, we suggest that different γ values should be applied in modeling studies depending on the environment conditions; the γ value obtained here can be used as an upper limit value for urban areas in the summer due to possible aerosol phase changes. The analysis of ambient air backward trajectories indicates that the predominant NO 2 emission sources originated from the mainland of Japan. However, no significant differences regarding HO 2 uptake coefficients were observed when air masses came through the mainland or from the coastal direction. This study provides considerably reliable γ, which could increase the modeling accuracy of heterogeneous processes in tropospheric chemistry. However, combining online and offline methods appears to be more suitable for addressing the variation in γ and model discrepancies in further studies.