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Airborne measurement of OH reactivity during INTEX-B

机译：空中测量INTEX-B期间的OH反应性

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The measurement of OH reactivity, the inverse of the OH lifetime, provides a powerful tool to investigate atmospheric photochemistry. A new airborne OH reactivity instrument was designed and deployed for the first time on the NASA DC-8 aircraft during the second phase of Intercontinental Chemical Transport Experiment-B (INTEX-B) campaign, which was focused on the Asian pollution out-flow over Pacific Ocean and was based in Hawaii and Alaska. The OH reactivity was measured by adding OH, generated by photolyzing water vapor with 185 nm UV light in a moveable wand, to the flow of ambient air in a flow tube and measuring the OH signal with laser induced fluorescence. As the wand was pulled back away from the OH detector, the OH signal decay was recorded; the slope of-△ln(signal)/△ time was the OH reactivity. The overall absolute uncertainty at the 2σ confidence levels is about 1 s-1 at low altitudes (for decay about 6 s~(-1)), and 0.7 s~(-1) at high altitudes (for decay about 2 ~(s-1)). From the median vertical profile obtained in the second phase of INTEX-B, the measured OH reactivity (4.0±1.0 s-1) is higher than the OH reactiv-ity calculated from assuming that OH was in steady state (3.3±0.8 s-1), and even higher than the OH reactivity that was calculated from the total measurements of all OH reactants (1.6±0.4 s~(-1)). Model calculations show that the missing OH reactivity is consistent with the over-predicted OH and under-predicted HCHO in the boundary layer and lower troposphere. The over-predicted OH and under-predicted HCHO suggest that the missing OH sinks are most likely related to some highly reactive VOCs that have HCHO as an oxidation product.
机译：OH反应性的测量是OH寿命的倒数，它是研究大气光化学的有力工具。在洲际化学品运输实验B（INTEX-B）活动的第二阶段中，美国国家航空航天局（NASA）DC-8飞机首次设计并部署了一种新的机载OH反应性仪器，该仪器的重点是亚洲污染排放太平洋，总部位于夏威夷和阿拉斯加。 OH反应性的测量方法是：将可移动棒中的185 nm紫外线光分解水蒸气产生的OH加入到流管中的环境空气中，并用激光诱导的荧光测量OH信号。当棒从OH检测器中拉回时，会记录OH信号的衰减。 -△ln（信号）/△时间的斜率是OH反应性。在2σ置信水平下的总绝对不确定度在低海拔时约为1 s-1（对于衰减约6 s〜（-1）），在高海拔时约0.7 s〜（-1）（对于衰减约2 s（（s）） -1））。根据在INTEX-B第二阶段获得的中值垂直分布，测得的OH反应性（4.0±1.0 s-1）高于假设OH处于稳定状态（3.3±0.8 s- 1），甚至高于从所有OH反应物的总测量值计算得出的OH反应性（1.6±0.4 s〜（-1））。模型计算表明，在边界层和对流层中，缺少的OH反应性与高估的OH和低估的HCHO一致。 OH的过度预测和HCHO的预测不足表明，缺少的OH汇很可能与某些具有HCHO氧化产物的高反应性VOC有关。

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