Measurements of hydroxyl and hydroperoxy radicals during CalNex-LA: Model comparisons and radical budgets
Measurements of hydroxyl and hydroperoxy radicals during CalNex-LA: Model comparisons and radical budgets
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DOI：
10.1002/2015jd024358
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发表时间：
2016-04-27
影响因子：
4.4
通讯作者：
Stevens, P. S.
中科院分区：
文献类型：
--
作者：
Griffith, S. M.;Hansen, R. F.;Stevens, P. S.
在 CalNex-LA 2010 活动期间，使用气体膨胀技术的激光诱导荧光-荧光测定法在帕萨迪纳地面进行了羟基 (OH) 和氢过氧 (HO2*) 自由基浓度的测量。测得的 OH 和 HO2* 浓度表现出明显的周末效应，周末观察到的自由基浓度较高，对应的氮氧化物 (NOx) 水平较低。将自由基测量结果与使用受 NOx 和其他测量的痕量气体约束的区域大气化学机制 2 的零维模型的结果进行比较。化学模型以大约 1.4 +/- 0.3 (1 sigma) 的系数高估了周末测量的 OH 浓度，但工作日的一致性更好（比率为 1.0 +/- 0.2）。模型预测的周末 HO2* 浓度低预测了 1.3 +/- 0.2 倍，而测量的工作日浓度低预测了 3.0 +/- 0.5 倍。然而，增加建模的 OH 反应性以匹配测量的总 OH 反应性可改善 OH 和 HO2* 在所有日子中的总体一致性。自由基预算分析表明，羰基和甲醛的光解合计约占自由基引发的40%，在测量高度，亚硝酸的光解占30%，臭氧光解的贡献不到20%。对臭氧产生敏感性的分析表明，在一周内，活动期间全天的臭氧产生受到挥发性有机化合物的限制，但周末下午的氮氧化物产生受到限制。
Measurements of hydroxyl (OH) and hydroperoxy (HO2*) radical concentrations were made at the Pasadena ground site during the CalNex-LA 2010 campaign using the laser-induced fluorescence-fluorescence assay by gas expansion technique. The measured concentrations of OH and HO2* exhibited a distinct weekend effect, with higher radical concentrations observed on the weekends corresponding to lower levels of nitrogen oxides (NOx). The radical measurements were compared to results from a zero-dimensional model using the Regional Atmospheric Chemical Mechanism-2 constrained by NOx and othermeasured trace gases. The chemical model overpredicted measured OH concentrations during the weekends by a factor of approximately 1.4 +/- 0.3 (1 sigma), but the agreement was better during the weekdays (ratio of 1.0 +/- 0.2). Model predicted HO2* concentrations underpredicted by a factor of 1.3 +/- 0.2 on the weekends, while measured weekday concentrations were underpredicted by a factor of 3.0 +/- 0.5. However, increasing the modeled OH reactivity to match the measured total OH reactivity improved the overall agreement for both OH and HO2* on all days. A radical budget analysis suggests that photolysis of carbonyls and formaldehyde together accounted for approximately 40% of radical initiation with photolysis of nitrous acid accounting for 30% at the measurement height and ozone photolysis contributing less than 20%. An analysis of the ozone production sensitivity reveals that during the week, ozone production was limited by volatile organic compounds throughout the day during the campaign but NOx limited during the afternoon on the weekends.