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HO_x observations over West Africa during AMMA: Impact of isoprene and NO_x

机译：在AMMA期间对西非的HO_x观测：异戊二烯和NO_x的影响

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摘要

Aircraft OH and HO_2 measurements made over West Africa during the AMMA field campaign in summer 2006 have been investigated using a box model constrained to observations of long-lived species and physical parameters. "Good" agreement was found for HO_2 (modelled to observed gradient of 1.23 ± 0.11). However, the model significantly overpredicts OH concentrations. The reasons for this are not clear, but may reflect instrumental instabilities affecting the OH measurements. Within the model, HOx concentrations in West Africa are controlled by relatively simple photochemistry, with production dominated by ozone photolysis and reaction of O(1D) with water vapour, and loss processes dominated by HO_2 + HO_2 and HO_2 + RO_2. Isoprene chemistry was found to influence forested regions. In contrast to several recent field studies in very low NOx and high isoprene environments, we do not observe any dependence of model success for HO_2 on isoprene and attribute this to efficient recycling of HOx through RO_2 + NO reactions under the moderate NOx concentrations (5-300 ppt NO in the boundary layer, median 76 ppt) encountered during AMMA. This suggests that some of the problems with understanding the impact of isoprene on atmospheric composition may be limited to the extreme low range of NOx concentrations.
机译：已使用限定于长寿命物种和物理参数观测的箱形模型调查了2006年夏季在AMMA野战期间在西非进行的飞机OH和HO_2测量。发现HO_2具有“良好”的一致性（建模为观察到的1.23±0.11的梯度）。但是，该模型大大高估了OH的浓度。其原因尚不清楚，但可能反映了影响OH测量值的仪器不稳定。在该模型中，西非的HOx浓度是通过相对简单的光化学控制的，其生产以臭氧光解和O（1D）与水蒸气的反应为主，而损失过程则以HO_2 + HO_2和HO_2 + RO_2为主。发现异戊二烯化学影响林区。与最近在非常低的NOx和高异戊二烯环境中进行的几项野外研究相比，我们没有观察到HO_2对异戊二烯的模型成功有任何依赖性，而是将其归因于中等NOx浓度下RO_2 + NO反应对HOx的有效再循环（5-边界层中出现300 ppt的NO，中间值为76 ppt）。这表明了解异戊二烯对大气成分影响的一些问题可能仅限于NOx浓度极低的范围。

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