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首页> 外文期刊>Atmospheric chemistry and physics >Measurements of ambient HONO concentrations and vertical HONO flux above a northern Michigan forest canopy
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Measurements of ambient HONO concentrations and vertical HONO flux above a northern Michigan forest canopy

机译：密歇根州北部森林冠层上方环境HONO浓度和垂直HONO通量的测量

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Systems have been developed and deployed at a North Michigan forested site to measure ambient HONO and vertical HONO flux. The modified HONO measurement technique is based on aqueous scrubbing of HONO using a coil sampler, followed by azo dye derivatization and detection using a long-path absorption photometer (LPAP). A Na_2CO_3-coated denuder is used to generate "zero HONO" air for background correction. The lower detection limit of the method, defined by 3 times of the standard deviation of the signal, is 1 pptv for 1-min averages, with an overall uncertainty of ±(1 + 0.05 [HONO]) pptv. The HONO flux measurement technique has been developed based on the relaxed eddy accumulation approach, deploying a 3-D sonic anemometer and two HONO measurement systems. The overall uncertainty is estimated to be within ±(8 × 10~(-8) + 0.15 HONO) mol m~(-2) h~(-1), with a 20-min averaged data point per 30 min. Ambient HONO and vertical HONO flux were measured simultaneously at the PROPHET site from 17 July to 7 August 2008. The forest canopy was found to be a net HONO source, with a mean upward flux of 0.37 × 10~(-6) moles m~(-2) h~(-1). The HONO flux reached a maximal mean of ～0.7 × 10~(-6) moles m~(-2) h~(-1) around solar noon, contributing a major fraction to the HONO source strength required to sustain the observed ambient concentration of ～70 pptv. There were no significant correlations between [NO_x] and daytime HONO flux and between JNO_2 × [NO_2] and HONO flux, suggesting that NO_x was not an important precursor responsible for HONO daytime production on the forest canopy surface in this low-NO_x rural environment. Evidence supports the hypothesis that photolysis of HNO_3 deposited on the forest canopy surface is a major daytime HONO source.
机译：系统已开发并部署在密歇根州北部的森林地带，以测量环境HONO和垂直HONO通量。改进的HONO测量技术基于使用线圈采样器对HONO进行水洗，然后进行偶氮染料衍生化并使用长路径吸收光度计（LPAP）进行检测。涂有Na_2CO_3的剥蚀仪可用于产生“零HONO”空气以进行背景校正。该方法的检测下限由信号标准偏差的3倍定义，平均1分钟的平均值为1 pptv，总不确定度为±（1 + 0.05 [HONO]）pptv。 HONO通量测量技术是基于松弛涡流累积方法开发的，它部署了3-D声波风速计和两个HONO测量系统。总体不确定度估计在±（8×10〜（-8）+ 0.15 HONO）mol m〜（-2）h〜（-1）范围内，每30分钟平均20分钟数据点。从2008年7月17日至8月7日，在PROPHET现场同时测量了大气HONO和垂直HONO通量。森林冠层是HONO的净来源，平均向上通量为0.37×10〜（-6）摩尔m〜。 （-2）h〜（-1）。 HONO通量在太阳正午前后达到最大平均值〜0.7×10〜（-6）摩尔m〜（-2）h〜（-1），对维持观测到的环境浓度所需的HONO源强度贡献了很大比例约70 pptv。 [NO_x]与白天的HONO通量之间以及JNO_2×[NO_2]与HONO的通量之间没有显着相关性，这表明在这种低NO_x的农村环境中，NO_x并不是造成林冠层白天HONO产生的重要前体。有证据支持以下假设：白天沉积在森林冠层表面的HNO_3的光解是主要的HONO来源。

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