A comparison of measured HONO uptake and release with calculated source strengths in a heterogeneous forest environment
A comparison of measured HONO uptake and release with calculated source strengths in a heterogeneous forest environment
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DOI：
10.5194/acp-15-9237-2015
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发表时间：
2015-08
影响因子：
6.3
通讯作者：
M. Sörgel;I. Trebs;Dianming Wu;A. Held
中科院分区：
文献类型：
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作者：
M. Sörgel;I. Trebs;Dianming Wu;A. Held
抽象的。垂直混合比剖面的亚硝酸（HONO）进行了测量，在一个农村森林环境中的清除和森林地面。对于森林地面，HONO被发现主要是存款，而清除，净沉积占主导地位，只有在夜间和净排放量在白天观察。对于选定的几天，HONO的净通量计算从测量的配置文件使用的空气动力学梯度法。排放通量在0.02至0.07 nmol m−2 s−1之间，因此处于先前观测的较低范围。将这些通量与假设的HONO源的强度进行比较。对两个地点不同土壤样品的实验室测量显示，土壤生物源HONO排放通量的上限为0.025 nmol m−2 s−1。在调查的天数内，光诱导NO2转化产生的HONO计算值低于0.03 nmol m−2 s−1，这与潜在的土壤通量相当。由于在低辐照度下的光饱和，该反应途径在很大程度上被发现与光强度无关，即它仅依赖于环境NO2。我们使用了三种不同的方法的基础上测得的叶片硝酸盐负荷计算HONO形成HNO3光解。虽然前两种方法的基础上的经验HONO形成率产生的值在相同的数量级的估计通量，第三种方法的基础上，现有的动力学数据的假设路径未能产生显着的量的HONO。吸附HNO3的截面的基础上报告的估计表明，吸附HNO3的寿命只有约15分钟，这意味着大量的再氧化。虽然HNO3的光解在表面显著增强，但光解产物NO2随后的光诱导转化并没有产生大量的HONO。因此，该反应可能通过替代机制发生。通过基于可用的动力学数据和简单的参数化明确计算HONO形成，我们表明：（a）对于低NOx，腐殖酸上NO2的光诱导转化在清晨已经光饱和，（B）吸附的HNO3光解形成HONO似乎是通过另一种机制进行的，以及（c）对土壤中HONO排放量的估计对质量转移非常敏感，酸性土壤不一定有利于HONO排放。
Abstract. Vertical mixing ratio profiles of nitrous acid (HONO) were measured in a clearing and on the forest floor in a rural forest environment. For the forest floor, HONO was found to predominantly deposit, whereas for the clearing, net deposition dominated only during nighttime and net emissions were observed during daytime. For selected days, net fluxes of HONO were calculated from the measured profiles using the aerodynamic gradient method. The emission fluxes were in the range of 0.02 to 0.07 nmol m−2 s−1 and thus were in the lower range of previous observations. These fluxes were compared to the strengths of postulated HONO sources. Laboratory measurements of different soil samples from both sites revealed an upper limit for soil biogenic HONO emission fluxes of 0.025 nmol m−2 s−1. HONO formation by light-induced NO2 conversion was calculated to be below 0.03 nmol m−2 s−1 for the investigated days, which is comparable to the potential soil fluxes. Due to light saturation at low irradiance, this reaction pathway was largely found to be independent of light intensity, i.e. it was only dependent on ambient NO2. We used three different approaches based on measured leaf nitrate loadings for calculating HONO formation from HNO3 photolysis. While the first two approaches based on empirical HONO formation rates yielded values in the same order of magnitude as the estimated fluxes, the third approach based on available kinetic data of the postulated pathway failed to produce noticeable amounts of HONO. Estimates based on reported cross sections of adsorbed HNO3 indicate that the lifetime of adsorbed HNO3 was only about 15 min, which would imply a substantial renoxification. Although the photolysis of HNO3 was significantly enhanced at the surface, the subsequent light-induced conversion of the photolysis product NO2 did not produce considerable amounts of HONO. Consequently, this reaction might occur via an alternative mechanism. By explicitly calculating HONO formation based on available kinetic data and simple parameterizations, we showed that (a) for low NOx the light-induced conversion of NO2 on humic acids is already light saturated by the early morning, (b) HONO formation from photolysis of adsorbed HNO3 appears to proceed via an alternative mechanism and (c) estimates of HONO emissions from soil are very sensitive to mass transfer and acidic soils do not necessarily favour HONO emissions.