Singh H B, Salas L J, Viezee W
Nature. 1986;321(6070):588-91. doi: 10.1038/321588a0.
Nitrogen oxides (NOx) have a central role in the chemistry of the atmosphere, especially in key processes relating to ozone, hydroxyl-radical (OH) and acid formation. High reactivity of NOx (lifetime of 0.5-2 days) precludes hemispheric-scale transport and it has been proposed that non-methane hydrocarbons present in the troposphere can transform NOx into its organic forms principally as peroxyacetyl nitrate (PAN). PAN is highly stable in the colder regions of the middle and upper troposphere and can provide a mechanism for NOx storage and transport. Once transported, PAN and its homologues can easily release free NOx in warmer atmospheric conditions. PAN is probably ubiquitous and its concentrations could exceed those of NOx in clean tropospheric conditions. Here we present the first view of the global distribution of PAN based on extensive shipboard and aircraft measurements. PAN is more abundant in the Northern than in the Southern Hemisphere and in the continental than in the marine troposphere. In contrast to its behaviour in polluted atmospheres, PAN mixing ratios in winter greatly exceed those in summer. These measurements provide a basis for assessing the significance of PAN as a reservoir of NOx and for extending and validating reactive nitrogen chemistry theory in the troposphere.
氮氧化物（NOx）在大气化学中起着核心作用，尤其是在与臭氧、羟基自由基（OH）和酸形成相关的关键过程中。NOx的高反应活性（寿命为0.5 - 2天）排除了半球尺度的传输，并且有人提出对流层中存在的非甲烷碳氢化合物可以将NOx主要转化为其有机形式，即过氧乙酰硝酸酯（PAN）。PAN在对流层中层和上层较冷的区域高度稳定，并且可以提供一种NOx储存和传输的机制。一旦传输，PAN及其同系物在温暖的大气条件下可以很容易地释放出游离的NOx。PAN可能无处不在，并且在清洁的对流层条件下其浓度可能超过NOx的浓度。在这里，我们基于广泛的船上和飞机测量结果首次展示了PAN的全球分布情况。PAN在北半球比在南半球更丰富，在大陆对流层比在海洋对流层更丰富。与它在污染大气中的行为相反，冬季的PAN混合比大大超过夏季。这些测量结果为评估PAN作为NOx储存库的重要性以及扩展和验证对流层中活性氮化学理论提供了基础。
