Investigation of Organic Nitrogen in Atmospheric Aerosols

有机氮（ON）在大气中无处不在。大气颗粒通常具有高浓度的氮，是环境中固定氮的重要来源（通过沉积过程），这可能对陆地和水生生态系统产生不利影响。近年来，人们对大气中含氧有机物的来源、形成和组成进行了广泛的研究，但氮化土却没有受到同样的重视。对大气相关过程（如光化学转化）的研究已经对单个氮化合物进行了，但这些研究基本上是有限的，因为大气颗粒中的大部分氮没有被表征。颗粒内ON的组成可能会影响其性质（如吸湿性、毒性和生物利用度），这些性质也会随着颗粒在远距离运输过程中的老化而改变，并可能最终导致腐殖质样物质的形成。研究表明，当大气气溶胶中大量氮的水萃取物暴露于模拟的阳光和臭氧中时，很大一部分氮转化为铵、硝酸盐和氮氧化物。大气颗粒与人类死亡率的增加有关，并且若干氮类物质与气溶胶的毒性有关（例如，氮化多环芳烃、喹啉、亚硝基胺）。该项目的目的是建立一种新型的，高分辨率的ON分析仪，能够测量大气气溶胶的半挥发性ON成分，目前对其知之甚少。它基于高分辨率色谱技术（综合二维气相色谱- GCXGC），非常适合分离高度复杂的混合物。这将与高选择性氮化学发光检测器相结合，该检测器仅对含氮的有机化合物提供响应。这消除了气溶胶中发现的复杂有机背景的干扰。将气溶胶样品放在过滤器上，并使用气溶胶热解吸注射器提取ON内容。这种新型仪器将用于研究不同环境下气溶胶中ON物种的组成，从受污染的城市中心路边（约克）到清洁的沿海农村（韦伯恩），反映出光化学年龄的增加。由于真实大气的复杂性，将排放到大气中的初始物质与其气溶胶中的反应产物联系起来是很困难的。我们将使用ON分析仪来研究烟雾室模拟中形成的二次有机气溶胶中ON的成分，从而在前体和产品之间建立直接联系。该项目的成果将增加我们对大气中有机氮物种的组成、形成和转化的理解，为包括空气质量、气候变化和生态学在内的一系列学科提供有价值的信息。

Organic nitrogen (ON) is ubiquitous in the atmosphere. Atmospheric particles typically have high concentrations of nitrogen and are a significant source of fixed nitrogen to the environment (though deposition processes), which may have an adverse impact on terrestrial and aquatic ecosystem. While the sources, formation and composition of oxygenated organics in the atmosphere have been extensively studied in recent years, ON has not received the same attention. Studies of atmospherically relevant processes (such as photo-chemical transformations) have been carried out on individual ON compounds but these studies are fundamentally limited since the bulk of ON in atmospheric particles is not characterized. The composition of ON within a particle may have an effect on its properties (such as hygroscopicity, toxicity and bio-availability) which will also change as the particle ages during long-range transport and may ultimately lead to the formation of humic-like substances. Studies have shown that when aqueous extracts of bulk ON from atmospheric aerosols were exposed to simulated sunlight and ozone, a significant portion of the ON was transformed into ammonium, nitrate and oxides of nitrogen. Atmospheric particles have been linked to increased mortality in the human population and a number of ON species are implicated in the toxicity of aerosols (e.g. nitrogentated polycyclic aromatic hydrocarbons, quinolines, nitroso-amines). The aim of this project is to build a novel, high resolution ON-Analyser capable of measuring the semi-volatile ON composition of atmospheric aerosols, for which there is currently very little known. It is based on a high resolution chromatographic technique (comprehensive two-dimensional gas chromatography - GCXGC) which is ideally suited to separating highly complex mixtures. This will be coupled to a highly selective nitrogen chemiluminescence detector, which provides a response for organic compounds containing nitrogen only. This removes interferences from the complex organic background found in aerosols. Aerosols will be samples onto filters and the ON content extracted using an Aerosol Thermal Desorption Injector. This novel instrument will be used to investigate the composition of ON species in aerosol in different environments, reflecting increasing photo-chemical age, from a polluted city centre roadside location (York) to a clean coastal rural site (Weybourne). Due to the complexity of the real atmosphere, linking the initial species emitted to the atmosphere to their reaction products in aerosol can be difficult. We will use the ON-Analyser to investigate the composition of ON in secondary organic aerosol formed in smog chamber simulations, allowing a direct link between pre-cursors and products. The outcomes of this project will increase our understanding of the composition, formation and transformation of organic nitrogen species in the atmosphere, providing valuable information across a range of disciplines including air quality, climate change and ecology.