In Situ monitoring of NO3 radicals in a atmospheric chamber by cavity ring down spectroscopy

大气室在阐明对流层的反应机制方面起着至关重要的作用。在NE/C513493/1资助下在化学学院建造的高度仪表化的大气化学反应堆(HIRAC)是一个2立方米的不锈钢小室，能够在各种条件下进行测量。独一无二的是，对于这样的腔室，它可以使用基于激光的技术来测量OH和HO2自由基浓度。Hirac背后的原则是测量尽可能多的反应物、中间体和产品，以便约束用于解释和理解结果的化学模型。所有的测量都会受到潜在的系统误差的影响，因此我们认为最初使用两种或两种以上的互补技术(例如FTIR和GC)进行测量很重要。对于激进物种来说尤其如此，它们的寿命很短，这使得测量变得特别繁重。我们已经证明了检测和监测OH和HO2的能力(Acpd 2007，7,10687)，现在寻求将我们的测量能力扩展到NO3自由基，这是一种重要的夜间氧化剂。提出了用腔衰荡光谱(CRDS)测量NO_3的方法。这是一种非常敏感的技术，与激光诱导荧光(LIF)不同，它可以产生绝对浓度。对于CRDS，我们的检测下限应该是~1PPTV，远远低于典型的夜间N3浓度。一旦建成，CRDS系统将与宽带腔增强吸收光谱仪(BB-CEAS)进行比较，方法是与Steve Ball博士和LIF合作(将我们目前的系统从OH检测中改装)。我们还将通过测定NO3与乙醛反应的速率系数来测试这项技术，这一反应具有很好的特征。最后，我们将把该技术应用于大气条件下NO_3与烯烃反应的速率系数和产物分布的测定。反应速度相对较快，确定速率系数需要知道NO3的绝对浓度(CRDS相对于BB-CEAS和LIF的优势)。产品将通过GC和FTIR进行检查；有关NO3的时间依赖性的知识将对限制用于提取定量分支比的化学模型至关重要。

Atmospheric chambers have a vital role to play in the elucidation of reaction mechanisms for the troposphere. The highly instrumented reactor for atmospheric chemistry (HIRAC) constructed in the School of Chemistry under grant NE/C513493/1 is a 2 m3 stainless steel chamber capable of making measurements over a wide range of conditions. Uniquely for such a chamber it can measure OH and HO2 radical concentrations using a laser based technique. The principal behind HIRAC is to measure as many reactants, intermediates and products as possible in order to constrain the chemical models used to interpret and understand the results. All measurements are subject to potential systematic errors and therefore we consider it important to initially measure using two or more complimentary techniques (e.g. FTIR and GC). This is especially true for radical species, where the short lifetimes make measurements particularly taxing. We have demonstrated an ability to detect and monitor OH and HO2 (ACPD 2007, 7, 10687) and now seek to extend our measurement capability to the NO3 radical, an important nighttime oxidant. It is proposed to measure NO3 using cavity ring down spectroscopy (CRDS). This is an extremely sensitive technique, that unlike laser induced fluorescence (LIF), yields absolute concentrations. With CRDS we should have a detection limit of ~1 pptv, well below typical nighttime NO3 concentrations. Once constructed the CRDS system will be compared with a broadband cavity enhanced absorption spectrometer (BB-CEAS) via a collaboration with Dr Steve Ball and LIF (adapting our current system from OH detection). We will also test the technique by determining rate coefficients for the reaction of NO3 with ethanal, a reaction that is well characterised. Finally, we will apply the technique to the determination of the rate coefficients and product distributions to the reaction of NO3 with alkenes under atmospheric conditions. The rates of reaction are relatively fast and determination of the rate coefficient requires knowledge of the absolute NO3 concentrations (an advantage of CRDS over BB-CEAS and LIF). Products will be examined by GC and FTIR; knowledge of the temporal dependence of NO3 will be vital in constraining the chemical model used to extract quantitative branching ratios.