Com-Part: Combustion Particles in the Atmosphere: Properties, Transformations, Fate & Impacts

燃烧颗粒对空气质量和气候有重大影响。除了直接排放的初级颗粒外，次级颗粒是通过废气中也存在的气相有机化合物的大气氧化而形成的。传统上，主要和次要颗粒是根据颗粒的总质量来量化的，然而，人们越来越认识到，人类健康和气候影响高度依赖于颗粒的确切大小和混合状态。发动机废气排放是城市环境中主要的颗粒来源，由于主要颗粒由纯有机和混合有机和单质碳颗粒的混合物组成，有机部分与气相接近平衡，这一事实使其复杂化。确切的混合气取决于发动机的转速、负荷和温度。废气排放的复杂性依赖于燃烧条件，严重影响了初级颗粒的组成和性质，并决定了次级颗粒产生的大小和方式。com - part将使用气溶胶仪器的新发展，全面表征柴油发动机在各种操作条件下排放的复杂废气，代表现实世界的使用情况。然后用气溶胶反应室进行稀释和光化学处理。将特别注意耐火炭黑与初级和次级有机物的混合状态，以及它们对颗粒质量的分数贡献。除了柴油废气，小型电器发动机（包括二冲程）的排放也将被调查，因为从二次有机气溶胶的角度来看，这些排放物目前还没有得到充分的表征。除了成分测量外，还将研究波长相关的光吸收、光消和云凝结核（CCN），因为这些参数是确定气溶胶对气候影响的关键参数。基于颗粒组成的知识和关于颗粒形态的各种假设，可以使用各种模型处理来预测光学性质。这些与发动机排放相关的模型的性能将被严格评估，并将推导出适合纳入辐射传输模型的参数化。同样，也将推导出粒子CCN行为的参数化（使用简化的单参数有效“kappa”方法或类似方法）。为了将测量结果置于环境环境中，在一系列操作条件下获得的轮廓将根据典型的城市驾驶条件进行缩放，并以标准的欧洲排放测试周期为基础。然后，这将用于生成典型的城市排放和相关的SOA形成概况，然后可以将其与环境测量值进行比较。这些环境测量将使用与实验室研究中使用的相同的仪器进行，也可以与ClearfLo和CalNex等密集测量活动的存档数据进行比较。将根据通过室内实验得出的“光化学年龄”，推导出初级粒子和形成的次级物质转化的时间尺度。这将通过直接测量已知对主要大气氧化剂OH自由基具有反应性的挥发性有机化合物的衰变率而得出。

Combustion particles have major impacts on air quality and climate. As well as primary particles emitted directly, secondary particles are formed through the atmospheric oxidation of vapour phase organic compounds that are also present in the exhaust. Traditionally, primary and secondary particles have been quantified in terms of the total mass of particulate, however the human health and climate impacts are increasingly recognised to be highly dependent on the exact size and mixing state of particles. Engine exhaust emissions, the dominant particle source in urban environments, are complicated by the fact that primary particles comprise a mixture of pure organic and mixed organic and elemental carbon particles, with the organic fraction near equilibrium with the vapour phase. The exact mixture is dependent on the engine speed, load and temperature. The complexity of the exhaust emission dependence on combustion conditions heavily influences the composition and properties of the primary particles and determines the magnitude and manner of secondary particle production.Com-Part will use new developments in aerosol instrumentation to comprehensively characterise the complex exhaust emitted from a diesel engine under various operating conditions, representative of real-world usage, and subsequently subjected to dilution and photochemical processing using an aerosol reaction chamber. Particular attention will be paid to the mixing state of the refractory black carbon with respect to the primary and secondary organic matter and the fractional contributions of these to the particle mass. In addition to the diesel exhaust, emissions from small appliance engines (including 2-stroke) will be investigated, as these are currently under-characterised from a secondary organic aerosols perspective.In addition to the composition measurements, the wavelength-dependent optical absorption, optical extinction and cloud condensation nuclei (CCN) will be studied, as these are the parameters key to determining the climate impacts of the aerosol. Various model treatments can be used to predict the optical properties based on knowledge of the particulate composition and various assumptions concerning particle morphology. The performance of these models relevant to engine emissions will be critically evaluated and parameterisations will be derived that are suitable for inclusion in radiative transfer models. Similarly, parameterisations of the CCN behaviour of the particles (using simplified single parameter effective "kappa" approaches or similar) will also be derived.To place the measurements in an ambient context, the profiles obtained over a range of operating conditions will be scaled according to typical urban driving conditions, using the standard EURO emissions testing cycles as a basis. This will then be used to generate a typical urban emission and associated SOA formation profile, which can be in turn compared with ambient measurements. These ambient measurements will be made using the same instrumentation as used in the laboratory studies and can also be compared to archived data from intensive measurement campaigns such as ClearfLo and CalNex. Timescales for transformation of the primary particles and of the secondary material that is formed will be derived, based on the "photochemical age" through the chamber experiments. This will be derived by direct measurement of the decay rate of volatile organic compounds of known reactivity towards the major atmospheric oxidant, the OH radical.