The effects of organic material on warm and cold cloud formation: from the laboratory to regional and global impacts

云对天气和气候有着深远的影响。人们对水汽凝结在粒子上形成云滴的研究已有几十年了。对于惰性非挥发性颗粒，这一过程及其影响相对较好地理解。然而，在某些大气条件下，相当大比例的细颗粒材料会蒸发。我们最近的《自然地球科学快报》表明，这一部分对云滴形成的作用足够大，具有全球意义，通常在云块模型中不被考虑，在大尺度模型中完全没有被处理。这是由于在液滴活化期间部分挥发性材料沿着水蒸气的共冷凝。间接证据支持这种效应，但无法直接测量。在冷云和混合相云中，无定形的“玻璃状”粒子作为冰晶种子的潜在作用也引起了相当大的兴趣。《自然》出版物和项目合作伙伴Virtanen随后的工作确定，生物和人为前体产生的二次有机气溶胶可能以无定形状态存在，取决于相对湿度和温度。玻璃状粒子作为冰核的影响可能非常重要，但目前的直接证据是混乱的，现实的支持测量稀疏。建议通过模拟室测量来量化有机成分对暖云和冷云形成的影响，使用测量来评估最近开发的模型处理，参数化模型并使用参数化来量化对云物理和辐射特性的区域影响。我们已经进行了概念实验室工作的证明，表明我们能够研究这两个过程。我们已经将曼彻斯特气溶胶室（MAC）与曼彻斯特冰云室（MICC）相结合，在那里我们可以从自然植物排放和人为排放的大气化学中制造颗粒，在那里我们可以在合理的大气条件下形成云。我们进一步测量了粒子作为液滴云凝结核（CCN）种子的有效性的变化，沿着挥发性、组成和相行为。我们建议在此概念验证的基础上，系统地量化一系列具有代表性的大气系统的影响，并量化其影响。拟议的工作将分4部分进行。前两个是基于实验室的数值模型解释，后两个仅使用数值模拟：i）在现场和实验室使用的两种仪器中量化有机蒸汽的影响，一种测量低于100% RH的颗粒吸水率，另一种测量形成刚好高于100% RH的云滴的能力。颗粒将暴露于受控浓度的半挥发性蒸汽中，并引入仪器中。第二台仪器的详细流动建模将与作者作为项目合作伙伴合作进行。ii）涉及MAC和MICC室的耦合，如概念验证中所述，但涵盖了在各种自然、人造和混合系统中形成的颗粒。我们将测量所有相关参数，以量化在合理范围的大气条件下暖云和冷云的形成。iii）通过实验，有机化合物对暖云和冷云的影响将包括在一个数值模式中，这将用于发展大尺度模式中使用的基于物理的参数化。由我们的项目合作伙伴Nenes提供信息的大尺度模型，用于评估对云特性和辐射的影响，从而量化有机化合物与代表性条件下天气和气候之间的耦合。

Clouds have a profound influence on weather and climate. Formation of cloud droplets by condensation of water vapour on particles has been studied for many decades. For inert involatile particles, this process and its impacts are relatively well understood. However, a substantial proportion of fine particle material can evaporate under some atmospheric conditions. Our recent Nature Geoscience Letter suggests that the role of this fraction on cloud droplet formation is large enough to be globally significant, is not normally considered in cloud parcel models and is completely untreated in large-scale models. This results from the co-condensation of partly volatile material along with the water vapour during droplet activation. Indirect evidence supports this effect, but direct measurements are unavailable. There has also been considerable interest in the potential role of amorphous "glassy" particles as seeds for ice crystals in cold and mixed-phase clouds. The Nature publication and subsequent work by project partner Virtanen identified that secondary organic aerosol from both biogenic and anthropogenic precursors could exist in an amorphous state dependent on relative humidity and temperature. The impact of glassy particles as ice nuclei is potentially very significant, but direct evidence is currently confused and realistic supporting measurements are sparse. It is proposed to quantify the impacts of organic components on warm and cold cloud formation by both processes through simulation chamber measurements, to use the measurements to evaluate a recently developed model treatment, to parameterise the model and use the parameterisation to quantify the regional impacts on cloud physical and radiative properties.We have conducted proof of concept laboratory work showing that we are able to study both processes. We have coupled the Manchester Aerosol Chamber (MAC), where we can make particles from the atmospheric chemistry of both natural plant emissions and man-made emissions, to the Manchester Ice Cloud Chamber (MICC), where we can form a cloud under reasonable atmospheric conditions. We have further measured the changes in the effectiveness of the particles to act as seeds for liquid cloud droplets, cloud condensation nuclei (CCN), along with the volatility, composition and phase behaviour. We propose to build on this proof-of-concept to systematically quantify the effects in a range of atmospherically-representative systems and quantify their impacts.The proposed work will be carried out in 4 parts. The first two are laboratory-based with numerical model interpretation and the second two solely use numerical modelling: i) quantification of the effect of organic vapours in two instruments that are used in the field and laboratory, one measuring particle water uptake below 100% RH and the other the ability to form a cloud droplet just above 100% RH. Particles will be exposed to controlled concentration of semi-volatile vapour and introduced into the instruments. Detailed flow modelling of the second instrument will be carried out, in collaboration with the author as project partner.ii) involves the coupling of the MAC and MICC chambers as in the proof-of-concept, but covering particles formed in a wide range of natural, manmade and mixed systems. We will measure all relevant parameters to quantify the formation of warm and cold clouds under a reasonable range of atmospheric conditions.iii) informed by the experiments, the effects of organic compounds on warm and cold clouds will be included in a numerical model and this will be used to develop physically-based parameterisations for use in large-scale models.iv) the parameterised process description will be used in large-scale models informed by our project partner Nenes to estimate the impact on cloud properties and radiation, hence quantifying the couplings between organic compounds and weather and climate under representative conditions.