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

云对天气和气候有深远的影响。水蒸气在粒子上凝结形成云滴的现象已经研究了几十年。对于惰性的渐开式粒子，这一过程及其影响已相对较好地了解。然而，在某些大气条件下，相当大比例的细颗粒物质会蒸发。我们最近的《自然地球科学快报》表明，这部分在云滴形成中的作用足够大，具有全球意义，在云包模型中通常不被考虑，在大规模模型中完全未被处理。这是由于在液滴活化过程中，部分挥发性物质与水蒸气共冷凝造成的。间接证据支持这种效应，但没有直接测量。在冷云和混合相云中，无定形“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。发表在《自然》杂志上的文章以及项目伙伴Virtanen随后的工作发现，生物和人为前体产生的二次有机气溶胶可能以无定形的状态存在，这取决于相对湿度和温度。玻璃粒子作为冰核的影响可能是非常重要的，但目前直接的证据是混乱的，现实的支持测量是稀疏的。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，使用这些测量来评估最近开发的模型处理，对模型进行参数化，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验证的实验室工作，表明我们能够研究这两个过程。我们将曼彻斯特气溶胶室（MAC）与曼彻斯特冰云室（MICC）结合起来，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。我们进一步测量了这些粒子作为液态云滴、云凝结核（CCN）种子的有效性变化，以及它们的挥发性、组成和相行为。我们建议在这一概念验证的基础上，系统地量化一系列具有大气代表性的系统的影响，并量化它们的影响。建议的工作将分为四个部分进行。前两项是基于实验室的数值模型解释，后两项仅使用数值模型：i)在现场和实验室使用的两种仪器中对有机蒸汽的影响进行量化，一种测量低于100% RH的颗粒水分吸收率，另一种测量略高于100% RH的云滴形成能力。颗粒将暴露在控制浓度的半挥发性蒸汽中，并引入仪器。将与作为项目伙伴的作者合作，对第二个仪器进行详细的流动建模。ii)与概念验证中一样，涉及MAC和MICC室的耦合，但涵盖在广泛的自然、人造和混合系统中形成的颗粒。我们将测量所有相关参数，以量化在合理范围内的大气条件下冷暖云的形成。Iii)根据实验结果，有机化合物对冷暖云的影响将包含在数值模型中，这将用于开发基于物理的参数化，用于大规模模型。iv)参数化过程描述将用于由我们的项目合作伙伴Nenes提供信息的大型模型中，以估计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.