Determining the impact of soot on climate

气候变化对加拿大人来说是一个重要的问题，因为它有可能极大地影响他们的生活质量。人们普遍认为，全球变暖主要可归因于温室气体和气溶胶引起的辐射强迫(传入太阳辐射和地球传出热辐射之间的热平衡发生变化)的变化。气溶胶通过散射和吸收太阳辐射直接影响全球气候，而通过改变云的性质(即其反射率和寿命)间接影响气候。像黑碳或煤烟这样的吸光颗粒具有变暖效应，并增加了大气中保留的能量。最近的估计表明，煤烟造成的大气强迫是全球变暖的第二大组成部分，仅次于二氧化碳--甚至比甲烷更大。重要的是，烟尘辐射强迫估计的相对不确定性比二氧化碳或甲烷高得多。重要的是要了解烟尘在气候变化中的作用，以便减少强迫估计中的不确定性。这些信息对于各国政府在制定可能对经济发展产生重大影响的适当气候政策时至关重要。烟尘强迫估计中的不确定性很大一部分是由于大气中烟尘颗粒的演变造成的。已经观察到，在大气中停留几个小时后，气相物质可以凝聚在煤烟颗粒上，形成内部混合物(即由煤烟和凝结物质的混合物组成的颗粒)。已经观察到，这种内部混合物可以有两种物理形式：i)凝聚的物质均匀分布，在烟尘颗粒上形成一层‘涂层’，或者ii)烟尘颗粒位于液体材料液滴的边缘，这有时被称为‘缔合’颗粒。如果材料覆盖了煤烟，那么由于涂层的表面张力，凝聚的材料可能会导致煤烟的分形结构崩溃。这会对粒子吸收太阳辐射的能力产生深远的影响，原因有两个：i)粒子的坍塌将导致其横截面减小，粒子的吸收率将降低；但ii)粒子上的光学透明涂层将导致吸收的增加，因为额外的光被折射到粒子的吸收核心。因此，随着粒子的演化，这两种效应可能会在粒子的总吸收方面相互竞争。然而，如果烟尘颗粒位于冷凝材料(相关颗粒)的边缘，则与涂层烟尘颗粒相比，吸收效率不会那么高。此外，目前还不清楚这种类型的内部混合是否会导致烟尘颗粒的崩溃。申请人的研究计划的目标是了解影响烟尘吸收的机制，并调和实验室和实地研究之间的明显差异。为此，将尝试在实验室复制大气涂层过程，方法是使用煤烟老化试验室，通过有机前体的光氧化产生可凝结材料，并参与实地研究，以比较实验室和现场结果。此外，还将进一步开发和使用一种新的仪器(气动气溶胶分类器)，以提高这些实验的准确性。

Climate change is an important issue for Canadians as it has the potential to drastically affect their quality of life. It is generally accepted that global warming can mostly be attributed to changes in the radiative forcing (changes to the heat balance between incoming solar radiation and Earth’s outgoing thermal radiation) due to greenhouse gases and aerosols. Aerosols directly affect global climate by scattering and absorbing solar radiation, while they indirectly affect climate by changing the properties of clouds (i.e. their reflectivity and lifetime). Light-absorbing particles like black carbon or ‘soot’ have a warming effect and increase the amount of energy retained in the atmosphere. Recent estimates suggest that the atmospheric forcing due to soot is the second most important component of global warming after CO2 - even greater than that of methane. Importantly, the relative uncertainty in the radiative forcing estimate for soot is much higher than that of CO2 or methane. It is important that the role of soot in climate change is understood so that the uncertainties in the forcing estimates can be reduced. This information is essential for governments as they develop appropriate climate policies that may have a large impact on economic development. A large portion of the uncertainty in the soot forcing estimates is due to the evolution of soot particles in the atmosphere. It has been observed that after a few hours in the atmosphere, gas-phase material can condense on soot particles causing an internal mixture (i.e. a particle composed of a mixture of soot and condensed material). It has been observed that this internal mixture can take two physical forms: i) the condensed material is uniformly distributed, forming a ‘coating’ on the soot particle, or ii) the soot particle is located on the edge of a droplet of the liquid material, which is sometimes referred to as an ‘associated’ particle. If the material is coating the soot, then the condensed material may cause the collapse of the soot’s fractal structure due to the surface tension of the coating. This can have a profound effect on the particle’s ability to absorb solar radiation due to two effects: i) the collapse of the particle will result in a decrease in its cross-section and the particle absorption will decrease but ii) the optically-transparent coating on the particle will cause an increase in the absorption because additional light is refracted to the absorbing core of the particle. Thus, these two effects may compete against each other in terms of the total particle absorption as the particle evolves. However, if the soot particle is located at the edge of the condensed material (an associated particle), then the absorption would not be as efficient compared to a coated soot particle. Also, it is unclear if this type of internal mixing would result in a collapse of the soot particle. The goal of the applicant’s research program is to understand the mechanisms effecting soot absorption and to reconcile the apparent differences between laboratory and field studies. This will be done by trying to replicate atmospheric coating processes in the lab by using a soot ageing chamber and producing condensable material through the photo-oxidation of organic precursors, and also by participating in field studies to compare laboratory and field results. Also, a novel instrument (the Aerodynamic Aerosol Classifier) will be further developed and used in these experiments to improve the accuracy of these experiments.