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造成的辐射强迫的变化（入射太阳辐射和地球输出热辐射之间热平衡的变化）。气溶胶通过散射和吸收太阳辐射直接影响全球气候，而它们通过改变云的性质（即反射率和寿命）间接影响气候。像黑碳或“煤烟”这样的吸光粒子具有变暖效应，并增加了大气中保留的能量。最近的估计表明，烟灰造成的大气强迫是全球变暖的第二大因素，仅次于二氧化碳，甚至超过了甲烷。重要的是，烟尘的辐射强迫估算的相对不确定性远远高于二氧化碳或甲烷。重要的是要了解烟尘在气候变化中的作用，这样才能减少强迫估算中的不确定性。这些信息对政府制定可能对经济发展产生重大影响的适当气候政策至关重要。烟尘强迫估算的不确定性很大一部分是由于大气中烟尘颗粒的演变。据观察，在大气中几个小时后，气相物质可以凝结在烟灰颗粒上，造成内部混合物（即由烟灰和冷凝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采取两种物理形式：i)凝聚的物质均匀分布，在烟灰颗粒上形成一层“涂层”，或ii)烟灰颗粒位于液体物质液滴的边缘，有时被称为“伴生”颗粒。如果材料是对煤烟进行涂层，那么由于涂层的表面张力，凝结的材料可能会导致煤烟的分形结构崩溃。这可能会对粒子吸收太阳辐射的能力产生深远的影响，因为有两种影响：1)粒子的塌陷将导致其横截面的减少，粒子的吸收量将减少；2)粒子上的光学透明涂层将导致吸收量的增加，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，这两种效应可能在总粒子吸收方面相互竞争。然而，如果煤烟颗粒位于冷凝材料的边缘（伴生颗粒），那么与涂覆的煤烟颗粒相比，吸收将没有那么有效。此外，尚不清楚这种内部混合是否会导致煤烟颗粒的坍塌。申请人研究计划的目标是了解影响烟灰吸收的机制，并调和实验室和实地研究之间的明显差异。这将通过在实验室中使用烟灰老化室和通过有机前体的光氧化生产可冷凝材料来尝试复制大气涂层过程，并通过参加实地研究来比较实验室和实地结果来实现。此外，为了提高实验的准确性，还将进一步开发一种新的仪器（气动气溶胶分级器）用于这些实验。

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.