A top-down approach for apportioning black carbon aerosols to emission sources in regions with multiple competing contributors

黑碳（BC）是由含碳燃料不完全燃烧产生的，是导致气候变化和降低区域空气质量的两种主要空气污染物之一。BC的升温潜能值仅次于CO2，由于其在大气中的停留时间短，对混合、沉积和各种排放源的贡献知之甚少，因此对气候模拟的不确定性最大。来自化石燃料和生物质燃烧的BC具有不同的光吸收特性和老化过程，因此具有不同的变暖潜力。因此，改善源特性对于确定目标、制定减缓战略和提高气候模式中人为气溶胶输入的准确性至关重要。然而，传统的自下而上的排放清单（EI）方法存在固有的局限性，如排放因子不准确、源/汇覆盖不完整等，造成很大的不确定性。 这项研究旨在开发一种创新的、基于双同位素（14 C-13 C）的自上而下的方法，将BC分配给主要来源，因为这种方法消除了测量排放因子或全面调查来源的需要。近期目标是通过改进实验程序来建立方法，以通过在阿尔伯塔的试点研究来最小化或量化干扰水平，其中1/3的加拿大BC是从多个竞争源排放的。结合遥感数据和气团轨迹分析的分子示踪剂研究将有助于在野火季节验证这种方法的结果。通过机理研究，探讨了两种污染物的去除机理，从而解释了自下而上和自上而下方法的差异。中长期目标是应用这一方法调查加拿大重要的BC排放区域，以构建包含源解析BC排放的多区域数据库，并在此基础上评估源区分BC对区域气候的影响。 这项研究的成果预计将带来直接的好处，BC社区，这种方法，具有更大的适应性，可以通过其他研究，在世界其他重要的排放区域采购BC。从中长期来看，本研究中收集的数据集将通过提供更准确的源参数化来更好地模拟加拿大气候系统。模拟结果将反过来影响监管部门，为自下而上的排放清单提供具体的限制，这将有助于政策制定者通过选择正确的目标部门来制定区域性的黑碳减排战略。

Black carbon (BC), generated from incomplete combustion of carbonaceous fuels, is one of the two major airborne pollutants that drive climate change and degrade regional air quality. With a warming potential second to CO2, BC contributes the most uncertainty to climate modeling due to its short retention time in the atmosphere and poorly understood mixing, deposition, and contribution from various emission sources. BC from fossil fuel and biomass burning possesses distinct light absorbing properties and aging processes, and hence differing warming potentials. Therefore, improved source characterization is crucial for determining targets, formulating mitigation strategies, and increasing the accuracy of input anthropogenic aerosols in climate models. However, conventional bottom-up emission inventory (EI) methods have intrinsic limitations such as inaccurate emission factors, incomplete coverage of sources/sinks that cause large uncertainties. This research aims to develop an innovative, dual-isotope (14C-13C) based top-down approach to apportion BC to major sources as this approach eliminates the need of measuring emission factors or comprehensive surveying of sources. The near objective is to establish the method by improving the experimental procedures to minimize or quantify the level of interferences through a pilot study in Alberta where 1/3 of Canada BC is emitted from multiple competing sources. Molecular tracer studies combined with remote sensing data and air mass trajectory analysis will serve to validate the results of this method during the wildfire season. A mechanistic study is designed to investigate the removal mechanism of the two types of BC, so as to explain the discrepancy between the bottom-up and top-down approaches. The mid- and long term objectives are to apply this approach for investigating important BC emission regions in Canada to construct a multi-region database containing source-resolved BC emissions, based on which the impact of source-differentiated BC on the regional climate will be assessed. The outcome of this research is anticipated to bring immediate benefit to the BC community in that this method, with increased adaptivity, can possibly be adopted by other researches for sourcing BC at other important emission regions in the world. In the mid-long run, the datasets to be collected in this research will enable a better simulation of the Canadian climate system by providing more accurate source parameterization. The simulation results will in turn impact the regulatory sector by providing specific constraints for bottom-up emission inventories, which will assist policymakers to develop regionally tailored mitigation strategies for black carbon by selecting the right sector to target.