College of Global Change and Earth System Science, Beijing Normal University, Beijing, 100875, China.
College of Global Change and Earth System Science, Beijing Normal University, Beijing, 100875, China.
Environ Pollut. 2020 Aug;263(Pt B):114507. doi: 10.1016/j.envpol.2020.114507. Epub 2020 Apr 5.
The accurate derivation of the proportion and absorption enhancement of black carbon (BC)-containing aerosols in the atmosphere is critical to assess their effect on air quality and climate. Here, using the field measured size-resolved volatility shrink factor, BC bulk mass concentration and the BC mass fraction in BC-containing particles in winter Beijing, we retrieved and quantified both the number and mass concentration of (1) non-BC, (2) internally mixed BC and (3) externally mixed BC of ambient fine aerosol particles. The reliability of the retrieval method has been evaluated by comparing with the simultaneously measured data. The number fraction of BC-containing particles accounts for 60-78% of ambient fine particles, with internally (both BC core and coating materials) and externally mixed BC of 51-64% and 9-23%, respectively. Only for nucleated particles on clean days, when nucleation is a major source of aerosol particles, did the non-BC component dominate (54%). A large amount of aerosols are BC-containing particles, with mass fraction of 32-52%, suggesting the dominant role of BC in elevating mass concentration of particulate matter (PM) in a polluted urban area. We also show that the BC particles are thickly coated with coating thickness (characterized by D/D, ratio of the BC diameter before and after heating at 300 °C) of 1.6-2.2, implying efficient aging of BC particles in polluted urban area. Our results imply a large proportion of BC-containing particles in the atmosphere, which could help towards understanding the role of BC on regional haze formation and climate forcing.
准确推导大气中含黑碳（BC）气溶胶的比例和吸收增强对于评估其对空气质量和气候的影响至关重要。在这里，我们使用现场测量的粒径分辨挥发性收缩因子、BC 体质量浓度和冬季北京含 BC 颗粒中 BC 质量分数，反演并量化了（1）非 BC、（2）内部混合 BC 和（3）环境细颗粒中外部混合 BC 的数量和质量浓度。通过与同时测量的数据进行比较，评估了反演方法的可靠性。含 BC 颗粒的数分数占环境细颗粒的 60-78%，其中内部混合（BC 核和涂层材料）和外部混合 BC 分别占 51-64%和 9-23%。只有在清洁日的核化粒子中，当核化为气溶胶粒子的主要来源时，非 BC 成分才占主导地位（54%）。大量的气溶胶是含 BC 的颗粒，其质量分数为 32-52%，这表明在污染的城市地区，BC 在提高颗粒物（PM）的质量浓度方面起着主导作用。我们还表明，BC 颗粒被厚厚的涂层覆盖，涂层厚度（以 D/D 表示，即 300°C 加热前后 BC 直径的比值）为 1.6-2.2，这意味着在污染的城市地区 BC 颗粒的老化效率很高。我们的结果表明大气中含有大量的含 BC 颗粒，这有助于理解 BC 在区域霾形成和气候强迫中的作用。
