State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, 100029, China; College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China.
Guangzhou Hexin Analytical Instrument Company Limited, Guangzhou, 510530, China.
Environ Pollut. 2020 Aug;263(Pt B):114455. doi: 10.1016/j.envpol.2020.114455. Epub 2020 Apr 3.
Black carbon (BC) exerts a large impact on climate radiative forcing and public health, and such impacts depend strongly on chemical composition and mixing state. Here a single particle aerosol mass spectrometry (SPA-MS) along with an aerosol chemical speciation monitor was employed to characterize the composition and mixing state of BC-containing particles in summer and winter in Beijing. Approximately 2 million BC-containing particles were chemically analyzed, and the particles were classified into nine and eight different types in summer and winter, respectively, according to mass spectral signatures and composition. The BC-containing particles in summer were dominated by the type of nitrate-related BC (BC-N, 56.7%), while in winter the BC mixed with organic carbon (OC) and sulfate (BCOC-S), and OC and nitrate (BCOC-N) were two dominant types accounting for 44.9% and 16.6%, respectively. The number fractions of BC-N in summer, and BCOC-N and BC-SN in winter increased largely during periods with severe air pollution, suggesting the enhanced secondary formation on BC-containing particles. We also found that the primary emissions of the biomass burning and coal combustion can affect BC mixing state substaintially as indicated by the considerable fraction of BC mixed with levoglucosan and polycyclic aromatic hydrocarbons in winter. Bivariate polar plots and back trajectory analysis indicated that the sulfate-associated BC-containing particles were mostly from regional transport while the nitrate-related type was more from local production. The optical parameter of absorbing Ångström exponents (AAE) of BC was 1.2 and 1.5 in summer and winter, respectively, and the AAE dependence of BC mixing state was also different in the two seasons. While higher fractions of BC-N were observed during lower AAE periods in summer, the variations of dominant OC-related BC-containing particles in winter were fairly stable as a function of AAE.
黑碳（BC）对气候辐射强迫和公众健康有很大影响，这种影响强烈依赖于化学组成和混合状态。本研究采用单颗粒气溶胶质谱（SPA-MS）和气溶胶化学特征监测仪，于夏冬两季在北京对含 BC 颗粒的组成和混合状态进行了研究。共对约 200 万个含 BC 的颗粒进行了化学分析，根据质谱特征和组成，将这些颗粒在夏冬两季分别分为九种和八种不同类型。夏季含 BC 的颗粒主要为硝酸盐相关 BC（BC-N，56.7%），而冬季则是 BC 与有机碳（OC）和硫酸盐（BCOC-S）混合，OC 和硝酸盐（BCOC-N）为两种主要类型，分别占 44.9%和 16.6%。在空气污染严重时期，夏季 BC-N 和冬季 BCOC-N 和 BC-SN 的数分数大大增加，表明含 BC 颗粒的二次形成增强。我们还发现，生物质燃烧和煤炭燃烧的一次排放对 BC 的混合状态有很大影响，冬季 BC 与左旋葡聚糖和多环芳烃混合的比例相当大。双变量极图和后轨迹分析表明，与硫酸盐相关的含 BC 颗粒主要来自区域传输，而与硝酸盐相关的类型则更多来自本地生成。BC 的吸光 Ångström 指数（AAE）的光学参数在夏季和冬季分别为 1.2 和 1.5，BC 混合状态的 AAE 依赖性在两个季节也不同。夏季 AAE 较低时，BC-N 的比例较高，而冬季主要与 OC 相关的含 BC 颗粒的变化相对稳定，作为 AAE 的函数。
