Department of Civil and Environmental Engineering , National University of Singapore , 117576 , Singapore.
NUS Environmental Research Institute , National University of Singapore , 117411 , Singapore.
Environ Sci Technol. 2019 Aug 20;53(16):9429-9438. doi: 10.1021/acs.est.9b03064. Epub 2019 Aug 2.
The mixing state of black carbon (BC) affects its environmental fate and impacts. This work investigates particle diversity and mixing state for refractory BC (rBC) containing particles in an urban environment. The chemical compositions of individual rBC-containing particles were measured, from which a mixing state index and particle diversity were determined. The mixing state index (χ) varied between 26% and 69% with the average of 48% in this study and was slightly enhanced with the photochemical age of air masses, indicating that most of the rBC-containing particles cannot be simply explained by fully externally and internally mixed model. Clustering of single particle measurements was used to investigate the potential effects of different primary emissions and atmospheric processes on rBC-containing particle diversity and mixing state. The average particle species diversity and the bulk population species diversity both increased with primary traffic emissions and elevated nitrate concentrations in the morning but gradually decreased with secondary organic aerosol (SOA) formation in the afternoon. The single particle clustering results illustrate that primary traffic emissions and entrainment of nitrate-containing rBC particles from the residual layer to the surface could lead to more heterogeneous aerosol compositions, whereas substantial fresh SOA formation near vehicular emissions made the rBC-containing particles more homogeneous. This work highlights the importance of considering particle diversity and mixing state for investigating the chemical evolution of rBC-containing particles and the potential effects of coating on BC absorption enhancement.
这项工作研究了城市环境中含难熔黑碳 (rBC) 颗粒的粒子多样性和混合状态。测量了单个含 rBC 颗粒的化学成分，从中确定了混合状态指数和颗粒多样性。混合状态指数 (χ) 在本研究中在 26%到 69%之间变化，平均值为 48%，略微随着空气团光化学年龄的增加而增强，表明大多数含 rBC 颗粒不能简单地用完全外部和内部混合模型来解释。单颗粒测量的聚类用于研究不同的一次排放和大气过程对含 rBC 颗粒多样性和混合状态的潜在影响。平均颗粒种类多样性和总体种群多样性都随着早晨的主要交通排放和硝酸盐浓度的升高而增加，但随着下午二次有机气溶胶 (SOA) 的形成而逐渐降低。单颗粒聚类结果表明，主要交通排放和从残留层夹带含硝酸盐的 rBC 颗粒到地表会导致气溶胶组成更加不均匀，而在车辆排放附近大量形成新鲜的 SOA 会使含 rBC 颗粒更加均匀。这项工作强调了考虑颗粒多样性和混合状态对于研究含 rBC 颗粒的化学演化以及涂层对 BC 吸收增强的潜在影响的重要性。
