Refractory black carbon (rBC) aerosols play an important role in air quality and climate change, yet highly time-resolved and detailed investigations on the physicochemical properties of rBC and its associated coating are still scarce. In this work, we used a laser-only Aerodyne soot particle aerosol mass spectrometer (SP-AMS) to exclusively measure rBC-containing (rBCc) particles, and we compared their properties with those of the total nonrefractory submicron particles (NR-PM₁) measured in parallel by a high-resolution AMS (HR-AMS) in Shanghai. Observations showed that, overall, rBC was thickly coated, with an average mass ratio of coating to rBC core (R_BC) of ∼5.0 (±1.7). However, the ratio of the mass of the rBC-coating species to the mass of those species in NR-PM₁ was only 19.1 (±4.9) %; sulfate tended to condense preferentially on non-rBC particles, so the ratio of the sulfate on rBC to the NR-PM₁ sulfate was only 7.4 (±2.2) %, while the majority (72.7±21.0 %) of the primary organic aerosols (POA) were associated with rBC. Positive matrix factorization revealed that organics emitted from cooking did not coat rBC, and a portion of the organics that coated rBC was from biomass burning; such organics were unidentifiable in NR-PM₁. Small rBCc particles were predominantly from traffic, while large-sized ones were often mixed with secondary components and typically had a thick coating. Sulfate and secondary organic aerosol (SOA) species were generated mainly through daytime photochemical oxidation (SOA formation, likely associated with in situ chemical conversion of traffic-related POA to SOA), while nocturnal heterogeneous formation was dominant for nitrate; we also estimated an average time of 5–19 h for those secondary species to coat rBC. During a short period that was affected by ship emissions, particles were characterized as having a high vanadium concentration (on average 6.3±3.1 ng m⁻³) and a mean vanadium/nickel mass ratio of 2.0 (±0.6). Furthermore, the size-resolved hygroscopicity parameter (κ_rBCc) of rBCc particles was obtained based on their full chemical characterization, and was parameterized as κ_rBCc(x)=0.29–0.14 × $\exp (-\mathrm{0.006}\times x)$ (where x ranges from 150 to 1000 nm). Under critical supersaturations (SS_C) of 0.1 % and 0.2 %, the D₅₀ values were 166 (±16) and 110 (±5) nm, respectively, and 16 (±3) % and 59 (±4) %, respectively, of the rBCc particles by number could be activated into cloud condensation nuclei (CCN). Our findings are valuable for advancing the understanding of BC chemistry as well as the effective control of atmospheric BC pollution.

中文翻译：

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上海市区亚微米含黑碳气溶胶的化学性质、来源及尺寸分辨吸湿性

难熔黑碳 (rBC) 气溶胶在空气质量和气候变化中发挥着重要作用，但对 rBC 及其相关涂层的物理化学性质的高度时间分辨和详细研究仍然很少。在这项工作中，我们使用仅限激光的 Aerodyne 烟尘颗粒气溶胶质谱仪 (SP-AMS) 专门测量含 rBC (rBCc) 颗粒，并将它们的性质与总非耐火亚微米颗粒 (NR-PM ₁ ) 由上海的高分辨率 AMS (HR-AMS) 并行测量。观察表明，总体而言，rBC 被厚涂层，涂层与 rBC 核心 ( R _BC )的平均质量比为∼5.0  ( ±1.7）。_{然而，在 NR-PM 1}中，rBC 涂层物质的质量与这些物质的质量之比仅为 19.1 ( ±4.9 ) %；硫酸盐倾向于优先凝结在非rBC颗粒上，因此rBC上的硫酸盐与NR-PM ₁硫酸盐的比例仅为7.4（±2.2）％，而大部分（72.7±21.0  ％）的初级有机气溶胶（ POA）与红细胞相关。正矩阵分解表明，烹饪排放的有机物没有包裹 rBC，而包裹 rBC 的部分有机物来自生物质燃烧；_{NR-PM 1}中无法识别此类有机物. 小的 rBCc 颗粒主要来自交通，而大尺寸的颗粒通常与次要成分混合并且通常具有厚涂层。硫酸盐和次生有机气溶胶（SOA）主要通过白天的光化学氧化（SOA 的形成，可能与交通相关的 POA 到 SOA 的原位化学转化有关）产生，而夜间非均相形成主要是硝酸盐；我们还估计这些次要物种覆盖 rBC 的平均时间为 5-19 小时。在受船舶排放影响的短时间内，颗粒被表征为具有高钒浓度（平均为 6.3±3.1  ng m ^-3）和平均钒/镍质量比为 2.0（±0.6）。此外，rBCc 颗粒的尺寸分辨吸湿性参数 ( κ _rBCc ) 是基于其完整的化学表征获得的，参数化为κ _rBCc ( x )=0.29 –0.14  × $\mathrm{经验}(-\mathrm{0.006}\times X)$（其中x 范围从 150 到 1000 nm）。在0.1 % 和 0.2 % 的临界过饱和度 (SS _{C ) 下，} D ₅₀值分别为 166 ( ±16 ) 和 110 ( ±5 ) nm，分别为 16 ( ±3 ) % 和 59 ( ±4 ) % ，按数量计算的 rBCc 粒子可以被激活成云凝聚核 (CCN)。我们的研究结果对于促进对 BC 化学的理解以及有效控制大气 BC 污染具有重要价值。