We evaluate the sensitivity of the size calibrations of two commercially available, high-resolution optical particle sizers to changes in aerosol composition and complex refractive index (RI). The Droplet Measurement Technologies Ultra-High Sensitivity Aerosol Spectrometer (UHSAS) and the TSI, Inc. Laser Aerosol Spectrometer (LAS) are two commonly used instruments for measuring the portion of the aerosol size distribution with diameters larger than nominally 60–90 nm. Both instruments illuminate particles with a laser and relate the single-particle light scattering intensity and count rate measured over a wide range of angles to the size-dependent particle concentration. While the optical block geometry and flow system are similar for each instrument, a significant difference between the two models is the laser wavelength (1054 nm for the UHSAS and 633 nm for the LAS) and intensity (about 100 times higher for the UHSAS), which may affect the way each instrument sizes non-spherical or absorbing aerosols. Here, we challenge the UHSAS and LAS with laboratory-generated, mobility-size-classified aerosols of known chemical composition to quantify changes in the optical size response relative to that of ammonium sulfate (RI of 1.52+0i at 532 nm) and NIST-traceable polystyrene latex spheres (PSLs with RI of 1.59+0i at 589 nm). Aerosol inorganic salt species are chosen to cover the real refractive index range of 1.32 to 1.78, while chosen light-absorbing carbonaceous aerosols include fullerene soot, nigrosine dye, humic acid, and fulvic acid standards. The instrument response is generally in good agreement with the electrical mobility diameter. However, large undersizing deviations are observed for the low-refractive-index fluoride salts and the strongly absorbing nigrosine dye and fullerene soot particles. Polydisperse size distributions for both fresh and aged wildfire smoke aerosols from the recent Fire Influence on Regional to Global Environments Experiment and Air Quality (FIREX-AQ) and the Cloud, Aerosol, and Monsoon Processes Philippines Experiment (CAMP²Ex) airborne campaigns show good agreement between both optical sizers and contemporaneous electrical mobility sizing and particle time-of-flight mass spectrometric measurements. We assess the instrument uncertainties by interpolating the laboratory response curves using previously reported RIs and size distributions for multiple aerosol type classifications. These results suggest that, while the optical sizers may underperform for strongly absorbing laboratory compounds and fresh tailpipe emissions measurements, sampling aerosols within the atmospherically relevant range of refractive indices are likely to be sized to better than ±10 %–20 % uncertainty over the submicron aerosol size range when using instruments calibrated with ammonium sulfate.

中文翻译：

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超高灵敏度气溶胶光谱仪 (UHSAS) 和激光气溶胶光谱仪 (LAS) 对亚微米气溶胶成分和折射率变化的尺寸响应

我们评估了两种市售的高分辨率光学粒度仪的尺寸校准对气溶胶成分和复折射率 (RI) 变化的敏感性。液滴测量技术超高灵敏度气溶胶光谱仪 (UHSAS) 和 TSI, Inc. 激光气溶胶光谱仪 (LAS) 是两种常用仪器，用于测量直径大于标称 60-90 纳米的气溶胶尺寸分布部分。两种仪器都用激光照射颗粒，并将在大范围角度测量的单颗粒光散射强度和计数率与尺寸相关的颗粒浓度相关联。虽然每个仪器的光学块几何形状和流动系统相似，两个模型之间的显着差异是激光波长（UHSAS 为 1054 nm，LAS 为 633 nm）和强度（UHSAS 大约高 100 倍），这可能会影响每个仪器测量非球形或吸收性气溶胶的方式. 在这里，我们用实验室生成的、已知化学成分的、按流动性大小分类的气溶胶挑战 UHSAS 和 LAS，以量化相对于硫酸铵的光学尺寸响应的变化（RI1.52+0 i在 532 nm）和 NIST 可追踪的聚苯乙烯乳胶球（在 589 nm 下RI 为1.59+0 i的 PSL）。选择气溶胶无机盐种类以覆盖 1.32 至 1.78 的真实折射率范围，而选择的吸光碳质气溶胶包括富勒烯烟灰、苯胺黑染料、腐殖酸和富里酸标准品。仪器响应通常与电迁移率直径非常吻合。然而，对于低折射率氟化物盐和强吸收性苯胺黑染料和富勒烯烟灰颗粒，观察到较大的尺寸不足偏差。多分散尺寸从最近的火灾对区域到全球环境实验和空气质量的影响 (FIREX-AQ) 和菲律宾的云、气溶胶和季风过程实验 (CAMP ² ) 中新鲜和老化的野火烟雾气溶胶的分布Ex) 机载运动显示出光学尺寸测定仪和同时进行的电迁移率测定和粒子飞行时间质谱测量之间的良好一致性。我们通过使用先前报告的 RI 和多种气溶胶类型分类的尺寸分布对实验室响应曲线进行插值来评估仪器的不确定性。这些结果表明，虽然光学尺寸仪在强烈吸收实验室化合物和新鲜尾气排放测量方面可能表现不佳，但在大气相关折射率范围内的采样气溶胶可能在亚微米范围内的尺寸不确定性优于± 10 %–20 %使用用硫酸铵校准的仪器时的气溶胶尺寸范围。