Abstract. The Plantower PMS5003 sensors (PA-PMS) used in the PurpleAir (PA) monitor PA-II-SD configuration are equivalent to cell-reciprocal nephelometers using a 657 nm perpendicularly polarized light source that integrates light scattering from 18 to 166 degrees. Yearlong field data at the National Oceanic and Atmospheric Administration’s (NOAA) Mauna Loa Observatory (MLO) and Boulder Table Mountain (BOS) sites show that the 1 h average of the PA-PMS first size channel, labeled “> 0.3 μm” (“CH1”) is highly correlated with submicrometer aerosol scattering coefficients at the 550 nm and 700 nm wavelengths measured by the TSI 3563 integrating nephelometer, from 0.4 Mm⁻¹ to 500 Mm⁻¹. This corresponds to an hourly average submicrometer aerosol mass concentration of approximately 0.2 to 200 ug m⁻³. A physical-optical model of the PA-PMS is developed to estimate light intensity on the photodiode, accounting for angular truncation as a function of particle size. Predictions are then compared with yearlong fine aerosol size distribution and scattering coefficient field data at the BOS site. It is shown that CH1 is linearly proportional to the model-predicted intensity of the light scattered by particles in the PA-PMS laser to its photodiode over 4 orders of magnitude. This is consistent with CH1 being a measure of the scattering coefficient and not the particle number concentration or particulate matter concentration. Field data at BOS confirm the model prediction that the ratio of CH1 to the scattering coefficient would be highest for aerosols with median scattering diameters < 0.3 μm. The PA-PMS detects aerosols smaller than 0.3 μm diameter in proportion to their contribution to the scattering coefficient. The model predicts that the PA-PMS response to particles > 0.3 μm decreases relative to an ideal nephelometer by about 75 % for particle diameters ≥ 1.0 μm. This is a result of using a laser that is polarized, the angular truncation of the scattered light, and particle loss in the instrument before reaching the laser. The results of this study indicate that the PA-PMS is not an optical particle counter and that its six size fractions are not an accurate representation of particle size distribution. The relationship between the PA-PMS 1 h average CH1 and b_sp1, the scattering coefficient in Mm⁻¹ due to particles below 1 μm aerodynamic diameter, at wavelength 550 nanometers, is found to be b_sp1 = 0.015 ± 2.07 × 10⁻⁵ × CH1, for relative humidity below 40 %. The coefficient of determination R² is 0.97. This suggests that the low-cost and widely used PA monitors can be used to measure and predict the aerosol light scattering coefficient in the mid-visible nearly as well as integrating nephelometers.

中文翻译：

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评估作为气溶胶光散射仪器的 PurpleAir 监测仪

摘要。PurpleAir (PA) 监视器 PA-II-SD 配置中使用的 Plantower PMS5003 传感器 (PA-PMS) 等效于使用 657 nm 垂直偏振光源的细胞互易比浊计，该光源集成了 18 到 166 度的光散射。美国国家海洋和大气管理局 (NOAA) 莫纳罗亚天文台 (MLO) 和博尔德桌山 (BOS) 站点的长达一年的现场数据显示，PA-PMS 第一尺寸通道的 1 小时平均值标记为“> 0.3 μm”（“ CH1”) 与 TSI 3563 积分浊度计在 550 nm 和 700 nm 波长处测量的亚微米气溶胶散射系数高度相关，范围为 0.4 Mm ^-1至 500 Mm ^-1. 这对应于大约 0.2 至 200 ug m ^-3的每小时平均亚微米气溶胶质量浓度. 开发了 PA-PMS 的物理光学模型来估计光电二极管上的光强度，将角度截断作为粒度的函数。然后将预测结果与 BOS 站点的一年细气溶胶粒径分布和散射系数场数据进行比较。结果表明，CH1 与模型预测的 PA-PMS 激光器中粒子散射到其光电二极管的光强度成线性比例超过 4 个数量级。这与 CH1 是散射系数的量度而不是颗粒数浓度或颗粒物浓度的量度一致。BOS 的现场数据证实了模型预测，即对于中值散射直径 < 0.3 μm 的气溶胶，CH1 与散射系数的比率最高。PA-PMS 检测小于 0 的气溶胶。3 μm 直径与其对散射系数的贡献成正比。该模型预测 PA-PMS 对大于 0.3 μm 的颗粒的响应相对于理想的浊度计，对于 ≥ 1.0 μm 的颗粒直径会降低约 75%。这是使用偏振激光器、散射光的角截断以及在到达激光器之前仪器中的粒子损失的结果。这项研究的结果表明 PA-PMS 不是光学粒子计数器，它的六个粒度分数不能准确表示粒度分布。PA-PMS 1 h平均CH1与b的关系 对于 ≥ 1.0 μm 的粒径，3 μm 相对于理想的浊度计降低约 75%。这是使用偏振激光器、散射光的角截断以及在到达激光器之前仪器中的粒子损失的结果。这项研究的结果表明 PA-PMS 不是光学粒子计数器，它的六个粒度分数不能准确表示粒度分布。PA-PMS 1 h平均CH1与b的关系 对于 ≥ 1.0 μm 的粒径，3 μm 相对于理想的浊度计降低约 75%。这是使用偏振激光器、散射光的角截断以及在到达激光器之前仪器中的粒子损失的结果。这项研究的结果表明 PA-PMS 不是光学粒子计数器，它的六个粒度分数不能准确表示粒度分布。PA-PMS 1 h平均CH1与b的关系 这项研究的结果表明 PA-PMS 不是光学粒子计数器，它的六个粒度分数不能准确表示粒度分布。PA-PMS 1 h平均CH1与b的关系 这项研究的结果表明 PA-PMS 不是光学粒子计数器，它的六个粒度分数不能准确表示粒度分布。PA-PMS 1 h平均CH1与b的关系_sp1，由于粒子空气动力学直径小于 1 μm，波长为 550 纳米，在 Mm ^{-1 中}的散射系数为 b _sp1  = 0.015 ± 2.07 × 10 ^-5  × CH1，相对湿度低于 40%。决定系数R ²为0.97。这表明低成本和广泛使用的 PA 监测器可用于测量和预测中间可见光中的气溶胶光散射系数，几乎与积分浊度计一样。