a Handix Scientific, LLC , Boulder , CO , USA.
b National Park Service , Denver , CO , USA.
J Air Waste Manag Assoc. 2018 Aug;68(8):824-835. doi: 10.1080/10962247.2018.1452801. Epub 2018 May 31.
The Handix Scientific open-path cavity ringdown spectrometer (OPCRDS) was deployed during summer 2016 in Great Smoky Mountains National Park (GRSM). Extinction coefficients from the relatively new OPCRDS and from a more well-established extinction instrument agreed to within 7%. Aerosol hygroscopic growth (f(RH)) was calculated from the ratio of ambient extinction measured by the OPCRDS to dry extinction measured by a closed-path extinction monitor (Aerodyne's cavity-attenuated phase shift particulate matter extinction monitor [CAPS PMex]). Derived hygroscopicity (relative humidity [RH] < 95%) from this campaign agreed with data from 1995 at the same site and time of year, which is noteworthy given the decreasing trend for organics and sulfate in the eastern United States. However, maximum f(RH) values in 1995 were less than half as large as those recorded in 2016-possibly due to nephelometer truncation losses in 1995. Two hygroscopicity parameterizations were investigated using high-time-resolution OPCRDS+CAPS PMex data, and the κ model was more accurate than the gamma model. Data from the two ambient optical instruments, the OPCRDS and the open-path nephelometer, generally agreed; however, significant discrepancies between ambient scattering and extinction were observed, apparently driven by a combination of hygroscopic growth effects, which tend to increase nephelometer truncation losses and decrease sensitivity to the wavelength difference between the two instruments as a function of particle size. There was not a statistically significant difference in the mean reconstructed extinction values obtained from the original and the revised IMPROVE (Interagency Monitoring of Protected Visual Environments) equations. On average, IMPROVE reconstructed extinction was ~25% lower than extinction measured by the OPCRDS, which suggests that the IMPROVE equations and 24-hr aerosol data are moderately successful in estimating current haze levels at GRSM. However, this conclusion is limited by the coarse temporal resolution and the low dynamic range of the IMPROVE reconstructed extinction.
Although light extinction, which is directly related to visibility, is not directly measured in U.S. National Parks, existing IMPROVE protocols can be used to accurately infer visibility for average humidity conditions, but during the large fraction of the year when humidity is above or below average, accuracy is reduced substantially. Furthermore, nephelometers, which are used to assess the accuracy of IMPROVE visibility estimates, may themselves be biased low when humidity is very high. Despite reductions in organic and sulfate particles since the 1990s, hygroscopicity, particles' affinity for water, appears unchanged, although this conclusion is weakened by the previously mentioned nephelometer limitations.
2016 年夏季，在大烟山国家公园（GRSM）部署了 Handix Scientific 开放路径腔衰荡光谱仪（OPCRDS）。相对较新的 OPCRDS 和更为成熟的消光仪器得出的消光系数相差在 7%以内。气溶胶吸湿性增长（f（RH））是根据 OPCRDS 测量的环境消光与封闭路径消光监测仪（Aerodyne 的腔衰减相移颗粒物消光监测仪[CAPS PMex]）测量的干燥消光之比计算得出的。本次活动中得出的吸湿性（相对湿度[RH] <95%）与同一地点和时间（1995 年）的数据一致，这是值得注意的，因为美国东部的有机物和硫酸盐呈下降趋势。然而，1995 年的最大 f（RH）值是 2016 年记录值的一半，这可能是由于 1995 年的浊度计截断损失。使用高时间分辨率的 OPCRDS+CAPS PMex 数据研究了两种吸湿性参数化，κ 模型比γ模型更准确。两个环境光学仪器，OPCRDS 和开放路径浊度计的数据通常是一致的；然而，观察到环境散射和消光之间存在显著差异，这显然是由吸湿性增长效应的组合驱动的，随着粒径的增加，吸湿性增长效应会增加浊度计截断损失并降低两个仪器之间波长差的灵敏度。从原始和修订的 IMPROVE（机构间保护视觉环境监测）方程中获得的重建消光值的平均值没有统计学差异。平均而言，IMPROVE 重建的消光值比 OPCRDS 测量的消光值低约 25%，这表明 IMPROVE 方程和 24 小时气溶胶数据在估算 GRSM 目前的霾水平方面相当成功。然而，这一结论受到 IMPROVE 重建消光的时间分辨率粗糙和动态范围低的限制。
尽管美国国家公园没有直接测量与能见度直接相关的光衰减，但现有的 IMPROVE 协议可用于准确推断平均湿度条件下的能见度，但在湿度高于或低于平均水平的一年中的大部分时间里，准确性会大大降低。此外，当湿度非常高时，用于评估 IMPROVE 能见度估计准确性的浊度计本身可能会偏低。尽管自 20 世纪 90 年代以来有机和硫酸盐颗粒有所减少，但颗粒的吸湿性（对水的亲和力）似乎没有变化，尽管这一结论因前文提到的浊度计限制而减弱。
