The influence of impactor size cut-off shift caused by hygroscopic growth on particulate matter loading and composition measurements
The influence of impactor size cut-off shift caused by hygroscopic growth on particulate matter loading and composition measurements
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DOI：
10.1016/j.atmosenv.2018.09.049
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发表时间：
2018-12-01
影响因子：
5
通讯作者：
Wiedensohler, Alfred
中科院分区：
文献类型：
--
作者：
Chen, Ying;Wild, Oliver;Wiedensohler, Alfred
大气颗粒物的质量负荷和组成对于确定其气候和健康影响非常重要，通常通过过滤器采样进行测量。然而，在环境条件下的颗粒取样可导致由吸湿生长引起的尺寸截止阈值的偏移，并且这对颗粒负载和组成的测量的影响尚未被充分量化。在这里，我们提出了一种方法来评估这种影响的基础上kappa-Kohler理论。一个全球的角度来看，根据以往报道的年度气候值的吸湿性能，气象参数和颗粒体积大小分布。在欧洲的背景站点的测量可能比其他大陆的测量更受截止偏移的影响，对采样颗粒总质量的影响中值为10-20%。然而，在城市地区，这种影响通常要小得多（< 7%），对北极地区的灰尘和颗粒物来说可以忽略不计。海盐粒子受到的影响最大（中值接近50%），这是由于它们的大尺寸、高吸湿性和海洋气团中的高相对湿度（RH）。我们估计，在相对干燥（RH = 60%）和潮湿（RH = 90%）的条件之间的海盐颗粒采样的影响类似于30%的差异。考虑到在不同地点和不同时间的截止偏移的变化，使用我们在这里介绍的方法对这种影响进行一致的考虑对于颗粒负荷和组成的长期和空间分布的观测研究至关重要，并且对于建模研究中气溶胶模块的稳健验证至关重要。
The mass loading and composition of atmospheric particles are important in determining their climate and health effects, and are typically measured by filter sampling. However, particle sampling under ambient conditions can lead to a shift in the size cut-off threshold induced by hygroscopic growth, and the influence of this on measurement of particle loading and composition has not been adequately quantified. Here, we propose a method to assess this influence based on kappa-Kohler theory. A global perspective is presented based on previously reported annual climatological values of hygroscopic properties, meteorological parameters and particle volume size distributions. Measurements at background sites in Europe may be more greatly influenced by the cut-off shift than those from other continents, with a median influence of 10-20% on the total mass of sampled particles. However, the influence is generally much smaller (< 7%) at urban sites, and is negligible for dust and particles in the Arctic. Sea-salt particles experience the largest influence (median value similar to 50%), resulting from their large size, high hygroscopicity and the high relative humidity (RH) in marine air-masses. We estimate a difference of similar to 30% in this influence of sea-salt particle sampling between relatively dry (RH = 60%) and humid (RH = 90%) conditions. Given the variation in the cut-off shift in different locations and at different times, a consistent consideration of this influence using the approach we introduce here is critical for observational studies of the long-term and spatial distribution of particle loading and composition, and crucial for robust validation of aerosol modules in modelling studies.