The humidified tandem differential mobility analyzer (HTDMA) is widely used to measure the hygroscopic properties of submicron particles. The size-resolved aerosol hygroscopicity κ measured by a HTDMA will be influenced by the contribution of multiply charged aerosols, but this effect on field measurements has seldom been discussed for previous field measurements. Our calculations demonstrate that the number ratio of multiply charged particles is quite considerable for some specific sizes between 100 and 300 nm, especially during a pollution episode. The presence of multiple charges will lead to a compression effect on the aerosol hygroscopicity in HTDMA measurements. Therefore, we propose a new algorithm that performs multi-charge correction of the size-resolved hygroscopicity κ, taking both the compression effect and the multi-charge number contribution into consideration. Application of the algorithm to field measurements showed that the relatively high hygroscopicity in the accumulation size range leads to the overestimation of the hygroscopicity of particles smaller than 200 nm. The low hygroscopicity of coarse-mode particles leads to the underestimation of the hygroscopicity of accumulation particles between 200 and 500 nm in size. The difference between the corrected and measured κ values can be as large as 0.05, highlighting that special attention must be paid to the multi-charge effect when a HTDMA is used for aerosol hygroscopicity measurements.

中文翻译：

---

多电荷对HTDMA气溶胶吸湿性测量的影响

加湿串联差动迁移率分析仪（HTDMA）被广泛用于测量亚微米颗粒的吸湿性能。HTDMA测得的尺寸分辨的气溶胶吸湿性κ将受到多电荷气溶胶的贡献的影响，但以前的现场测量很少讨论这种对现场测量的影响。我们的计算表明，对于100至300 nm之间的某些特定尺寸，带多重电荷的粒子的数量比非常可观，尤其是在污染事件期间。多个电荷的存在将导致HTDMA测量中对气溶胶吸湿性的压缩作用。因此，我们提出了一种新算法，可以对尺寸分辨的吸湿性κ进行多次电荷校正，同时考虑压缩效果和多电荷数贡献。该算法在现场测量中的应用表明，在累积尺寸范围内相对较高的吸湿性会导致对小于200 nm的颗粒的吸湿性的高估。粗模式颗粒的低吸湿性导致低估了200至500 nm尺寸的堆积颗粒的吸湿性。校正后的κ值和测得的κ值之间的差异可能高达0.05，这突出表明，当将HTDMA用于气溶胶吸湿性测量时，必须特别注意多电荷效应。