A dry-ambient aerosol size spectrometer (DAASS) was previously developed to conduct measurements of aerosol water content at ambient relative humidity (RH) conditions. However, the RH difference of ambient RH and DAASS conditioning humidity (i.e., 10–20%, particularly when the DAASS operated at a high ambient RH) may introduce uncertainties in estimation of aerosol water content. In this study, we present a prototype of an RH-controlled DAASS. By employing an active RH controlling method, we resolve the discrepancy between the ambient RH and the DAASS conditioning RH, therefore extending the accurate measurement of aerosol water content to a wide RH range. The performance of this RH-controlled DAASS was characterized by both the laboratory evaluation and a 10-day field deployment. Results showed that the DAASS conditioning RH agreed well with the ambient RH (R² of 0.993 when ambient RH up to 90%), with an average RH offset of less than 1.5%. The fraction of aerosol-bound water in the total ambient aerosol volume was ~10% under RHs below 50% and increased to ~50% when the ambient RH reached above 85%.

之前开发了一种干燥环境气溶胶尺寸光谱仪 (DAASS)，用于在环境相对湿度 (RH) 条件下测量气溶胶水含量。然而，环境 RH 和 DAASS 调节湿度的 RH 差异（即 10-20%，特别是当 DAASS 在高环境 RH 下运行时）可能会给气溶胶水含量的估计带来不确定性。在这项研究中，我们展示了 RH 控制的 DAASS 的原型。通过采用主动 RH 控制方法，我们解决了环境 RH 与 DAASS 调节 RH 之间的差异，从而将气溶胶水含量的准确测量扩展到较宽的 RH 范围。这种由 RH 控制的 DAASS 的性能通过实验室评估和 10 天的现场部署来表征。当环境相对湿度高达 90% 时为 0.993 中的²），平均相对湿度偏移小于 1.5%。在 RH 低于 50% 时，气溶胶结合水在总环境气溶胶体积中的比例为~10%，当环境 RH 达到 85% 以上时增加到~50%。