Novel Device for in Situ and Real-Time Detection of the Acidity of Ambient Aerosols: Laboratory Characterization and Ambient Measurements

Aerosol acidity, defined as pH, is a critical property
that influences
the formation, evolution, and health and climate effects of atmospheric
aerosol particles. Direct measurement of ambient aerosol pH, however,
remains challenging for atmospheric scientists. Here, based on the
method of colorimetric analysis on aerosol-loaded pH-indicator papers,
we develop a new device that can achieve in situ and real-time measurement
of the pH of ambient aerosol droplets at a fixed relative humidity
of 90%. The design of this device provides a more convenient and efficient
method than the pH paper methods used in previous studies by allowing
automated sample switching and data recording. The size range of ambient
aerosols that are collected on pH papers is determined to be ∼0.4–2.5
μm. In addition, a standardized calibration procedure is established
using pH buffer standards. An intensive ambient measurement was performed
with the device to examine its operational stability as well as the
reliability of the measured results. The measured aerosol pH reveals
good agreement with those calculated by two commonly used thermodynamic
models, i.e., ISORROPIA and E-AIM. These comparisons further demonstrate
that the thermodynamic models are capable of predicting aerosol pH
with a reasonable range of uncertainty.

气溶胶酸度（以pH值表征）是影响大气气溶胶颗粒形成、演化过程以及健康与气候效应的关键属性。然而，大气科学家对环境气溶胶pH值的直接测量至今仍颇具挑战。本研究基于负载气溶胶的pH试纸上的比色分析法，开发了一款可在固定相对湿度90%条件下，对环境气溶胶液滴pH值进行原位实时测量的新型装置。相较于此前研究中使用的pH试纸法，该装置支持自动样品切换与数据记录，提供了更为便捷高效的检测方案。经测定，可在pH试纸上收集的环境气溶胶粒径范围约为0.4–2.5 μm。此外，本研究采用pH缓冲标准品建立了标准化校准流程。研究人员利用该装置开展了密集的现场测量，以验证其运行稳定性及测量结果的可靠性。实测气溶胶pH值与ISORROPIA、E-AIM这两种常用热力学模型的计算结果吻合良好。上述对比进一步证明，上述热力学模型可在合理的不确定度范围内对气溶胶pH值进行预测。