A hygroscopicity tandem differential mobility analyzer (HTDMA) was used to measure the water uptake (hygroscopicity) of secondaryorganic aerosol (SOA) formed during the chemical and photochemical oxidationof several organic precursors in a smog chamber. Electron ionization massspectra of the non-refractory submicron aerosol were simultaneouslydetermined with an aerosol mass spectrometer (AMS), and correlations betweenthe two different signals were investigated. SOA hygroscopicity was found tostrongly correlate with the relative abundance of the ion signal m/z 44expressed as a fraction of total organic signal (f44). m/z 44 is due mostlyto the ion fragment CO2+ for all types of SOA systems studied, andhas been previously shown to strongly correlate with organic O/C for ambientand chamber OA. The analysis was also performed on ambient OA from two fieldexperiments at the remote site Jungfraujoch, and the megacity Mexico City,where similar results were found. A simple empirical linear relation betweenthe hygroscopicity of OA at subsaturated RH, as given by the hygroscopicgrowth factor (GF) or "?org" parameter, and f44 was determined andis given by ?org = 2.2 × f44 − 0.13. This approximation canbe further verified and refined as the database for AMS and HTDMAmeasurements is constantly being expanded around the world. The use of thisapproximation could introduce an important simplification in theparameterization of hygroscopicity of OA in atmospheric models, since f44 is correlated with the photochemical age of an air mass.
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机译：使用吸湿串联差动迁移率分析仪（HTDMA）来测量烟雾室中几种有机前体的化学和光化学氧化过程中形成的次要有机气溶胶（SOA）的吸水率（吸湿性）。用气溶胶质谱仪（AMS）同时测定了难熔亚微米气溶胶的电子电离质谱，并研究了两种不同信号之间的相关性。发现SOA吸湿性与离子信号 m / z 44的相对丰度紧密相关，离子信号表示为总有机信号（ f 44 的一部分） 。 m / z 44主要归因于所研究的所有类型SOA系统的离子片段CO 2 + ，并且先前已证明与用于环境和腔室OA的有机O / C。这项分析还对来自偏远地区少女峰（Jungfraujoch）和特大城市墨西哥城的两个现场实验的环境OA进行了分析，结果也得到了类似的结果。由吸湿生长因子（GF）或“？ org ”参数给出的OA在不饱和RH下的吸湿性与 f 44 <确定/ sub>并由？ org = 2.2× f 44 -0.13给出。随着全球范围内AMS和HTDMA测量数据库的不断扩展，这种近似可以得到进一步的验证和完善。由于 f 44 与空气团的光化学年龄相关，因此使用这种近似值可以大大简化OA模型中OA的吸湿性参数化。
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