Abstract

The size distribution, volatility and hygroscopicity of ambient aerosols and cloud residuals were measured with a differential mobility particle sizer (DMPS) and a volatility–hygroscopicity tandem differential mobility analyser (VHTDMA) coupled to a counterflow virtual impactor (CVI) inlet during the Cloud and Aerosol Experiment at Åre (CAEsAR) campaign at Mt. Åreskutan during summer 2014. The chemical composition of particulate matter (PM) and cloud water were analysed offline using thermo-optical OC/EC analysis and ion chromatography. The importance of aerosol particle size for cloud droplet activation and subsequent particle scavenging was clearly visible in the measured size distributions. Cloud residuals were shifted towards larger sizes compared to ambient aerosol, and the cloud events were followed by a size distribution dominated by smaller particles. Organics dominated both PM (62% organic mass fraction) and cloud water (63% organic mass fraction) composition. The volatility and hygroscopicity of the ambient aerosols were representative of homogeneous aged aerosol with contributions from biogenic secondary organics, with median volume fraction remaining (VFR) of 0.04–0.05, and median hygroscopicity parameter κ of 0.16–0.24 for 100–300 nm particles. The corresponding VFR and κ for the cloud residuals were 0.03–0.04 and 0.18–0.20. The chemical composition, hygroscopicity and volatility measurements thus showed no major differences between the ambient aerosol particles and cloud residuals. The VFR and κ values predicted based on the chemical composition measurements agreed well with the VHTDMA measurements, indicating the bulk chemical composition to be a reasonable approximation throughout the size distribution. There were indications, however, of some more subtle changes in time scales not achievable by the offline chemical analysis applied here. Further, online observations of aerosol and cloud residual chemical composition are therefore warranted.

摘要

使用差动迁移率粒度仪（DMPS）和结合了逆流虚拟撞击器（CVI）入口的差动迁移率粒度分析仪（DMPS）和波动率-吸湿性串联差动迁移率分析仪（VHTDMA）来测量周围的气溶胶和云残留量阿雷山（AAE）的气溶胶实验（CAEsAR）。2014年夏季，在Åreskutan。使用热光学OC / EC分析和离子色谱法离线分析了颗粒物（PM）和云水的化学成分。气溶胶粒径对于云滴活化和随后的清除粒子的重要性在测量的粒径分布中清晰可见。与周围的气溶胶相比，云的残留物向更大的方向移动，云事件之后是由较小颗粒占主导的尺寸分布。有机物占PM（62％有机物质量分数）和云水（63％有机物质量分数）组成。周围气溶胶的挥发性和吸湿性代表了均质的老化气溶胶，由生物成因的次生有机物贡献，剩余的中值体积分数（VFR）为0.04-0.05，中值的吸湿性参数100-300 nm粒子的κ为0.16-0.24。云残留的相应VFR和κ分别为0.03-0.04和0.18-0.20。因此，化学成分，吸湿性和挥发性的测量结果表明，周围的气溶胶颗粒和云残留之间没有重大差异。基于化学成分测量值预测的VFR和κ值与VHTDMA测量值非常吻合，表明整个尺寸分布中的总体化学成分是合理的近似值。但是，有迹象表明，时标的一些细微变化无法通过此处应用的离线化学分析来实现。此外，因此需要在线观察气溶胶和云的残留化学成分。