期刊
ATMOSPHERIC CHEMISTRY AND PHYSICS
卷 16, 期 7, 页码 4423-4438出版社
COPERNICUS GESELLSCHAFT MBH
DOI: 10.5194/acp-16-4423-2016
关键词
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资金
- Seventh Framework Programme of the European Union (Marie Curie-Networks for Initial Training MC-ITN CLOUD-TRAIN) [316662]
- Swiss National Science Foundation (SNSF) [200021 140663]
- US National Science Foundation [AGS-1447056, AGS-1439551]
- Dreyfus Award [EP-11-117]
- German Federal Ministry of Education and Research BMBF [01LK1222A]
- Davidow Foundation
- German Federal Ministry of Education and Research (BMBF) through CLOUD12 project
- CERN
- CLOUD
- NERC [NE/H019049/1] Funding Source: UKRI
- Natural Environment Research Council [NE/H019049/1] Funding Source: researchfish
- Div Atmospheric & Geospace Sciences [1447056, 1439551] Funding Source: National Science Foundation
Under certain conditions, secondary organic aerosol (SOA) particles can exist in the atmosphere in an amorphous solid or semi-solid state. To determine their relevance to processes such as ice nucleation or chemistry occurring within particles requires knowledge of the temperature and relative humidity (RH) range for SOA to exist in these states. In the Cosmics Leaving Outdoor Droplets (CLOUD) experiment at The European Organisation for Nuclear Research (CERN), we deployed a new in situ optical method to detect the viscous state of alpha-pinene SOA particles and measured their transition from the amorphous highly viscous state to states of lower viscosity. The method is based on the depolarising properties of laboratory-produced non-spherical SOA particles and their transformation to non-depolarising spherical particles at relative humidities near the deliquescence point. We found that particles formed and grown in the chamber developed an asymmetric shape through coagulation. A transition to a spherical shape was observed as the RH was increased to between 35aEuro-% at -10aEuro-A degrees C and 80aEuro-% at -38aEuro-A degrees C, confirming previous calculations of the viscosity-transition conditions. Consequently, alpha-pinene SOA particles exist in a viscous state over a wide range of ambient conditions, including the cirrus region of the free troposphere. This has implications for the physical, chemical, and ice-nucleation properties of SOA and SOA-coated particles in the atmosphere.
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