In-cloud measurements highlight the role of aerosol hygroscopicity in cloud droplet formation
The relationship between aerosol hygroscopicity and cloud droplet activation was studied at the Puijo measurement station in Kuopio, Finland, during the autumn 2014. The hygroscopic growth of 80, 120 and 150 nm particles was measured at 90 % relative humidity with a hygroscopic tande...
| Main Authors: | , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-08-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/16/10385/2016/acp-16-10385-2016.pdf |
| Summary: | The relationship between aerosol hygroscopicity and cloud
droplet activation was studied at the Puijo measurement station in Kuopio,
Finland, during the autumn 2014. The hygroscopic growth of 80, 120 and 150
nm particles was measured at 90 % relative humidity with a hygroscopic
tandem differential mobility analyzer. Typically, the growth factor (GF)
distributions appeared bimodal with clearly distinguishable peaks around
1.0–1.1 and 1.4–1.6. However, the relative contribution of the two modes
appeared highly variable reflecting the probable presence of fresh
anthropogenic particle emissions. The hygroscopicity-dependent activation
properties were estimated in a case study comprising four separate cloud
events with varying characteristics. At 120 and 150 nm, the activation
efficiencies within the low- and high-GF modes varied between 0–34
and 57–83 %, respectively, indicating that the less hygroscopic
particles remained mostly non-activated, whereas the more hygroscopic mode
was predominantly scavenged into cloud droplets. By modifying the measured
GF distributions, it was estimated how the cloud droplet concentrations
would change if all the particles belonged to the more hygroscopic group.
According to <i>κ</i>-Köhler simulations, the cloud droplet
concentrations increased up to 70 % when the possible feedback effects on
effective peak supersaturation (between 0.16 and 0.29 %) were assumed
negligible. This is an indirect but clear illustration of the sensitivity of
cloud formation to aerosol chemical composition. |
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| ISSN: | 1680-7316 1680-7324 |