Relationship of anthropogenic aerosols to CCN and to fog / cloud droplets

The above described measurement of the “ability of aerosol particles to form cloud droplets” is linked to the microphysical properties of fog and cloud droplets via measurements of their number-size distribution in situ using a Fog Monitor (FM-100, Droplet Measurement Technologies). This optical spectrometer continuously samples droplet-laden ambient air and produces size distributions in the range from 2 - 50 µm.

The independent and parallel measurement of 1) the droplet size distribution inside clouds and fog, 2) the size distribution of the total aerosol, and 3) the number of CCN allows us to perform detailed studies of cloud-microphysical processes related to droplet activation and droplet growth. The described set of instruments has therefore been deployed in several field experiments studying aerosol-cloud interactions, e.g. at the high Alpine research station Jungfraujoch, and at the global atmospheric watch station Pallas, Finland.

For the investigation of the influence of anthropogenic aerosols on fog/cloud droplet properties during winter time high stratus periods in the Zurich lake area, this setup was fully integrated into the measurement trailer of our group. The setup also included the Aerosol Time-of-Flight Mass Spectrometer coupled to a Counterflow Virtual Impactor (CVI) that separates the larger cloud droplets from the unactivated, interstitial aerosol, to gain knowledge on the chemical composition of the activated particles.

Measurement trailors of IAC-Physics and IAC-Chemistry during the FOX field campaign