In particular, he performed both theoretical and experimental studies on the growth and condensation of water droplets on hygroscopic nuclei.

The following year (1914) he accepted an offer by Axel Hamberg to be assistant at the newly established meteorological observatory on the Pårtetjåkko mountain north of Kvikkjokk in the region known as Sarek, now a national park.

Köhler's interest in cloud physics started while in the years 1914-1916 he was first assistant and later director (observator) of the meteorological observatory on top of Pårtetjåkko [fr] at 1830 meter altitude in the Sarek region in northern Sweden.

He left the following year with the closure of the Haldde observatory (after a short time in Tromsö) to become 'docent' at the Meteorological Institute in Uppsala and was elected professor in 1936 to succeed Filip Åkerblom.

The professorship did then include an adjacent eight-room house, very suitable for his family of six children and a new wife.

The 'Instrumenthuset', another separate small building housed the Theorell meteorograph [8] an automatic weather station, registering the temperature since 1853.

A second professorship in meteorology to specialize on weather prognosis was on Köhler's recommendation instituted and upheld by Tor Bergeron in 1949.

The chlorine in form of salts (in particular sodium-chlorate) in the fog and clouds as well as droplet-sizes was the subject of his 1933 article ref.