Long-term Changes in Fog Frequency at Swedish Airports and its Potential Drivers

Abstract. Fog is a major hazard at airports that can result in delays, financial losses and even fatal accidents. We have investigated changes in fog occurrence at 12 Swedish airports from the 1970's to 2022. We have utilised meteorological data from the airports, sulphate data from five measurement stations in Sweden and sulphur dioxide emissions data over Europe. The meteorological data consist of recordings of visibility, temperature, pressure, dew-point temperature, wind speed, and wind direction.

The results show that fog frequencies at airports in southern Sweden have decreased by about 50 % when comparing the periods before and after the year 2000. The decline is primarily associated with fog occurring at wind speeds above 2 m s^-1, that is, advection fog. Our investigation indicate that these changes are driven by decreasing concentrations of aerosol particles. At the airports in the mid-Sweden, we do not find any changes in fog frequency. This is also true for two of the airports in northern Sweden. Nevertheless, three airports in northern Sweden are experiencing increasing fog frequencies. For two of these airports this is an increase in radiation fog during late summer and autumn. We find this to be coupled to increased moisture transport from warming rivers adjacent to the airports, in combination with low wind speeds. For the third airport, warmer air temperatures, coupled to climate change, can explain the weak increase in the fog frequency. Thus, both climate change and decreasing air pollution impact fog formation at Swedish airports.