Aerosol-fog interactions

Lead Research Organisation: University of Leeds
Department Name: School of Earth and Environment


The goal of this project is to improve the forecasts of radiation fog; i.e. fog that forms on a cold, humid, calm night. Fog is one of the highest impact weather events in the UK. The Met Office is the CASE partner. A poor forecast of fog -- e.g predicting that fog will occur over Heathrow and no fog forms -- could result in losses of millions of pounds. Equally, thick fog that was not forecast properly can cause severe traffic accidents resulting in loss of life. Major health problems can also occur due to air-pollution events that are caused by the same meteorological conditions, which can cause enhancements in fog intensity (e.g. the Beijing smog). The formation of radiation fog can occur when there are calm or light winds, high relative humidity and rapid cooling. However, whether fog does or does not form depends on the balance between radiative cooling, turbulent mixing, the growth of aerosol particles by the uptake of water vapour, the activation of fog droplets on the aerosol particles and cold-air advection. The development of the fog upwards depends on condensation on aerosols above the fog and continued cooling.


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Description Aerosols are important for fog, as they act as the substrate for which fog droplets can form. Within this project, a number of objectives have been shown so far:

- We've shown the importance of the cloud drop number on the development of the fog layer, whereby the number being too high will result in the fog's visibility decreasing too rapidly
- To capture the correct cloud drop number, aerosol-fog interactions have to be considered in simulations of fog, which have shown to be more important in cases of fog within "cleaner" environments such as the UK
- When simulating aerosol-fog interactions and the formation of fog droplets (known as aerosol activation), the physics should be correctly interpreted within the model. For this example, aerosol activation schemes should take into account cooling through heat release from the ground (radiative cooling) rather than a cooling that's associated with adiabatic lifting (found in convective clouds such as cumulus)
Exploitation Route - A paper has recently been accepted by the journal Weather, titled "How important are aerosol-fog interactions for the successful modelling of nocturnal radiation fog?". The main objective that can be put forward is showing why it's important to consider the role of aerosols within simulations of fog, a finding which can be used within future research of fog
- The framework that has been developed to account for aerosol activation in fog can be applied to other cases that are more heavily polluted (for example, fog in India) where it can demonstrate how important aerosol-fog interactions are for fog formation in different environments
Sectors Environment