We Rep STEM aims to promote the work of inspiring people in the STEM community. Today, we’re featuring Craig Poku, a post-doctoral researcher with a focus on fog and aerosol at the University of Leeds Institute for Climate and Atmospheric Science.

Here are five interesting facts about fog and aerosol — and a bit about Craig’s research, in his own words.

1) Fog has a big impact on human activity and health: The UK is receptive to fog in the winter months, and in particular, nocturnal radiation fog. Nocturnal radiation fog is formed through low wind speeds, minimal cloud cover and the Earth’s surface cooling through infrared radiation. All of these variables combined may result in the air becoming saturated, and consequently, result in a decreased surface visibility. As such, fog has been associated with economic losses equivalent to winter storms, and the cause of multiple crashes every year.

2) You cannot have fog without aerosol: A fog layer is made up of millions of liquid droplets. The atmosphere contains small airborne particles called aerosols, and droplets can form with or without an aerosol. Fog droplets without aerosols are extremely rare at the Earth’s surface and are more likely formed through water vapour condensing on highly soluble aerosols. 

3) The number of droplets can determine the fog’s thickness: Fog droplets can both absorb and emit infrared radiation and will result in cooling at the fog top. Enough droplets present may lead to a stronger cooling rate at the fog top than at the surface. This will trigger convective motion in the fog layer, allowing it to become well-mixed and thicker, and decrease further in surface visibility. Consequently, a well-mixed fog has the potential to persist for days.

4) Most models poorly capture the transition to a well-mixed fog: to simulate the fog evolution, aerosols should be considered to account for fog droplet formation. A method to model droplet formation is to use an “aerosol activation” scheme. However, most of these schemes are unsuitable for fog, as they were designed for convective clouds in mind. These schemes will form too many droplets during initial fog formation, causing the transition to a well-mixed layer to occur too quickly. 

Here at Leeds, we have developed a new aerosol activation scheme to account for the physics during fog formation. Our results have shown that this scheme calculates a more appropriate fog droplet number, resulting in a slower transition to a thicker fog i.e. more in line with observations.

5) Understanding aerosol impacts on fog can provide recommendations to cleaner air policies: So far, we have discussed how aerosols indirectly influence the fog’s evolution. However, they can directly interact with solar radiation and alter the state of the atmosphere, which may change the timing when fog forms and dissipates. In places such as India, there has been a steady increase in fog episodes alongside increased air pollution. Understanding how the interactions between solar radiation and aerosols won’t only improve our understanding of fog but could provide new motivation to policymakers who investigate initiating air quality initiatives. 

Craig can be found on Twitter.

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EDITOR’S NOTE: Minor grammatical edits were made to the original text.

Photo courtesy of Craig Poku.