COVID-19 resulted in an unprecedented impact on our daily life. As many countries - including the Netherlands - impose(d) lockdowns in an effort to slow the spread of the disease, and air travel was reduced globally, there have been noticeable reductions in pollution. This has also resulted in increased solar radiation reaching the Earth's surface. Here, we take a quick look at whether or not we can seen the impact of COVID-19 on the occurrence of fog in the Netherlands.
Given that aerosols are important for the formation of fog, and "cleaning" of the air has been shown to decrease the occurrence of fog over long periods of time (e.g., Boers et al. 2015), one might expect that the reduction in pollution associated with the lockdown might result in a decrease in fog. Conversely, perhaps the clearer skies mean reduced downwelling longwave radiation, and subsequently stronger nocturnal cooling which is more favourable for fog?
In the Dutch Fog analysis, the De Bilt weather station was shown to be representative of the mean Dutch fog climate. We therefore use the observations from the De Bilt location for this analysis. We take hourly observations of visibility from 2011, up to, and including, 2020. We look specifically at the fraction of observations that are foggy (visibility < 1 km) in the months since the outbreak of COVID-19 in the Netherlands. We specifically focus on April-June as these represent the primary (complete) months where working from home was encouraged in the Netherlands.
Although this spring is roughly 1.25 times foggier than the mean over the previous decade, the figure clearly shows that the amount of fog seen this year cannot be distinguished from the natural variability. In fact, 2017 was the foggiest spring of the past decade. Even looking more closely at individual months, there is no discernible difference.
Why do we not see an impact? It could be, as mentioned above, that there are competing influences on the fog occurrence. It may also be that the influence is more subtle than an impact on occurrence alone. Perhaps there are changes in the duration, timing, or type of events. Or, maybe there are regional influences (as seen inn the climate analysis), with more polluted settings showing a greater change in fog occurrence? Particularly interesting would be to see if Schiphol has more fog than usual given the reduction in air travel.
Ultimately, the Netherlands never really shut down like other regions. At the same time, the Dutch fog climate, while influenced by aerosol content and composition, is not as strongly affected by pollution as other locations. It may be that areas such as the Po River valley, or regions in China - which not only impacted significantly by pollution, but also experienced more extreme lockdown conditions - will show a greater signal. Attributing such a short-term signal to COVID-19 alone will nonetheless be a challenge.
Given that aerosols are important for the formation of fog, and "cleaning" of the air has been shown to decrease the occurrence of fog over long periods of time (e.g., Boers et al. 2015), one might expect that the reduction in pollution associated with the lockdown might result in a decrease in fog. Conversely, perhaps the clearer skies mean reduced downwelling longwave radiation, and subsequently stronger nocturnal cooling which is more favourable for fog?
In the Dutch Fog analysis, the De Bilt weather station was shown to be representative of the mean Dutch fog climate. We therefore use the observations from the De Bilt location for this analysis. We take hourly observations of visibility from 2011, up to, and including, 2020. We look specifically at the fraction of observations that are foggy (visibility < 1 km) in the months since the outbreak of COVID-19 in the Netherlands. We specifically focus on April-June as these represent the primary (complete) months where working from home was encouraged in the Netherlands.
Although this spring is roughly 1.25 times foggier than the mean over the previous decade, the figure clearly shows that the amount of fog seen this year cannot be distinguished from the natural variability. In fact, 2017 was the foggiest spring of the past decade. Even looking more closely at individual months, there is no discernible difference.
Why do we not see an impact? It could be, as mentioned above, that there are competing influences on the fog occurrence. It may also be that the influence is more subtle than an impact on occurrence alone. Perhaps there are changes in the duration, timing, or type of events. Or, maybe there are regional influences (as seen inn the climate analysis), with more polluted settings showing a greater change in fog occurrence? Particularly interesting would be to see if Schiphol has more fog than usual given the reduction in air travel.
Ultimately, the Netherlands never really shut down like other regions. At the same time, the Dutch fog climate, while influenced by aerosol content and composition, is not as strongly affected by pollution as other locations. It may be that areas such as the Po River valley, or regions in China - which not only impacted significantly by pollution, but also experienced more extreme lockdown conditions - will show a greater signal. Attributing such a short-term signal to COVID-19 alone will nonetheless be a challenge.