Large plumes of Saharan dust regularly travel thousands of kilometres from North Africa into Europe, shaping skies, air quality, and atmospheric conditions far from their source. These events are closely monitored by scientists, as mineral dust is one of the most abundant types of airborne particles in the atmosphere and can influence everything from visibility and public health to weather patterns and climate processes.
CAMS, operated by the European Centre for Medium-Range Weather Forecasts (ECMWF), provides detailed forecasts and monitoring of atmospheric composition, including desert dust. By combining satellite observations with advanced atmospheric modelling, CAMS tracks how dust is lifted from the Sahara and transported across continents, helping authorities and researchers understand where and when impacts may occur.
As a new Saharan dust plume develops and moves towards Europe, CAMS scientists are analysing its scale, trajectory, and potential effects across the region. Mark Parrington, Senior Scientist at CAMS, spoke to Innovation News Network’s Managing Editor, Jack Thomas, about how these events form, how they are monitored across large distances, and what they can reveal about the movement of particles through the atmosphere.
Mark is speaking this week from Budapest, where CAMS experts and policymakers have gathered for the CAMS Policy User Workshop to discuss the role of atmospheric monitoring in supporting air quality management across Europe.
What is happening right now with this dust event? How does it compare to the one we saw in late February?
What we’re seeing now is linked to a borrasca storm that was named Regina by the Portuguese weather service (IPMA). It’s a very strong, tightly wound cyclonic low-pressure system. That produces strong easterly and southerly winds, which can rapidly transport dust from the Sahara across the western Mediterranean.
Typically, this affects the Iberian Peninsula first and then moves towards France. Some dust particles, especially those higher in the atmosphere, are transported much farther and can reach the UK, the North Sea, and Scandinavia.
In our data, we look at a parameter called aerosol optical depth, which measures the amount of particulate matter in the atmosphere between the ground and the top of the atmosphere and how it affects the transmission of solar radiation. An aerosol optical depth value of around one usually corresponds to hazy conditions.
Data source: Copernicus Atmosphere Monitoring Service (CAMS). Credit: CAMS / ECMWF.
In this event, compared with those at the end of February, aerosol optical depth values are generally higher. So overall, it appears stronger, particularly across Europe, and our forecasts show it persisting over the coming days.
The February event was slightly different. That one involved what are known as calima-type winds, which usually produce an outflow towards the North Atlantic. These calima events often lead to poor visibility and worse air quality in places like the Canary Islands and Madeira due to the Saharan dust plume.
In that case, the circulation meant that dust blown into the North Atlantic was then recirculated northwards. With this borrasca event, it’s a more direct transport across the western Mediterranean into southwest Europe.
Is this unusual for this time of year, or broadly in line with what you would expect? Are we seeing these events more frequently?
It’s fairly typical for this time of year. I haven’t personally looked at the statistics in our own dataset, but there are studies that examine the Mediterranean and North Atlantic basins and look at how often these events occur.
They’re certainly not unknown in late winter and early spring. At this time of year, we often see calima-type events as well as extra-tropical storms that produce the circulation patterns needed to transport dust. If there’s enough dust in the atmosphere, it can then be carried into European airspace.
It’s difficult to compare individual events directly, but I believe that in 2022, and possibly also in 2024, there were similar borrasca-type wind patterns that resulted in high dust concentrations over southern Spain. Because these cyclonic storms also bring strong winds and heavy rainfall, they can have quite noticeable impacts.
For example, in early spring 2022, there was flooding as well as dust deposition. The combination of heavy rain and large amounts of atmospheric dust meant that a significant amount of dust was deposited at ground level.
Which regions are likely to be most affected, and what impacts might people see in terms of air quality or visibility?
In recent days, the most affected areas have been Spain and Portugal, along with parts of southern France. That makes sense because these countries are directly downwind from the Sahara.
We should also remember Algeria, Morocco, and Tunisia, which can experience very severe air quality and visibility impacts when mineral dust enters the atmosphere.
Our forecasts show that in Spain and Portugal, there is an increase in PM10 concentrations at the ground surface. That has the potential to affect air quality, with dust contributing enough to push the air quality index into the “poor” category under the UK Environment Agency classification.
This doesn’t tend to persist for very long, but over the last couple of days and today, we see those surface impacts. After that, conditions begin to clear.
By the time the Saharan dust plume reaches France, there can still be some surface air-quality effects. Further north, when it reaches the UK, the North Sea, and Scandinavia, the dust is usually transported higher up in the atmosphere. So it doesn’t typically affect ground-level air quality in any noticeable way.
What people might notice instead are more colourful sunrises and sunsets. If rain mixes with the dusty air mass, it can also lead to wet deposition, leaving a dusty residue on cars or windows.
These events can develop quickly. How do you track them across continents, and how important is monitoring them?
At CAMS, we run a five-day forecast. The amount of dust entering the atmosphere is modelled based on meteorological conditions such as winds, circulation patterns, and surface pressure.
This relies on meteorological modelling from ECMWF, which is widely recognised as one of the most accurate forecasting systems in the world. That allows us to model the dust source regions in the Sahara and then track how the air mass moves over the following days.
By combining those dust emissions with the forecast winds, we can see where the air mass is likely to travel and where it might affect air quality.
Part of my day-to-day work is reviewing these forecasts as they come in and evaluating how well they perform against independent measurements when available. In general, over a three- to four-day period, these events are usually described quite accurately by the forecast system.
Another important aspect is that we also use satellite observations to update the starting point of each forecast. Satellites measure aerosol optical depth, and we combine those observations with the model’s estimate of how much dust is in the atmosphere.
That gives us the benefits of both approaches. The modelling provides a detailed representation of how the Saharan dust plume is transported, while the observations help ensure that the forecast starts from the most accurate possible picture of the atmosphere.
This process is updated every 12 hours, so each new forecast incorporates the latest observations.
Is that a newer development?
No, that approach has been used throughout the operational lifetime of CAMS, which is now about 10 or 11 years. Even before that, during the development of the system, the whole framework was built around combining satellite observations with modelling.
It’s also one of the reasons ECMWF forecasts are so accurate. By assimilating large numbers of observations into the models, we create better initial conditions for the forecasts. Forecasts naturally drift over time because they are sensitive to those starting conditions, so using real observations helps reduce that uncertainty.
So the system gives a more holistic view of what’s happening in the atmosphere?
Exactly. At the heart of what we do is combining very sophisticated numerical modelling with millions of observation points every day.
We’ve been talking about desert dust and aerosols here, but the same approach is used for other atmospheric components such as ozone, carbon dioxide, and wildfire smoke. Carbon monoxide, for example, is very useful for tracking wildfire smoke, and we also use the system to study the ozone layer and the ozone hole.
Within the modelling, we also represent chemical reactions in the atmosphere, so we can understand how emissions of one pollutant influence others and affect overall atmospheric composition.