Many parts of western Europe woke up this morning in a cloud of Saharan dust—from yellow skies in Paris to dangerously high levels of particulate matter in Madrid.

I had a chance to sit down with our lead atmospheric scientist and particulate matter transportation expert Dr. Boris Quennehen to discuss some of the key questions that have come up around this topic.

What are some of the air pollution levels in Spain?

The map below shows the PM10 measurements at monitoring stations over Spain at 6 AM UTC today (March 15). PM10 concentrations reach extremely high levels (up to the saturation level for some stations) on a large band crossing the entire country from South to North. In Madrid, concentrations above 600 µg/m3 have been recorded this morning but such levels have been reached almost everywhere over the band. To give some context, WHO exposure recommendations are set to 15 µg/m3 on an annual basis, and 45 µg/m3 on a daily basis. As shown in fig. 2 and 3, the peak in concentrations only lasts a few hours and is shifted in time between southern and northern stations. 

Yellow skies and dusty rain have been reported in France as well but it is not associated with higher concentrations at the monitoring station levels. This can be explained by the geographical barrier represented by the Pyénées mountains at the Spain/French border, which would prevent most of the dust loads to be transported to France.

Maps courtesy of European Environment Agency

How does this compare to poor air quality from human-created pollution?

In the case of a dust storm like the one moving into Western Europe from the Sahara Desert, the dominant pollutant is particulate matter (PM), also known as aerosols. Even though much particulate matter is so small as to be invisible to the naked eye, it is possible to see others in high concentrations like smoke from a chimney, a candle, or cigarette – and dust storms! 

Particulate matter can come from natural sources: fine sand like in this case; wildfires; volcanic eruptions; and even sea salt. It can also come from human activities, usually involving some kind of incomplete combustion—internal combustion engines, cooking, fireworks, Intensive agriculture, and energy production for example.

What types of health issues can people experience during dusty conditions like what is currently unfolding over western Europe?

The impact of particulate matter on our health has been well documented in many studies over the last decade. According to the World Health Organization (WHO), particulate matter is the most dangerous type of pollution when it comes to human health. Even low levels of particulate matter (PM) can have serious consequences. Particulate matter has been classified as carcinogenic by the International Agency for Research on Cancer (IARC), and there are countless studies that link particulate matter exposure to shortened life spans.

PM can penetrate into our respiratory system, causing simple eye or throat irritation, or more serious issues in our lungs, hearts, and brains. Particulate matter has been linked to diabetes and high blood pressure, and some studies have even linked prenatal PM exposure to serious issues like premature births and developmental issues for the baby.

PM is classified by size, not by what it’s made up of. For example, when you read that PM10 is high today in Los Angeles, the number 10 actually refers to the diameter of the dust being measured. In this case the PM10 means that the dust measures less than 10 micrometers. That’s smaller than a human hair. PM is categorised this way because the size of the dust actually determines how bad the PM is for our health. The smaller the size (and number), the more dangerous they are to breathe.

The size of each particle is directly linked to how dangerous they are. The smaller they are, the deeper they can penetrate into our bodies, causing more damage. PM2.5 can actually pass through the membranes in our lungs into the bloodstream. Whereas PM10 is largely filtered by the nose and remains in our respiratory system.

Do you have any records of how frequent Saharan Dust events like this happen in Spain?

The remnants of 2017’s Hurricane Ophelia brought hurricane-force winds to the British Isles when the storm made landfall in Ireland.

Those in the path of the storm experienced its full devastation. However, as Ophelia made its way across the Atlantic, the turning air mass also transported particulate matter from forest fires in Portugal as well as sand from the Sahara Desert.

This confluence of natural phenomena had an unprecedented air quality impact. Much of the smoke and dust stayed high in the atmosphere, minimising health impacts for those on the ground. However, there were reports from across France and the UK of a grim, yellow sky bearing a red sun for the length of the transportation episode.

What can people in these areas do to protect themselves from the poor air quality from the Saharan Dust?

If the particulate matter exists at ground-level as it is in some areas of Spain, it’s important for people to minimise exposure by limiting outdoor activities, spending time indoors—particularly in buildings and houses with filtered air exchange systems. High quality, well-fitting anti-pollution masks can help filter out particulate matter as well.

Keep up to date by checking your local air quality forecast and plan your activities accordingly!

Stay safe and breathe free!