In essence, haze is a meteorological phenomenon that occurs when dust and sand are suspended in the atmosphere. It consists of small solid particles that are in suspension and, when found in a specific space and in large quantities, cause the air to appear opaque to our eyes.
The sky looks quite cloudy, orange
As in other parts of the world, the wind can blow strongly over deserts, blowing dust and sand high into the sky. And it can reach us. In Madrid, for example, and other highly polluted cities, the origin of this haze – called haze B – comes from pollution or ashes from forest fires. In the absence of wind and precipitation, the stagnation of pollutants reduces visibility and thus also air quality. In other areas, such as the Canary Islands, this haze -called haze A- comes from the sand of the desert, when the winds drag the dust from the Sahara desert to here. It is called natural haze because the suspended particles are naturally present in the environment.
Dust-laden winds blowing from the Sahara desert therefore cause “seasonal haze episodes” that can even cause mud or mud rain. The sky also looks yellowish or even orange.
Where does the haze come from?
In total, two regions have been identified as major sources of dust from the Sahara desert: the Bodélé depression in northeastern Chad, which forms part of the now-dry-Lake Megachad, which is also the largest source of dust in the world, and the mountainous region of Tibesti in northern Chad. Depending on where they come from, dust particles can range from 0.7 µm (microns) to 20 µm.
When the wind direction changes to the southwest in early spring, the dust is carried across the Mediterranean to northern Europe and the UK. These episodes end when there is a change in the air masses and the suspended particles are dispersed.
