Saharan dust: how it affects health and air quality

'Haze' is the presence in ambient air of large quantities of suspended particles that have been transported from natural emission sources.

PHOTOS | The haze fills the skies with orange and covers the streets with dust

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The origin of these particles is the aeolian (wind) resuspension of particles present in sandy soils or with little or no vegetation cover. This haze can have a local or distant origin, as is the case of the called “Saharan intrusion or episode” that we are experiencing this week in many regions of Spain. In this last situation and due to regional meteorological phenomena (anticyclones and storms) huge amounts of particles are dragged (emitted) into the atmosphere.

If these masses cross the mixed layer (located around 500 meters high) they are exposed to the prevailing free winds and can be dragged and travel great distances.

Consequently, these particles can reach large areas (regions) such as the distribution throughout the Mediterranean basindepositing in the countries located on its northern shore (Spain, France, Italy, etc.) and even in the central or northern Europe.

Impressive extent of #SaharanDust across the Atlantic to South America & across W Europe and Mediterranean in the @CopernicusECMWF Atmosphere Monitoring Service @ECMWF 5-day aerosol optical depth 14 March 00 UTC forecast. Data available from https://t.co/W84Bwszpqr pic.twitter.com/CfdJ30QpC4

— Mark Parrington (@m_parrington) March 14, 2022

On the other hand, usually these masses can cross the Atlantic Ocean and reach the Caribbean and the south coast of the United States. These intense episodes are very common in the Canary Islands and, to a lesser extent and intensity, in the peninsula and the Balearic Islands.

In fact, for some years there have been documents, carried out by the CSIC and supported by data from the General Directorate of Environmental Quality (MITERD), of episode prediction for each day and impact zone.

These reports include an estimation of the importance of the Saharan episodes. It is made from different dispersion models (MONARCH, SKIRON, NAAPs, etc.) that include the dust load, its transport and deposition (dry and wet). In this document, the Iberian Peninsula (Portugal and Spain) has been divided and includes the Balearic and Canary Islands.

Why are we alerted to unfavorable air quality?

Due to their size, these particles are grouped into two groups: PM10 (thoracic) and PM2.5 (breathable high risk). These indicate the aerodynamic diameters and consequently the degree of pulmonary penetration thereof, their subsequent deposition depending on the physiological state of the lung.

Regarding their composition, these Saharan particles present a large number of elements and compounds alkali and alkaline earth. Compared to the particles emitted in urban and industrial areas, they appear other characteristic compounds. For example, heavy metals (Pb, Cd, As, Ni, Cu, etc.), organic compounds such as PAHs (Polycyclic Aromatic Hydrocarbons) and organic and elemental carbon.

Due to their origin, these natural particles are presented in large concentrations in Europe and even exceed the levels of their local congeners of both natural and anthropogenic origin.

As an example, in Madrid the usual concentrations of PM10 do not usually exceed the limit value of 50 µg/m³. However, particulate matter forecasts for the current episode are between 4 and 500 µg/m³.

In fact, these high concentrations of particles, when added to those of local origin, saturate the particle measurement systems placed in the monitoring stations of the Air Quality Network (RCA). Hence the colorful changes in the maps of our mobile phones that show the quality of the air.

As a result of this increase, the networks indicate the existence of low or poor air quality and the health authorities recommend adopting some protection measures for citizens.

What risks does dust have for health?

However, when counting the episodes with high concentrations of PM10 and PM2.5 as exceedances of the legislated limit values ​​(RD 102/2011), the concentrations provided by these episodes can be discounted from the total concentrations measured, given that the networks cannot carry out any control measures for this natural emission.

Obviously, these differences in composition would lead to the production of different risks to the health of the population, which have been adequately reported in many scientific articles.

In most cases, these risks are associated with the anthropogenic elements and compounds mentioned. However, there is also scientific evidence indicating that PM10 and PM2.5 particles by themselves, and regardless of their composition, can produce effects at the pulmonary level.

In addition, PM2.5 and smaller particles (PM1) can be transported through the pulmonary alveoli into the bloodstream, which implies their subsequent systemic distribution. so could produce damage to different systems such as the heart or immune system and even increase mortality.

Consequently, during these episodes it is advisable to reduce and even not perform intense exercise or sports outdoors.

In addition, it is recommended that people with underlying respiratory diseases such as asthma or COPD (Chronic Obstructive Pulmonary Disease) stay at home.

Regarding the use of masks, their effectiveness depends on the type used and how they are used. Thus, the so-called FFP2 would be the most recommended as they reduce the entry of particles into the pulmonary system.

In short, in the event of an intense Saharan episode, such as the current one, it would be recommended that the most vulnerable people due to respiratory pathologies reduce the time they spend outdoors.

This article comes from The Conversation. read here the original.