A significant episode of Saharan dust transport was observed by Cnr-Isac on the morning of August 27 at the Ottavio Vittori Climate Observatory on Monte Cimone, the research station of the Institute of Atmospheric Sciences and Climate of the National Research Council, located at 2,165 meters altitude in the northern Apennines.
Measurements taken directly in the atmosphere showed, starting from the early hours of August 27, a strong and rapid increase in the concentration of coarse particles, with a diameter greater than one micrometer, attributable to dust coming from the Sahara.
Saharan dust, PM10 close to 100 micrograms
According to Cnr-Isac observations, the PM10 concentration reached values close to 100 micrograms per cubic meter, while the number of coarse particles reached about 5 particles per cubic centimeter.
These values are significantly higher than those recorded in the previous days and about an order of magnitude above the threshold of 0.4 particles per cubic centimeter calculated for the Monte Cimone observatory.
Reduced visibility due to the arrival of sand from the Sahara
The particulate transport was also evident from the images of the Observatory’s webcam. The comparison between footage taken at the same time on August 26 and 27 shows the transition from good visibility conditions to a heavily veiled atmosphere, with a marked reduction in visibility.
The concentrations of desert dust indeed caused a drop in atmospheric visibility, from over 20 kilometers to about 12 kilometers with the arrival of the air mass coming from the Sahara.
Saharan dust, particulate matter reaches up to 5 kilometers altitude
The episode did not only affect the air immediately in contact with the ground but involved several kilometers of the atmosphere.
Observations made at Monte Cimone through a remote sensing system, the Automated-Lidar-Ceilometer, active in the national ALICENET network, highlighted in real time the distribution of particles at different altitudes.
The aerosol signal was present in the troposphere throughout the day, with particularly intense structures between about 2 and 5 kilometers altitude. After 12 UTC, 14 in Italy, the particles showed a progressive descent towards the ground.
For the Cnr, the presence of this thick dust layer and the increase in coarse particles measured at the surface are consistent with the passage of an air mass containing a significant amount of mineral particulate, namely the so-called Saharan sand.
Trajectories confirm origin from the Sahara
The origin of the air mass is also confirmed by the backward trajectories calculated through the NOAA HYSPLIT model.
The forecasts of the Copernicus Atmosphere Monitoring Service (CAMS) also indicate the presence of an area characterized by high concentrations of aerosol and dust over Italy and the Mediterranean.
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The combination of measurements taken directly in the atmosphere, remote observations, and forecast models thus allows not only to reconstruct the presence of the episode but also its three-dimensional dynamics and the transport of particles through the atmosphere.
PM10 above the guideline value indicated by WHO
The episode is particularly significant also regarding air quality.
At Monte Cimone, the PM10 concentration exceeded 45 micrograms per cubic meter, a value indicated by the World Health Organization (WHO) as a guideline for the 24-hour average in the global air quality recommendations.
The presence of mineral dust can therefore significantly contribute to the increase in PM10 concentrations, even in urban areas.
Why Saharan sand increases PM10
Desert particulate matter is mainly composed of relatively large particles. This characteristic can cause particularly marked increases in the coarse component of atmospheric particulate matter.
The phenomenon observed by the Cnr thus represents an example of how long-distance dust transport can affect the composition of the atmosphere even thousands of kilometers from the areas of origin.
Monte Cimone, a strategic observatory for atmospheric study
The episode confirms the importance of measurements taken at high altitude. Monte Cimone is indeed the main Italian station for studying the composition of the atmosphere at altitude and is the only GAW-WMO Global Station present nationally and in the Mediterranean area.
The position of the Ottavio Vittori Observatory, at over 2,000 meters altitude and far from major local pollution sources, allows observing the arrival of air masses from distant regions and studying aerosol transport on a regional and continental scale.
Saharan dust, Cnr monitoring continues
The combined monitoring of particles present at ground level and aerosols along the atmospheric column allows distinguishing long-distance transport episodes from variations in air composition related to local sources.
These observations are also important for understanding interactions between aerosols, air quality, and climate. Atmospheric particles can influence both human health and the radiative balance and hydrological cycle of the atmosphere.
Measurements at the Ottavio Vittori Observatory will continue in the coming hours to follow the evolution of the episode and verify the duration and characteristics of dust transport over the Northern Italy area.
