Abstract

Nowadays, the dust coming from the Sahara desert (SD), is widely recognised having a strong impact on the air quality in Europe (Remoundaki, 2011). Whereas in the past, the events of long-range transport of the mineral dust from the African desert mainly reached southern Europe, now, due to climate change, they can also travel to higher latitudes. The presence of this dust in the atmospheric aerosol has several direct effects on the weather and climate as absorbing incoming solar radiation on earth through scattering and absorbing phenomena. It has also some indirect effects as increasing cloud coverage and reducing precipitations throught the cloud condesation nuclei particles´s ability. These events generally alter the normal level of Particulate Matter (PM), even exceeding the limits of the directive for the air quality in Europe, affecting aerosol mass load, its size distribution and its chemical speciation. Moreover, the concentrations of several chemical species are raised, causing potential damages to the environment and human health (Tositti, 2022).

The present study focuses on the evaluation of the elemental and ionic fractions of PM2.5 samples collected during several SD storm events that crossed the city of Munich, Germany. The PM2.5 samples have been daily collected on quartz fiber filters from March to May 2022. The elemental fraction was evaluated by Inductively Coupled Plasma Mass Spectrometry (ICPMS), while the ionic fraction was evaluated by Ion Chromatography (IC). In the first case, samples were extracted by microwave-assisted acid digestion, followed by aqueous dilution. The quantification was performed with an external calibration line. In the second case, samples were extracted in aqueous solution and quantification was performed with an external calibration line.

These results were combined with Optical Particle Sizer (OPS) data, meteorological data, and physical transport-based models as backtrajectory analysis.

The dataset was treated with advanced chemometric techniques, such as Varimax analysis and Self-Organising Maps (SOM) that allows to group daily observations in order to find patterns of samples and variables. SOM was applied to our dataset to fully describe the atmospheric alterations due to SD events. Moreover, SOM was evaluated as a possible alternative to source apportionment methods for a reduced dimension dataset.

First results have shown a general increase in PM concentrations during the SD events of March 2022. In addition, it was also possible to identify some differences in the chemical composition of the two SD events due to a different aerosol enrichment, possibly related to their different paths, as shown in Figure 1. SOM well discriminated the SD events from the normal urban pollution of Munich, indicating the enrichment of some elements (in particular, but not limited to, crustal ones) due to the presence of SD. Correlating SOM results with other data analyses, as meteorological time-series, Varimax, and enrichment factor analysis, made it possible to fully describe the effects of SD on the urban pollution in Munich.

Remoundaki, E. (2011) PM10 composition during an intense Saharan dust transport event over Athens (Greece). Science of the Total Environment.

Tositti, L. (2022) Development and evolution of an anomalous Asian dust event across Europe in March 2020. Atmospheric Chemistry and Physics.