Analysis of the role of Saharan Dust Intrusions in PM10 precipitation scavenging in the NW Mediterranean Region

Nowadays, atmospheric pollution is one of the most relevant environmental issues. Some pollutants such as fine particulate matter with a diameter of 10 μm or less (PM₁₀) have a considerable impact on human health. In Catalonia (NE Spain), Saharan Dust Intrusions are a major source of PM₁₀. In recent decades, a positive trend of these intrusion episodes has been detected in the NW Mediterranean basin. Moreover, precipitation plays a role in pollutant scavenging processes.

In our work, we make an analysis of the changes in PM₁₀ concentrations with the precipitation episodes. Moreover, we put a special emphasis in the precipitation episodes which happen simultaneously with a Saharan Dust Intrusion. In consequence, we have analysed PM₁₀ concentration data from the Catalan Network for Pollution Control and Prevention and precipitation data from Automatic Weather Stations Network of the Meteorological Service of Catalonia. We use data from four measurement points in Catalonia (Montsec Observatory, Fabra Observatory, Vic and Sort) which are the unique points with precipitation and PM₁₀ measurement instruments at the same location. Dataset contains 4-year data from 2019 to 2022. Specifically, we evaluate how daily mean PM₁₀ concentration values for all the days in the dataset change in comparison to the values of the same variable for the previous day. Moreover, we do a separate analysis for days with observed precipitation (wet days) and days without precipitation (dry days). Also, we perform the analysis for days with Saharan Dust Intrusion and days without Saharan Dust Intrusion. Furthermore, we filter daily PM₁₀ concentration changes for different absolute values of this daily variation to see the differences between great and small changes of daily PM₁₀ concentration. To our knowledge, this is the first study of these characteristics in this region of study.

In general, we observe a decrease of daily PM₁₀ mean concentration levels with precipitation in approximately 60% of the days. This percentage increases to 80% for daily changes of PM₁₀ concentration higher than 10 µg m^-3. In wet days with Saharan Dust Intrusion, daily PM₁₀ mean concentration decreases only in 50% of the cases independently of the absolute value of PM₁₀ concentration variation. However, in wet days without Saharan Dust Intrusion, daily PM₁₀ mean concentration decreases approximately in 60% of the cases. This percentage grows up to 90% if we only consider changes of PM₁₀ concentration higher than 10 µg m^-3. In consequence, Saharan Dust Intrusions clearly interfere with the usual pollutant precipitation scavenging processes. In addition, we find that scavenging processes are more effective above a certain PM₁₀ concentration variation threshold. This study was performed in the framework of the project "Towards a climate resilient cross-border mountain community in the Pyrenees (LIFE22-IPC-ES-LIFE PYRENEES4CLIMA)".