Investigating the contribution of sea salt to PM10 concentration values on the coast of Portugal

The contribution of natural sources to PM10 is generally unknown, being sea salt one of these sources, which is especially important in coastal countries. The objective of this work is to evaluate the contribution of sea salt to the PM10 concentration values along the Portuguese coast. For that, four air quality monitoring sites distributed along the coast and with PM10 valid data were selected, using the 2018 reference year. Each monitoring site was characterized in terms of the air mass trajectory patterns associated to the PM10 concentrations, using the HYSPLIT model and cluster analysis. The contribution of sea salt was assessed using data simulated by the WRF-CHIMERE modelling system, used for the air quality operational forecast for Portugal and extensively validated each year. The modelling results for each study site were extracted and processed to calculate the contribution of sea salt to the simulated total PM10 values. The results show that most trajectories came from the Atlantic Ocean, and the higher sea salt concentrations were associated to these trajectories. The sea salt contribution ranged from 7 to 15%, being higher at Atlantic-centre site and lower at the southernmost (Atlantic-Mediterranean) station. This sea salt contribution is expected to be higher during spring and lower during autumn.