African dust influence on ambient PM levels in South-Western Europe (Spain and Portugal): a quantitative approach to support implementation of Air Quality Directives

Abstract

This manuscript proposes and validates a methodology for the quantification of the daily African PM load during dust outbreaks in southern Europe. The daily net dust load in PM10 attributable to an African episode can be obtained by subtracting the daily regional background (RB) level from the PM10 concentration value at a RB station. The daily RB level can be obtained by applying a monthly moving 30th percentile to the PM10 time series at a RB station after a prior extraction of the data coincident with African dust transport. For days with influence of African dust, the dust load is given by the difference between the daily PM10 values minus the daily PM10 RB levels. This method allows us to quantify the net African dust load without chemical speciation. The comparison between the estimated net load during African dust outbreaks (ADO) and the crustal load determined by chemical speciation of PM10 filters at three RB stations in Spain had resulted in a very good correlation (R2=0.60-0.83), being the equivalence (correlation lines’ slopes ~ 1) highly significant in the three cases.