Sources of PM2.5 impacting on Gran Canaria, Spain

Abstract

This paper reports on sequential aerosol sample sets collected at the Campus de Tafira, University of Las Palmas de Gran Canaria (ULPGC), in 2010. Gran Canaria is located approximately 250km off the coast of North Africa and at the northern margin of the dominant Saharan dust plumes being blown westward across the Atlantic Ocean. PM2.5 aerosol samples were collected on 47mm filter substrates of Teflon®, quartz fiber and Nuclepore®, generally at weekly sampling intervals. Subsets of these were analyzed for their mass, as well as elemental and ionic compositions. The 2010 annual geometric mean PM2.5 concentration at Tafira was 6.2μg/m3, with only two particularly dusty events. From a simultaneous PM10 study at the same site, a PM2.5/PM10 mass ratio of 0.35 was calculated.Diagnostic chemical ratios for PM2.5, for both moderate and severe Saharan dust events (calimas) in 2010 are:Al:Si:K:Ti:Mn:Fe:Sr1:2.818:0.330:0.078:0.012:0.847:0.0088.To better understand the mineralogy of the aerosols and for inter-comparison purposes, normative mineral compositions were calculated from the chemical compositions. Depending on their transport patterns, four source regions, each with a distinct mineralogical signature were distinguished. The Northwest to North sector (Oceanic NW) aerosols contain evaporites, secondary ammonium sulfate, lesser amounts of organic carbon, and minor amounts of quartz and other silicates. The North to Northeast sector (Europe NE) generated aerosols of evaporites, ammonium sulfate and organic carbon. The Northeast (Africa NE) sector, with influx of air from the Iberian Peninsula and North Africa, contained evaporites and secondary ammonium sulfate with some organic carbon, and minor amounts of silicates and quartz. In 2010, the main African transport pathway from the Sahara region and across northern Mali, northern Mauritania, Western Sahara and Morocco was responsible for elevated concentrations of mineral dust during calima events.