Inventory of African desert dust events in the north-central Iberian Peninsula in 2003–2014 based on sun-photometer–AERONET and particulate-mass–EMEP data

Abstract

Abstract. A reliable identification of desert dust (DD) episodes over north-central Spain is carried out based on the AErosol RObotic NETwork (AERONET) columnar aerosol sun photometer (aerosol optical depth, AOD, and Ångström exponent, α) and European Monitoring and Evaluation Programme (EMEP) surface particulate-mass concentration (PMx, x = 10, 2.5, and 2.5–10 µm) as the main core data. The impact of DD on background aerosol conditions is detectable by means of aerosol load thresholds and complementary information provided by HYSPLIT (Hybrid Single Particle Lagrangian Integrated Trajectory Model) air mass back trajectories, MODIS (Moderate Resolution Imaging Spectroradiometer) images, forecast aerosol models, and synoptic maps, which have been carefully reviewed by a human observer for each day included in the DD inventory. This identification method allows the detection of low and moderate DD intrusions and also of mixtures of mineral dust with other aerosol types by means of the analysis of α. During the period studied (2003–2014), a total of 152 DD episodes composed of 418 days are identified. Overall, this means ∼ 13 episodes and ∼ 35 days per year with DD intrusion, representing 9.5 % days year−1. During the identified DD intrusions, 19 daily exceedances over 50 µg m−3 are reported at the surface. The occurrence of DD event days during the year peaks in March and June, with a marked minimum in April and lowest occurrence in winter. A large interannual variability is observed showing a statistically significant temporal decreasing trend of ∼ 3 days year−1. The DD impact on the aerosol climatology is addressed by evaluating the DD contribution in magnitude and percent (in brackets) for AOD, PM10, PM2.5, and PM2.5 − 10, obtaining mean values of 0.015 (11.5 %), 1.3 µg m−3 (11.8 %), 0.55 µg m−3 (8.5 %) and 0.79 µg m−3 (16.1 %), respectively. Annual cycles of the DD contribution for AOD and PM10 present two maxima – one in summer (0.03 and 2.4 µg m−3 for AOD in June and PM10 in August) and another in March (0.02 for AOD and 2.2 µg m−3 for PM10) – both displaying a similar evolution with exceptions in July and September. The seasonal cycle of the DD contribution to AOD does not follow the pattern of the total AOD (close to a bell shape), whereas both PM10 cycles (total and DD contribution) are more similar to each other in shape, with an exception in September. The interannual evolution of the DD contribution to AOD and PM10 has evidenced a progressive decrease. This decline in the levels of mineral dust aerosols can explain up to 30 % of the total aerosol load decrease observed in the study area during the period 2003–2014. The relationship between columnar and surface DD contribution shows a correlation coefficient of 0.81 for the interannual averages. Finally, synoptic conditions during DD events are also analysed, observing that the north African thermal low causes most of the events ( ∼ 53 %). The results presented in this study highlight the relevance of the area studied since it can be considered representative of the clean background in the western Mediterranean Basin where DD events have a high impact on aerosol load levels.

Spatiotemporal evolution of a severe winter dust event in the western Mediterranean: Aerosol optical and physical properties

“…As explained in section 1, desert dust outbreaks affect the Iberian Peninsula more frequently during spring and summer months [ Querol et al ., , ; Rodríguez et al ., ; Escudero et al ., , Pey et al ., ; Cachorro et al ., ]. Winter events are less frequent but usually of higher intensity [ Prospero et al ., ].…”

“…It has also significant implications for cloud microphysics [e.g., Creamean et al, 2013], atmospheric chemistry [e.g., Querol et al, 2009], human health [e.g., Perez et al, 2008;Pandolfi et al, 2014a], and the carbon cycle via the fertilization of marine and terrestrial ecosystems [e.g., Koren et al, 2006]. A great attention has been paid over the last years to characterize dust transport processes in the western Mediterranean [Rodríguez et al, 2001;Escudero et al, 2005;Querol et al, 2009;Pey et al, 2013;Salvador et al, 2014] and their impact on dust surface concentrations [e.g., Querol et al, 1998Querol et al, , 2009Rodríguez et al, 2011;Cabello et al, 2012;Pey et al, 2013;Salvador et al, 2013;Cachorro et al, 2016] and aerosol optical properties [e.g., Valenzuela et al, 2012aValenzuela et al, , 2012bValenzuela et al, , 2015. Despite this, up to date, atmospheric mineral dust is still recognized as one of the main uncertainties in climate change projections [IPCC, 2013], related to its high temporal and spatial variability, different transport pathways, and vertical distribution in the atmosphere, among other factors.…”

Multiyear Typology of Long-Range Transported Aerosols over Europe

“…Southwestern circulations were mostly linked with Dust events, while southern, southeastern, and eastern circulation types were associated with Marine/Clouds. Western (19.0% anticyclonic, 4.8% cyclonic) and southwestern (12.9% anticyclonic, 3.4% cyclonic) circulation types characterized the Southwestern cluster, explaining the presence of Dust particles [60] and Marine/Clouds. In addition, northwestern and northern and eastern circulations allowed the humid air masses to transport Marine/Clouds from the Atlantic and the Mediterranean Sea toward the Iberian Peninsula.…”

“…particles [60] and Marine/Clouds. In addition, northwestern and northern and eastern circulations allowed the humid air masses to transport Marine/Clouds from the Atlantic and the Mediterranean Sea toward the Iberian Peninsula.…”

Transport of Mineral Dust and Its Impact on Climate

“…Less in amount but still significant and regularly occurring, dust originating from the Sahara and its northern margins is transported towards the Mediterranean and Europe. On average, 13 events per year were observed over the Iberian Peninsula preferably occurring during May to August [76,77], Flentje et al [78] observed about 5-15 events per year over southern Germany. These events are associated with a mid-latitude disturbance entering the North African continent [79][80][81].…”