African dust contribution to ambient aerosol levels across central Spain:Characterization of long-range transport episodes of desert dust.

This work presents a summary of the results obtained from a study of the impact of African dust on levels of atmospheric suspended particulate matter registered among different monitoring sites in the Madrid Air Basin, in the centre of the Iberian Peninsula. African dust outbreaks were identified over the period 2001–2008. Lidar measurements helped to assess thetemporal evolution of the dust layers and subsequent impact on the surface boundary layer. Monthly trends were analyzed, revealing a late spring/summer maximum occurrence of episodes. The most common synoptic meteorological situations causing the transport of the African dusty air masses were also identified o ver the seasons. Time series of particulate matter daily concentrations recorded across Air Quality Network monitoring stations and sampling campaigns were collected and analysed. Our results show the contribution of mineral dust to PM10 (particulate matter lower than 10 μm, aerodynamic diameter) during African dust outbreaks to be significantly high at rural and urban sites of the Madrid Air Basin, giving rise to exceedances of the PM10 daily limit value (50 μg/m3). This result is especially relevant since European directive 2008/50/EC on air quality, takes into account the potential exceedance of the PM10 daily limit value, due to the transport of natural particles from arid regions.This work was funded by the Spanish Ministry of the Environment and Rural and Marine Affairs (010/PC08/3-04.1), research project GRACCIE-CSD2007-00067 and Acción IntegradaPT2009-0151. The authors wish to thank the Environmental Department of the D.G. Environmental Quality, Control and Assessment of the Madrid City Government and the Comunidad de Madrid for the support provided for sampling at Escuelas Aguirre, Alcobendas and Chapineria stations and for providing the time series of pollutants concentrations recorded at the Air Quality Networks monitoring stations. We acknowledge the Atmospheric Modelling & Weather Forecasting Group in the University of Athens, the Atmospheric Modelling Laboratory from the Barcelona Supercomputing Centre, NOAA Air Resources Laboratory (ARL), the Naval Research Laboratory and the SeaWiFS project (NASA) for the provision of the SKIRON, DREAM, NAAPs aerosol maps, and the satellite imagery, respectively. ECMWF and NILU are acknowledged for providing the data sets and the FLEXTRA trajectories computed from Madrid site (http://www.nilu.no/trajectories/). The developers of the FLEXTRA model (Andreas Stohl, Gerhard Wotawa and Petra Seibert) are also acknowledged. The authors would like to thank the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA for providing the meteorological dataset files (http://www.cdc.noaa.gov/) used for the composition of the synoptic situations.Peer Reviewe