Atmospheric Chemistry and Physics www.atmos-chem-phys.net 1680-7316 1680-7324 4 5 2004 10.5194/acp-4-1201-2004 http://www.atmos-chem-phys.net/4/1201/2004/ http://www.atmos-chem-phys.net/4/1201/2004/acp-4-1201-2004.html http://www.atmos-chem-phys.net/4/1201/2004/acp-4-1201-2004.pdf 1201 1215 2004-08-03 Aerosol-ozone correlations during dust transport episodes P. Bonasoni P. Cristofanelli F. Calzolari U. Bonafè F. Evangelisti A. Stohl S. Zauli Sajani R. van Dingenen T. Colombo Y. Balkanski National Research Council, Institute for Atmospheric Science and Climate, via Gobetti 101, 40129, Bologna, Italy Cooperative Institute for Research in the Environmental Sciences, University of Colorado/NOAA Aeronomy Laboratory, USA Agenzia Regionale Prevenzione e Ambiente dell’Emilia-Romagna, Struttura Tematica Epidemiologia Ambientale, Modena, Italy Joint Research Center, Ispra, Italy Ufficio Generale per la Meteorologia, Pratica di Mare, Roma, Italy Laboratoire des Sciences du Climat et de l’Environment, Gif-Sur-Yvette Cedex, France Its location in the Mediterranean region and its physical characteristics render Mt. Cimone (44&deg;11&prime; N, 10&deg;42&prime; E), the highest peak of the Italian northern Apennines (2165 m asl), particularly suitable to study the transport of air masses from the north African desert area to Europe. During these northward transports 12 dust events were registered in measurements of the aerosol concentration at the station during the period June&ndash;December 2000, allowing the study of the impact of mineral dust transports on free tropospheric ozone concentrations, which were also measured at Mt. Cimone. Three-dimensional backward trajectories were used to determine the air mass origin, while TOMS Aerosol Index data for the Mt. Cimone area were used to confirm the presence of absorbing aerosol over the measurement site. <P style="line-height: 20px;"> A trajectory statistical analysis allowed identifying the main source areas of ozone and aerosols. The analysis of these back trajectories showed that central Europe and north and central Italy are the major pollution source areas for ozone and fine aerosol, whereas the north African desert regions were the most important source areas for coarse aerosol and low ozone concentrations. During dust events, the Mt. Cimone mean volume concentration for coarse particles was 6.18 &micro;m³/cm³ compared to 0.63 &micro;m³/cm³ in dust-free conditions, while the ozone concentrations were 4% to 21% lower than the monthly mean background values. Our observations show that surface ozone concentrations were lower than the background values in air masses coming from north Africa, and when these air masses were also rich in coarse particles, the lowest ozone values were registered. Moreover, preliminary results on the possible impact of the dust events on PM₁₀ and ozone values measured in Italian urban and rural areas showed that during the greater number of the considered dust events, significant PM₁₀ increases and ozone decreases have occurred in the Po valley.