Saharan Dust Advection Research Articles

Effects of Saharan Dust Advection on Atmospheric Aerosol Properties in the West-Mediterranean Area

Eight measurement campaigns for the characterization of atmospheric aerosol properties were conducted from 2001 until 2008 at five sites located in the Western Mediterranean basin. Radiometric measurements were used to obtain Aerosol Optical Depth, &#xc5;ngstr&#xf6;m parameters, and aerosol size distributions, allowing differentiation of background conditions from anthropogenic, marine, or Saharan dust aerosol advection. The analysis was focused on the study of optical and physical properties variation of atmospheric aerosols under Saharan outbreaks. Dust-affected data were analysed all together, independently from the measurements site, thus allowing the highlighting of similarities and differences among them. The scatter-plot &#xc5;ngstr&#xf6;m exponent versus AOD at 780&#x2009;nm shows a correlation among all dust data, while an overlapping region with no-dust data reveals the simultaneous presence of mineral, anthropogenic, and marine particles. Daily averaged volume size distributions can be unimodal or bimodal functions and one three-modal distribution, with a coarse mode generally prevailing. Finally, considering the ratio of small/large particles <svg style="vertical-align:-3.2316pt;width:29.762501px;" id="M1" height="14.7125" version="1.1" viewBox="0 0 29.762501 14.7125" width="29.762501" xmlns="http://www.w3.org/2000/svg"> <g transform="matrix(1.25,0,0,-1.25,0,14.7125)"> <g transform="translate(72,-60.23)"> <text transform="matrix(1,0,0,-1,-71.95,63.5)"> <tspan style="font-size: 12.50px; " x="0" y="0">𝑛</tspan> </text> <text transform="matrix(1,0,0,-1,-65.74,60.37)"> <tspan style="font-size: 8.75px; " x="0" y="0">𝑠</tspan> </text> <text transform="matrix(1,0,0,-1,-61.39,63.5)"> <tspan style="font-size: 12.50px; " x="0" y="0">/</tspan> <tspan style="font-size: 12.50px; " x="3.4758339" y="0">𝑛</tspan> </text> <text transform="matrix(1,0,0,-1,-51.7,60.37)"> <tspan style="font-size: 8.75px; " x="0" y="0">𝑙</tspan> </text> </g> </g> </svg> and plotting the corresponding histogram for all dust data, a sharp frequency distribution is obtained with 89&#x25; of data in the range 5&#x2013;65, while 89&#x25; of no-dust data extend from 5 to 135, in spite of different sources, pathways, and arrival sites.

Effect of Atmospheric Pollutants on the Air Quality in Tunisia

This paper presents the evolution of Saharan dust advection when the PM10 (particles with an aerodynamic diameter below 10 μm) concentration exceeds standard limits in different Tunisian sites. Meteorological and concentration data (from 2004 to 2010) obtained from several monitoring stations and in situ measurements were used to identify African dust change in seasonal occurrence, their source origin, and their impact on surface PM10 concentrations. We pointed out that the Saharan dust contribution caused frequently the surpassing of the maximum number of days in excess of EU standard limits as well as of the maximum yearly average in the Mediterranean Tunisian coasts. The maximum daily concentration reaches 439 μg/m3 during the Saharan events. The decrease in particulate levels recorded at the end of each event is due to the injection of European air masses and rainfalls. Primary pollutants peaks were much higher in winter than in summer which can be explained on the basis of the lower ventilation and mixing.

Saharan dust episodes in Italy: influence on PM10 daily limit value (DLV) exceedances and the related synoptic

The relevance of dust outbreaks from the Sahara into Italy was evaluated for the period from 2001 to 2007. To this end, days affected by Saharan dust were recognized at four PM(10) background stations belonging to the Regional Agencies for Environmental Protection (ARPA) monitoring networks (one working in the 2005-2007 period only). The analysis included computation of back trajectories, complemented with satellite images and meteorological charts. Results from other models are also collected for comparison. Saharan Dust contribution to PM(10) was calculated referring to a method developed for Iberian monitoring networks. PM(10) exceeding the daily limit value (DLV) of the European Union air quality standard were reviewed also. The provenience of air masses yielding the exceedances was also recognized, allowing to distinguish the Atlantic-European episodes from the (Atlantic)-Saharan ones. The European episodes are due to anthropogenic pollution that affected mainly northern Italy in winter; instead, the Saharan ones are due to dust outbreaks that affected mainly southern Italy in summer. Central Italy is characterised by a transitional situation that is experienced from north to south. A number of dust affected days with DLV exceedance (from 4 to 108 at the considered stations) were identified and grouped into 55 Saharan dust episodes. Analysis showed that DLV exceedances due to Saharan dust advection vanish at all stations when dust contributions are subtracted. A synoptic analysis based on the meteorological charts was carried out allowing a view of Saharan dust transport into Italy for each meteorological season. Notwithstanding that summer is the season most influenced by Saharan episodes at all of the stations, the analysis showed a low-high system of anomalies on the geopotential height distribution causing south-southwesterly flow carrying dust into Italy during the other seasons.

Chemical characterization of fine particulate matter during peak PM10 episodes in Apulia (South Italy)

Some peak PM10 episodes, occurred during PM monitoring campaigns performed on October 2005 and February and June 2006 in Bari town, have been characterized. Moreover back trajectories of air masses and Principal Component Analyses were applied. Three of the peak PM10 episodes investigated were related to local emissions of primary pollutants during poor atmospheric dispersion conditions. The other two peak PM10 episodes considered are related with long range transport air masses toward Apulia region: in one case the chemical characterization and the back trajectories analysis indicate that high PM10 value detected is due to the Saharan dust advection in the Apulia region; in the other case air masses with different origin give rise to high PM10 value. Moreover PM10 daily mean concentrations, presented in this paper collected from January 2005 to August 2007 and obtained by automatic device in six stations of air quality monitoring networks in Bari territory, do not show a seasonal trend for PM10 concentrations, contrary to the PM10 trend shown in the towns of North Italy. This can be explained mostly considering that our region presents generally meteo-climatic conditions that favour pollutants dispersion.

Estimating the impact of Saharan dust on the year 2001 PM 10 record of Rome, Italy

This paper evaluates the role of Saharan dust advection in the exceeding of the PM 10 thresholds in the city of Rome, Italy. To this purpose, a series of observations and model forecasts recorded in the year 2001 are analysed and discussed. Lidar profiles collected over 168 days of the year are employed to both assess the presence and magnitude of Saharan dust layers over the city and to evaluate the depth of the planetary boundary layer. Backtrajectories are used to verify the Saharan origin of the lidar-sounded air masses. Model predictions of the presence of Saharan dust over the area are employed to fill the time gaps between lidar observations. PM 10 and carbon monoxide records of both a city background (Villa Ada) and a heavy traffic station (Magna Grecia) are cross-analysed with the dust events record and meteorological data. The analysis shows that: (1) Saharan dust was advected over Rome on about 30% of the days of 2001; (2) mean contribution of Saharan dust transport events to daily PM 10 levels was of the order of 20 μg m −3; (3) at the urban background station of Villa Ada, the Saharan contribution caused the surpassing of the maximum number of days in excess of 50 μg m −3 fixed by the current legislation (35 per year). Conversely, at the heavy traffic station of Magna Grecia the Saharan contribution was not determinant at causing the observed large exceeding of that limit, as well as of the maximum yearly average of 40 μg m −3; (4) 25% of the Saharan advection days (of the order of 100/year at Rome) led to a PM 10 increase >30 μg m −3, 4% caused an increase >50 μg m −3, thus leading on their own to surpassing the 50 μg m −3 daily limit.

Size-segregated aerosol mass closure and chemical composition in Monte Cimone (I) during MINATROC

Abstract. Physical and chemical characterizations of the atmospheric aerosol were carried out at Mt. Cimone (Italy) during the 4 June-4 July 2000 period. Particle size distributions in the size range 6nm-10µm were measured with a differential mobility analyzer (DMA) and an optical particle counter (OPC). Size-segregated aerosol was sampled using a 6-stage low pressure impactor. Aerosol samples were submitted to gravimetric and chemical analyses. Ionic, carbonaceous and refractory components of the aerosol were quantified. We compared the sub- and superµm aerosol mass concentrations determined by gravimetric measurements (mGM), chemical analyses (mmCA), and by converting particle size distribution to aerosol mass concentrations (mmSD). Mean random uncertainties associated with the determination of mmGM, mmCA, and mmSD were assessed. The three estimates of the sub-µm aerosol mass concentration agreed, which shows that within experimental uncertainty, the sub-µm aerosol was composed of the quantified components. The three estimates of the super-µm aerosol mass concentration did not agree, which indicates that random uncertainties and/or possible systematic errors in aerosol sampling, sizing or analyses were not adequately accounted for. Aerosol chemical composition in air masses from different origins showed differences, which were significant in regard to experimental uncertainties. During the Saharan dust advection period, coarse dust and fine anthropogenic particles were externally mixed. No anthropogenic sulfate could be found in the super-µm dust particles. In contrast, nitrate was shifted towards the aerosol super-µm fraction in presence of desert dust.