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RESEARCH
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The Research Station of the IfT near Melpitz
The research station of the Institut für Troposphärenforschung is situated near the village of Melpitz in the vicinity of the city Torgau in the river Elbe valley (Figure 1). The station is located on a flat 100-years-old meadow surrounded by agricultural land. The distance to Leipzig is 41 km (51°32' N and 12°54 ' E, 87 m a.s.l.). The main wind direction for this location is west-south-west (WSW, Leipzig), the second wind direction is east (O, Lusatia). The research station was founded as a boundary layer-meteorological station in 1992 during the national research project SANA. The target was to quantify the change in concentration and deposition of troposheric trace gases and PM (particulate matter) caused by big changes in industry and traffic during the unification process in Germany. The decreasing of the yearly PM10 mass concentration for the Melpitz site is shown in Figure 2. The size-segregated chemical composition of particles depending on air mass origin was investigated at Melpitz because mass and number concentration of airborne PM are in the focus of environmental sciences and policy. In joint projects with the Umweltbundesamt (projects 351 01 031 and 351 01 038) and in different EMEP-campaigns supported by the Umweltbundesamt PM was extensive physically and chemically characterised.
Particle sources can be caused naturally and antropogenically by industrial, volcanic and mechanical processes at the earth surface (primary particle formation) or by different tropospheric processes (secondary particle formation). In a first step the EU-Council Directive established 2005 gave a strong regulation for the atmospheric daily mean mass concentration of PM10 to a maximum value of 50 µg m-³ limited to 35 days per year. The yearly mean for PM10 have to be < 40 µg m-³. The new Directive established in 2008 integrated particles PM2.5 also. Exceeding of the daily maximum mean value for PM10 in cities are caused by complex reasons (e.g. traffic, domestic heating, and resuspension of particles). But also high particle mass concentrations observed over a wide area in the surrounding of a conurbation can be contribute to the number of days with exceeded PM10 values. From May 2004 until April 2007 at Melpitz particle filter samples were collected daily (24 hour samples) for PM10 and PM2.5 and every six days for PM1 on quartz fiber filters using high volume samplers DIGITEL DHA-80. Figure 1. The particle mass concentration was determined gravimetrically with a micro balance (20 °C, 50% relative humidity). Water-soluble ions were quantified using standard ion chromatography. The determination of organic Carbon (OC) and elemental Carbon (EC) was performed by a 2-step thermographic method applying a Ströhlein C-mat 5500 carbon analyzer. The days for the average determination were selected following the two main air stream directions west (maritime and continental) and east (continental) from the data set of measurements PM10, PM2.5 and PM1 using 96-backward trajectories (level 200, 500 and 1500 m above ground) for 10:00 and 18.00 (CET). A distinction for summer (first of May until 31 of October) and winter (first of November until 30 of April) was done additionally.
Figure 3 presents the means distinguished for particle size, air mass origin and season. In principle the concentration means for continental air masses are higher than for maritime air masses. Reasons are the different meteorological conditions. During days with westerly winds the mean wind velocity is often high and rain showers are integrated, as opposite, during easterly winds high-pressure conditions exist with dry air masses and moderate wind velocities. The main source regions for maritime air masses are Germany, Benelux, France and sea surfaces, for continental air masses these are Poland, Belarus, Ukraine and the Czech Republic. In these areas in contrast to Western Europe coal-heated power plants with little exhaust treatment, old industry and older cars still exist. For the maritime air masses the differences between summer and winter are low but in summer more coarse particles (PM10-PM2.5) exist resuspended mostly from dry surfaces. In winter higher mass concentration was detected for SO4--, NO3-, and NH4+ from semi-volatile inorganic components. The highest values for PM2.5 and PM10 were reached in continental air masses during winter. The anthropogenic emission rates are than the highest and the mixing heights are low. In this situation the (PM10-PM2.5) fraction is relatively small. That means more particles situated for long-range transport are in the troposphere. Therefore continental weather conditions in winter are often connected with high particle mass concentrations in a wide area. In these situations PM10 mass concentrations reach often more than 50 µg m-3 but also concentrations somewhat lower contributes in larger cities to an unavoidable exceeding of the daily maximum value of 50 µg m-³. These results are part of a national contribution to the EMEP/TFMM PM Assessment Report.
The IfT-research station Melpitz is a supersite in the European Network for the extensive characterization of aerosol EUSAAR and a place with infrastructure for field experiments.
In a joint project with Gewerbeaufsichtsamt Hildesheim a new photo-acoustic detection for Ammonia (Omnisens, CH), was tested by IfT at Melpitz site (background), Hannover (traffic station) and Bösel (high NH3-concetration from agriculture) in comparison with other physical and wet chemical ammonia detection methods. Results can be found in the AMMONISAX-report.
The Melpitz site was established as a background station in relation to the city of Dresden and as place for estimation of the influence of changing weather conditions caused by climate change at PM in the atmosphere in the national project REGKLAM from 2008 until 2013.
Melpitz is one point in the German network for the characterization of ultra-fine PM, supported by Umweltbundesamt (research project 3703 43 200).
Figure 1: Research station Melpitz with high-volume samplers for PM1, PM2.5 and PM10.
Figure 2: PM10 mass concentration (yearly means) at Melpitz site from 1992 until 2007.
The error bars represent the variation of daily means. The precipitation amount is plotted as invers.
Figure 3: Mean PM1, PM2.5 and PM10 mass concentrations, the concentrations of the main ions (nitrate, sulfate and ammonium) and of OC and EC in winter and summer. Only days with air mass transport explicitly from West (blue frame) or from East (green frame) are considered. The error bars are the standard deviation for the particle mass concentration. "n" is the number of measurement days. Averages of three winters (2004/05 till 2006/07 and summers (2004 till 2006) are shown.
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