The Influence of the Moselle Valley on Urban Air Quality at Trier / Germany
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THE INFLUENCE OF THE MOSELLE VALLEY ON URBAN AIR QUALITY AT TRIER / GERMANY Alfred Helbig*, Jürgen Junk*, *University of Trier, Germany Abstract The center of Trier is located in the valley of the Moselle river. The wind field and the vertical turbulent exchange, modified by the topography, determine the emission concentration of air pollutants in city area. Trend analyses of the emission concentration of NO2, SO2 and CO show significant negative trends for the period from 1996 until 2002. A similar situation can be observed at the total dust values. In contrast to that the emission concentration of PM10 measured at Trier is higher than in towns with even more traffic and industry. Especially during calm weather situations, the air quality at the city is substantially reduced. Daily courses of emission concentration of pollutants mentioned above at selected days with reduced turbulent exchange are presented and discussed. Finally, some advices are given for urban planning and traffic control to reduce air pollution at Trier. Key words: air pollution, PM10 concentration, trend analysis, wind field air temperature inversion 1. INTRODUCTION Trier is situated in the southwest of Germany near the border to Luxembourg and France in the Moselle valley. The city covers an area of about 117 km2 including all suburbs. With approx. 100.000 inhabitants Trier is one of densely populated districts of the region. The main settlement is located at the lower terrace in the NE/SW Moselle Valley (140 m asl). The partly inhabited adjacent areas of middle and main terrace are at altitudes between 260 m and 330 m. The NE/SW channel shaped valley forces the average wind field into these main directions The intensifying urban sprawl leads to separation between living and working sites, to a shift from public to individual traffic with all well known negative consequences of increasing number of cars. The increase of traffic combined with rising consumption of material and energy in industry, trade and private households creates a permanent challenge for environmental protection and air pollution management. During calm autochthonous weather situations, local air flows modify the wind and temperature field in the urban canopy layer. The side valleys, the inhabited hillsides, and the wine-growing region cause spatial pattern of meteorological parameters that differs from those in a city on flat land. The relief-influenced wind field and the vertical turbulent exchange determine the concentration of air pollutants in the city area. The vertical mixing depends on the thermal stratification, which shows typical modifications in the valley, especially during the existence of air temperature inversion. After JACOB and MICHELS (2001) the citizen of Trier often complains about discomforting micro climate conditions and insufficient air circulation. The most mentioned reason for a higher stress cause by air pollutants is the city location at the valley bottom. Reported in the "Regional State Health Survey for the City of Trier", the specific inner city bioclimate especially during summer seems to be responsible for increasing problems with the cardiovascular system and headaches. Our investigations should show if the perception of the inhabitants can be verified by meteorological and air pollution measurements. 2. DATA AND METHODS For this study climatological data from the Deutscher Wetterdienst (DWD) weather Stations Trier - Petrisberg, situated at the main terrace, 120 m above valley bottom as well as meteorological and air quality data from the ZIMEN stations Trier-Weberbach, Trier - Ostallee, Koblenz - Friedrich-Ebert-Ring and Kaiserslautern - Rathaus are available. Our own network consists of four automatic meteorological stations and five DWD screen houses with thermo- hygrographs. Since June 2001 wind speed and wind direction is measured at a meteorological tower in the industrial area southwest of the city. Unfortunately the data series cover different time intervals therefore a synoptic comparison is not always possible. An instrumented van for mobile meteorological and air quality measurements is available. This van enables us to make continuous measurements during drive or singular registrations at specific sites within and outside the city area. * Corresponding author address: Jürgen Junk, Department of Climatology, University of Trier, Germany, 54286 Trier, Germany e-mail: [email protected] 3. AIR QUALITY SITUATION AT TRIER 3.1 Trends of emission concentration of air pollutants In the city of Trier the air quality is primarily controlled by the emissions of the vehicles, combustion plants in industry and trade. Depending on the meteorological situation the gaseous and particle emissions from single point, line or area sources are being transported over great or small distances. These particles were removed from the air by dry, humid or wet deposition A general overview about NO2, SO2 and O3 concentrations (monthly means) in the years 1996 - 2002 in the city of Trier is given in figure 1. In contrast to the NO2 emission concentration the pollutants SO2 and O3 shows clear annual variations. 70 Table 1: Trends of O3, SO2 und NO2 based on NO2: y = -0.134x + 51.67 R² = 0.283 NO2 SO2 Ozon SO2: y = -0.118x + 12.17 R² = 0.280 monthly mean values 60 O3: y = 0.019x + 24.72 R² = 0.002 trend value [µg/m³] significance[%] ³ 50 O3 +2.95 86.0 SO2 -9.11 > 99.5 n, µg/m o ati 40 NO2 -10.26 > 99.5 entr nc o 30 All trend analyses of the air quality data were on c i s s performed with a Statistic Program Library mmi i 20 (Version 1.0) of the Potsdam Institute for Climate Impact Research (PIK 1999). The emission 10 concentration of SO2 as well as the concentration 0 of NO2 show significant negative trends (table 1). Jan 96 Jul 96 Jan 97 Jul 97 Jan 98 Jul 98 Jan 99 Jul 99 Jan 00 Jul 00 Jan 01 Jul 01 Jan 02 Jul 02 This is the consequence of successful state-aided measures concerning air pollutant control. In Figure 1: Monthly means of emission concentration of contrast to this the trend of O concentration is NO , SO , O , at Trier – Ostallee, 1996 - 2002 3 2 2 3 positive but not statistically significant. The maximum values of O3 concentration are decreasing in the last years but the mean values show a small increase (JUNK, HELBIG, LÜERS 2003). Besides these "classical" air pollutants, the stress caused by dust is becoming more and more important. Particles with an aerodynamic diameter less than 10 µm can intrude deep into the lung and carry polycyclic aromatic hydrocarbons which are dangerous to the human health. With increasing PM10 concentration more chronic illnesses of the respiratory organs can be observed. A positive correlation between PM10 concentrations and mortality rates are discussed WORDLEY et al. 1997. In accordance with the new European 50 Commission Council Directive Trier Kaiserstr Trier Ostallee 45 1999/30/EC, new threshold values for Kaiserslautern Koblenz PM10 were defined. The limit values /m³ 40 obligatory from 2005 on permit an µg in annual mean of 40 µg/m³ PM10. On 35 10 M 35 P days a year the daily mean on of concentration may exceed 50 µg/m³. i 30 rat Since January 2001 the hourly 25 concentrations of PM10 are measured at two sites in Trier as well as in 20 Koblenz and Kaiserslautern. Figure 2 emission concent shows the monthly mean values of 15 PM10 concentrations at these selected sites. The stations Kaiserslautern and 10 Jan 01 Jul 01 Jan 02 Jul 02 Koblenz as well as the stations at Trier are situated in streets with heavy traffic. Because the three towns have Figure 2: PM10 emission concentration at selected ZIMEN stations, 2001 - 2002 nearly the same number of inhabitants and they are situated in valleys we can expect a similar air quality. Table 2 contains the annual mean values and the yearly number of days with PM10 concentration greater than 50 µg/m³. A detailed statement of the situation in Rhineland-Palatinate can be found by JUNK, HELBIG 2003. In view of increasing PM10 dust loads it is planed to model the spatial structure of PM10 concentration at Trier with the computer program STREET 4.1 (KTT 2003). Table 2: Annual means and number of days with PM10 concentration > 50 µg/m³ at selected ZIMEN stations 2001 2002 ZIMEN Station Annual means Number of days Annual means Number of days (Threshold with concentration (Threshold with concentration = 40 µg/m³) > 50 µg/m³ = 40 µg/m³) > 50 µg/m³ Trier - Kaiserstr. 29 18 30 29 Trier - Ostallee 34 40 31 40 Kaiserslautern - Rathaus Platz 17 5 21 11 Koblenz - Friedrich-Ebert-Ring 21 5 24 13 3.2. Air temperature inversion and emission concentrations of air pollutants The trends in figure 1 showed only the mean emission concentration of pollution in the area under investigation. To estimate the impact of air pollution to human health it is necessary to analyze periods with extreme air pollution concentrations. Due to the location of Trier at the bottom of the valley those situations often connected with the presence of ground air temperature inversions. The accumulation of emissions in the valley is a result of the reduced ventilation and air exchange during of persistent air temperature inversions. Because no regular radiosonde ascents were performed in the region 8 7,2 of Trier we used the differences 6,7 7 between the daily mean air 6,3 5,7 temperature at urban station Trier - 6 Ostallee (140 m asl) and at rural 5,3 station Trier - Petrisberg (240 m asl). s 5 4,4 4,4 4,0 day Figure 3 shows the average monthly 4 3,3 frequency of air temperature 2,8 number of 3 inversions as defined above within the 2,3 valley with a difference greater 1 K in 1,8 2 the period from 1996 until 2002.