Assessing the Effect of Traffic Density and Cold Airflows on the Urban Air Quality of a City with Complex Topography Using Continuous Measurements

Abstract

Abstract: The air quality in cities is affected by many factors such as topography, weather, emission sources, etc. In order to assess the influence of these factors on a certain location, continuous measurements of air quality as well as meteorological parameters are essential. The city of Stuttgart in Germany is known for its unique topography and air quality problems making it a very interesting place to investigate the impact of topography and thermal induced wind systems on the air quality. Stuttgart city center is surrounded by hills, elevated plains where cold air masses are produced during nights with autochthonous weather situations. Due to the varying topography, these cold air masses stream through valleys and gullies into the city centre. In this study, a stationary monitoring station was installed at Marienplatz, Stuttgart where the cold airflows from the valleys and gullies are collected together and enter the city, hence making it the optimum location for this investigation. The air pollutants such as nitrogen oxides (NOX, NO, NO2), ozone (O3), carbon monoxide (CO), Particulate Matter (PM) and Black Carbon (BC) were monitored continuously along with the meteorological parameters such as air temperature, relative humidity, air pressure, wind speed, wind direction, precipitation intensity and global radiation from March 2017 till now. In this paper, the results from March 2017 until December 2019 are presented. The influence of wind speed and wind direction on the concentration of pollutants is interpreted using wind and pollution roses. Temperature roses are plotted to understand the effect of cold airflows that bring fresh and cold air into the city. The traffic data for the federal highway passing by the monitoring station are obtained and the pollutant concentrations are related to the traffic, as it is the dominant source of emission in the city. Key words: air quality monitoring, cold airflows, urban air quality, traffic and air quality, air pollution in Stuttgart, continuous measurements, air pollutants