Abstract
AbstractMeteorological and air pollutant measurements were conducted in the area of Stuttgart during winter and summer seasons. Stuttgart is situated in moderate mountainous terrain in southwestern Germany. We focus on the connection between atmospheric conditions and air pollutants in the urban nocturnal boundary layer. This is done by relating the bulk Richardson number (Rib), turbulence intensity, cloudiness, and winds, as well as NOx and O3 data. Turbulence intensity is inversely related to Rib, with the lower values occurring at Rib >0.33. The coefficient of determination for the exponential regression is only moderate, which partly can be attributed to sporadic turbulence in the transition from dynamically unstable to stable flows. Dynamically unstable flows (Rib <0.33) occur frequently in winter, as a result of the presence of low‐level clouds and strong winds, supporting low buoyant suppression and strong shear generation of turbulence. Dynamically stable flows (Rib >1.25) are found preferably under clear skies in summer with the build‐up of strong surface inversions, so that buoyant suppression is strong and shear generation of turbulence is weak. The nocturnal NOx concentrations are positively correlated with Rib. The correlation is weak, which is mainly related to the large variability of air pollutant concentrations in a range around Rib = 0.33. In this range, many low‐level jets are present that can cause sporadic turbulent coupling between the atmosphere and the surface. Reduced mixing under dynamically stable flows causes NOx values about 3 times higher than under dynamically unstable flows. The overall lowest NOx concentrations occur during winter when low clouds and strong winds are present.
Highlights
Air quality is a well-known issue in many populated areas of the world
We focus on the examination of the characteristics of the nocturnal boundary layer (NBL), its relation to cloudiness and winds, and on the conditions aloft in the NBL and the associated nearsurface air pollutant concentrations (NOx = NO + NO2; and O3) both for winter and summer episodes
We assume that the nocturnal NOx concentrations, which were slightly lower during S2 compared to S1 (Figure 12e,f), besides being affected by shear-driven turbulent mixing, were favoured by the deeper and less stable NBL present during S2 compared to S1
Summary
Air quality is a well-known issue in many populated areas of the world. Besides the emission strength of air pollutants, the wind speed and atmospheric stratification determine the air quality considerably. Tethered balloons (Glaser et al, 2003; Güsten et al, 1998; Pisano et al, 1997), radiosondes (Corsmeier et al, 2006), and meteorological towers (Li et al, 2005; Mathieu et al, 2005) have been used in this context These studies have shown a strong dependence of air pollutants on the thermodynamic structures and turbulence processes in the NBL. Stuttgart is situated in a basin-shaped valley (Stuttgart basin), which opens into the Neckar valley in the northeast (Figure 1) This complex environment makes Stuttgart predestined for studying the connection between the state of the atmospheric boundary layer (ABL) and air pollutant concentrations. Do we see a connection between cloudiness and winds and the processes determining the atmospheric stratification?
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
