Open AccessNocturnal atmospheric conditions and their impact on air pollutant concentrations in the city of Stuttgart
Author(s) -
Kiseleva Olga,
Kalthoff Norbert,
Adler Bianca,
Kossmann Meinolf,
Wieser Andreas,
Rinke Rayk
Publication year - 2021
Publication title -
meteorological applications
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.672
H-Index - 59
eISSN - 1469-8080
pISSN - 1350-4827
DOI - 10.1002/met.2037
Subject(s) - turbulence , atmospheric sciences , environmental science , atmosphere (unit) , meteorology , turbulence kinetic energy , atmospheric instability , climatology , geology , wind speed , physics
Meteorological 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 NO x and O 3 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 NO x 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 NO x values about 3 times higher than under dynamically unstable flows. The overall lowest NO x concentrations occur during winter when low clouds and strong winds are present.