doctrine must be revised – University of Innsbruck
Long-term measurements in the city of Innsbruck show that the proportion of ground-level ozone in atmospheric models tends to be overestimated. As a consequence, a classic doctrine for air quality forecasting has to be reinterpreted for urban areas. The measurements by an international team led by atmospheric researcher Thomas Karl also show that direct nitrogen dioxide emissions are overestimated.
The 40 meter high measuring tower of the Atmospheric Observatory Innsbruck at the university crossing in the city of Innsbruck continuously provides data on the composition of the ground-level atmosphere. 36,000 data points are recorded per hour. With a special measuring method – the so-called eddy covariance method – the concentration of air components can be continuously monitored. An international team around Thomas Karl from the Institute for Atmospheric and Cryosphere Sciences from the University of Innsbruck has now used this data to study the chemistry of ozone, nitrogen monoxide and nitrogen dioxide in urban areas in detail. The high proportion of diesel vehicles in European cities leads to high concentrations of nitrogen monoxide. This reacts with ozone, producing nitrogen dioxide. In the atmosphere, nitrogen dioxide breaks down again into nitrogen monoxide and atomic oxygen, which immediately combines with the oxygen in the air to form ozone.
doctrine needs to be specified
This chemical cycle was mathematically described in Philip Leighton’s first textbook on air pollution over 60 years ago. The relationship between the two processes has since been referred to as the Leighton relationship. Computer models of atmospheric chemistry use the Leighton relationship to minimize complexity by deriving the concentrations of ozone, nitric oxide, and nitrogen dioxide from the concentrations of the other two. In practice, this serves, for example, to derive the ozone concentration in at least ones that are polluted by nitrogen oxides. The data from the Innsbruck atmospheric researchers now show that in the presence of high nitrogen monoxide emissions, mathematical expectations that Leighton assumed lead to incorrect results. “In cities with high nitrogen monoxide emissions, this ratio is overestimated by up to 50 percent,” warns Thomas Karl. “As a result, model calculations overestimate the concentration of ground-level ozone in urban areas. This is also reflected in the air quality forecasts.” This effect should not be neglected when modeling the lowest layer of the atmosphere, up to 200 meters above the ground.
Responsible for the effect investigated by the Innsbruck scientists are, in addition to the existing high nitrogen monoxide emissions, the stronger turbulence in urban areas. The mixing of the gases combined with the relatively fast chemical processes mean that more ozone is converted into nitrogen dioxide. The researchers’ data also show that the direct emission of nitrogen dioxide from urban traffic is largely negligible in comparison. “It is important to note that environmental policy regulations do not refer to model calculations, but rather come into force depending on the concentrations of pollutants actually measured,” emphasizes Thomas Karl.
to die Results have now been published in the journal Science Advances.
publication
High urban NOx triggers a significant chemical downflow of ozone. Thomas Karl, Christian Lamprecht, Martin Graus, Alexander Cede, Martin Tiefengraber, Jordi Vila-Guerau de Arellano, David Gurarie, Donald Lenschow. Scientific Advances January 18, 2023 Volume 9 Issue 3 DOI: 10.1126/sciadv.add2365
information
The research was carried out jointly with the National Center for Atmospheric Research (USA), Case Western Reserve University (USA), Wageningen University (NL) and Luftblick (AT) and was financially supported by the Austrian Science Fund FWF and the European Space Agency ESA, among others .