Air pollution deriving from road traffic and aviationis the subject of this lesson. The most relevant traffic induced substance is NOx, which is a combination of NO, nitrogen oxide and NO2, nitrogen dioxide. NOx has different lifetimes depending on altitude - the higher the longer but generally is "short lived" compared to e.g. ozone.
Triggered by solar radiation the presence of NOx in the air leads to O3, ozone formation. Ozone itself has a lifetime which is about 10 times longer than that of NOx.
The exercises (model results) presented here are based on simplified model simulations of the global distribution of NOx and its chemical product O3 emitted (a) at ground level (road traffic) and (b) at subsonic flight altitude (air traffic). In nature every NOx molecule emitted causes the production of 10-50 ozone molecules (depending on latitude and altitude) before it is removed from the air primarily by the rain. In the model this mechanism is parameterised for this study in a way that emissions of ozone are scaled to the emissions of aircraft-NOx. This is acceptable as a first guess, because NOx due to its short lifetime cannot travel far away from the source region which means that the chemical ozone source basically coincides with the locations of NOx emissions.
The model output is presented in form of a "picture galery". A page with "thumbnails" opens on mouse click. Another click on one of these thumbnails starts the show providing color plots of global crossections through the troposphere of the distribution of the substance in consideration: Horizontal planes are shown at ground level and at 500hPa which is at about 5km altitude for ground bound traffic and 200hPa / ~12km for aircraft. Colorbars give a qualitative indication for the concentration of the species in the air. The last picture always depicts "station records" at selected receptor sites.
Here we go:
Three-panel plates of colored concentration distributions are the results of numerical dispersion simulation runs for:
- Aircraft NOx - lifetime 8 d.
- Aircraft O3 - lifetime 360 d.
- Road traffic NOx - lifetime 1 d.
- Road traffic O3 - lifetime 100 d.
For a better understanding and aid of interpretation of the results corresponding circulation patterns are provided in form of wind arrows at the same crossections as the tracer distributions are depicted:
- "Info boxes" to each of the examples
- and a "Quiz box" with questions allows for self test.
The author of the model very much appreciates any kind of feedback, questions, and suggestions, so this tutorial can undergo a continous development based on a dialogue with students and visitors of this page.
Please mail to Peter Zimmermann
PS:A bunch of more sophisticated exercises, much more explanatory text and sets of more or less smart questions to the exercises are in preparation. Web based students own model runs started from the browser will be possible in the near future.