These exercises are developed for the IMPRS Research School. The learning goal is to get familiar with numerical atmospheric computer modelling.
Topic of the investigation is the global impact of traffic and aviation on the tropospheric ozone distribution. With the aid of tracer transport models the dispersion of emitted gases by air motion can be simulated under given assumtions. Here it is virtually demonstrated how aircraft exhaust causes a significant enhancement of the ozone concentration in the NH upper troposphere.
"Natural" ozone is predominantly produced by photochemical reactions in the stratosphere. A merit of computer models their ability to specify purturbations such as initiated by human activities like road and air traffic. The only way to quantify effects like these is the numerical simulation. They hardly can be measured because any changes in concentrations are camouflaged by the strong stratospheric ozone intrusion up in the flight corridors. Road traffic pollution in contrast is one major source for tropospheric ozone increase over the industrialised continents. The whole extend of the traffic ozone contribution can also be quantified by numerical models in a way that scenarios with and without those perturbations are compared. In the exercises presented here we look at isolated traffic emissions disregarding all other natural and anthropogenic sources just in order to learn how to interpret model output.
Our working tool is the MOGUNTIA tropospheric Chemical Tracer Model model (CTM).The General purpose
is to study the interaction between the global circulation and the lifetime of tracers,emitted at well defined geographical locations at different altitudes into the atmosphere. Emissions with varying chemical lifetimes are released into the model domain - a grid space, representing the global troposphere. Transport genarally tries to mix the tracer until its mixing ratio is uniformly distributed.
Typically, the mixing time of the troposphere is several years. However, if the trace constituent is (photo-) chemically or radioactively depleted on its way through the air, a uniform distribution cannot be reached and more or less steep concentration gradients develop - depending on the decay intensity (rate). In general the spatial distribution of a tracer is the result of a combination of inhomogenious emissions (source distribution) and inhomogenious depletion.This lesson:
Model simulation output is presented in form of time series of monthly mean tracer distributions which result from four scenarios based on different emission and depletion assumptions which roughly describe global air pollution induced by ground bound traffic and aircraft.
The time dependent concentration behaviour and development at selected receptor sites ("stations") is depicted for theoretical spatiotemporal considerations as well as for comparison with measurments in case of realistic trace species.All the student needs for the level I exercises is an up-to-date(!) internet browser.
The learning target
is supposed to produce a first insight into the mechanisms of the atmospheric mixing processes concidering simplified real world examples. The different behaviour of emissions having different lifetimes and injected at low and high altitudes is demonstrated and explained.
A "quiz box" with instructional questions is provided.