Back Trajectory for Pollution Events

[user4444]

I am trying to study the sources of different ozone precursors in a region. I want to use back trajectories to model where the air parcels are coming. I have a couple questions on the usage of back trajectories:
-Is the "start time" that I input actually the time that the final air parcel reaches the desired location?
-I put 100 m AGL for Level 1 height and then 0 m for both Level 2 and Level 3. Is that reasonable for studying local air transport or should I make it higher?
-All other parameters I just left in their default setting. Does that seem good for my intended uses?

Thanks!

[ariel.stein]

The start time for the back-trajectories should correspond to the time of your measurements.
For the height, if you are dealing with a well mixed boundary layer (say summer afternoon measurements), I would select at least 3 that sample through the planetary boundary layer (e.g. 100, 750 and 1500 m).
As a starting point you could leave the rest of the parameters as default.

As your studies progress you might find that you will need to perform more sophisticated back-trajectory approaches. See for example: http://www.ready.noaa.gov/documents/Tut ... _freq.html