Ecosystem Science Reports

Atmospheric Sciences

Project Title: A User's Guide to Back Trajectories

Completion Date: March 31, 2004

Investigators: Brad Snyder, Aquatic and Atmospheric Sciences Division, Environment Canada, Pacific and Yukon Region

Study Overview

Air parcel trajectories help in answering the questions such as “where did our air originate?” or “where is this pollution destined for?” The goal of this report was to describe the fundamental aspects of trajectories and give the reader an understanding of the limitations of this information. The report was prepared for readers with limited meteorological background.

This report provides a scientific foundation and background for users of trajectory output. The report highlights the various sources of error one can expect with trajectory output. In addition, a summary of steps to consider when using trajectory output was presented. Finally, a list was given of some of the models being used to generate trajectory output.

Key Points for Decision-Makers

Key Scientific Findings

Key Points for Decision-Makers

• Trajectory output from meteorological models can provide valuable information, however decision-makers should ensure that potential sources of error in the trajectory analysis have been considered when reviewing results.

• The best quality trajectory guidance is based on a probabilistic approach that uses multiple outputs to provide a level of understanding of the certainty to the trajectory analysis.

Key Scientific Findings

• Trajectory output from meteorological models can provide valuable information to those in the air quality science field. Ultimately, the best quality trajectory guidance is based on multiple outputs: either through multiple levels and multiple source/receptor locations; through multiple models; and/or multiple days. This provides a probabilistic approach and hence a level of certainty to the trajectory output.

References

This report may be obtained directly from the author at brad.snyder@ec.gc.ca

The correct citation of the paper is:

Snyder, B. 2004. A user's guide to back trajectories. Environment Canada, Environmental Conservation Branch, Pacific and Yukon Region, Vancouver, BC. eReport #2004-004. 2 April 2004.