Description:

Forward trajectories from 20 receptor sites evenly distributed over the Eastern US. The trajectories extend for three days after their release from each source during the three months June - August for the years 1991 - 1995. The source release time, in Eastern Standard Time (EST), is located at the bottom of the movie, and has a four hour time increment. The transport of each source airmass is simulated by three trajectories. The squares along each trajectory identify the location of the airmass every four hours along its pathway from the source.

Purpose:

This movie can be used as a resource to provide meteorological context to the interpretation of air quality data. The trajectories identify the pathway of airmasses that originate at specific locations. They also identify whether the airmass is stagnating, recirculating, or part of a well defined flow field.

Method:

The forward trajectories were calculated using the CAPITA Monte Carlo model, and 3-D Eulerian wind fields generated from the National Meteorological Centers Nested Grid Model. Three particles were released from each site at four hour time increments and tracked for three days.

Interpretation:

Transport in the lower layers of the atmosphere is a random process resulting from a mean advecting flow and turbulent mixing. The mixing processes are generally very efficient during the day causing individual airmasses to lose their identity and become a part of a larger regional airmass. This mixing can cause emissions from a source to be dispersed over large regions. This is represented in the movie by simulating the transport of am airmass at a source by three particles whose trajectories are then followed. As shown in the movie, the particles comprising each source's airmass tend to spread apart as the airmass is transported away from the source. This is the result of random fluctuations imposed upon the position of each particle simulating the turbulent mixing in the atmosphere.