ARL News

Joint Urban 2003 Briefings For Homeland Security Leadership


October 6, 2003

The Joint Urban 2003 study recently completed in Oklahoma City is receiving a lot of attention. Its findings are important, and will rapidly be incorporated in urban dispersion models. The Air Resources Laboratory was the major player in the study (which was funded primarily by DOD and DOE, but with a small amount of actual NOAA support).

Kirk Clawson of the ARL Field Research Division in Idaho Falls led the outdoor tracer part of the overall program. (There was an independent tracer component addressing indoor behaviors.) At the request of leadership of the Department of Homeland Security, the initial findings of the program have been summarized for the attention of Governor Ridge.

1. Material released at street-level during moderate winds can immediately disperse to the tops of the tallest buildings near the release location.

2. Material released in an urban area during moderate winds can remain at significant concentrations in the urban area for up to 1/4 hour or more after the release stops.

3. Material released at street-level can be channelled down street canyons at angles approaching 60-80 degrees from the downwind direction.

The relevant processes are not typically treated in conventional dispersion models used in emergency response. DCNet is designed to account for the behaviors described, and the relevant processes will be incorporated in the models running on the DCNet system. The importance of these processes will doubtlessly vary from location to location. We have yet to start looking into this worrying aspect of the overall problem.

Contact information: Kirk L. Clawson
Phone: (208) 526-2742