This program was originally published in 1981 by Roland R. Draxler as
NOAA Technical Memorandum ERL ARL-100,
titled, "Forty-eight
hour Atmospheric Dispersion Forecasts at Selected Locations in the United States."
The program has been updated to produce quick forecasts of atmospheric dispersion via the
web by combining the simple techniques of estimating dispersion
from Bruce Turner's Workbook of Atmospheric Dispersion Estimates (1994,1969) with
National Weather Service (NWS)
forecasts of wind direction, wind speed, cloud cover, and cloud ceiling.
The NWS forecasts come from the NAM and GFS
Model Output Statistics (MOS), which are statistically derived
surface conditions produced for over 1000 locations in the CONUS, Alaska, Puerto Rica,
and Hawaii.
Model Assumptions:
6-hour, straight-line flow, Gaussian dispersion forecasts from 1 to 100 km downwind
are produced independently for each 3 hour forecast time given by the MOS forecast. That is, a
continuous 6-hour emission is assumed to occur every 3 hours. The user chooses the
dispersion forecast time to display on a graph (all the other forecasts are available in
the text file) as well as the release height, receptor height, and the maximum daytime and
nighttime mixing heights. The wind speed (not the direction) is adjusted to the pollutant
source height by the relation:
u = u10 (z/z10)P
where u10 is the wind speed at height z10 (10 m) and u is the wind
speed at emission height z. The exponent P is a function of the stability (Draxler, 1980).
A daytime mixing depth is calculated with a nomogram (Smith and Hunt, 1978). At night
an optional constant maximum mixing depth of 400 m is assumed. The constant nighttime
value of 400 m will only affect ground-level concentrations
during "D" stability at distances greater than 20 km downwind. Hence, the assumption
of a constant nighttime maximum mixing depth is not considered to be a serious limitation.
Draxler, R.R., 1981: Forty-eight hour atmospheric dispersion forecasts at selected locations in the
United States, NOAA Technical Memorandum ERL ARL-100, 11 pp.
Draxler, R.R., 1980: An improved Gaussian model for long-term average air concentration estimates,
Atmos. Environ., 14: 597-601.
Smith, F.B., and R.D. Hunt, 1978: Meteorological aspects of the transport of pollution
over long distances, Atmos. Environ., 12: 461-477.
Turner, D.B., 1969: Workbook of Atmospheric Dispersion Estimates, Public Health Service
Publication No. 999-AP-26, U.S. Government Printing Office, Washington, DC 20402, 84 pp.