Session: Science-Policy Linkages
‘Just in Time’ Science Support to Air Quality Management During Extreme Events
R. Husar, B. Schichtel and S. Falke, Center for Air Pollution Impact and Trend Analysis,
CAPITA, Washington University, St. Louis, MO 63130
Dust storms and forest fires are major PM events that occur several times a year over different
parts of N. America. State AQ management agencies are required to provide evidence that such
events have occurred outside their jurisdiction. Hence, there is a need to detect and document the
impact of such events. The existing tools and procedures for such documentation are poorly
developed. The Asian dust and the Central American smoke events of 1998 have demonstrated
that space-based and surface aerosol monitoring data are now available to detect and to follow
the evolution of major unpredictable aerosol events. It was also shown that ad-hoc, web-based
collaboration of scientists and AQ managers is a practical way to share observations and to
collectively generate the explanatory knowledge as the events unfold. Such ‘just in time’ science
support AQ management has occurred during the two extreme events in 1998. However a more
organized infrastructure that would facilitate such science-management collaboration would
assure that understanding and managing these unusual atmospheric events is not left to chance.
Session: Visibility Impact and Assessment
Visibility Pattern and Trends Over North America
J. Husar and R. Husar, Center for Air Pollution Impact and Trend Analysis, CAPITA,
Washington University, St. Louis, MO 63130
Visibility is a standard meteorological variable recorded globally at all synoptic weather stations.
The continental haze pattern is evaluated based on two visibility data sets. The first one is the
Global Summary of Day (SOD) database derived from the data exchanged under the World
Meteorological Organization (WMO) World Weather Watch Program. Over 8000 stations' data
are typically included each month. The online data files begin with January 1994 and the latest
month used in this work was November 1998. A second data set used in this work is
International Surface Weather Observations 1982-1997, jointly produced by the US Department
of Commerce, National Oceanic and Atmospheric Administration and U.S. Department of Air
Force AFCCC, Asheville, NC. The visibility data were subjected to three broad categories of
filters including (1) validity of individual data points, (2) filters based on statistics for specific
stations, and (3) filters based on spatial analysis of the data. The surface aerosol extinction
coefficient data (Bext=1.9/visibility) reveal a patchy haze pattern over N. America with distinct
aerosol regions. For each region, the environmental context is given including the topographic
features, weather and climate, natural processes as well as the human population and its relevant
activities. The haze is presented in terms of data quality and quantity, spatial pattern, and
temporal (seasonal and synoptic) pattern of horizontal extinction coefficient. Finally, the
presumed aerosol type, dust, smokes and haze is given for each region. The spatial haze pattern
based on horizontal visibility was compared qualitatively to SeaWiFS and geostationary satellite
data. All the data are available through an interactive website and the authors are seeking
community-based collaboration on the development of the global aerosol pattern and trends.
Session: Aerosol Satellites
Fusion of SeaWiFS, TOMS and GOES Satellite Data with Surface Observations During Extreme
Aerosol Events.
S. Falke, B. Schichtel and R. Husar, Center for Air Pollution Impact and Trend Analysis,
CAPITA, Washington University, St. Louis, MO 63130
Spaceborne sensors now allow near continuous aerosol monitoring throughout the world. This
paper illustrates the fusion of SeaWiFS, TOMS and GOES satellite data with surface
observations during two extreme aerosol events, 1) the April 1998 Asian dust impacting the
West Coast of North America and 2) the May 1998 Central American forest fire smoke
impacting Eastern North America. The dust and smoke events were observed through satellite
data, lidar instruments, and a large array of surface-based monitors. Between April 15 and 19,
1998 unusually intense dust storms began in northwestern China and Mongolia. The dust cloud
was detected by SeaWiFS satellite images as a yellow dye that visualized its own path as it was
transported across western Asia and the Pacific Ocean. Geostationary satellite sensors such as
GMS-5 and GOES also tracked the dust cloud and provided evidence that the dust plume
reached North America on April 27. Surface monitors recorded exceedances of the PM standard
due to the dust. During the ten-day period, May 7-17, 1998, smoke from fires in Central America
drifted northward into the USA and Canada. The smoke caused exceedances of the PM standard
and major reductions in visual range. SeaWiFS and other satellite imagery indicated that thick
smoke lingered over southern Mexico, Guatemala and Honduras and adjacent oceans throughout
the spring season. On May 12, a remarkably thick pall of smoke accumulated over the entire
Gulf of Mexico and began a swift journey north along the Mississippi Valley. By May 15, the
smoke pall stretched from Central America to the Hudson Bay. Data from the TOMS instrument
and surface visibility and optical thickness observations were merged with the satellite data to
analyze the events. The experience during these extreme aerosol events has demonstrated that
currently available satellite sensors can provide valuable support to science and air quality
management.