Near Real-Time Monitoring of Air Pollution Over US Using ... - Capita

MODIS aerosol optical depth is shown to provide the pseudo-synoptic view of aerosol events
across North America unlike any other measurements, including the EPA’s current network of
isolated stations. Note MODIS’s ability to separate aerosol from clouds. However, aerosol optical
depth cannot be retrieved in cloud covered regions, resulting in spatial gaps in the synoptic
view. Nevertheless, the minor deficiency does not undermine MODIS capability for use in monitoring
regional air pollution.
Figure 7. The composites of MODIS-derived aerosol optical depth (color) and cloud optical depth (black-white)
with superimposed winds (red arrow) from June 23 to 26, 2002.
The relationship of MODIS-derived τa and surface PM2.5 concentrations was examined over
the upper mid-west and eastern US (including 11 states and Washington DC) during June 2002.
Time series of hourly PM2.5 measurements and temporally co-located MODIS τa observations
are shown in Figure 8 for 4 representative ground sites. There is a high degree of correlation between
the surface and column-integrated quantities at these sites with correlation coefficients
ranging from 0.75 to 0.9. These high correlations are typical for other sites throughout the region
during June. The time series depicts generally in-phase variations at Chicago (Illinois), Lansing-
East Lansing (Michigan), and Canton-Massillon (Ohio), indicating similar regional pollution
sources and air mass control in the region. At these three sites, episodic maximums in PM2.5 concentrations
occurred from June 9-11 and June 20-26. Farther to the east, at Wilmington-Newark
(Delaware), similar maximums occurred, although at later dates (June 10-13 and 24-27).
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