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Figure 7.24.
U.S. maps of corrected light extinction coefficient (
σ
t
), derived from prevailing visibility
measurements (
V
)withtheequation
1.9/
V
for winter (quarter 1) and summer (quarter 3) 1991-1995
(Schichtel et al., 2001). Large extinction coefficients correspond to poor visibility. Data obtained during rain,
snow, and fog were eliminated. Corrected extinction coefficients were obtained by applying relative humidity
correction factors to adjust all extinction coefficients to a “dry” relative humidity of 60 percent, and then
selecting the “dry” extinction coefficient at each monitoring site and for each season corresponding to the
75th percentile of all extinction coefficients at the site and for the season.
σ
t
≈
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