Each frame represents a three-year precipitation-weighted mean concentration or three-year mean annual deposition. For example, the
1985 concentration map displays the precipitation-weighted mean concentration for 1984 - 1986.
To maintain consistency throughout the animation, a
subset of NTN sites that
operated for the entire period was used. At least three factors are at work changing the spatial
patterns from year to year and over the period of record: emissions changes, changes in weather
patterns, and chemical changes in the airborne pollutants that are removed by precipitation.
If you intend on reprinting any of these maps for use in a publication, please read our
Use Conditions.
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