Those scenic vistas that are colored and highly textured are perceptually sensitive to small changes in air pollution, Conversely, those vistas that lack color or textural detail show little sensitivity to small increases in atmospheric pollution. Visitors rank clean, clear air among the top 4 most important features of each park studied. The second most important group of features is associated with the underlying theme for which the park is famous. Visitors' awareness of haze is closely correlated with standard visual range. Impaired visibility detracts from visitors' enjoyment and satisfaction with their visit.
Visitors appear to be more disturbed by deterioration in visibility when air is relatively clean.
This is called preservation value.