Visibility impairment is the most obvious impact of air pollution. Impairment can occur as a plume or as white or brown haze that affects not only how far we can see, but also the colors, textures and clarity of natural and historic vistas. All North Coast and Cascades parks currently experience some degree of haze.
Views are monitored with web cameras, while the particles that contribute to visibility impairment are collected on filters by air samplers; the filters are then analyzed in a laboratory. Identifying the types of particles on the filters can help park managers determine the sources that contribute to visibility impairment. Further research is needed to quantify the contribution of international sources to visibility impairment in North Coast and Cascades parks and to evaluate various pollution reduction strategies to identify those which would most likely result in improved visibility in parks.