If you are like many visitors to the White Mountains and other natural wonders of the East Coast, a key part of the wilderness experience is the chance to feast your eyes on clear, beautiful vistas. Under ideal natural conditions, you should be able to see for 130 miles from the summit of Mount Washington, but unfortunately, vistas are often impaired by haze. This ugly haze is largely due to tiny airborne pollution particles — known as fine particulate matter — belched out of industrial smokestacks and automobile exhaust pipes. Coal-fired power plants are a common source of this pollution. These fine particles travel on air currents, forming a sweeping "regional haze."

While it may seem obvious that people value clear vistas and dislike haze, AMC researchers undertook a study to determine quantitatively just how much haze was too much for White Mountain visitors. The researchers felt that a "red line value" — a level of haze deemed unacceptable by the public — could help those who implement clean-air policies to make decisions such as whether to permit new or modified smokestacks in the vicinity of Wilderness Areas. The AMC found that for the White Mountains' Great Gulf Wilderness, the threshold value of acceptable visibility was 33 miles. The AMC shared these findings with the U.S. Forest Service at a 1999 conference on "Wilderness Science in a Time of Change."

Methods
To determine the threshold value, researchers showed survey participants 23 photographs depicting a range of haze conditions in the Great Gulf Wilderness and asked the participants to rate visibility on a one to five scale and to decide whether the visibility conditions depicted were "acceptable" or "unacceptable." The median unacceptable value reported was a visibility of 33 miles or less. Surveys were completed by visitors at the Tuckerman Ravine trailhead at the AMC's Pinkham Notch Visitor Center, in the Mount Washington Observatory at the summit of Mount Washington, at a trailhead at the AMC's Cardigan Lodge in central New Hampshire, and — in a parallel study conducted by mail — by respondents in Amherst, Mass. 

Additionally, respondents were asked to put a monetary value on clear vistas by indicating whether they would be willing to sacrifice visibility in exchange for a lower electric bill. Only 20 percent of the polled participants from the trailhead surveys said that they would prefer lower electric bills even if that meant hazier air.

If you value clear vistas, learn important steps you can take to combat haze caused by particulate matter pollution.