A comprehensive review of visual air quality at the Grand Canyon

The Grand Canyon, located in Northern Arizona, is one of the seven natural wonders of the world, and has been set aside as a National Park to preserve its unique character. Several million visitors from all over the world travel to the Grand Canyon each year to witness its awesome beauty, As a natural preserve, the area protects numerous values such as genetic diversity, solitude, non-mechanized recreation, etc, but the majority of visitors travel to the Grand Canyon for one reason: to view the scenery.There have been reports in the general press (and even in the United States Congressional Hearings) that visual conditions at the Grand Canyon have been seriously degraded by air pollution. Over the past nine years, a vast array of visibility-related research and monitoring has been conducted to determine the extent and probable cause of this visible degradation. Studies have included optical measurements, pollution characterization, source-receptor relationship analysis, and human perception of visual air quality. The resulting data document the visual air quality of the Grand Canyon and provide a basis to qualitatively and quantitatively evaluate significant events and trends.This poster comprehensively assembles, updates, analyzes and summarizes these various studies to report what has happened to air clarity at the Grand Canyon. The authors examine: - the extent and variation of optical conditions through an examination of reported standard visual range data and a qualitative review of standard photographic monitoring record; - the scientific basis and measurement techniques used to quantify optical conditions; - the probable causes of visual degradation by analyzing the chemical properties of collected aerosols, and through investigation of air mass trajectories; - how visitors to the Grand Canyon perceive and value visual air quality; - the implications study results have for control of air pollutants outside protected natural areas. By examining the situation at the Grand Canyon, managers of other natural preserves may gain insights into ways to determine the extent and causes of visual degradation in all lands afforded special protection.