The changing environment of a desert boomtown.

World population growth has prompted the exploration and habitation of geographical regions previously considered undesirable or unsuitable for human comfort. The impact of humans and their civilization on desert regions, where water and vegetation are scarce, is not well understood. The high plains desert of the southwestern United States is the fastest growing region of the nation. Historically, the desert atmosphere was distinguished by extraordinary visibility and negligible particle and chemical pollution. Unfortunately, visitors and residents of the region have perceived a decline in the air quality during a 15-20-year period which corresponds to a rapid influx of population and the development of isolated urban areas. This study attempts to assess the relative impacts of demography, meteorology and air chemistry on the air quality of a rapidly growing, small city located in the Mohave Valley on the Nevada/Arizona border. Statistically significant trends were identified in the local meteorology and air quality over a 10-year period. Temperature and relative humidity values were observed to increase at the urban site. Increases were also noted in the concentrations of total suspended particulates (TSP) and the oxides of nitrogen. Observations at the urban site were compared with similar measurements at nearby non-urban sites and with the results of studies at two larger cities in the desert southwest, Phoenix and Tucson, AZ. Conclusions based on the combined analyses indicate that the desert environment has been strongly influenced in the immediate urban area and that the changes are due primarily to demographic influences. Changes in urban air quality observed in the Mohave Valley were more pronounced and were apparent over a shorter period of time than air quality changes observed elsewhere in the southwest.

Background continental ozone levels in the rural U.S. southwest desert.

From 1969 through 1978 an extensive ambient air quality monitoring program, including the measurement of atmospheric concentrations of ozone, has been conducted in a remote section of the desert in the southwestern U.S. Using a Monitor Labs chemiluminescent ozone instrument, these levels were measured atop a small mountain 500 feet above the valley floor of the Colorado River. During the winter months, when the prevailing low level winds are northerly in this river valley, rural continental background levels of ozone are attainable. From this continuous ozone data base, 13 of these representative high pressure periods have been selected for analysis. Results indicate a very distinct diurnal trend with an ozone minimum occurring from 0800-1000 hours Mountain Standard Time (MST) and an ozone maximum from 1600-1900 hours MST. Ozone concentrations range from a low of 19 ppb to a high of 44 ppb with the diurnal pattern exhibiting marked repeatability with respect to time of minima and maxima, seasonal changes and concentration levels.