INTRODUCTION
The primary emphasis of this Trend Report is to present data on monitoring for various airborne pollutants and identify trends in these pollutant levels. The United States Environmental Protection Agency (EPA) has established National Ambient Air Quality Standards (NAAQS). The EPA set these standards to protect human health and welfare. Primary standards are designed to protect human health, including sensitive populations such as the elderly and children. Secondary standards protect public welfare and address the effects of air pollution on vegetation, materials, and visibility. Air pollution comes from a variety of sources. These include "stationary sources," such as factories, power plants and smelters; smaller sources, such as dry cleaners and degreasing operations; "mobile sources," such as cars, trucks, buses, trains and planes; and "natural sources," such as windblown dust and wildfires.
The six principal air pollutants ("criteria" pollutants) with primary standards are carbon monoxide (CO), lead (Pb), nitrogen dioxide (NO2), ozone (O3), particulate matter (with an aerodynamic size less than or equal to 10 microns, or PM10, and with an aerodynamic size less than or equal to 2.5 microns, or PM2.5), and sulfur dioxide (SO2). Effective September 16, 1997, new standards for eight-hour ozone concentrations and for particulate matter less than or equal to 2.5 microns in size (PM2.5) were added to the list of standards for the principal pollutants. The finer particle size standards for PM2.5 provide increased protection against a wide range of health effects related to respiration of particulate matter. Monitoring for the new PM2.5 standards began in 1999.
The State of Nevada has its own air quality standards that are generally based on the national standards for air quality. In addition to the state standards for the criteria pollutants, Nevada has an air quality standard for the non-criteria pollutant hydrogen sulfide (H2S), which is a toxic gas characterized by a disagreeable odor. Monitoring for hydrogen sulfide is generally confined to the proximity of industrial sources of this pollutant.
The Nevada Revised Statute 445B.100 establishes public policy regarding air quality in Nevada. This statute states:
It is the public policy of the State of Nevada . . . to achieve and maintain levels of
air quality which will protect human health and safety, prevent injury to plant and
animal life, prevent damage to property, and preserve visibility and scenic, esthetic
and historic values of the state.
One goal of the Nevada Division of Environmental Protection (NDEP), Bureau of Air Quality Planning (BAQP) is to determine current and projected concentrations of ambient air contaminants within the state, and to develop and implement measures by which the ambient air quality standards will be achieved and maintained.
Continuing increases in the population base and industrial community necessitate measures to control the attendant deterioration of the air quality. Programs requiring air quality operating permits for stationary sources of air pollution minimize the pollution of the air by industrial facilities. Similarly, an inspection and maintenance program for the urban areas of Reno and Las Vegas is in place to reduce harmful automotive exhaust emissions from mobile sources.
There have been important successes in counteracting the tendency toward worsening air quality with growth. The most significant success has been from the elimination of lead from gasoline, the improvement of automotive engine design with the winter use of oxygenated fuels, and the vapor recovery program for refilling underground gasoline tanks.
In Nevada, the highest 24-hour concentrations of PM10 are often the result of high winds and dry desert terrain. Because these conditions can occur at any time throughout the year, the PM10 concentrations are likely to show more variation than the data for other pollutants. Weather also affects pollutant levels in other ways. In the winter, when strong temperature inversions occur in basins surrounded by mountains, CO and suspended particulates are trapped near ground level, causing poor air quality. Thus air pollution trends may reflect the occurrence or absence of strong inversions during winter. In the summer, O3 concentrations increase as the temperature and amount of sunlight increase.
Considering all the air quality pollutants within the State's jurisdiction, the monitoring data generally show no deterioration in the air quality of Nevada over the report period and improvement in CO levels. Pollution trends for specific monitoring sites are presented in the Monitoring Data section of this report.