Data

These data is part of the effort to provide the most detailed data on air quality in CAPLTER. This dataset represents spatially interpolated ozone (O3) levels as measured by monitroring stations of the Maricopa County Air Quality Department. O3 is a naturally occurring compound in which three oxygen atoms combine together. This is an unstable combination, and ozone is continually going through a natural cycle of being formed and then converting back to the more stable “normal� double oxygen compound (O2). The cycle occurs fairly rapidly. In the stratosphere (6 miles and more above the earth), naturally occurring ozone has a beneficial effect of screening out harmful ultraviolet light from the sun. However, ground-level ozone is a pollutant and is a major component of the brown haze that is often observed in the Maricopa County valley. Ozone is not directly emitted into the air, but rather forms in a complex reaction that involves heat, sunlight, and a “soup� of toxic pollutants, especially volatile organic compounds (VOCs). Some of the most common sources of VOCs are gasoline vapors, chemical solvents, and combustion products of fuels and consumer products. Ozone is created by sunlight acting on nitrates (NOX) and VOCs from motor vehicles and stationary sources, and can be carried hundreds of miles from their origins. Ozone affects the respiratory system in people and animals, and also affects the growth of plants.

Data acquisition and spatial interpolations

Data were obtained from the Maricopa Air Quality Deprtment and station locations were geocoded using coordinates provided in the Air Monitoring Network Review. I then linked data tables to these locations and performed ordinary kriging to interpolate concentrations. The maps were created using Geostatistical Analyst, the ArcGIS 9.1 extension. Spherical models were used in all semivariogram models and predictions were checked interactively using the built-in tools. Standard Error maps were also produced along with prediction surfaces that were all rasterized to a 250 meter resolution grid