The following sections of this BookRags Literature Study Guide is offprint from Gale's For Students Series: Presenting Analysis, Context, and Criticism on Commonly Studied Works: Introduction, Author Biography, Plot Summary, Characters, Themes, Style, Historical Context, Critical Overview, Criticism and Critical Essays, Media Adaptations, Topics for Further Study, Compare & Contrast, What Do I Read Next?, For Further Study, and Sources.
(c)1998-2002; (c)2002 by Gale. Gale is an imprint of The Gale Group, Inc., a division of Thomson Learning, Inc. Gale and Design and Thomson Learning are trademarks used herein under license.
The following sections, if they exist, are offprint from Beacham's Encyclopedia of Popular Fiction: "Social Concerns", "Thematic Overview", "Techniques", "Literary Precedents", "Key Questions", "Related Titles", "Adaptations", "Related Web Sites". (c)1994-2005, by Walton Beacham.
The following sections, if they exist, are offprint from Beacham's Guide to Literature for Young Adults: "About the Author", "Overview", "Setting", "Literary Qualities", "Social Sensitivity", "Topics for Discussion", "Ideas for Reports and Papers". (c)1994-2005, by Walton Beacham.
All other sections in this Literature Study Guide are owned and copyrighted by BookRags, Inc.
The air pollution index is a value derived from an air quality scale which uses the measured or predicted concentrations of several criteria pollutants and other air quality indicators, such as coefficient of haze (COH) or visibility. The best known index of air pollution is the pollutant standard index (PSI).
The PSI has a scale that spans from 0 to 500. The index represents the highest value of several subindices; there is a subindex for each pollutant, or in some cases, for a product of pollutant concentrations and a product of pollutant concentrations and COH. If a pollutant is not monitored, its subindex is not used in deriving the PSI. In general, the subindex for each pollutant can be interpreted as follows
| Air Pollution Stages | |
| Index Value | Interpretations |
| 0 | No concentration |
| 100 | National Ambient Air Quality Standard |
| 200 | Alert |
| 300 | Warning |
| 400 | Emergency |
| 500 | Significant harm |
The subindex of each pollutant or pollutant product is derived from a PSI nomogram which matches concentrations with subindex values. The highest subindex value becomes the PSI. The PSI has five health-related categories:
| PSI Range | Category |
| 0 to 50 | Good |
| 50 to 100 | Moderate |
| 100 to 200 | Unhealthful |
| 200 to 300 | Very unhealthful |
| 300 to 500 | Hazardous |