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Limitations

AirData has a lot of air pollution information in formats that are easy to use. But there are some limitations and minimal requirements for using the AirData Web site. This page describes them.

Data Limitations

 

Browser Limitations

Accuracy of Data

AirData reports and maps are produced using data extracted periodically from EPA's primary air pollution databases. EPA and state environmental agencies, which provide much of EPA's air pollution data, make diligent efforts to ensure the accuracy of those data. However, some values may be absent due to incomplete reporting, and some values subsequently may be changed due to quality assurance activities. If you find an error in an AirData report or map, we hope you will let us know so that we may correct it. You may use the Contact Us link near the top and bottom of every AirData Web page, or you may contact directly the people responsible for the data:

Air monitoring: state environmental agencies
Emissions (criteria pollutants): EPA criteria emissions data specialist
Emissions (hazardous pollutants): EPA HAP emissions data specialist

Timeliness of Data

Because AirData uses extracts of the primary air pollution databases, the values in AirData reports and maps may be slightly out of date. We do endeavor to keep AirData synchronized with the primary databases through regular updates. The database status page has details.

EPA regulations require state environmental agencies to report air monitoring data at least quarterly. Data for one calendar quarter are due to EPA by the end of the following quarter. Most state agencies submit their data monthly. We refresh AirData's air monitoring data every month.

EPA staff collect air pollutant emissions data from state environmental agencies and other sources every three years, and they apply corrections and additions periodically between major updates. We refresh AirData's emissions data whenever the database administrators notify us that a new "release" of quality-assured data is available. This usually occurs about twice per year.

Interpretation of Data

Readers are cautioned not to infer a qualitative ranking order of geographic areas based on AirData reports and maps. Air pollution levels measured in the vicinity of a particular monitoring site may not be representative of the prevailing air quality of a county or urban area. Pollutants emitted from a particular source may have little impact on the immediate geographic area, and the amount of pollutants emitted does not indicate whether the source is complying with applicable regulations.

Occasionally EPA adopts new methods for estimating emissions to improve accuracy and consistency. When this happens, schedules and resources may allow revising emissions data only for the most recent year. For that reason, you should not use AirData reports to deduce trends in emissions data, unless you first confirm that EPA used equivalent methods for the years being compared. The latest, most consistent emissions trends are provided in national totals at EPA's Air Pollutant Emission Trends Web site.

Hourly Monitoring Data

Although hourly and daily air monitoring values (raw data) are not available in AirData reports, you can obtain those data from EPA's Air Quality System (AQS) Web site. The Download Detailed AQS Data page has national data files for the last 10 years. The AQS Data Mart is a web service through which you can retrieve hourly, daily, and annual values for years 1980 through the present. See the related links page for more sources of hourly and daily air monitoring values.

Accessibility

In 1998 the U.S. Federal government enacted a law establishing standards for accessibility to information technology by people with disabilities. Section 508 of the act defines the standards, and thus they are commonly called Section 508 accessibility standards. Federal government Web sites must have met the standards as of July 2001. More information about Section 508 standards is available at the U.S. Access BoardExit EPA Disclaimer Web site.

AirData maps and charts are inherently visual entities, images that visually impaired people may not be able to see. Section 508 standards specify that a description be provided to convey the sense, the content of an image to those who cannot see it. But because AirData produces maps and charts when they are requested, with thousands of possible variations in data selection criteria and, hence, in image content, providing a meaningful description of an individual image is not feasible. Thus, AirData maps and charts are not accessible to visually impaired people.

Section 508 standards specify that information that cannot be made accessible in one format must be available in an alternative format that is accessible. AirData reports provide that alternative. The same types of information available in maps and charts are also available in reports

JavaScript-Enabled Browser Required

AirData Web pages use JavaScript extensively to mediate the dynamic generation of reports and maps. To use AirData successfully, your browser must be capable of running the JavaScript embedded in AirData Web pages.

We have kept the JavaScript as simple as possible so that it will work with many browsers. The AirData Web site works best with recent versions of popular browsers, such as Microsoft Internet Explorer (version 5 and later) and Netscape Navigator (version 4 and later).

Java Applet for Maps

By default, AirData displays maps using a Java applet that lets you zoom (enlarge) and pan (move) the image. In most AirData maps, the applet displays additional information in a "tool tip" as you place your mouse pointer on parts of a map - county name, for example. If your browser does not support Java applets, or if you prefer not to use the applet, change your AirData preferences to select standard GIF image format for maps.

Information that the Java applet uses to display a map is sent to your browser in a web page. For a complex map, one that includes numerous markers or geographic features, the amount of information generated is voluminous - as much as several megabytes. Some browsers cannot handle that much information, and they will fail to display the map. As a general rule, it is better to choose the GIF image type for complex maps instead of the default Java applet format.

Flash Player for Geographic Selection

AirData lets you select the geographic coverage for a report or map visually, by clicking an interactive map with your mouse pointer. We use Macromedia Flash™ software to provide the interactive map. To make it work, Macromedia Flash Player software must be installed in your browser. The player software is free, and it is included with recent versions of mainstream browsers.

You do not need Flash Player software to generate AirData reports and maps. You can select geographic areas from lists of area names instead of using the Flash-mediated interactive map.

Cookies

AirData saves information in temporary cookies, if your browser has cookies enabled. A temporary cookie is not saved on your computer; it is destroyed when you close your browser. Only information that is directly related to the use of AirData is stored in the temporary cookies. No personal information of any kind is collected or stored. AirData poses no threat to your privacy.

AirData saves two types of information in temporary cookies:

You can use AirData if you disable cookies or if your browser does not support cookies, but you may have to set preferences prior to generating each map. If you use the default preference settings, a temporary cookie is not needed. Its sole function is to preserve non-default map preferences during your visit to the AirData Web site. The second temporary cookie, related to Flash installation, allows you to avoid being prompted to install Flash Player software every time you visit the AirData geographic selection Web page.

 

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