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Border Air Quality Data - About the Monitor Trends Report

What Does the Report Tell Me ?

The border air quality data Monitor Trends Report displays exceedance counts -- the number of times air pollutant concentrations exceeded U.S. air quality standards -- for the pollutants and years you select. Comparing year-to-year exceedance counts at a particular geographic location gives a rough indication of whether air quality there is improving, worsening, or staying the same. (Since data for the latest year usually are incomplete, a comparison with prior years may not be meaningful.)

Each row of the Monitor Trends Report displays exceedance counts for one pollutant at one monitoring site (or in one geographic area). Report columns display exceedance counts for each year you select. Nonzero counts are highlighted.

How Can I Customize the Report ?

Sort Order

You can use the SORT buttons in each report column to change the order of rows in the report. The default sort order is Monitor ID, which arranges rows in order of state, county, and monitoring site.

Detail or Summary

Omitting optional report columns can change the level of summarization in the report. The default, detail report lists the number of exceedances per year for each monitor in the geographic area you select, for the pollutants you select. You can produce summary reports for monitoring sites, cities, counties, states, or border regions by omitting certain report columns. A summary report totals the exceedance counts of individual monitors within each geographic entity (site, city, county, etc.).

To create a summary report, omit the Monitor ID report column. The report displays exceedance count totals, by pollutant, for each unique combination of the other descriptive columns -- site address, city, county, state, and border region. For example, including all five of these columns would produce a site-level summary report. Including only the city column would produce a report of exceedance counts by city. However, all monitors without a city name would be grouped together in this report. Including both city and county columns would still produce a report of city totals, but with a "non-city" total for each county.

Be aware, however, that summary reports may be misleading when the number of monitoring sites varies among geographic areas. For example, suppose county "A" has three monitors and county "B" has one. If the same high pollutant concentration occurred in both counties, a summary report could show three exceedances for county "A," but only one for county "B". Although both counties had similar pollution levels, the summary report would give the impression that air quality was worse in county "A."

What Do the Report Columns Mean ?

The Monitor Trends Report includes the following columns:

Row #
Sequence number of report rows (lines). Sequence numbers are not associated with particular rows; they simply enumerate the rows of a report from first to last. Thus, choosing an alternate sort order for a report would change the sequence numbers associated with particular rows.

No. of Exceedances of EPA Standard
Number of times pollutant concentration exceeded a U.S. air quality standard. The report has an exceedance count column for each year you selected. Nonzero counts are highlighted. If a count is absent (blank), no monitoring data were reported for that pollutant and year.

Some pollutants have multiple air quality standards. The following table lists the specific type of exceedances tabulated in the Monitor Trends Report. The applicable air quality standards are listed at the top of each report page.

Pollutant Type of Air Quality Standard What Counts as an Exceedance Exceedances Per Year Allowed by the Standard
Carbon Monoxide
8-Hour average
Number of nonoverlapping 8-hour values above the standard (9 ppm) 1
Nitrogen Dioxide
Annual average
1 exceedance if annual average value is above the standard (0.053 ppm) 0
8-Hour average
1 exceedance if 4th-highest daily maximum value is above the standard (0.08 ppm) 0
Sulfur Dioxide
24-Hour average
Number of days above the standard (0.14 ppm) 1
Particulate Matter
24-Hour average
1 exceedance if 98th percentile value is above the standard (65 µg/m3) 0
Particulate Matter
24-Hour average
Estimated number of days above the standard (150 µg/m3) 1

Quarterly average

Number of quarters above the standard (1.5 µg/m3) 0
Name of the pollutant to which exceedance counts pertain.

Monitor ID
The AQS database identification code for a monitor. An AQS monitor ID has the following parts:
  • FIPS state code (2 digits)
  • FIPS county code (3 digits)
    FIPS is the acronym for Federal Information Processing Standards, which defines codes used in most U.S. government information systems.
  • AQS site code (4 characters) - an arbitrary code that identifies a particular monitoring site within a county
  • AQS parameter code (5 digits) - not displayed in AirData reports - identifies the pollutant measured:
    • 42101 - carbon monoxide
    • 42602 - nitrogen dioxide
    • 42401 - sulfur dioxide
    • 44201 - ozone
    • 81102 - particulate matter smaller than 10 micrometers (PM10)
    • 88101 - particulate matter smaller than 2.5 micrometers (PM2.5)
    • 12128 - lead
  • AQS parameter occurrence code (1 or 2 digits) - an arbitrary number that distinguishes among monitors for the same pollutant at the same site. This code is called Monitor Number in some AirData reports.
For example, AQS monitor ID 04-013-0019-44201-1 is an ozone monitor in Phoenix, AZ (04 = Arizona, 013 = Maricopa County, 0019 = a monitoring site in Phoenix, 44201 = ozone, 1 = first/only ozone monitor at the site). In AirData reports, this monitor ID is displayed as 040130019 - 1 (parameter code is omitted).

Site Address
Address where the monitoring site is located.

Name of the city, town, village or other municipality in which the site is located. Blank if the site is not located within such a jurisdiction, or if no value was provided.

Name of the county (or equivalent jurisdiction) in which a site is located.

Postal abbreviation for the U.S. state in which a site is located. The nation of Mexico has the "state" abbreviation MX. Details ]

Border Region
Name of a section of the U.S.-Mexico border area in which the site is located. A border region is usually encompasses adjacent U.S. and Mexican urban areas. A border region is the smallest geographic area that you may select for border air quality reports.

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