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About the County Air Quality Report - Criteria Air Pollutants

What does the report tell me?

The AirData County Air Quality Report displays air pollution values related to national standards for air quality. This report includes pertinent values for all six criteria pollutants, similar to the "Maximum Concentrations by County" data table in Appendix A of EPA's annual Air Quality Trends Report. The County Air Quality Report lets you see easily if a county's peak air pollution levels were above the national standards during a particular year. Counties that persistently exceed the standards may be classified "nonattainment" by EPA, and be required to take measures to improve their air quality.

Each row of the County Air Quality Report lists standards-related air pollution values for all six criteria pollutants, for a single county, for one year. The values shown are the highest reported during the year by all monitoring sites in the county. A value that exceeded the level of an air quality standard is highlighted.

What does the report look like?

The image below shows part of a County Air Qualityreport. Each row shows the highest reported EPA standard-related values for criteria pollutants for a year and county. While the County Air Quality report covers all six criteria pollutants, this excerpt only shows values for PM2.5, PM10, and Lead (Pb), along with the year and the county population.

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 County, which arranges rows in order of county, state, region, and year.

AirData automatically adds year as a secondary sort key for most report columns. If a report includes data for multiple years, rows having identical values for the primary sort key, which you choose with the SORT buttons, are arranged in ascending order by year.

Detail or Summary

The County Air Quality report is always a summary report -- a summary by county, state, or EPA region. Omitting optional report columns can change the level of summarization in the report. See the table below for details. A summary report gives the highest reported value during the year by all monitoring sites in the geographic area being summarized (county, state, or region).

Report Column Including This Column Has What Effect ?
County Name Report shows county summary -- the highest reported value during the year by all monitoring sites in each county. Omit this column to summarize at a higher level.
State Abbreviation Report shows state summary -- the highest reported value during the year by all monitoring sites in each state. Omit this column to summarize at a higher level.
EPA Region Number Report shows regional summary -- the highest reported value during the year by all monitoring sites in each EPA region. This is the highest summary level available.

What do the report columns mean?

EPA uses annual summary measures of air pollution to gauge compliance with air quality standards established by the Clean Air Act. The standards are framed in terms of different summary measures for each pollutant. This report lists standards-related air pollution annual summary values for all six criteria pollutants, for a county (or state or region). The values shown represent all monitoring sites in a county (or state or region) that reported data during the year.

Some air pollution values in the report are labeled "2nd max," which means the next-to-highest (second highest) value recorded for a geographic area. The report gives the second highest value when the applicable air quality standard allows one "exceedance" per year - one day when the measured pollutant concentration is higher than the value set in the standard. Thus the second highest value indicates whether the level of the standard was exceeded during a year. This reporting convention allows you to see easily if a geographic area could be in jeopardy of failing to meet an air quality standard. (Exceedances are averaged over multiple years to determine attainment of the standards, so the results for a single year are not determinant.) Any pollutant concentration listed in the County Air Quality report that is higher than the applicable air quality standard is an exceedance, and the value is highlighted.

The units of measure of pollutant concentrations are:

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.

CO - Carbon Monoxide
Air Quality Standards
These levels may not be exceeded more than once per year:
  • 1-hour average concentration -- 35 ppm
  • 8-hour average concentration -- 9 ppm
2nd Max 1-hr
Second-highest 1-hour average concentration (in ppm) for the year. This value, rounded to the nearest 1 ppm, should not exceed the level of the 1-hour standard (35 ppm).
2nd Max 8-hr
Second-highest nonoverlapping 8-hour concentration (in ppm) for the year. This value, rounded to the nearest 1 ppm, should not exceed the level of the 8-hour standard (9 ppm). AQS software computes an 8-hour average concentration for each hour of the day as a moving average of eight 1-hour values. Nonoverlapping means that the highest and second-highest 8-hour values do not have any hours in common - they are separated in time by at least eight hours.

NO2 - Nitrogen Dioxide
Air Quality Standard
Annual average concentration -- 0.053 ppm
Annual Mean
Arithmetic average of all 1-hour values for the year. This value should not exceed the level of the annual standard (0.053 ppm).

O3 - Ozone
Air Quality Standards
  • 1-hour average concentration -- 0.12 ppm
    This level may not be exceeded more than one day per year, after compensating for missing data (estimated number of exceedances).
    In June 2005 EPA revoked the ozone 1-hour standard except in 13 Early Action Compact areas.
  • 8-hour average concentration -- 0.075 ppm
    Fourth-highest value in a year, rounded to the nearest 0.001, may not exceed this level.
    In March 2008 EPA strengthened the ozone 8-hour standard. The 2008 standard applies retrospectively to monitoring data for prior years. Some locations that previously met the ozone standard may exceed the level of the 2008 standard.
2nd Max 1-hr
The second-highest "daily max value" -- take the highest 1-hour value of each day, pick the second-highest of those values. This value, rounded to the nearest 0.01 ppm, should not exceed the level of the 1-hour standard (0.12 ppm).
4th Max 8-hr
The fourth-highest "daily max value" -- take the highest 8-hour value of each day, pick the fourth-highest of those values. This value, rounded to the nearest 0.001 ppm, should not exceed the level of the 8-hour standard (0.075 ppm). AQS software computes an 8-hour value for each hour of the day as a moving average of eight 1-hour values.

SO2 - Sulfur Dioxide
Air Quality Standards
  • 24-hour average concentration -- 0.14 ppm
    This level may not be exceeded on more than one day per year.
  • Annual average concentration -- 0.030 ppm
2nd Max 24-hr
Second-highest 24-hour average concentration (in ppm) for the year. This value, rounded to the nearest 0.01 ppm, should not exceed the level of the 24-hour standard (0.14 ppm). AQS software computes a midnight to midnight 24-hour average value for each day from 1-hour values.
Annual Mean
Arithmetic average of all 1-hour values for the year. This value should not exceed the level of the annual standard (0.030 ppm).

PM2.5 - Particulate Matter smaller than 2.5 micrometers
Air Quality Standards
  • 24-hour average concentration -- 35 µg/m3
    The 98th percentile of 24-hour values for a year may not exceed this level.
    In December 2006 EPA strengthened the PM2.5 24-hour standard. The 2006 standard applies retrospectively to monitoring data for prior years. Some locations that previously met the PM2.5 standard may exceed the level of the 2006 standard.
  • Annual average concentration -- 15.0 µg/m3
98th Percentile
The 98th percentile 24-hour value (in µg/m3). This value, rounded to the nearest 1 microgram, should not exceed the level of the 24-hour standard (35 µg/m3). The 98th percentile value is higher than 98 percent of 24-hour values for the year.
Annual Mean
Arithmetic mean of 24-hour values for the year. This value, rounded to the nearest 0.1 microgram, should not exceed the level of the annual standard (15.0 µg/m3).

PM10 - Particulate Matter smaller than 10 micrometers
Air Quality Standards
  • 24-hour average concentration -- 150 µg/m3
    This level may not be exceeded on more than one day per year, after compensating for days when monitoring did not occur (estimated number of exceedances).
  • Annual average concentration
    In December 2006 EPA revoked the PM10 annual standard due to a lack of evidence linking health problems to long-term exposure to coarse particle pollution. Before its revocation, the level of the annual standard was 50 micrograms per cubic meter of air.
2nd Max 24-hr
Second-highest 24-hour value (in µg/m3) for the year. This value, rounded to the nearest 10 µg/m3, should not exceed the level of the 24-hour standard (150 µg/m3).
Annual Mean
Weighted arithmetic mean of 24-hour values for the year. The method of calculation compensates for scheduled sampling that did not occur.

Pb - Lead
Air Quality Standard
Quarterly average concentration -- 1.5 µg/m3
This level may not be exceeded in any quarter of a year.
Quarterly Mean
Highest of the quarterly mean values. This value, rounded to the nearest 0.1 µg/m3, should not exceed the level of the quarterly standard (1.5 µg/m3). Each quarterly mean is the arithmetic average of 24-hour values for a calendar quarter: January-March (1), April-June (2), July-September (3), and October-December (4).

Population
Population within the geographic entity represented by a row of the report -- a county, state, or EPA region. Populations are based on 2000 census data.

Year
The calendar year to which the data pertain. This column is displayed only when you select multiple years for the report.

County
Name of the county (or equivalent jurisdiction) to which the summary measures pertain.

State
Postal abbreviation for the state or territory to which the summary measures pertain. [ Details ]

EPA Region
EPA Region number to which the summary measures pertain. There are ten EPA regions. [ Details ]

 

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