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Border Air Quality Data - About the Monitor Values Report

What Does the Report Tell Me ?

The border air quality data Monitor Values Report displays air pollution measurements recorded by monitoring sites within approximately 65 miles (100 kilometers) of the U.S.-Mexico border. The report shows a yearly summary of the measurements at individual monitoring sites, and descriptive information about the sites. EPA uses the types of air pollution values shown in this report to determine attainment or nonattainment of national air quality standards. (Additional factors are involved in a formal EPA designation of nonattainment or attainment, which this report does not provide.) The report uses highlighted text to denote values that exceed a U.S. air quality standard.

Each row of the Monitor Values Report displays air pollution levels measured at a single monitoring site in a single year. The same site may appear in multiple report rows if it has more than one monitor for the same pollutant, or if you include multiple data years in the report.

Air monitoring data usually are incomplete for the latest year available in this report. Therefore, comparing reported values for the latest year with prior years may not be meaningful.

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 monitoring site ID, which arranges rows in order of state, county, and monitoring site.

The reporting software usually 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

This is always a detail report. Omitting optional report columns does not change the level of summarization. A row of the report always displays data for a single monitoring site for a single year.

Report Width

This report potentially can include over 120 columns of data if you select all pollutants and optional columns. Viewing such a "wide" report in a browser requires a lot of horizontal scrolling, and printing the full report width probably is not possible.

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. Thus, depending on the pollutant you select, the Monitor Values Report includes a different collection of summary values (columns) relevant to the air quality standards for the pollutant.

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
U.S. 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
Mexico Air Quality Standard
This level may not be exceeded more than once per year:
  • 8-hour average concentration -- 11 ppm
1-Hour values
Hourly average concentrations measured by monitoring equipment and reported to AQS.
# Obs
Number of 1-hour values (observations) reported for the year. Uninterrupted monitoring would produce 8760 values per year (24 hours * 365 days).
1st Max, 2nd Max
Highest and second-highest 1-hour values in the year, in parts per million by volume (ppm).
# Exceed
Number of 1-hour values exceeding the U.S. 1-hour standard during the year. If the number is greater than one, it is highlighted.
8-Hour values
Computed by AQS software for each hour of the day as a moving average of eight 1-hour values.
1st Max, 2nd Max
Highest and second-highest non-overlapping 8-hour values in the year, in parts per million by volume (ppm). Non-overlapping means that the 8-hour averages do not include any of the same 1-hour values.
# Exceed
Number of non-overlapping 8-hour values exceeding the U.S. 8-hour standard during the year. If the number is greater than one, it is highlighted.

NO2 - Nitrogen Dioxide
U.S. Air Quality Standard
Annual average concentration -- 0.053 ppm
Mexico Air Quality Standard
1-hour average concentration -- 0.21 ppm
1-Hour values
Hourly average concentrations measured by monitoring equipment and reported to AQS.
# Obs
Number of 1-hour values (observations) reported for the year. Uninterrupted monitoring would produce 8760 values per year (24 hours * 365 days).
1st Max, 2nd Max
Highest and second-highest 1-hour values in the year, in parts per million by volume (ppm).
Annual values
Computed by AQS software from the 1-hour values reported in each calendar year.
Mean
Arithmetic average of 1-hour values for the year, in parts per million by volume (ppm). If this value exceeds the U.S. annual standard, it is highlighted.
# Exceed
Indicates whether the mean exceeded the U.S. annual standard. (1: yes, 0: no) The sum of these values, in the Grand Total line, tells how many times monitors exceeded the standard.

O3 - Ozone
U.S. Air Quality Standards
  • 1-hour average concentration -- 0.12 ppm
    May not be exceeded more than one day per year, after compensating for missing data (estimated number of exceedances).
  • 8-hour average concentration -- 0.08 ppm
    Fourth highest value in a year, rounded to the nearest 0.01, may not exceed this level.
Mexico Air Quality Standard
  • 1-hour average concentration -- 0.11 ppm
    May not be exceeded more than one day per year.
1-Hour values
Hourly average concentrations measured by monitoring equipment and reported to AQS.
1st Max, 2nd Max, 3rd Max, 4th Max
The four highest "daily max values" in parts per million by volume (ppm). Take the highest 1-hour value of each day, and pick the top four of those values.
# Exceed - Actual
Number of days in the year when a 1-hour value exceeded the U.S. 1-hour standard.
# Exceed - Est.
Calculated number of days in the year when 1-hour values are estimated to exceed the U.S. 1-hour standard, after compensating for days when scheduled monitoring did not occur. If the number is greater than 1.0, it is highlighted.
Required Days
Number of days in the year when 1-hour ozone monitoring is required. This is normally the length of the "ozone season" -- warm months when ozone is a potential problem -- at the monitoring site. Due to the warm climate of the border area, ozone monitoring all year is the norm.
# Days
Number of days in the year when the requisite number of 1-hour values were reported: at least 9 values between 9:00 a.m. and 9:00 p.m. (local time).
% Days
Percentage of required monitoring days having valid 1-hour data: 100*(# Days)/(Required Days).
Missing Days
Number of days in the year presumed not to have exceeded the U.S. 1-hour standard even though the requisite number of 1-hour values were not available.
8-Hour values
Computed by AQS software for each hour of the day as a moving average of eight 1-hour values.
1st Max, 2nd Max, 3rd Max, 4th Max
The four highest "daily max values" in parts per million by volume (ppm). Take the highest 8-hour value of each day, and pick the top four of those values. The 4th Max value is highlighted if it exceeds the U.S. 8-hour standard (after rounding to the nearest 0.01 ppm).
Days > Std
Number of days in the year when an 8-hour average concentration exceeded the U.S. 8-hour standard. The sum of these values, in the Grand Total line, tells how many times monitors in the report reported values above the level of the U.S. standard.
Required Days
Number of days in the year when 8-hour ozone monitoring is required. This is normally the length of the "ozone season" -- warm months when ozone is a potential problem -- at the monitoring site.
# Days
Number of days in the year having valid 8-hour average values for at least 18 hours of the day. A least six 1-hour values must be available during an 8-hour period to calculate a valid 8-hour average.
% Days
Percentage of required monitoring days having valid 8-hour data: 100*(# Days)/(Required Days).

SO2 - Sulfur Dioxide
U.S. Air Quality Standards
  • 3-hour average concentration -- 0.5 ppm
    May not be exceeded more than once per year. NOTE: This is a secondary standard, which pertains to societal welfare rather than health.
  • 24-hour average concentration -- 0.14 ppm
    May not be exceeded more than one day per year.
  • Annual average concentration -- 0.030 ppm
Mexico Air Quality Standards
  • 24-hour average concentration -- 0.13 ppm
    May not be exceeded more than one day per year.
  • Annual average concentration -- 0.030 ppm
1-Hour values
Hourly average concentrations measured by monitoring equipment and reported to AQS.
# Obs
Number of 1-hour values (observations) reported for the year. Uninterrupted monitoring would produce 8760 values per year (24 hours * 365 days).
1st Max, 2nd Max
Highest and second-highest 1-hour values in the year, in parts per million by volume (ppm).
3-Hour values
Computed by AQS software for each hour of the day as a moving average of three 1-hour values.
1st Max, 2nd Max
Highest and second-highest 3-hour average SO2 concentrations in the year, in parts per million by volume (ppm).
# Exceed
Number of 3-hour average SO2 concentration values that exceeded the U.S. 3-hour standard during the year. If the number is greater than one, it is highlighted. (Concentrations are rounded to the nearest 0.1 ppm for comparison with the 3-hour standard.)
24-Hour values
Computed by AQS software for each day as an average of 1-hour values.
1st Max, 2nd Max
Highest and second-highest 24-hour average SO2 concentrations in the year, in parts per million by volume (ppm).
# Exceed
Number of 24-hour average SO2 concentration values that exceeded the U.S. 24-hour standard during the year. If the number is greater than one, it is highlighted. (Concentrations are rounded to the nearest 0.01 ppm for comparison with the 24-hour standard.)
Annual values
Computed by AQS software from the 1-hour values reported in each calendar year.
Mean
Arithmetic average of 1-hour SO2 concentration values for the year, in parts per million by volume (ppm). If this value exceeds the U.S. annual standard, it is highlighted.
# Exceed
Indicates whether the mean exceeded the U.S. annual standard. (1: yes, 0: no) The sum of these values, in the Grand Total line, tells how many times monitors exceeded the U.S. annual standard.

PM2.5 - Particulate Matter smaller than 2.5 micrometers
U.S. Air Quality Standards
  • 24-hour average concentration -- 65 micrograms per cubic meter of air
    The 98th percentile of 24-hour values for a year may not exceed this level.
  • Annual average concentration -- 15.0 micrograms per cubic meter of air
24-Hour values
Daily average concentrations measured by monitoring equipment and reported to AQS.
# Obs
Number of days in the year for which values (observations) were reported. Many sites take measurements every day.
1st Max, 2nd Max, 3rd Max, 4th Max
The four highest 24-hour values of the year, in micrograms per cubic meter.
98th Pct
The 98th percentile 24-hour value, in micrograms per cubic meter. This value is higher than 98 percent of 24-hour values for the year. If this value exceeds the U.S. 24-hour standard, it is highlighted.
# Exceed
Indicates whether the 98th percentile value exceeded the U.S. 24-hour standard. (1: yes, 0: no) The sum of these values, in the Grand Total line, tells how many times monitors exceeded the U.S. 24-hour standard.
Annual values
Computed by AQS software from 24-hour values.
Mean
Arithmetic mean of 24-hour values, in micrograms per cubic meter. If this value exceeds the U.S. annual standard, it is highlighted.
# Exceed
Indicates whether the mean exceeded the U.S. annual standard. (1: yes, 0: no) The sum of these values, in the Grand Total line, tells how many times monitors exceeded the U.S. annual standard.

PM10 - Particulate Matter smaller than 10 micrometers
U.S. Air Quality Standards
  • 24-hour average concentration -- 150 micrograms per cubic meter of air
    May not be exceeded more than one day per year, after compensating for days when monitoring did not occur (estimated number of exceedances).
  • Annual average concentration -- 50 micrograms per cubic meter of air
Mexico Air Quality Standards
  • 24-hour average concentration -- 150 micrograms per cubic meter of air
  • Annual average concentration -- 50 micrograms per cubic meter of air
24-Hour values
Daily average concentrations measured by monitoring equipment and reported to AQS.
# Obs
Number of 24-hour values (observations) reported for the year. PM10 is typically measured every sixth day, which results in about 60 values per year. Some sites take measurements every day.
1st Max, 2nd Max, 3rd Max, 4th Max
The four highest 24-hour values of the year, in micrograms per cubic meter.
# Exceed - Actual
Number of days in the year when a 24-hour value exceeded the 24-hour standard. .
# Exceed - Est.
Calculated number of days in the year when 24-hour values would be estimated to exceed the 24-hour standard if monitoring took place every day. If the number is greater than 1.0, it is highlighted.
Annual values
Computed by AQS software from 24-hour values.
Mean
Arithmetic mean of 24-hour values, in micrograms per cubic meter. If this value exceeds the U.S. annual standard, it is highlighted.
# Exceed
Indicates whether the mean exceeded the U.S. annual standard. (1: yes, 0: no) The sum of these values, in the Grand Total line, tells how many times monitors exceeded the U.S. annual standard.

TSP - Total Suspended Particulate Matter
Mexico Air Quality Standards
  • 24-hour average concentration -- 260 micrograms per cubic meter of air
  • Annual average concentration -- 75 micrograms per cubic meter of air
24-Hour values
Daily average concentrations measured by monitoring equipment and reported to AQS.
# Obs
Number of 24-hour values (observations) reported for the year. TSP is typically measured every sixth day, which results in about 60 values per year. Some sites take measurements every day.
1st Max, 2nd Max, 3rd Max, 4th Max
The four highest 24-hour values of the year, in micrograms per cubic meter.
Annual values
Computed by AQS software from 24-hour values.
Mean
Arithmetic mean of 24-hour values, in micrograms per cubic meter.

Pb - Lead
U.S. and Mexico Air Quality Standard
This level may not be exceeded in any quarter of a year:
  • Quarterly average concentration -- 1.5 micrograms per cubic meter of air
24-Hour values
Daily average concentrations measured by monitoring equipment and reported to AQS. Lead is captured with particulate matter and extracted from it for analysis.
# Obs
Number of 24-hour values (observations) reported for the year. Lead is typically measured every sixth day (as a constituent of particulate matter), which results in about 60 values per year. Some sites take measurements every day.
1st Max, 2nd Max
Highest and second-highest 24-hour values in the year, in micrograms per cubic meter.
Quarterly averages
Computed by AQS software from 24-hour values.
Qtr 1, Qtr 2, Qtr 3, Qtr 4
Arithmetic average of all 24-hour values for a calendar quarter, in micrograms per cubic meter. Quarters are January-March (1), April-June (2), July-September (3), and October-December (4).
# Exceed
Number of quarters in which the average lead concentration exceeded the quarterly standard value. If nonzero, this value is highlighted.

The following five columns, like the pollutant values above, pertain to an individual monitor at a monitoring site. Therefore, these columns are repeated for each pollutant (monitor) you include in the report.
 
Monitor Number
An ID number that distinguishes among monitors for the same pollutant at a particular monitoring site. In the AQS database, this identifier is called parameter occurrence code (POC).

Monitor Type
The administrative classification of an air monitoring station. This value indicates what type of agency established the monitor or what monitoring program it is associated with. A monitor with several roles may have multiple monitor types. Values are:
  • SLAMS (State and Local Air Monitoring Stations)
  • NAMS (National Air Monitoring Stations)
  • PAMS (Photochemical Assessment Monitoring Stations - detailed study of ozone and its precursors)
  • Unofficial PAMS (site certification pending)
  • Other
  • Industrial
  • Index Site
  • Non-EPA Federal (operated by a Federal agency other than EPA)
  • Trends Speciation (Speciation Trends Network for fine particulate matter)
  • Tribal
  • Unknown

Measurement Scale
The geographic extent of air quality measurements made at the site. Measurements made elsewhere within that geographic scope should be equivalent. Values are:
  • Microscale
  • Middle Scale
  • Neighborhood
  • Regional Scale
  • Urban Scale

Dominant Source Type
The class of air pollution sources that normally produce most of the air pollution measured at the site. Values are:
  • Area - small stationary sources (homes, offices) and diffuse sources (agriculture, wildfires)
  • Mobile - vehicles of all types
  • Point - stationary sources (factories, power plants)

Monitoring Objective
The primary reason for measuring air pollution levels at the site. When an objective pertains to a specific city, urbanized area, metropolitan statistical area (MSA), or consolidated metropolitan statistical area (CMSA), the name of the area is given in parentheses. Typical monitoring objectives are:
  • General/Background concentration
  • Population Exposure
  • Highest Concentration

The following columns pertain to a monitoring site.
 
Year
The calendar year to which data pertain - the year in which pollutant concentrations were measured. The report includes this column only when you select multiple years.

Site ID
The AQS database identification code for an air monitoring site. An AQS site 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

For example, AQS site ID 48-141-0058 is a monitoring site in El Paso, Texas (48 = Texas, 141 = El Paso County, 0058 = a monitoring site in El Paso city). In border air quality reports, this site ID is displayed as 481410058, with no hyphens separating the parts of the ID.

For compatibility with U.S. state/county coding, Mexico is assigned "state" code 80, and Mexican states are coded as "counties." For example, a monitoring site in Ciudad Juarez (Juarez city), Chihuahua State, Mexico, has AQS site ID 80-006-0007 (80 = Mexico, 006 = Chihuahua State), which is displayed as 800060007 in border air quality reports.

Site Address
Address where the monitoring site is located.

City
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.

City Code
The 5-digit FIPS code for the city, town, village or other municipality (a "named populated place") in which the monitoring site is located. Blank or zero if the site is not located within such a jurisdiction, or if no value was provided.

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

County Code
Code for the county (or equivalent jurisdiction) in which a site is located, consisting of 2-digit FIPS state code and 3-digit FIPS county code. FIPS is the acronym for Federal Information Processing Standards, which defines codes used in most U.S. government information systems.

State
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.

Land Use
The prevalent land use within 1/4 mile of the site. Values are:
  • Agricultural
  • Blighted Area
  • Commercial
  • Desert
  • Forest
  • Industrial
  • Military Reservation
  • Mobile
  • Residential
  • Unknown

Location Type
A general characterization of the setting where the site is located. Values are:
  • Rural
  • Suburban
  • Urban and Center City
  • Unknown

Latitude/Longitude
Coordinates of the site location, in degrees. Negative values of longitude indicate locations west of the prime meridian. Blank if no value was provided.

Locational Accuracy
The estimated accuracy (uncertainty) of the site location, in meters, as specified by latitude-longitude coordinates. Blank if no value was provided.

Locational Method
The method used to determine the site location, as specified by latitude-longitude coordinates. Blank if no value was provided.

Distance to City Center
Distance in miles to the city central business district. Direction may be given also, as a compass point: N for north, NE for northeast, etc. Blank if the site is not located in a city, or if no value is available.

City Population
Population (in year 2000) 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 is available.

Urbanized Area
Name of the urbanized area in which the site is located. Blank if the site is not located within such a jurisdiction, or if no value was provided. The U.S. Census Bureau defines an urbanized area as a place (city) and the adjacent densely-settled surrounding territory that together have a minimum population of 50,000 people.

UA Code
The 4-digit Census Bureau code for the 1990 urbanized area in which the site is located. Blank or zero if the site is not located within such an urbanized area, or if no value was provided.

MSA (Metropolitan Statistical Area)
Name of the MSA in which the site is located. Blank if the site is not located within an MSA, or if no value was provided.

A metropolitan statistical area consists of one or more counties having a combined population of at least 100,000 people, containing a city or urbanized area with a population of at least 50,000 people. (In New England states, the population threshold is 75,000 and MSAs comprise cities and towns rather than counties.) An MSA may contain more than one city larger than 50,000 population, and it may include counties in multiple States.

MSA Code
The 4-digit FIPS code for the metropolitan statistical area (MSA) in which the site is located. Blank or zero if the site is not located within a metropolitan statistical area, or if no value was provided.

CMSA (Consolidated Metropolitan Statistical Area)
Name of the CMSA in which the site is located. Blank if the site is not located within a CMSA, or if no value was provided.

A consolidated metropolitan statistical area consists of one or more MSAs that have a combined population of at least one million people. The constituent MSAs are called primary MSAs (PMSA).

CMSA Code
The 4-digit FIPS code for the consolidated metropolitan statistical area (CMSA) in which the site is located. Blank if the site is not located within a consolidated metropolitan statistical area, or if no value was provided.

AQCR (Air Quality Control Region)
Name of the AQCR in which the site is located. Blank if no value was provided.

An air quality control region is a group of counties within a state (or multiple adjacent states) that share common geographical or pollutant concentration characteristics based on a common pollutant source.

AQCR Code
The 3-digit AQS code for the air quality control region (AQCR) in which the site is located. Blank if no value was provided.

Site Established
The date (day, month, year) when the monitoring site began measuring air pollutant concentrations. This date pertains to the entire site, and not necessarily to a specific pollutant (monitor).

Site Terminated
The date (day, month, year) when the monitoring site stopped operating. No value is displayed if the site is still operating.

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