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Border Air Quality Data

What Kind of Data Are Available?

This Web site has air quality data for criteria and hazardous air pollutants.

Criteria air pollutants are airborne substances for which the United States and Mexico have established health-based exposure limits. In the U.S., EPA sets limits called national ambient air quality standards. In Mexico, the Secretaria del Medio Ambiente Recursos Naturales (SEMARNAT) sets limits called Normas Ambientales para Aire.

The criteria air pollutants are:

Nitrogen dioxide and sulfur dioxide each serve as indicators of the concentrations of several chemically similar compounds, nitrogen oxides (NOx) and sulfur oxides (SOx). Lead is a component of particulate matter.

Hazardous air pollutants (HAPs) are substances that are known or suspected to cause serious health problems. Section 112(b) of the U.S. Clean Air Act identifies a list of 188 pollutants as HAPs. Some of those are further subdivided for air monitoring procedures, resulting in about 200 HAPs that may be monitored for their ambient concentrations in air. In practice, air monitoring is done for about one-third of the HAPs.

Data presented here pertain to the ambient concentration of criteria and hazardous air pollutants in the border area. We provide yearly summaries of criteria air pollutant concentrations, extracted monthly, and hazardous air pollutant concentrations, extracted quarterly, from EPA's Air Quality System (AQS) database. The data extract includes monitors located within approximately 100 kilometers (62 miles) of the U.S.-Mexico border that reported data in the last ten years. State agencies in the U.S. have reviewed the data to assure quality.

There are some differences in U.S. and Mexican air quality standards (see the table below). Reports generated by this Web site compare pollutant concentrations to U.S. standards only. When a report lists how many times pollutant concentrations exceeded an air quality standard, it refers to the U.S. standard, even for air monitoring sites in Mexico.

Other Sources of Border Air Quality Data

EPA's AIRNOW Web site provides links to real-time ozone air pollution data and ozone forecasts for all U.S. states along the border, as well as ozone data for other non-border states.   

EPA's AirData Web site provides access to air quality data similar to that available at this site for all states within the U.S.

Are Data From Monitors in Mexico Included?

A significant amount of data from sites in Mexico and along the U.S. border is available. As per agreement with the Government of Mexico, these data are subject to quality assurance and control measures as the data are processed by Mexico and U.S. border states for entry into EPA's air quality database, AQS.

What Are Standard-Relevant Air Quality Data?

Standard-relevant air quality data are the particular values used in determining whether an area is attaining national air quality standards for each criteria pollutant, plus descriptive information about monitoring sites. The air quality standards are defined to protect the health of people working or playing outdoors. For most pollutants, there is a standard for short-term exposure and another standard for longer-term exposure. Measured air pollutant concentrations are averaged over the time intervals of the applicable standards, and compared with the value of the standards.

Reports generated at this Web site give pollutant concentrations relevant to each air quality standard. For example, a report of total suspended particulate matter (TSP) data includes a 24-hour average concentration and an annual average concentration. These values correspond to Mexico's short-term and long-term air quality standards (Normas) for TSP.

The following table lists the air quality standards for the U.S. and Mexico. The table includes the time period over which pollutant concentrations are averaged (i.e., exposure time), and the numerical value of each standard. Values are in parts per million by volume (ppm) and micrograms per cubic meter of air (µg/m3).

Health-Based Ambient Air Standards

United States Mexico
Carbon monoxide (CO)
    8-hour Average 9 ppm 11 ppm
    1-hour Average 35 ppm  
Nitrogen dioxide (NO2)
    Annual Average 0.053 ppm  
    1-hour Average   0.21 ppm
Ozone (O3)
    8-hour Average 0.08 ppm  
    1-hour Average 0.12 ppm 0.11 ppm
Sulfur dioxide (SO2)
    Annual Average 0.030 ppm 0.030 ppm
    24-hour Average 0.14 ppm 0.13 ppm
Particulate matter smaller than 2.5 micrometers (PM2.5)
    Annual Average 15 µg/m3  
    24-hour Average 65 µg/m3  
Particulate matter smaller than 10 micrometers (PM10)
    Annual Average 50 µg/m3 50 µg/m3
    24-hour Average 150 µg/m3 150 µg/m3
Total suspended particulate matter (TSP)
    Annual Average   75 µg/m3
    24-hour Average   260 µg/m3
Lead (Pb)
    Quarterly Average 1.5 µg/m3 1.5 µg/m3

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