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Quality Assurance for Ambient Air Monitoring

Ambient air is the air we all breathe; it may be affected by nearby or far-off emissions. The Division of Air Resources (DAR) calibrates and checks the accuracy of ambient air monitors and maintains calibration standards used for data collected by air monitors. This work is organized so that the staff who analyze monitoring systems do not take orders from the staff who designed the systems. That independence allows impartial reviews of the installations and data, which is a defining feature of quality assurance.

Monitors are calibrated by measuring standard samples with known properties to confirm the monitor gives correct results. Their accuracy is checked by comparing the monitors' readings to readings from a standard device known to be accurate. These samples and devices are primary standards certified by the National Institute of Standards and Technology (NIST). Field operators may use "transfer standards" certified by comparison with primary standards at DAR's laboratory.

The Division keeps primary standards for:

  • temperature;
  • pressure;
  • time;
  • flow rates; and
  • concentrations of gases:
    • carbon monoxide
    • sulfur dioxide
    • nitrogen oxides
    • ozone

To assure the quality of ambient air monitoring operations, DAR reports whether the State's monitors are properly maintained and whether the data collected is valid. DAR also does independent audits of monitors run by the State, by public organizations, and by permit-holders. (Permits often require sites to operate air monitors.)

There are two main types of audit:

  • Performance audits use DAR's calibration standards to check the accuracy of equipment.
  • Systems audits make sure ambient air monitors are useful by checking that:
    • monitoring programs use appropriate procedures, techniques, and schedules;
    • databases are well-organized and the data is valid; and
    • the supervising engineers are thorough when reviewing on-site log books.

Emissions Monitoring & Stack Tests

DAR also reviews stack test protocols and designs for continuous monitoring systems, and may review reports generated by those tests and systems. These reviews support work done in DEC's regional offices and allow DAR to respond to inquiries from facilities, consultants, and engineers.

Stack tests collect samples from emission streams to test the efficiency of equipment that captures or destroys pollutants. Some applicants must run tests before getting a permit, and some sites must run tests as a condition of their permit.

DAR also uses its own calibration standards to evaluate devices that are permanently installed, and can take measurements at any time. For example:

  • Continuous Emissions Monitoring Systems (CEMS) analyze emissions to find concentrations of nitrogen oxides, sulfur dioxide, and some other pollutants. DEC uses that data and data about the rate of emissions to calculate compliance with laws like the limits that reduced acid rain in NY.
  • Continuous opacity monitors measure how much light a stream of particles blocks to determine if permit conditions are being met.

Stack tests, CEMS, and opacity analysis all use methods approved by EPA. You can read about these methods at EPA's Technical Air Pollution Resources site (leaves DEC website).


  • Contact for this Page
  • NYSDEC
    Division of Air Resources
    Quality Assurance
    625 Broadway
    Albany, NY 12233-3258
    518-402-8401
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