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AQS Codes and Descriptions

Links go to HTML pages that are refreshed nightly. The pages can be downloaded as comma separated values (CSV) files. File format information here.

Click on the information for more information on each topic.

Parameters/Methods/Units/Durations General Geographic
information Valid Combinations - All Parameters information Qualifiers - all information Agencies - all
Met only spacerinformation QA only spacerTribal only
Criteria only spacerinformation Null only  
HAPS only spacerinformation Inform only information States & Counties
Core HAPS only spacerinformation ReqExc only information Cities
PAMS only   information CBSAs
PAMS VOC only information Parameters information CSAs
Improve Carbon only information Parameters -  Disallowed Qualifiers  
Improve Speciation only informationUnits information Legacy MSAs
PM10 Speciation only informationDurations informationLegacy CMSAs
PM10-2.5 only    
PM2.5 Continuous nonreference only informationCollection Frequencies Urban Areas
PM2.5 Mass and QA only informationNetwork Affiliations for Monitors Air Quality Control Region (AQCR)
Speciation only    
Speciation cation/anion only informationPollutant Standard IDs  
Speciation carbon only informationAQI breakpoints  
Speciation metals only information Legacy Null data codes  
information UATMP Carbonyl only information Quality Assurance Project Plans (QAPPS)  
UATMP VOC only information Certifying Agencies by Monitor  
Audit Levels - Criteria Gases information NPAP data  
Audit Levels - Lead information Certification Flags  

Valid Combinations of Parameters and Methods
Allowed combinations of parameter + sampling methodology (collection and analysis) + reported unit + duration (sometimes called "Protocols").   If you do not see the combination here, it is not allowed into AQS. If you believe that we are missing a valid combination, please contact the EPA Call Center. This list also includes other information, such as the standard unit, the summary scale and the minimum sample value that is allowed into AQS.  To make the files smaller, we also broke out selected groups of parameters and show the valid combinations for just those.
Parameters not just pollutants but anything that is measurable, including meteorology measurements, i.e., wind speed.
UATMP Urban Air Toxics Monitoring Program.
Qualifiers all Qualifiers are used when reporting data to AQS. Qualifiers further explain the data.
  • "Null" qualifiers
    • required when submitting a null (i.e., nothing was collected) sample measurement; All Null qualifiers are available for every parameter
  • "QA" qualifiers - optional
    • quality assurance qualifiers are used when data is valid but you want to note something. i.e. measurement was "Below lowest calibration level"
  • "Inform" qualifiers - optional
    • informational qualifiers are used in place of a REQuest EXClusion qualifier; use only when an exclusion of the data will not be requested
  • "ReqExc" qualifiers
    • required when submitting data that is affected by an Exceptional Event and for which an exclusion will be requested
Parameters - Disallowed Qualifiers all List of disallowed qualifiers for each parameter.
Collection frequencies the amount of time between sample observations.
Durations required when reporting a measurement; the length of time used to acquire a sample measurement (can sometimes called the interval) E.g., measurements for ozone monitors that run continuously are reported as hourly average concentrations with AQS Duration Code = 1.
Units Units of measurement. Apply to both Reported and Standard Sample Values.
Monitor types Indicates the purpose of a monitor. Each monitor is required to have at least one monitor type.
Pollutant Standard IDs Every NAAQS has a unique Pollutant Standard in AQS, i.e. "2008 8-hour ozone NAAQS".
AQI breakpoints For select pollutants, the AQI transforms ambient concentrations to a scale from 0 to 500. Since AQS generates the AQI values, we also store the breakpoints for the AQI ranges ("Good", "Moderate", "Unhealthy" for sensitive groups" or "Unhealthy", "Very unhealthy", "Hazardous".).
Agencies Air pollution control agencies and other organizations reporting data to AQS.  If an agency you need already exists, but is not shown for your state within AQS, contact the EPA Call Center to have your state added to the list of states that can use that agency code.
State and Counties FIPS codes for all the states and the counties contained therein.
Cities FIPS codes for cities.
CBSAs Core-Based Statistical Areas (CBSAs) - defined by OMB in June 2003; areas based around an urban center of > 10,000 people and adjacent areas; designations are made using US Census numbers.
CSAs Combined Statistical Areas (CSAs) - defined by OMB in June 2003; areas based on adjacent CBSAs; designations are made using US Census numbers.
Legacy MSAs Metropolitan Statistical Areas (MSAs)  *** Informational purposes only.  MSAs were replaced by CBSAs.
Legacy CMSAs Combined Metropolitan Statistical Areas (CMSAs)   *** Informational purposes only.  CMSAs were replaced by CSAs.
Legacy Null data codes Mapping of the old mainframe codes to the newer Null qualifier codes.  *** Informational purposes only.
Quality Assurance Project Plans (QAPPS) Contains a list of all agencies that have submitted QAPPs and approval dates by EPA Region where appropriate
Certifying Ageincies by Monitor A list of criteria monitors that were active during 2012. For each monitor, the most recent Certifying agency, PQAO, Collecting Agency, and Reporting Organization is included
National Performance Audit Program (NPAP) data Independent site audits as required by the Monitoring Plan or Quality Assurance Program Plan (QAPP) for gaseous criteria monitors. These audits are usually performed by USEPA and reported to AQS as NPAP audits.
Certification Flags A list of all valid Certification Flags
Information on the format of the files:
  • You can download the full CSV (Comma Separated Values) file from any page that you are on
    • The CSV files have been designed to import into MS Excel with minimal effort
  • Each column is sortable
    • "<" - Sorts the column in Descending order
    • ">" - Sorts the column in Ascending order
    • Clicking the Title will reset the sort order using the default sort criteria

AQS Frequent Questions | Technology Transfer Network | Air & Radiation


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