Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock () or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

JavaScript appears to be disabled on this computer. Please click here to see any active alerts.

AQS Code List

AQS Codes and Descriptions

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

Methods	General	Geographic
All Parameters	Qualifiers	Agencies - all
Criteria only	Parameters	Agencies - Tribal only
Met only	Parameter Classifications	States & Counties
HAPS only	Parameters - Disallowed Qualifiers	Cities
PM2.5 Speciation only	Units	CBSAs
	Durations	CSAs
	Collection Frequencies	Urban Areas
	Network Affiliations	Air Quality Control Regions (AQCR)
	Monitor Types
	Pollutant Standards
	AQI breakpoints
	Quality Assurance Project Plans (QAPPS)
	Certifying Agencies by Monitor
	Certification Flags
	Audit Levels
	Ozone Seasons
	Cylinders
	Cylinder Producers

Methods	Allowed combinations of parameter + sampling methodology (collection and analysis). This list also includes other information, such as the standard unit, the summary scale and the minimum sample value that is allowed into AQS.
Parameters	Not just pollutants but anything that is measurable, including meteorology measurements, i.e., wind speed.
Qualifiers	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 a 24 hour sample are reported with AQS Duration Code = 7.
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	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.
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.
Quality Assurance Project Plans (QAPPS)	Contains a list of all agencies that have submitted QAPPs and approval dates by EPA Region where appropriate
Certifying Agencies by Monitor	A list of criteria monitors. For each monitor, the most recent Certifying agency, PQAO, Collecting Agency, and Reporting Organization is included
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