Monitoring in Pima County
The ultimate goal of the Pima County Department of Environmental Quality (PDEQ) air quality control program is to reduce harmful contaminants in ambient air to healthy levels and maintain those levels. Key to controlling air pollution is defining the nature and extent of air quality problems through monitoring.
Pima County is in attainment of U.S. Environmental Protection Agency (EPA) National Ambient Air Quality Standards with the exception of the Rillito area which is non-attainment for PM10. The Ajo area was redesignated as attainment of the PM10 standard by EPA on September 3, 2020. Pima County exceeded the 2015 EPA ground-level ozone standard several times during the 2018 and 2020 ozone season. The designation as attainment of the 2015 ozone standard will stay until EPA makes a change.
PDEQ monitors six criteria pollutants in the Tucson and Green Valley area in accordance with regulations established by the EPA. Data is reported hourly to PDEQ's air monitoring website, to the EPA's Air Now website and other agencies.
Air Quality Index
The Air Quality Index is the uniform procedure by which daily air pollution levels are reported to the public. AQI levels are set by the Environmental Protection Agency (EPA) in accordance with section 319 of the Federal Clean Air Act. Air Quality Index Historic Information.
Air quality information is collected by the Pima County Department of Environmental Quality monitors located throughout Eastern Pima County. The monitors collect concentration information in parts per million and parts per billion for gases and micrograms per cubic meter for particulates. The level of pollution in the air and the related health effects are relayed to the public using the Air Quality Index. If a pollutant such as ozone has an AQI value of 40, the corresponding qualitative descriptor would be GOOD (0-50) and if it was 79, it would be considered MODERATE (51-100). The AQI value of 100 generally corresponds to the National Ambient Air Quality Standard for the pollutant. AQI values below 100 are considered satisfactory while numbers above 100 are considered to be unhealthy.
The AQI is the highest value for the pollutant in a 24-hour period. The highest 8-hour average for ozone and CO, and the highest 24-hour average for PM10 and PM2.5 . Pima County uses this information for historical summaries and uses EPA's NowCast method for relating short-term (less than 24-hour) data to the Air Quality Index for the purposes of real -time reporting.
You can sign up to receive our air quality advisory notifications.
Air Pollution Data
Please note: Many of these reports display values for 1-hour PM10 and PM2.5 (particulate matter 10 and 2.5 microns or less in diameter) concentrations. These data values are provided for informational purposes only. The EPA Health Standard for PM10 and PM2.5 is a 24-hour standard, based on the average of 24 hourly readings from midnight to midnight. The EPA has not yet developed a 1-hour standard for PM10 or PM2.5.
Historic 24-Hour Particulate Data:
Quality Assurance of Air Pollution Data
Local agencies such as PDEQ involved in federal monitoring programs must comply with federal air quality assurance requirements. Each agency must develop and implement a Quality Assurance (QA) program consisting of policies, procedures, specifications, standards, and documentation necessary to:
- Provide data of adequate quality to meet monitoring objectives, and
- Minimize loss of air quality data due to malfunctions or out-of-control conditions.
It is the policy of PDEQ to conduct and support appropriate quality assurance activities to ensure that these objectives are met.
Monitoring Information
Pima County Department of Environmental Quality and its predecessors have conducted air monitoring in the Tucson, Arizona area since the 1960's. PDEQ monitors ambient (outdoor) air pollutants at 15 monitoring stations located throughout eastern Pima County, including the Tucson metropolitan area and Green Valley. More information regarding PDEQ's air monitoring program is available in the 2021 Ambient Air Monitoring Network Plan.
There are six principal pollutants, called “criteria” pollutants that are monitored in accordance with the National Ambient Air Quality Standards (NAAQS) set by the Environmental Protection Agency (EPA) to comply with the Federal Clean Air Act. The NAAQS were established to protect public health and the environment from harmful levels of air pollution.
The six criteria air pollutants monitored by PDEQ which are: carbon monoxide (CO), ozone (O3), particulate matter (PM10 and PM2.5), nitrogen dioxide (NO2), sulfur dioxide (SO2) and lead (Pb).
Map of monitoring locations and information about each site is located on PDEQ's Air Monitoring website, ENVISTA.PIMA.GOV. Click on the circles to get the site information. In addition to the sites located on this map, PDEQ operates four other monitoring stations that are not able to be polled electronically.
The air quality monitoring section is divided into 3 units; the Field Monitoring unit, the Data Management unit and the Quality Assurance (QA) unit. The field monitoring unit conducts all quality control procedures related to routine operations such as calibrations, equipment checks, troubleshooting and repair of equipment necessary for air quality monitoring. The data management unit handles all operations related to network operations, data acquisition, management, storing and reporting of data. The QA unit operates independently of the field monitoring unit to assure the quality and accuracy of the data recovered.
Almost all routine air quality monitoring data generated by PDEQ are submitted to the U.S. Environmental Protection Agency (EPA) AQS database system. Most air quality monitoring stations in the PDEQ network are equipped with electronic data loggers designed specifically for the logging of air quality data.
The data loggers are programmed to take the electrical outputs from air quality monitoring instruments at a monitoring station and transmit this information via a modem to a central computer data acquisition system (DAS) located in the PDEQ offices. This information is then validated to detect possible erroneous readings, and stored in a central database. The information is then reported to the EPA, documented in summary reports, and made available to local agencies, researchers and the public.
Reports
