Air Sensors FAQ | NC DEQ
Air sensors are devices for assessing air quality that are designed to be more accessible to the public than traditional federally certified regulatory monitors. As compared to the regulatory monitors in DAQ’s network, sensors are typically smaller, lower-cost, less accurate, and usually function based on different technological principles. Often, several different types of sensors will be assembled into a single device so that it can measure more than one pollutant, while regulatory monitors are generally specialized to measure a single type of pollutant. For more information on regulatory monitoring of criteria air pollutants, please visit DAQ’s Air Quality Monitoring page.
The United States Environmental Protection Agency (EPA) has a rigorous testing and certification process for regulatory monitors, with two designations: Federal Reference Method (FRM) and Federal Equivalent Method (FEM). FRM/FEM air quality monitors are highly regulated from site establishment through data collection.
The EPA lays out stringent guidelines for:
- siting regulatory monitors;
- calibration and maintenance according to specific criteria; and
- required equipment and data quality audits.
All of North Carolina’s regulatory monitors are installed, maintained and operated in accordance with EPA requirements, ensuring that policy decisions in our state are informed by high-quality monitoring data.
For air sensors, there are no federal standards on accuracy, calibration, siting, maintenance or data quality assurance/quality control (QA/QC). There is currently no certification program for sensors and the quality of both the hardware and software is highly variable between manufacturers and models. There is no governing body to verify that manufacturers are accurately characterizing the performance of their sensors. Often, software modifies the sensor data to account for different environmental conditions, but those correction algorithms are typically not available for review by customers or researchers. This makes it difficult to assess the true performance of the sensors and the quality of the resulting data.
However, the EPA has developed two reports detailing step-by-step testing protocols, performance metrics, and performance targets for sensors that measure ozone (O3) and particulate matter <2.5 microns (PM2.5). While sensor manufacturers are not required to follow these protocols, sensors that are able to meet these performance targets are more likely to provide users with useful data.
EPA’s Performance Targets and Testing Protocol Reports:
For additional information on the differences between air sensors and regulatory monitors, the EPA has also produced a short video that can be viewed in both English and Spanish.
