Technical Evaluation of Sensor Technology (TEST) Program

In response to the growing development and availability of low-cost air monitoring sensor technology, the District has established the Technical Evaluation of Sensor Technology (TEST) Program to evaluate the performance of a variety of low-cost sensors in the San Joaquin Valley. Performance results and related information will be made publically available on a periodic basis, with the goal of enhancing the understanding of the potential use and limitations of new sensor technologies.

The District’s main goals and objectives of evaluating low-cost sensors include the following:
  • Identify and evaluate the latest developments in low-cost sensor technology
  • Through the TEST Program, work independently, and in partnership with other agencies, to evaluate the accuracy of various sensor technologies in the conditions of the San Joaquin Valley, through collocating low-cost sensors at existing air monitoring sites
  • Develop low-cost sensor performance reports and make them available to the public on the TEST Program webpage, providing information on which sensors perform best in varying Valley locations and environmental conditions
  • Provide guidance and educational materials for how sensors should be sited, operated, and how data should be interpreted and used
  • Engage in partnerships with community groups and businesses who wish to use personal air monitoring sensors for monitoring projects
Importance of the District’s TEST Program and Educational Efforts

Air monitoring sensor technology has been developing at a rapid pace over recent years, increasing the number of analyzers that the general public can use to measure particulate matter, ozone, or other pollutants at their own home or business. In addition, these sensor technologies are becoming more affordable, making them more accessible to Valley citizens who wish to conduct personal air monitoring. As a result, there are now more options for personal air monitoring equipment than ever before.

However, since low-cost sensor technologies are equipped with low-precision components and do not follow strict maintenance and calibration guidelines that regulatory-grade monitors must adhere to, over time the accuracy of low-cost sensor data can diminish and drift from known performance standards. Due to this, the interpretation and use of data from low-cost sensors can cause confusion and mislead Valley residents regarding the status of current air quality conditions. To improve clarity on this issue, the need to evaluate and provide information on the performance and limitations of low-cost sensor technology will be key as sensor technology continues to advance and grow in its use.

In addition to providing the results of low-cost sensor performance evaluations, the development of education materials focused on the proper sensor placement, operation, and interpretation of collected data will also be valuable as low-cost sensors continue to be used for various monitoring projects. The District will also seek to provide technical and monitoring assistance to local community groups and businesses as they develop and implement a number of community air monitoring projects in the coming years.

Low-Cost Sensor Performance Analysis

PurpleAir PA-II Sensor

The PurpleAir PA-II sensor uses an optical laser-based particle counting methodology to estimate the concentration of PM1, PM2.5, and PM10. The PA-II sensor also measures temperature, pressure, and relative humidity.

The following documents summarize the performance of this sensor by quarter:

Clarity Node Sensor

The Clarity sensor uses optical laser-based particle counting methodology to estimate the concentration of PM2.5. The Clarity sensor also measures temperature and relative humidity.

The following documents summarize the performance of this sensor by quarter:

APIS Sensor

The APIS sensor uses an active flow and sample control system that measures CO, NO, NO2, and O3. The APIS sensor also measures temperature, pressure, and relative humidity.

The following documents summarize the performance of this sensor by quarter: