EPA Research Partner Support Story: Demonstrating the utility and challenges of low-cost sensors used for citizen science
Partner: Maricopa County (AZ) Air Quality Department
Challenge: Demonstrating the utility and challenges of using air sensors to investigate air quality issues in Phoenix, AZ
Resource: Reports, publications and presentations documenting the study and characterizing air sensor performance and air quality trends in Phoenix
Project Period: 2018 – 2021
A new generation of lower cost air sensors is increasingly being used by state, local and tribal agencies, researchers, participatory scientists, and others to supplement regulatory monitoring at the neighborhood level. However, air sensor performance and data quality can vary based on local conditions, such as temperature, relative humidity, and composition of particles. As a result, there is a need to understand how sensors behave in different environments when using them to study local air quality.
“The Maricopa County Air Quality Department was excited to work closely with EPA on this study. Developing an understanding of these new citizen science tools gives us the ability to help citizens put the data they are collecting into context. The data that were obtained in this study, and the expert analysis assistance provided by the EPA team, gave us a better understanding of the spatiotemporal patterns of PM 2.5 . Furthermore, the knowledge gained on the use and limitations of these sensors will assist our agency with the future utilization of these affordable monitoring tools.” – Ben Davis, Air Monitoring Division Manager, Maricopa County
During the Phoenix as a Testbed for Air Quality Sensors (PTAQS) project, EPA collaborated with the Maricopa County Air Quality Department (MCAQD) to deploy a network of PurpleAir fine particulate matter (PM 2.5 ) sensors across Phoenix. In Phase I (November 2018 – July 2019), multiple PurpleAir sensors were placed alongside more expensive and sophisticated regulatory monitors at three sites to study long-term sensor performance and data quality in Phoenix’s hot, dry and sunny environment. In Phase II (July 2019 – March 2021), PurpleAir and black carbon sensor packages were built and deployed at 20 non-regulatory sites to study air quality trends across the city. A mobile trailer with regulatory-grade PM 2.5 measurements was also transported between sites to validate sensor calibration methods. MCAQD provided important support by maintaining the sensor network, retrieving data, and sharing expertise on local air quality issues.
The PTAQS network was a great opportunity to understand air sensor performance in a new environment and answer specific air quality questions that have been challenging to address using the existing regulatory monitoring network alone. The work led to an increased density in observations that assisted interpolation of concentrations across the city, high time resolution data that helped visualize how pollutants move and how conditions can change during the day, additional supporting information for identifying exceptional events, and a greater understanding of how to correct and interpret data from air sensors.