In recent years, “low-cost” air quality monitors—such as PurpleAir monitors—have become more prevalent in the United States; as a result, their data readings have become more influential in driving public policy decisions at various levels of government and across the nation. PurpleAir monitors—in addition to other “low-cost” and recreational air quality monitors—often present severe data quality issues when monitoring and assessing particulate matter under 2.5 microns in diameter (PM 2.5). To understand some of the challenges in measuring PM 2.5, watch this video featuring the founder and CEO of PurpleAir discussing the difficulties associated with the data.
This whitepaper examines deficiencies related to these types of low-cost monitors and the potential issues that arise when policymakers are presented and rely on the monitor’s data to formulate public policy.
While PurpleAir sensors are lower in cost, portable, and easier to operate than regulatory-grade monitors, there is a trade-off with respect to data quality in exchange for simplicity and ease of operation. The white paper compares and contrasts reference monitors and low-cost sensors. The use of low-cost sensors, such as PurpleAir monitors, may provide useful data for research purposes, but caution should be exercised in using such data for regulatory purposes.
The United States Environmental Protection Agency (EPA) is currently reconsidering the primary and secondary standards for PM 2.5. The EPA has proposed lowering the annual primary standard for PM2.5 to a range of 9 to 10 µg/m3. In this context, the use of low-cost sensors to measure ambient air quality has increased. However, it is essential to understand these sensors’ capabilities to use their data to make policy changes effectively.
The paper’s findings raise significant concerns about the reliability of data obtained from low-cost sensors, including PurpleAir monitors. These sensors may be useful for general air quality monitoring, but they should not be relied upon for regulatory compliance monitoring. The EPA’s procedures for designing an ambient air monitoring network must be followed to ensure that representative ambient air PM concentrations are determined. It is crucial to understand the limitations and capabilities of low-cost sensors when using their data to make policy decisions.