Particulate matter (PM) is a common air quality metric, as it can lead to a number of adverse health effects including asthma, heart attacks, and premature death. PM measurements are classified by particle size, and different size classes indicate different contaminants, such as dust and smoke. The PurpleAir low-cost PM sensors use a fan to draw air past a laser, and particles that pass the laser scatter light. The sensor then measures scattered light, which correlates to PM counts and mass concentrations. A fraction of the PurpleAir sensors installed since June 2021 appear to report different PM concentrations compared to sensors installed prior to June 2021. We identified potentially anomalous sensors by comparing the measurements of these new sensors with the measurements of sensors installed prior to June 2021. Each sensor installed after June 2021 was paired with an older sensor installed in the same geographic location to understand whether localized PM readings were consistent. Historical PM concentration readings from the summer of 2022 were collected from each pair of sensors and used to determine the likelihood of the new sensor reporting anomalous values. This process also identified a threshold for which a newly installed sensor could be flagged if PM counts differed significantly from the previously installed sensor in the region. Our preliminary results suggest hundreds of PurpleAir sensors that measured significantly higher PM counts for the smallest particle sizes (less than or equal to 0.3 microns in diameter), while simultaneously reading significantly lower counts for large particle sizes (greater than 1.0 microns in diameter). These differences also suggest that these new sensors may require different PM correction factors than those not exhibiting this anomalous behavior. More research is needed to determine appropriate correction factors and the long-term prevalence of these newer PurpleAir PM sensors.