The PurpleAir PA-II unit is a low-cost sensor for monitoring changes in the concentrations of Particulate Matter (PM) of various sizes. There are currently more than 9000 PA-II units worldwide; some of them are located in areas where no other reference air monitoring system is present. Previous studies have examined the performance of these PA-II units (or the sensor within them) in comparison to a co-located reference air monitoring system. However, because PA-II units are installed by PurpleAir customers, the PA-II units are not co-located with a reference air monitoring system and, in many cases, are not near one. This study aimed to examine how PA-II units perform under atmospheric conditions when exposed to a variety of pollutants and PM2.5 concentrations. We were interested in knowing how accurate these PA-II units are when measuring PM2.5 concentrations with their sensitivity to concentration changes in comparison to the Environmental Protection Agency (EPA) Air Quality Monitoring Stations (AQMS) that are not co-located with them. For this study, we selected eight different locations, where each location contains multiple PA-II units (minimum of seven per location, a total of 86 units) and at least one AQMS (total of 14). PM2.5 measurements from each PA-II unit were compared to those from the AQMS and other PA-II units in its area. The comparisons were made based on hourly and daily PM2.5 measurements. In most cases, the AQMS and PA-II units were found to be in good agreement; they measured similar values and followed similar trends, that is, when the PM2.5 values measured by the AQMS increased or decreased, so did those of the PA-II. In some high-pollution events, the PA-II measured higher PM2.5 values compared to those measured by the AQMS. We found PA-II PM2.5 measurements to remain unaffected by changes in temperature or Relative Humidity (RH). Overall, the PA-II unit seems to be a promising tool for identifying relative changes in PM2.5 concentration with the potential to complement sparsely distributed monitoring stations and to aid in assessing and minimizing the public exposure to PM, particularly in areas lacking the presence of an AQMS.
|Journal||Atmospheric Measurement Techniques|
|State||Published - Dec 2020|