Measuring air pollution in wildfire conditions using PurpleAir monitors

Abstract

In November 2018, California experienced one of the most financially costly wildfires in history. Some PurpleAir monitors were available and collecting data in nearby cities like San Francisco, recording real-time measurements of particulate matter concentrations. Using this data, air quality data was assessed to determine how frequently the PM 2.5 concentrations were exceeding the National Ambient Air Quality standards. For approximately twelve days, the air concentrations for PM 2.5 exceeded the 24-hour limit of 35 ug/m3. Throughout this period, the sensors recorded data that was remarkably comparable between each sensor with an exception of one sensor (LPH). Compared to EPA data, the PurpleAir monitors typically had noticeably higher mass concentrations prior to the 16th of November. One of the potential issues with this data is that there are not an equal number of EPA monitors solely in the city of San Francisco. Many of the sensors are spread out throughout the Bay area. Depending upon the path of the air currents, particulates could be more concentrated in one area of the metropolitan area versus another area. An additional potential issue is that the exact location of the PurpleAir monitors are unknown, therefore it would be inappropriate to speculate whether these sensors were placed correctly to ensure accurate concentrations. Further investigation should take place to see how reliable these sensors are in extreme conditions to ensure the validity of this data as it could be a useful tool for communities' advocating for clean air while using low-cost sensors.