We have identified that the EQUATES CMAQ output includes some physically unrealistic PM2.5 (and PM10) values, on the order of >10,000 ug/m^3, at a few grid cells and hours. This seems to be due to an issue with the way fire emissions were processed and then modeled within CMAQ. We recommend screening for these values and removing them or capping them in some way before using the full spatial fields for an application. These high values are very isolated in space and time. If you are matching the model data to monitoring locations, or subsetting to a specific domain or time period these extreme values may not be an issue. The attached plot shows the daily maximum (across all grid cells) of the model estimated 24 hour average PM2.5. The years with values >10,000 ug/m^3 are 2003, 2012, 2015 and 2017.
For reference, the largest measured hourly PM2.5 value across 2002-2017 (looking at a all monitoring stations in the AQS database) was 1,401 ug/m^3 and the largest 24 hour average value was 985 ug/m^3. The largest hourly and 24 hour average observed PM10 values were 61,498 ug/m^3 and 16,619 ug/m^3, respectively.