Investigating Degraded Air Quality Despite A Lack of Smoke

Though most time spent as an Air Resource Advisor is spent working with the impacts of the fire, this isn’t always the case. At the end of May, the West Mims Fire was producing little smoke, but air quality was mysteriously degrading. All sites in the area were showing moderate air quality, with several showing brief periods of worse conditions on May 30, 2017.


The worse air quality did not match the smoke produced by the fire, and though there were some other fires in the area that could contribute, they likely still weren’t enough to produce such a noticeable region-wide response. Indeed the monitors nearest West Mims ironically showed some of the lowest PM 2.5 values in the area. MODIS satellite imagery confirmed an increase in particulates with a higher aerosol optical depth on May 30:


Though high clouds (or perhaps even the obscuring haze itself triggering the cloud flag) masked much of the area, it’s apparent the values were relatively high, especially compared to what was observed over the area a few days earlier:


Ultimately, after some discussions with a National Weather Service meteorologist and an environmental consultant with the Florida Department of Environmental Protection, the most likely culprit was an outbreak of Saharan dust. A US Navy model also analyzed the presence of dust in the region:


Though the 30th showed the poorest conditions associated with the dust, it took several days for regional PM 2.5 levels to return to more typical values.