Model output tracking smoke from agricultural fires in south Florida from October 2022 - May 2023

Smoke from agricultural fires is a potentially important source of fine particulate matter (PM2.5) in the US. Sugarcane is burned in Florida to facilitate the harvesting process, with the majority of these fires occurring in the Everglades Agricultural Area (EAA), where there is only one regulatory air quality monitor. During the 2022–2023 sugarcane burning season (October–May), we used public low-cost PurpleAir sensors, regulatory monitors, and 29 PurpleAir sensors deployed for this study to quantify PM2.5 from agricultural fires. We found satellite imagery is of limited use for detecting smoke from agricultural fires in Florida due to the cloud cover, overnight smoke, and the fires being small and short-lived. For these reasons, surface measurements are critical for capturing increases in PM2.5 from smoke, and we used multiple smoke-identification criteria. During the study period, median 24-hour PM2.5 concentrations increased by 2.3–6.9 µg m-3 on smoke-impacted days compared to unimpacted days, with smoke observed on 4–28% of the campaign days (ranges from the different smoke-identification criteria). Further, short-term PM2.5 increases were observed over 40 µg m-3 during smoke events. We contrast the region near the EAA with large populations of low-income and minoritized groups to the more affluent coastal region. The inland region experienced more smoke-impacted monitor days than the Florida east coast region, and there was a higher study-average smoke PM2.5 concentration in the inland area. These findings highlight the need to increase air quality monitoring near the EAA.

Methods
To track the near-source transport of smoke from fires in Florida, we used the NOAA HYbrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model. This model is commonly used to compute the trajectory of air parcels. We calculated 12-hour forward trajectories initiated from all HMS fire hotspots in southern Florida (-81.5o x  -80o; 26o x 27.5o) during the campaign (October 2022 - September 2023). The HMS fire hotspot product combines detections from the Geostationary Operational Environmental Satellite - R Series (GOES-R)/ Advanced Baseline Imager (ABI) Fire Detection product and the Joint Polar Satellite System (JPSS)/ Visible Infrared Imaging Radiometer Suite (VIIRS) products. We used meteorological data from the NOAA High-Resolution Rapid Refresh (HRRR) model (Dowell et al., 2022), which provides conditions every 4 hours. The HYSPLIT model produces trajectory locations for every hour; however, we interpolated between the reported locations to provide 10-minute observations. This finer temporal resolution allows for tracing of short-lived plumes and more accurate determination of smoke transport, which may vary significantly on a sub-hourly basis due to shifting wind patterns and rapid changes in plume behavior. If a calculated trajectory intercepts the surface (z = 0), all subsequent locations for this trajectory were removed. We acknowledge regional differences in weather patterns (e.g., clouds) may make it more challenging to detect hotspots in certain areas, possibly leading to a bias in the HYSPLIT results as winds may, on average, be different under clear sky versus cloudy conditions.