How NOAA Aerosol Satellite Products Aid Air Quality Forecasters in Tracking Smoke: A Case Study of the Historic Summer 2023 Canadian Wildfire Smoke Intrusions

To protect public health, state and local environmental agencies across the US issue operational forecasts of daily air quality, most commonly for ozone (O₃) and fine particulate matter (PM_2.5). Accurately predicting the impact of wildfire smoke on PM_2.5 conditions is one of the greatest challenges facing modern-day air quality forecasters. Wildfire seasons in North America are becoming more extreme due to prolonged heat waves and periods of drought. Wildfire smoke contains large amounts of primary PM_2.5 aerosols, and these plumes can travel long distances essentially undiluted, enhancing PM_2.5 concentrations near fires and at locations downwind. Smoke in the PBL can cause PM_2.5 concentrations to exceed the daily health standard set by the US Environmental Protection Agency. In anticipation of these situations, state/local forecasters issue air quality alerts so people will take action to limit their exposure to smoke. During wildfire smoke events, NOAA satellite observations play a crucial operational role because they are the only way to definitively ascertain the current presence and movement of smoke, particularly upwind of forecast areas. For example, the nationwide ground-based regulatory PM_2.5 monitor network detects increases in surface PM_2.5 concentrations but does not identify in near real-time the source of the deteriorating air quality, i.e. the presence of smoke. High-resolution, near real-time NOAA satellite products used by air quality forecasters include aerosol optical depth (AOD), a quantitative measure of atmospheric aerosols, and aerosol detection product (ADP), which identifies the presence of smoke aerosols. Over cloud-free locations during the daytime, AOD and ADP are generated at 2km spatial resolution every 5-10 minutes by the Advanced Baseline Imager (ABI) on the GOES-16 and GOES-18 geostationary satellites and at 750m spatial resolution once or twice per day by the Visible Infrared Imaging Radiometer Suite (VIIRS) on the SNPP, NOAA-20, and NOAA-21 polar-orbiting satellites. Surface PM_2.5 concentration, derived from AOD using a geographically weighted regression (GWR), is a new experimental product that is available over the CONUS from ABI every hour (1-hour average PM_2.5) at 2km spatial resolution and from VIIRS every day (24-hour average PM_2.5) at 4km spatial resolution. Satellite PM_2.5 is especially useful for forecasters because its regional view fills gaps in the regulatory PM_2.5 monitor network, which is vital in less populated areas where PM_2.5 monitors are scarce but wildfires are most common. ABI GeoColor and VIIRS true color imagery, along with fire radiative power from both sensors, are also used by forecasters to supplement the information on smoke provided by the aerosol products. Application of the NOAA satellite products during the historic Summer 2023 Canadian wildfire season will be demonstrated from an operational air quality forecaster perspective. Driven by synoptic weather features, large pulses of extremely thick smoke from the Canadian wildfires periodically flowed southward into the continental US, causing record-shattering daily PM_2.5 in major Northeastern US cities, including Washington, DC, Baltimore, and New York City. Examples will be presented of how air quality forecasters viewed ABI and VIIRS aerosol satellite imagery using the NOAA AerosolWatch website and used the observations to determine the impacts of smoke and to help predict its future consequences on air quality. The NOAA satellite imagery provided critically vital observations of smoke transport that were not available from surface measurement networks. In addition, the advantages of the near real-time NOAA aerosol satellite imagery will be discussed in light of the unique constraints on operational air quality forecasters, which include limited time to spend on preparing forecasts, forecast deadlines hours to days prior to the valid date, and little to no flexibility to update previously issued forecasts.

Disclaimer: The scientific results and conclusions, as well as any views or opinions expressed herein, are those of the author(s) and do not necessarily reflect those of NOAA or the Department of Commerce.