Tianjia Liu , Frances Marie Panday, Miah C Caine, Makoto Kelp, Drew C Pendergrass, Loretta Mickley

Background: NOAA’s Hazard Mapping System (HMS) smoke product comprises smoke plumes digitized from satellite imagery. Recent studies have used HMS as a proxy for surface smoke presence.

Aims: We quantify how well HMS agrees with airport observations, air quality station measurements, and model estimates of near-surface smoke.

Methods: We quantify the agreement in smoke days and trends, regional discrepancies in levels of near-surface smoke fine particulate matter (PM2.5) within HMS polygons, and separation of total PM2.5 on smoke and non-smoke days across the contiguous U.S. and Alaska from 2008-2021.

Key Results: We find large overestimates in HMS-derived smoke days and trends if we include light smoke plumes in the HMS smoke day definition. Outside of the western U.S. and Alaska, near-surface smoke PM2.5 within areas of HMS smoke plumes are low and almost indistinguishable across density categories, likely indicating frequent smoke aloft.

Conclusions: Compared to airport, EPA, and model data, HMS most closely reflects surface smoke in the Pacific and Mountain regions and Alaska when smoke days are defined using only heavy plumes or both medium and heavy plumes.

Implications: We recommend careful consideration of biases in the HMS smoke product for air quality and public health assessments of fires.