Long-range atmospheric transport (LRAT) of carbonaceous aerosols from biomass burning (BB) can influence urban air quality, complicating downwind source attribution. Routine monitoring (e.g., PM 2.5 bulk concentration) struggles to distinguish BB emissions from the complex, high background mixture of anthropogenic emissions typically found in urban areas. Therefore, a key challenge is distinguishing a unique, reliable BB tracer suitable for long-term urban monitoring, particularly when BB signatures are diluted from transport or masked by urban sources. Here, a three-year BB tracer study evaluated three unique approaches in Houston, TX with a complex mixture of local sources and frequent impacts from LRAT of BB and Saharan dust. The BB tracer approaches 1) absorption and scattering Ångström exponents (i.e., aerosol optical), 2) NOAA hazard mapping system smoke product (i.e., satellite observation), and 3) PM 2.5 /CO ratios (i.e., BB emission ratios) identified BB influence at varying rates due to fundamental methodological differences (i.e., composition, concentration, and remote sensing). The aerosol optical approach identified BB influence on ∼1 out of 5 days, compared to ∼3 in 5 days of smoke aloft for satellite observations. The emission ratio approach indicated BB ∼2 in 5 days, with periods of dust misclassified as BB. Using the aerosol optical approach as a conservative estimate, the average PM 2.5 during BB-influenced days was 10.5 ± 4.0 μg m -3 exceeding the 2024 annual PM 2.5 standard of 9 μg m -3 . This study provides a framework for identifying BB influence, improving understanding of its contribution to urban air quality, and thereby supporting effective monitoring and management. • Compared three BB-tracer approaches in a complex urban environment. • Wide variability between approaches, with some overestimating BB influence. • Houston, TX is routinely impacted by LRAT of smoke and dust aerosols. • Different source regions and seasonal activity impacted BB transport to Houston. • Site-specific dust thresholds improve emission ratio performance in urban air.
Ramirez et al. (Sun,) studied this question.