Rapidly evolving ultrafine and fine mode biomass smoke physical properties: Comparing laboratory and field results

Combining field and laboratory results, we present biomass smoke physical properties. We report sub-0.56 μm diameter (Dp) particle sizing (fast mobility particle sizer, FMPS) plus light absorption and scattering at 870 nm (photoacoustic extinctiometer). For Dp < 200 nm, the FMPS characterized sizing within ±20% compared to standards. As compared to the traditional scanning mobility particle sizer, the FMPS responded most accurately to single-mode polydispersions with mean Dp < 200 nm, which characterized the smoke sampled here. Smoke was measured from laboratory fresh emissions (seconds to hours old), the High Park Fire (hours to < 1 day), and from regional biomass burning (several days). During a High Park Fire episode, light extinction rapidly reached a maximum of σ ep = 569 ± 21 Mm 1 (10 min) with aerosol single scattering albedo peaking at ω = 0.955 ± 0.004. Concurrently, number concentration and size peaked with maximum Dp = 126 nm and a unimodal distribution with σ g = 1.5. Long-range transported smoke was substantially diluted (Ntot factor of 7 lower) and shifted larger (maximum Dp = 143) and wider (σ g = 2.2). We compared ambient data to laboratory burns with representative western U.S. forest fuels (coniferous species Ponderosa pine and Alaska black spruce). Smoldering pine produced an aerosol dominated by larger, more strongly light scattering particles (Dp > 100 nm), while flaming combustion produced very high number concentrations of smaller (Dp ~ 50 nm) absorbing particles. Due to smoldering and particle growth processes, Dp approached 100 nm within 3 h after emission. Increased particle cross-sectional area and Mie scattering efficiency shifted the relative importance of light absorption (flaming maximum) and light scattering (smoldering maximum), increasing ω over time. Measurements showed a consistent picture of smoke properties from emission to aging.