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 (D_p) particle sizing (fast mobility particle sizer, FMPS) plus light absorption and scattering at 870nm (photoacoustic extinctiometer). For D_p<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 D_p<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 ± 21Mm^-1 (10 min) with aerosol single scattering albedo peaking at ω= 0.955 ± 0.004. Concurrently, number concentration and size peaked with maximum D_p = 126nm and a unimodal distribution with σ_g = 1.5. Long-range transported smoke was substantially diluted (N_tot factor of 7 lower) and shifted larger (maximum D_p = 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 (D_p>100 nm), while flaming combustion produced very high number concentrations of smaller (D_p ~ 50 nm) absorbing particles. Due to smoldering and particle growth processes, D_p approached 100nm 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.