Smoke aerosol was collected on filters from a helicopter during a 400-acre (1.62 km2) prescribed chaparral burn in the San Dimas Experimental Forest on December 12, 1986. Hi-VoI samplers were used to collect particles on both Teflon and glass fiber filters. Scanning electron microscopy of the filters revealed particles that ranged in size from about 0.1 to 100 μm. Many of the large particles (>10 μm) that appeared irregularly shaped at low magnifications were found at higher magnification to be highly agglomerated smaller spheres, often showing signs of partial coalescence. Energy dispersive analysis of X rays (EDAX) revealed carbon, oxygen, magnesium, aluminum, silicon, calcium, and iron as the primary elemental composition of the aerosols. Extractions of aerosol components in water/methanol mixtures, followed by ion Chromatographic analysis, indicated that significant levels of nitrite (NO2−), nitrate (NO3−), sulfate (SO4=), chloride (Cl−), phosphate (PO4≡), oxylate (C2O4=), sodium (Na+), ammonium (NH4+), and potassium (K+) were associated with the particles. The proportions of NO3−, NO2−, PO4≡, Na+, and C2O4 = leached from the aerosol appeared to remain relatively constant in the smoke plume collections. Analysis of soluble NH4 +, Cl−, K +, and SO4 = ions, however, suggested that either possible changes in the nature of the emissions had occurred during different stages of combustion, or that ongoing smoke plume chemistry might have influenced the levels of these ions, or both. The soluble ionic portion of the aerosol was estimated to be about 2% by weight. The first known determinations of phosphate anion from particulates collected in a biomass burn plume are reported.