Low molecular weight organic acids in aerosol particles from Rondônia, Brazil, during the biomass-burning, transition and wet periods

[摘要] Particles from biomass burning and regional haze were sampled inRondônia, Brazil, during dry, transition and wet periods from Septemberto November 2002, as part of the LBA-SMOCC (Large-Scale Biosphere-AtmosphereExperiment in Amazonia – Smoke, Aerosols, Clouds, Rainfall, and Climate)field campaign. Water soluble organic and inorganic compounds in bulk (HighVolume and Stacked Filter Unit sampler) and size-resolved (Micro OrificeUniform Deposit Impactor – MOUDI) smoke samples were determined by ionchromatography. It was found that low molecular weight polar organic acidsaccount for a significant fraction of the water soluble organic carbon(WSOC) in biomass burning aerosols (C₂-C₆ dicarboxylic acidsreached up to 3.7% and one-ring aromatic acids reached up to 2% offine fraction WSOC during burning period). Short dicarboxylic(C₂-C₆) acids are dominated by oxalic acid followed by malonic andsuccinic acids. The largest ionic species is ammonium sulfate (60–70% ofionic mass). It was found that most of the ionic mass is concentrated insubmicrometer-sized particles. Based on the size distribution andcorrelations with K⁺, a known biomass burning tracer, it is suggestedthat many of the organic acids are directly emitted by vegetation fires.Concentrations of dicarboxylic acids in the front and back filters of highvolume sampler were determined. Based on these measurements, it wasconcluded that in the neutral or slightly basic smoke particles typical ofthis region, dicarboxylic acids are mostly confined to the particulatephase. Finally, it is shown that the distribution of water soluble speciesshifts to larger aerosols sizes as the aerosol population ages and mixeswith other aerosol types in the atmosphere.

[学科分类] 大气科学