Characterization of the organic composition of aerosols from Rondônia, Brazil, during the LBA-SMOCC 2002 experiment and its representation through model compounds

Abstract

Abstract. The chemical composition of carbonaceous aerosols collected during the LBA-SMOCC field experiment, conducted in Rondônia, Brazil, in 2002 during the transition from the dry to the wet season, was investigated by a suite of advanced analytical techniques. The period of most intense biomass burning was characterized by high concentrations of submicron particles rich in carbonaceous material and water-soluble organic compounds (WSOC). At the onset of the rainy period, submicron total carbon (TC) concentrations had decreased by about 20 times. In contrast, the concentration of supermicron TC was fairly constant throughout the experiment, pointing to a constant emission of coarse particles from the natural background. About 6–8% of TC (9–11% of WSOC) was speciated at the molecular level by GC-MS and liquid chromatography. Poly-hydroxylated compounds, aliphatic and aromatic acids were the main classes of compounds accounted for by individual compound analysis. Functional group analysis by proton NMR and chromatographic separation on ion-exchange columns allowed characterization of ca. 50–90% of WSOC into broad chemical classes (neutral species/light acids/humic-like substances). In spite of the significant change in the chemical composition of tracer compounds from the dry to the wet period, the functional groups and the general chemical classes of WSOC changed only to a lesser extent. Model compounds representing size-resolved WSOC chemical composition for the different periods of the campaign are then proposed in this paper, based on the chemical characterization by both individual compound analysis and functional group analysis deployed during the LBA-SMOCC experiment. Model compounds reproduce quantitatively the average chemical structure of WSOC and can be used as best-guess surrogates in microphysical models involving organic aerosol particles over tropical areas affected by biomass burning.

The ozonolysis of primary aliphatic amines in fine particles

“…These reactions represent new pathways by which amine nitrogen may be converted to lower volatility particle bound nitrogen. They may also help explain the mechanism of forming nitrogen enriched HULIS (Decesari et al, 2006;Likens and Galloway, 1983) and may be important in the atmospheric aging of organic aerosols. Moreover, amides, compared to other acylation products such as esters, are relatively stable to hydrolysis (Satchell, 1963), resulting in the potentially long atmospheric lifetime of these nitrogen containing species in particles.…”

“…There is growing evidence that organic nitrogen, including amines and amine-derived compounds, may form a substantial fraction of the organic aerosol load as evidenced in recent field studies in remote (Mäkelä et al, 2001;Beddows et al, 2004), urban (McGregor and Anastasio, 2001;Simoneit et al, 2003;Angelino et al, 2001;Tan et al, 2002), and agricultural (McGregor and Anastasio, 2001;Angelino et al, 2001) regions, and in regions near extensive biomass burning (Decesari et al, 2006;Mace et al, 2003;Simoneit et al, 2003).…”

“…HULIS) (Decesari et al, 2006;Likens and Galloway, 1983) found in aerosols and hydrometeors. Answering questions about how nitrogen is incorporated into HULIS and its subsequent atmospheric processing is important in developing a better understanding of the aging of fine particulate matter in the troposphere.…”

“…Animal husbandry is probably the most important anthropogenic emission source of amines into the troposphere (Filipy et al, 2006;Rabaud et al, 2003), with Schade and Crutzen (Schade and Crutzen, 1995) having estimated contributions up to 108±30 and 24±15 Gg N yr −1 for trimethylamine and methylamine to the atmosphere, respectively; albeit this is still 2-3 orders of magnitude lower than ammonia (23.3 Tg N yr −1 ). Agriculture (Beddows et al, 2004) and biomass burning (Decesari et al, 2006;Mace et al, 2003) may also be important sources of amines to the troposphere. Other anthropogenic sources of amine or amine-derived nitrogen to the troposphere include vehicular emissions (Angelino et al, 2001), industrial processes, and cooking (Rogge et al, 1991;Schauer et al, 1999).…”

Black carbon or brown carbon? The nature of light-absorbing carbonaceous aerosols

“…For example, extraction of hexane soot particles with various solvents showed it to contain up to 33 mass-% soluble material, consisting of polyaromatic hydrocarbons (PAHs), oxygenated polyaromatic hydrocarbons, and a small fraction of aliphatic compounds (Akhter et al, 1985). Particles from biomass burning also contain a large water-soluble fraction, including light-absorbing substances Decesari et al, 2006).…”