Characterization of nitrocatechols and related tracers in atmospheric biomass burning organic aerosol

One of the largest primary sources of organic aerosols in the atmosphere is biomass burning (Laskin et al., 2009). The chemistry of compounds present in biomass burning aerosol (BBA) is diverse and directly dependent on the chemical composition of the burning material and the combustion conditions (Simoneit et al., 2002). A well-established tracer for primary BBA is levoglucosan (1,6-anhydro-β-anhydroglucose), which originates from the pyrolysis of cellulose or hemicellulose (Fine et al., 2002). Secondary BBA, which is formed after physical and chemical changes (aging) of the primary BBA in the atmosphere, contains more oxidized and polar compounds. An important class of compounds of secondary organic aerosols (SOA) is nitrocatechols, which are strong absorbers of UV and Vis light, and therefore, can affect the earth's radiative balance and climate. Recently, methyl nitrocatechols were proposed as suitable tracers for highly oxidized secondary BBA (Iinuma et al., 2010). These compounds are primarily formed from the photooxidation of m-cresol, that is emitted from biomass burning, in the presence of NOx. The objective of the present study was to characterize nitrocatechols in ambient aerosols using mass spectrometric and chromatographic techniques. Ambient aerosol samples were collected during a cold winter episode from an urban site in Maribor, Slovenia, where substantial residential wood burning for domestic purposes takes place. Emphasis was put on the development of a suitable LC-ESI-MS technique. In an initial step the chromatographic conditions were optimized for methyl nitrocatechols and related nitro-aromatic compounds using diode array UV/Vis detection. The optimized LC conditions were used for the development and validation of an LC-ESI-MS/MS method for identification and quantification of nitrocatechols in aerosol samples. LC/ESI-MS/MS data will be presented and interpreted for the nitro-aromatic compounds that are present in the collected ambient aerosols.