New application of direct analysis in real time high-resolution mass spectrometry for the untargeted analysis of fresh and aged secondary organic aerosols generated from monoterpenes.

RATIONALE: Secondary organic aerosols (SOAs) represent a significant portion of total atmospheric aerosols. They are generated by the oxidation of volatile organic compounds (VOCs), and particularly biogenic VOCs (BVOCs). The analysis of such samples is usually performed by targeted methods that often require time-consuming preparation steps that can induce loss of compounds and/or sample contaminations. METHODS: Recently, untargeted methods using high-resolution mass spectrometry (HRMS) have been successfully employed for a broad characterization of chemicals in SOAs. Herein we propose a new application of the direct analysis in real time (DART) ionization method combined with HRMS to quickly detect several hundred chemicals in SOAs collected on a quartz filter without sample preparation or separation techniques. RESULTS: The reproducibility of measurements was good, with several hundred elemental compositions common to three different replicates. The relative standard deviations of the intensities of the chemical families ranged from 6% to 35%, with sufficient sensitivity to allow the unambiguous detection of 4 ng/mm2 of pinic acid. The presence of oligomers and specific tracers was highlighted by MSn (n ≤ 4) experiments, an achievement that is difficult to attain with other ultrahigh-resolution mass spectrometers. Contributions of this untargeted DART-HRMS method were illustrated by the analysis of fresh and aged SOAs from different gaseous precursors such as limonene, a ß-pinene/limonene mixture or scots pines emissions. CONCLUSIONS: The results show that it is possible to use DART-HRMS for the identification of tracers of specific aging reactions, or for the identification of aerosols from specific biogenic precursors.