Online atmospheric pressure chemical ionization ion trap mass spectrometry (APCI-IT-MS<sup>n</sup>) for measuring organic acids in concentrated bulk aerosol – a laboratory and field study

Abstract

Abstract. The field application of an aerosol concentrator in conjunction with an atmospheric pressure chemical ionization ion trap mass spectrometer (APCI-IT-MS) at the boreal forest station SMEAR II at Hyytiälä, Finland, is demonstrated in this study. APCI is a soft-ionization technique allowing online measurements of organic acids in the gas and particle phase. The detection limit for the acid species in the particle phase was improved by a factor of 7.5 to 11 (e.g. ∼40 ng m3 for pinonic acid) by using the miniature versatile aerosol concentration enrichment system (mVACES) upstream of the mass spectrometer. The APCI-IT-MS was calibrated in the negative ion mode with two biogenic organic acid standards – pinic acid and pinonic acid. Pinic acid was used as a surrogate for the quantification of the total amount of organic acids in the ambient aerosol based on the total signal intensities in the negative ion mode. The results were compared with the total organic signal of a C-ToF-AMS during the HUMPPA-COPEC 2010 field campaign. The campaign average contribution of organic acids measured by APCI-IT-MS to the total submicron organic aerosol mass was estimated to be about 60%, based on the response of pinic acid. Very good correlation between APCI-IT-MS and C-ToF-AMS (Pearson's R = 0.94) demonstrates soft-ionization mass spectrometry as a complimentary technique to AMS with electron impact ionization. MS2 studies of specific m/z ratios recorded during the HUMPPA-COPEC 2010 field campaign were compared to MS2 studies of selected monoterpene oxidation products formed in simulation chamber experiments. The comparison of the resulting fragments shows that oxidation products of the main VOCs emitted at Hyytiälä (α-pinene and Δ3-carene) cannot account for all of the measured fragments. Possible explanations for those unaccounted fragments are the presence of unidentified or underestimated biogenic SOA precursors, or that different products are formed by a different oxidant mixture of the ambient air compared to the chamber ozonolysis.

Biogenic and biomass burning organic aerosol in a boreal forest at Hyytiälä, Finland, during HUMPPA-COPEC 2010

“…Linear interpolation between the gas-phase measurements and subtraction from the total signal resulted in the particle-phase signal. A more detailed description is provided by Vogel et al (2013). Particulate organic acids correlated well with FTIR carboxylic acid functional groups and FTIR OM (see the Supplement for more details).…”

A novel method for online analysis of gas and particle composition: description and evaluation of a Filter Inlet for Gases and AEROsols (FIGAERO)

“…Particle into liquid samplers (PILS) have been coupled to ion chromatography and mass spectrometer systems to measure aerosol composition (Saarnio et al, 2013;Weber et al, 2001) but are generally used to measure water soluble compounds only. Another separation technique using a pumped counter flow virtual impactor coupled to a vaporizer and atmosphericpressure chemical-ionization ion trap mass spectrometer was developed for the detection of organic acids (Vogel et al, 2013). Moreover, instruments for atmospheric applications have typically been designed for either exclusive gas or particulate phase analysis.…”

Field intercomparison of the gas/particle partitioning of oxygenated organics during the Southern Oxidant and Aerosol Study (SOAS) in 2013

“…Organic acids are abundant in the atmosphere (Chebbi and Carlier, 1996;Yatavelli et al, 2015) and are important oxidation products of anthropogenic and biogenic volatile organic carbon (VOC) species and contributors to SOA (Veres et al, 2011;Andrews et al, 2012;Vogel et al, 2013). Despite their ubiquity and importance, the gas/particle partitioning dynamics and equilibria of organic acids are still poorly uncharacterized.…”