EGU Journal Logos (RGB) Open Access Open Access Open Access Advances in Annales Nonlinear Processes Geosciences Geophysicae in Geophysics Open Access Open Access Natural Hazards Natural Hazards and Earth System and Earth System Sciences Sciences Discussions Open Access Open Access Atmospheric Atmospheric Chemistry Chemistry and Physics and Physics Discussions Open Access Open Access Atmos. Meas. Tech., 6, 431–443, 2013 Atmospheric Atmospheric www.atmos-meas-tech.net/6/431/2013/ doi:10.5194/amt-6-431-2013 Measurement Measurement © Author(s) 2013. CC Attribution 3.0 License. Techniques Techniques Discussions Open Access Open Access Biogeosciences Biogeosciences Discussions Open Access Online atmospheric pressure chemical ionization ion trap mass Open Access n spectrometry (APCI-IT-MS ) for measuring organic acidsClimate in Climate of the Past of the Past concentrated bulk aerosol – a laboratory and field study Discussions A. L. Vogel1, M. Aij¨ al¨ a¨2, M. Bruggemann¨ 1, M. Ehn2,*, H. Junninen2, T. Petaj¨ a¨2, D. R. Worsnop2, M. Kulmala2, Open Access 3 1 Open Access J. Williams , and T. Hoffmann Earth System 1Institute of Inorganic Chemistry and Analytical Chemistry, Johannes Gutenberg-UniversityEarth Mainz, System 55128 Mainz, Germany 2Department of Physics, University of Helsinki, 00014 Helsinki, Finland Dynamics Dynamics 3Department of Atmospheric Chemistry, Max Planck Institute for Chemistry, 55128 Mainz, Germany Discussions *now at: IEK-8: Troposphere, Research Center Julich,¨ 52428 Juelich, Germany Open Access Correspondence to: T. Hoffmann ([email protected]) Geoscientific Geoscientific Open Access Instrumentation Instrumentation Received: 15 August 2012 – Published in Atmos. Meas. Tech. Discuss.: 30 August 2012 Revised: 21 January 2013 – Accepted: 25 January 2013 – Published: 20 February 2013 Methods and Methods and Data Systems Data Systems Discussions Open Access Abstract. The field application of an aerosol concentrator lected monoterpene oxidation products formedOpen Access in simula- Geoscientific in conjunction with an atmospheric pressure chemical ion- tion chamber experiments.Geoscientific The comparison of the resulting ization ion trap mass spectrometer (APCI-IT-MS) at the bo- fragments shows that oxidation products of the main VOCs Model Development real forest station SMEAR II at Hyytial¨ a,¨ Finland, is demon- emitted at HyytiModelal¨ a¨ (α-pinene Development and 13-carene) cannot account Discussions strated in this study. APCI is a soft-ionization technique al- for all of the measured fragments. Possible explanations for lowing online measurements of organic acids in the gas and those unaccounted fragments are the presence of unidentified Open Access Open Access particle phase. The detection limit for the acid species in the or underestimated biogenic SOA precursors, or that differ- Hydrology and particle phase was improved by a factor of 7.5 to 11 (e.g. ent products are formedHydrology by a different oxidant and mixture of the ∼ 40 ng m3 for pinonic acid) by using the miniature ver- ambient air compared to theEarth chamber System ozonolysis. Earth System satile aerosol concentration enrichment system (mVACES) Sciences Sciences upstream of the mass spectrometer. The APCI-IT-MS was calibrated in the negative ion mode with two biogenic or- Discussions Open Access Open Access ganic acid standards – pinic acid and pinonic acid. Pinic 1 Introduction acid was used as a surrogate for the quantification of the Ocean Science It is well known that atmosphericOcean Science aerosols play an important total amount of organic acids in the ambient aerosol based Discussions on the total signal intensities in the negative ion mode. The role in global climate and human health (IPCC, 2007; Pope et results were compared with the total organic signal of a C- al., 2009). Hence, a large scientific community is focussing their research on the physical properties and chemical com- Open Access ToF-AMS during the HUMPPA-COPEC 2010 field cam- Open Access paign. The campaign average contribution of organic acids position of submicron aerosol particles to understand radia- measured by APCI-IT-MS to the total submicron organic tive forcing and air quality (Kulmala et al., 2011). Organic Solid Earth Solid Earth aerosol mass was estimated to be about 60 %, based on the Aerosol (OA) represents the major fraction of non-refractory Discussions response of pinic acid. Very good correlation between APCI- submicron particle mass (between 18 and 70 %) and in tropi- IT-MS and C-ToF-AMS (Pearson’s R = 0.94) demonstrates cal forest regions OA can even account for 90 % of total fine soft-ionization mass spectrometry as a complimentary tech- aerosol mass (Zhang et al., 2007; KanakidouetOpen Access al., 2005). Open Access nique to AMS with electron impact ionization. MS2 studies OA makes up the most abundant but least characterized frac- of specific m/z ratios recorded during the HUMPPA-COPEC tion of atmospheric aerosolThe Cryosphere particles. This is because OA is The Cryosphere 2010 field campaign were compared to MS2 studies of se- a highly complex mixture consisting of thousands of differ- Discussions ent chemical species at very low concentrations. Goldstein Published by Copernicus Publications on behalf of the European Geosciences Union. 432 A. L. Vogel et al.: Online MS for ambient organic acid measurement and Galbally (2007) estimate a number of 104–105 measured achieved through low-energy ionization processes, resulting organic atmospheric species, which still might be only a frac- in no or minor fragmentation of the molecular tracers (soft- tion of the number actually present. However, a major frac- ionization techniques). In the extreme case, each ionized or- tion of OA is believed to consist of organic acids (or multi- ganic molecule results in a single signal representative for functional compounds including organic acid groups) since the molecular ion of the compound of interest. One possi- atmospheric oxidation not only favours the incorporation of bility is the use of corona discharge (CD) at atmospheric oxygen over the atmospheric lifetimes of atmospheric organ- pressure; a technique that is well established when liquid ics, but the low vapour pressure of organic acids also drives chromatography is hyphenated with mass spectrometry (at- these compounds into the particle phase (Kroll et al., 2011). mospheric pressure chemical ionization (APCI)). The tech- Common offline techniques for measuring single organic nique represents a soft-ionization method, where fragmenta- compounds from filter samples are liquid or gas chromatog- tion of the analyte molecules plays a minor role and mostly raphy coupled to mass spectrometry (LC/MS, GC/MS); molecular ions are observed. The application of this tech- offline techniques for measuring bulk properties such as nique measuring organic compounds in the particle phase functional group contributions are nuclear magnetic reso- was reported as early as 1998 by Hoffmann et al. (1998) us- − nance spectroscopy (NMR) or direct filter analysis using ing CD for the generation of O2 ions at atmospheric pres- Fourier transformation infrared spectroscopy (FTIR) (Hal- sure. Prior to the ionization process, the organic compounds lquist et al., 2009; Hoffmann et al., 2011). Unfortunately, are thermally evaporated from the particle phase by a va- offline techniques offer only relatively poor time resolution porizer within the ion source. Gas-phase compounds are re- (several hours to weeks) and can be seriously biased by moved upstream of the ion source by an activated charcoal positive (gas-phase condensation, reactions on the filter sur- denuder. For higher organic mass loadings, e.g. for mea- face) and/or negative (evaporation during sampling, degrada- surements in simulation chamber experiments, the atmo- tion on the filter surface, losses or degradation during sam- spheric pressure chemical ionization ion trap mass spectrom- ple preparation and analysis) sampling artefacts. Turpin et eter (APCI-IT-MS) is well suited for online measurements of al. (1994) showed that gas-phase adsorption is the domi- organic acids in the negative ionization mode, providing new nant artefact in sampling of organic aerosol. The question insights into product structures (Warscheid and Hoffmann, therefore arises whether filter samples faithfully display the 2001, 2002) and multiphase chemical mechanism of sec- real atmospheric organic aerosol composition (Prather et al., ondary organic aerosol ageing (Muller¨ et al., 2012). Measur- 2008). Warnke et al. (2006) mentioned that more volatile or- ing in the positive ion mode, hydroperoxides and hydroper- ganic compounds (pinonic acid) produce higher artefacts (up oxy acids, formed during ozonolysis of biogenic volatile or- to 50 %) than the less-volatile organics. As a consequence, ganic compounds (BVOCs), can be identified by a charac- further development and field application of online tech- teristic loss of 34 Da during MS2 experiments (Reinnig et niques for directly measuring the chemical composition of al., 2009). However, for measuring secondary biogenic or- the gas and particle phase is required in order to improve our ganic acids at ambient concentrations below 100 ng m−3, this understanding of formation, composition and fate of atmo- technique is not sensitive enough. spheric aerosols. Other approaches towards soft-ionization AMS are de- The Aerodyne aerosol mass spectrometer (AMS) enables scribed by Dreyfus and Johnston (2008), Dreyfus et online chemical composition measurements of aerosol