Semicontinuous measurements of gas–particle partitioning of organic acids in a ponderosa pine forest using a MOVI-HRToF-CIMS

Abstract

Abstract. Hundreds of gas- and particle-phase organic acids were measured in a rural ponderosa pine forest in Colorado, USA, during BEACHON-RoMBAS (Bio-hydro-atmosphere interactions of Energy, Aerosols, Carbon, H2O, Organics & Nitrogen – Rocky Mountain Biogenic Aerosol Study). A recently developed micro-orifice volatilization impactor high-resolution time-of-flight chemical ionization mass spectrometer (MOVI-HRToF-CIMS) using acetate (CH3C(O)O−) as the reagent ion was used to selectively ionize and detect acids semicontinuously from 20 to 30 August 2011, with a measurement time resolution of ~1.5 h. At this site 98% of the organic acid mass is estimated to be in the gas phase, with only ~2% in the particle phase. We investigated gas–particle partitioning, quantified as the fraction in the particle phase (Fp), of C1–C18 alkanoic acids, six known terpenoic acids, and bulk organic acids vs. carbon number. Data were compared to the absorptive partitioning model and suggest that bulk organic acids at this site follow absorptive partitioning to the organic aerosol mass. The rapid response (<1–2 h) of partitioning to temperature changes for bulk acids suggests that kinetic limitations to equilibrium are minor, which is in contrast to conclusions of some recent laboratory and field studies, possibly due to lack of very low ambient relative humidities at this site. Time trends for partitioning of individual and groups of acids were mostly captured by the model, with varying degrees of absolute agreement. Species with predicted substantial fractions in both the gas and particle phases show better absolute agreement, while species with very low predicted fractions in one phase often show poor agreement, potentially due to thermal decomposition, inlet adsorption, or other issues. Partitioning to the aqueous phase is predicted to be smaller than to the organic phase for alkanoic and bulk acids, and has different trends with time and carbon number than observed experimentally. This is due to the limited additional functionalization observed for the bulk acids. Partitioning to water appears to only play a role for the most oxidized acids during periods of high aerosol liquid water. Based on measurement–model comparison we conclude that species carbon number and oxygen content, together with ambient temperature, control the volatility of organic acids and are good predictors for partitioning at this site. Partitioning of bulk acids is more consistent with model predictions for hydroxy acids, hydroperoxyacids, or polyacids, and less so for keto acids.

Online molecular characterisation of organic aerosols in an atmospheric chamber using extractive electrospray ionisation mass spectrometry

“…The equilibrium partitioning of products between the gas and particle phases will favour the particle phase for pinic acid and OH-pinonic acid because their saturation concentrations (< 10 µg m −3 ; Müller et al, 2012;Yatavelli et al, 2014) are substantially lower than aerosol mass loadings (100-2400 µg m −3 ) in our experiments.…”

“…Pinonic acid is thought to have a significantly higher saturation concentration (in the range 10 2 -10 3 µg m −3 depending on the temperature and estimation method used; Müller Yatavelli et al, 2014). Hence, it is expected to reside across both phases in our experiments.…”

Estimating the contribution of organic acids to northern hemispheric continental organic aerosol

“…Similarly, since acetate ion sensitivity for glyoxal and methylglyoxal is very low, we assume that the contribution of these and similar species to the acid signal is also very small. Instrument configuration, operation, and analysis details are discussed by Yatavelli et al [2014]. Signal from m/z 150-400 is integrated to calculate the total particle-phase acid signal.…”

“…Biogenic VOC emissions are composed of mainly (based on volume mixing ratios) 2-methyl-3-butene-2-ol (50%) and monoterpenes (33%) [Kim et al, 2010]. Organic acid and OA mass concentrations were measured using a microorifice volatilization impactor high-resolution time-of-flight chemical ionization mass spectrometer (MOVI-HRToF-CIMS, Aerodyne Research, Inc., Billerica, MA) [Yatavelli and Thornton, 2010;Yatavelli et al, 2012Yatavelli et al, , 2014 and a high-resolution time-of-flight aerosol mass spectrometer (Aerodyne) [DeCarlo et al, 2006] [Hari and Kulmala, 2005]. HUMPPA-COPEC 2010 was conducted during July-August 2010 [Williams et al, 2011] while Hyytiälä-2013 was conducted during April-May 2013 (pre-PEGASOS campaign in Hyytiälä, www.pegasos.iceht.forth.gr).…”

Technical Note: Development of chemoinformatic tools to enumerate functional groups in molecules for organic aerosol characterization

“…Projecting specific molecular information available through various forms of mass spectrometry (e.g., Williams et al, 2006;Kalberer et al, 2006;Laskin et al, 2012;4402 G. Ruggeri and S. Takahama: Technical Note: Functional group enumeration Yatavelli et al, 2014;Schilling Fahnestock et al, 2015;Chhabra et al, 2015) or model simulations employing explicit chemical mechanisms (e.g., Jenkin, 2004;Aumont et al, 2005;Herrmann et al, 2005) to a reduced dimensional space represented by some combination of FGs can be useful for measurement intercomparisons, or model-measurement comparisons. For this task, the aerosol community can benefit from developments in the chemoinformatics community.…”