A Chemical Ionization High-Resolution Time-of-Flight Mass Spectrometer Coupled to a Micro Orifice Volatilization Impactor (MOVI-HRToF-CIMS) for Analysis of Gas and Particle-Phase Organic Species

Abstract

We describe a new instrument, chemical ionization (CI) highresolution time-of-flight mass spectrometer (ToFMS) coupled to a micro-orifice volatilization impactor (MOVI-HRToF-CIMS).The MOVI-HRToF-CIMS instrument is unique in that, within a compact field-deployable package, it provides (1) quantifiable molecular-level information for both gas and particle-phase organic species on timescales ranging from ≤1 s for gases to 10-60 min for particle-phase compounds that can be used to efficiently probe oxidation and secondary organic aerosol (SOA) formation mechanisms, and (2) relative volatility information of the detected compounds simultaneously estimated using the programmed thermal desorption information obtained from the MOVI. We demonstrate the capabilities of a prototype instrument using known test compounds and complex mixtures generated from the oxidation of biogenic and anthropogenic hydrocarbons. We present spectra obtained using both negative and positive ion CI with acetate (CH 3 C(O)O − ) and protonated water clusters (H 3 O + · (H 2 O) n ), respectively, as reagent ions. The instrument has high mass resolving power (R = 5000 above m/Q 250 Th) and mass accuracy (±20 ppm) enabling estimation of compound elemental composition. Instrument sensitivity in negative ion mode was tested using formic acid as a representative gas-phase compound, and that for particle-phase compounds was tested using palmitic, azelaic, and tricarballylic acids. With a heated MOVI inlet, an ion count rate of ∼15 Hz is achieved when sampling 1 pptv (= 1 pmol/mol) of formic acid (or other monocarboxylic acids) under typical operating conditions. This sensitivity translates to detection limits less than 1 ng/m 3 for carboxylic acids in the particle-phase. We also discuss the remaining challenges with this instrument to broadly characterizing gaseous and particulate oxygenated organic compounds in situ.

Multi-generational oxidation model to simulate secondary organic aerosol in a 3-D air quality model

“…While the SOM framework can be adapted to explicitly model other production and loss processes (e.g., oligomerization (Yatavelli et al, 2012), heterogeneous reactions (Shiraiwa et al, 2013)) in the atmosphere, in this work we consider only the multi-generational gas-phase oxidation of SOA precursors and their subsequent products. As with all existing SOA parameterizations that are used in 3-D models, inherent in the parameterization are the effects of condensed-phase (and other unaccounted for) processes.…”

Sources and Characteristics of Summertime Organic Aerosol in the Colorado Front Range: Perspective from Measurements and WRF-Chem Modeling

“…Similar to other aerosol particles, SOA particles deteriorate air quality and visibility and impact the climate directly through absorption and scattering of radiation and indirectly through interactions with clouds (Monks et al, 2009). Despite recent advances in the measurement and modeling aspects of SOA and their precursors (e.g., Donahue et al, 2006;Ervens and Volkamer 15 2010;Hodzic et al, 2010a;de Gouw et al, 2011;Hodzic and Jimenez 2011;Shrivastava et al, 2011;Ahmadov et al, 2012;Isaacman et al, 2012;Yatavelli et al, 2012;Ehn et al, 2014;Ensberg et al, 2014;Fast et al, 2014;Lopez-Hilfiker et al, 2014;Williams et al, 2014), the full extent of SOA sources, formation processes, and therefore their impact on air quality, human health, and climate are not fully understood.…”

An electrospray chemical ionization source for real-time measurement of atmospheric organic and inorganic vapors

“…The recent coupling of chemical ionization to high-resolution time-of-flight mass spectrometers (HR-ToF-MS) enables the simultaneous determination of the abundance and molecular composition of a wide array of atmospheric inorganic and organic compounds with fast time response and high sensitivity (Junninen et al, 2010;Bertram et al, 2011;Yatavelli et al, 2012;Aljawhary et al, 2013;Lee et al, 2014;Lopez-Hilfiker et al, 2014, 2016aFarmer, 2015, 2016;Yuan et al, 2016). The use of HR-ToF-CIMS has allowed for groundbreaking progress in atmospheric organic chemistry, such as the observation of 3610 Y.…”

“…In CIMS, the analyte molecule reacts with a specific reagent ion via one or more mechanisms, including ligand switching reaction forming an ion-molecule adduct (Huey et al, 1995;Kercher et al, 2009;Aljawhary et al, 2013;Lee et al, 2014;Farmer, 2015, 2016), proton addition (abstraction) forming a protonated (de-protonated) ion (Nowak et al, 2002;Veres et al, 2008;Yatavelli et al, 2012;Aljawhary et al, 2013;Farmer, 2015, 2016;Yuan et al, 2016), or by direct charge transfer forming a molecular ion (Huey et al, 1995;Kim et al, 2016). The reagent ions used mainly include I − , NO − 3 , acetate, CF 3 O − , and SF − 6 for negative ion CIMS, and H 3 O + , NO + , protonated ethanol, and benzene cation for positive ion CIMS.…”