An extractive electrospray ionization time-of-flight mass spectrometer (EESI-TOF) for online measurement of atmospheric aerosol particles

Abstract

Abstract. Real-time, online measurements of atmospheric organic aerosol (OA) composition are an essential tool for determining the emissions sources and physicochemical processes governing aerosol effects on climate and health. However, the reliance of current techniques on thermal desorption, hard ionization, and/or separated collection/analysis stages introduces significant uncertainties into OA composition measurements, hindering progress towards these goals. To address this gap, we present a novel, field-deployable extractive electrospray ionization time-of-flight mass spectrometer (EESI-TOF), which provides online, near-molecular (i.e., molecular formula) OA measurements at atmospherically relevant concentrations without analyte fragmentation or decomposition. Aerosol particles are continuously sampled into the EESI-TOF, where they intersect a spray of charged droplets generated by a conventional electrospray probe. Soluble components are extracted and then ionized as the droplets are evaporated. The EESI-TOF achieves a linear response to mass, with detection limits on the order of 1 to 10 ng m−3 in 5 s for typical atmospherically relevant compounds. In contrast to conventional electrospray systems, the EESI-TOF response is not significantly affected by a changing OA matrix for the systems investigated. A slight decrease in sensitivity in response to increasing absolute humidity is observed for some ions. Although the relative sensitivities to a variety of commercially available organic standards vary by more than a factor of 30, the bulk sensitivity to secondary organic aerosol generated from individual precursor gases varies by only a factor of 15. Further, the ratio of compound-by-compound sensitivities between the EESI-TOF and an iodide adduct FIGAERO-I-CIMS varies by only ±50 %, suggesting that EESI-TOF mass spectra indeed reflect the actual distribution of detectable compounds in the particle phase. Successful deployments of the EESI-TOF for laboratory environmental chamber measurements, ground-based ambient sampling, and proof-of-concept measurements aboard a research aircraft highlight the versatility and potential of the EESI-TOF system.

The fuel of atmospheric chemistry: Toward a complete description of reactive organic carbon

“…However, many laboratory studies focus instead only on the rates of degradation of the parent compound and/or the formation of some Dates correspond to the approximate timing that a given measurement approach was adopted for measuring atmospheric ROC. The major developments in analytical techniques depicted in this timeline (9,(34)(35)(36)(70)(71)(72)(73)(74)(75)(76)(77)(78)(79)(80)(81)(82)(83) are given in the Supplementary Materials; see (33) for a comprehensive review of modern analytical approaches.…”

Organic aerosol source apportionment in Zurich using an extractive electrospray ionization time-of-flight mass spectrometer (EESI-TOF-MS) – Part 1: Biogenic influences and day–night chemistry in summer

“…As a consequence DaySOA2 EESI and NightSOA1 EESI might represent first-generation chemistry with different oxidants reflecting the availability during the time of the day while DaySOA1 EESI and NightSOA2 EESI might represent second-generation chemistry oxidation products. As an example, some highly functionalized oxidation products from α-pinene photooxidation like C 10 H 16 O 5 are thought to be second-generation oxidation products (McVay et al, 2016). As a consequence of the extensive decomposition and fragmentation occurring in the AMS system, which particularly affects organonitrates (Farmer et al, 2010), we were not able to resolve any factor related to night chemistry or specific factor dominated by a nitrate signature to compare with the night-time SOA factors from the EESI-TOF-MS analysis.…”

Direct measurements of semi-volatile organic compound dynamics show near-unity mass accommodation coefficients for diverse aerosols

“…Measurements of particle-phase speciation and concentrations often suffer from slower time resolution (~1 h) due to the need of aerosol collection on a filter, and/or thermal decomposition when thermal desorption of OA is required 27,[32][33][34]37 . The recently developed technique of extractive electrospray ionization (EESI) provides soft ionization of many organic molecules in real time with minimum sample heating 39,40 and has been very recently improved to achieve higher sensitivities, making it now possible to be applied to ambient-level concentrations 41 . These qualities make EESI, when coupled with an inlet that sufficiently removes the gas phase, well-suited for fast online analysis of OA, as in partitioning kinetic measurements.…”