Abstract
Abstract. Herein we report on the first successful airborne deployment of the CHemical Analysis of AeRosol ONline (CHARON) particle inlet which allowed us to measure the chemical composition of atmospheric submicrometer particles in real time using a state-of-the-art proton-transfer-reaction time-of-flight mass spectrometry (PTR-ToF-MS) analyzer. The data were collected aboard the NASA DC-8 Airborne Science Laboratory on 26 June 2018 over California in the frame of NASA's Student Airborne Research Program (SARP). We show exemplary data collected when the airplane (i) shortly encountered a fresh (<1 h old) smoke plume that had emanated from the Lions Fire in the Sierra Nevada, (ii) intercepted a particle plume emitted from an amine gas treating unit of a petroleum refinery close to Bakersfield, (iii) carried out a spatial survey in the boundary layer over the San Joaquin Valley and (iv) performed a vertical profile measurement over the greater Bakersfield area. The most important finding from this pilot study is that the CHARON PTR-ToF-MS system measures fast enough to be deployed on a jet research aircraft. The data collected during 3 to 15 s long plume encounters demonstrate the feasibility of airborne point or small area emission measurements. Further improvements are, however, warranted to eliminate or reduce the observed signal tailing (1/e decay time between 6 and 20 s). The fast time response of the analyzer allowed us to generate highly spatially resolved maps (1–2 km in the horizontal, 100 m in the vertical) of atmospheric particle chemical constituents. The chemical information that was extracted from the recorded particle mass spectra includes (i) mass concentrations of ammonium, nitrate and total organics; (ii) mass concentrations of different classes of organic compounds (CH vs. CHO vs. CHN vs. CHNO compounds; monoaromatic vs. polyaromatic compounds); (iii) aerosol bulk average O:C‾ and H:C‾ ratios; (iv) mass concentrations of selected marker molecules (e.g., levoglucosan in particles emitted from a wildfire, an alkanolamine in particles emitted from a petroleum refinery) and (v) wildfire emission ratios (Δtotal organics/ΔCO = 0.054; Δlevoglucosan/ΔCO = 7.9×10-3; Δvanillic acid/ΔCO = 4.4×10-4 and Δretene/ΔCO = 1.9×10-4; all calculated as peak area ratios, in grams per gram). The capability of the CHARON PTR-ToF-MS instrument to chemically characterize submicrometer atmospheric particles in a quantitative manner, at the near-molecular level, and in real time brings a new and unprecedented measurement capability to the airborne atmospheric science community.
Highlights
Proton-transfer-reaction mass spectrometry (PTR-MS) is a well-established technique for online and real-time detection of organic trace gases in the Earth’s atmosphere (de Gouw and Warneke, 2007; Yuan et al, 2017; and references therein)
While Student Airborne Research Program (SARP) provided an excellent opportunity for test-flying the CHARON inlet, the flight plan was neither designed for best characterizing the instrument’s performance nor for addressing specific science questions related to the chemical composition and transformation of organic particles in the atmosphere
In the Müller at al. (2017) study we have shown that CHARON PTR-ToF-MS mass spectra can be quantitatively converted into a total organic mass concentration and bulk average O : C and H : C ratios
Summary
Proton-transfer-reaction mass spectrometry (PTR-MS) is a well-established technique for online and real-time detection of organic trace gases in the Earth’s atmosphere (de Gouw and Warneke, 2007; Yuan et al, 2017; and references therein). We developed and deployed the first airborne proton-transfer-reaction time-of-flight mass spectrometry (PTR-ToF-MS) instrument (Müller et al, 2014). We conceived and built the CHARON (CHemical Analysis of AeRosol ONline) particle inlet which enables PTR-MS analyzers to measure and chemically characterize submicrometer particles in real time (Eichler et al, 2015). In ground-based studies, we have successfully used the CHARON inlet in combination with a PTR-TOF 8000 analyzer for measuring (i) particle mass concentrations of total organics, ammonium and nitrate; (ii) aerosol bulk average O : C and H : C ratios; (iii) mass concentrations of selected tracers (e.g., levoglucosan, pyrene) and (iv) mass concentrations associated with different source-related multivariate factors (e.g., biomass burning, traffic and smoking) (Müller et al, 2017). We will show exemplary results from the first airborne CHARON PTR-ToF-MS deployment and discuss possibilities and current limitations
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