Abstract
Abstract. We deployed an extractive electrospray ionization time-of-flight mass spectrometer (EESI-MS) for airborne measurements of biomass burning aerosol during the Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) study onboard the NASA DC-8 research aircraft. Through optimization of the electrospray working solution, active control of the electrospray region pressure, and precise control of electrospray capillary position, we achieved 1 Hz quantitative measurements of aerosol nitrocatechol and levoglucosan concentrations up to pressure altitudes of 7 km. The EESI-MS response to levoglucosan and nitrocatechol was calibrated for each flight, with flight-to-flight calibration variability of 60 % (1σ). Laboratory measurements showed no aerosol size dependence in EESI-MS sensitivity below particle geometric diameters of 400 nm, covering 82 % of accumulation-mode aerosol mass during FIREX-AQ. We also present a first in-field intercomparison of EESI-MS with a chemical analysis of aerosol online proton-transfer-reaction mass spectrometer (CHARON PTR-MS) and a high-resolution Aerodyne aerosol mass spectrometer (AMS). EESI-MS and CHARON PTR-MS levoglucosan concentrations were well correlated, with a regression slope of 0.94 (R2=0.77). AMS levoglucosan-equivalent concentrations and EESI-MS levoglucosan showed a greater difference, with a regression slope of 1.36 (R2=0.96), likely indicating the contribution of other compounds to the AMS levoglucosan-equivalent measurement. The total EESI-MS signal showed correlation (R2=0.9) with total organic aerosol measured by AMS, and the EESI-MS bulk organic aerosol sensitivity was 60 % of the sensitivity to levoglucosan standards.
Highlights
Extractive electrospray ionization time-of-flight mass spectrometry (EESI-TOF-MS, hereafter electrospray ionization time-of-flight mass spectrometer (EESI-MS)) allows for rapid measurements of the chemical composition of organic aerosol (OA) (Lopez-Hilfiker et al, 2019; Chen et al, 2006; Doezema et al, 2012)
The advantage of EESI-MS is the lack of sample preparation – analytes are not collected onto a vaporizing element or filter, allowing many compounds to be sensitively detected without thermal decomposition (Lopez-Hilfiker et al, 2019; Stark et al, 2017)
Flights based out of Boise, Idaho, typically sampled wildland fire biomass burning organic aerosol (BBOA) above mountainous terrain, and the EESIMS was operated at a pressure-controlled inlet (PCI) pressure of 467 mbar for most of these flights
Summary
Extractive electrospray ionization time-of-flight mass spectrometry (EESI-TOF-MS, hereafter EESI-MS) allows for rapid measurements of the chemical composition of organic aerosol (OA) (Lopez-Hilfiker et al, 2019; Chen et al, 2006; Doezema et al, 2012). We deployed EESI-MS in a configuration that allowed for quantitative detection of components of biomass burning OA at pressure altitudes up to 7 km during the Fire Influence on Regional to Global Environments and Air Quality (FIREXAQ) study onboard the National Aeronautics and Space Administration (NASA) DC-8 aircraft. This was achieved by optimizing the electrospray solution for performance at pressures suitable for airborne sampling, development of an automated electrospray capillary stage, and extensive flightday and in-flight calibrations with a colocated AMS. We describe the instrument adaptations and its performance as deployed during FIREX-AQ and present comparisons to AMS and CHARON PTR-MS measurements during that campaign
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