Abstract
Abstract. Aerosol intercomparisons are inherently complex as they convolve instrument-dependent detection efficiencies vs. size (which often change with pressure, temperature, or humidity) and variations in the sampled aerosol population, in addition to differences in chemical detection principles (e.g., inorganic-only nitrate vs. inorganic plus organic nitrate for two instruments). The NASA Atmospheric Tomography Mission (ATom) spanned four separate aircraft deployments which sampled the remote marine troposphere from 86∘ S to 82∘ N over different seasons with a wide range of aerosol concentrations and compositions. Aerosols were quantified with a set of carefully characterized and calibrated instruments, some based on particle sizing and some on composition measurements. This study aims to provide a critical evaluation of inlet transmissions impacting aerosol intercomparisons, and of aerosol quantification during ATom, with a focus on the aerosol mass spectrometer (AMS). The volume determined from physical sizing instruments (aerosol microphysical properties, AMP, 2.7 nm to 4.8 µm optical diameter) is compared in detail with that derived from the chemical measurements of the AMS and the single particle soot photometer (SP2). Special attention was paid to characterize the upper end of the AMS size-dependent transmission with in-field calibrations, which we show to be critical for accurate comparisons across instruments with inevitably different size cuts. Observed differences between campaigns emphasize the importance of characterizing AMS transmission for each instrument and field study for meaningful interpretation of instrument comparisons. Good agreement (regression slope =0.949 and 1.083 for ATom-1 and ATom-2, respectively; SD =0.003) was found between the composition-based volume (including AMS-quantified sea salt) and that derived from AMP after applying the AMS inlet transmission. The AMS captured, on average, 95±15 % of the standard PM1 volume (referred to as the URG Corp. standard cut 1 µm cyclone operated at its nominal efficiency). These results support the absence of significant unknown biases and the appropriateness of the accuracy estimates for AMS total mass and volume for the mostly aged air masses encountered in ATom. The particle size ranges (and their altitude dependence) that are sampled by the AMS and complementary composition instruments (such as soluble acidic gases and aerosol, SAGA, and particle analysis by laser mass spectrometry, PALMS) are investigated to inform their use in future studies.
Highlights
Aerosols are ubiquitous in the atmosphere and have a lifetime of about a week, and they can travel long distances (Tsigaridis et al, 2014), and have important effects on climate forcing through both direct (Pilinis et al, 1995; Haywood and Boucher, 2000) and indirect effects (Lohmann and Feichter, 2005; IPCC, 2013)
Other than new particle formation and growth events, the small particle end of the transmission curve is less critical in determining submicron aerosol volume since volume is normally dominated by the accumulation mode (Seinfeld and Pandis, 2016) instead of the Aitken mode (10–100 nm dta)
The large range of conditions sampled by the high-quality aerosol instrument payload on board the NASA DC-8 during the Atmospheric Tomography Mission (ATom) missions provides a unique opportunity to quantitatively investigate the comparability of submicron volume derived from physical sizing vs. bulk chemical instruments, as well as to evaluate whether currently reported aerosol mass spectrometer (AMS) measurement uncertainties are realistic
Summary
Aerosols are ubiquitous in the atmosphere and have a lifetime of about a week, and they can travel long distances (Tsigaridis et al, 2014), and have important effects on climate forcing through both direct (Pilinis et al, 1995; Haywood and Boucher, 2000) and indirect effects (Lohmann and Feichter, 2005; IPCC, 2013). Remote regions account for much of the Earth’s surface and are infrequently sampled, and they have especially uncertain aerosol distributions and radiative impacts (IPCC, 2013; Hodzic et al, 2020). The NASA Atmospheric Tomography Mission (ATom) sampled the remote marine troposphere from 86◦ S to 82◦ N over four different seasons with a comprehensive suite of high-quality and carefully calibrated and operated physical and chemical aerosol instruments. AMS (Canagaratna et al, 2007) and aerosol chemical speciation monitor (ACSM; smaller, lower cost, and simpler to operate versions) (Ng et al, 2011) have been deployed extensively worldwide for ground aerosol monitoring (Jimenez et al, 2009; Crenn et al, 2015; Hu et al, 2015; Kiendler-Scharr et al, 2016; Zhang et al, 2018; ACTRIS, 2021). Concerns about AMS quantification raised by Murphy (2016a) motivate rigorous evaluation of this topic despite some questions being solved in the following discussions (Jimenez et al, 2016; Murphy, 2016b)
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