Effect of secondary organic aerosol coating thickness on the real-time detection and characterization of biomass-burning soot by two particle mass spectrometers

Abstract

Abstract. Biomass burning is a large source of lightabsorbing refractory black carbon (rBC) particles with a wide range of morphologies and sizes. The net radiative forcing from these particles is strongly dependent on the amount and composition of non-light-absorbing material internally mixed with the rBC and on the morphology of the mixed particles. Understanding how the mixing state and morphology of biomass-burning aerosol evolves in the atmosphere is critical for constraining the influence of these particles on radiative forcing and climate. We investigated the response of two commercial laser-based particle mass spectrometers, the vacuum ultraviolet (VUV) ablation LAAPTOF and the IR vaporization SP-AMS, to monodisperse biomass-burning particles as we sequentially coated the particles with secondary organic aerosol (SOA) from α-pinene ozonolysis. We studied three mobility-selected soot core sizes, each with a number of successively thicker coatings of SOA applied. Using IR laser vaporization, the SP-AMS had different changes in sensitivity to rBC compared to potassium as a function of applied SOA coatings. We show that this is due to different effective beam widths for the IR laser vaporization region of potassium versus black carbon. The SP-AMS's sensitivity to black carbon (BC) mass was not observed to plateau following successive SOA coatings, despite achieving high OA : BC mass ratios greater than 9. We also measured the ion fragmentation pattern of biomass-burning rBC and found it changed only slightly with increasing SOA mass. The average organic matter ion signal measured by the LAAPTOF demonstrated a positive correlation with the condensed SOA mass on individual particles, despite the inhomogeneity of the particle core compositions. This demonstrates that the LAAPTOF can obtain quantitative mass measurements of aged sootparticle composition from realistic biomass-burning particles with complex morphologies and composition.

Laser ablation aerosol particle time-of-flight mass spectrometer (LAAPTOF): performance, reference spectra and classification of atmospheric samples

“…There are only very few studies so far that discuss mass spectral patterns of different particle types measured by LAAPTOF. Gemayel et al (2016) presented spectra from ambient particles collected in the city centre of Marseille, France; spectra (positive only) from pure soot and SOA-coated soot particles were shown by Ahern et al (2016); spectra from potassium rich feldspar, soot, Argentinian soil dust, and Snomax (commercial ice nuclei) were shown by Zawadowicz et al (2017); PSL and potassium rich feldspar spectra were measured by Marsden et al (2018); and radiolytically formed particles spectra were measured by Wonaschuetz et al (2017). Reitz et al (2016) presented peak assignments for pure ammonium nitrate and sulfate particles, as well as for ambient particles measured at a suburban site of Düsseldorf, Germany, but did not show any spectra.…”

Concept for an electrostatic focusing device for continuous ambient pressure aerosol concentration

“…Several studies have examined the effective field strength, voltage distribution, and charge densities of the edges of finite plates of infinite width (Pillai, 1970;Parker, 2002). The two relevant voltage distributions, described by Bertram (1942; inlet lens-outlet lens) and Parker (2002; outlet lens-collection probe), were combined in order to estimate their relative effects on the total electric field. In the worst-case scenario of an uninsulated collection probe, the magnitude of the radial component of the combined electric field becomes negligible within the outer radius of the collection probe.…”

“…Immersion lenses are a commonly used method of manipulating streams of lowenergy electrons and particle beams (Páris, 1966; Heddle, Table 1. Cylindrical lens functions X 0 , X 1 (adapted from Bertram, 1942). Humphries, 1999;Read, 1971;Gillespie and Brown, 1997).…”

“…The electric field generated from this assembly can be described as the gradient of the applied voltage field resulting from the immersion lens, which was approximated by Bertram (1942) for our geometry aŝ…”

“…For example, the leading techniques for detailed chem-ical characterization of the organic fraction of ambient particulate matter rely on particle collection-volatilization cycles (Williams et al, 2006;Lopez-Hilfiker, 2014). Other techniques that explore size-dependent properties of ambient (Mei et al, 2013;Thalman et al, 2017) or laboratorygenerated (Ahern et al, 2016;Petters et al, 2006;Vaden et al, 2011) organic aerosol using differential mobility analyzers (DMAs), such as Humidified Tandem DMA (HT-DMA) or cloud condensation nuclei counters (CCNCs), are complicated by the necessity of size selection of polydisperse samples, which work with a small mass fraction of a given aerosol sample's original population. Online (continuousflow) aerosol concentration would improve instrument signal and time response in these types of studies, simplifying data analysis.…”