Measuring Mass-Based Hygroscopicity of Atmospheric Particles through in Situ Imaging

Abstract

Quantifying how atmospheric particles interact with water vapor is critical for 32 understanding the effects of aerosols on climate. We present a novel method to measure the 33 mass-based hygroscopicity of particles while characterizing their elemental and carbon 34 functional group compositions. Since mass-based hygroscopicity is insensitive to particle 35 geometry, it is advantageous for probing the hygroscopic behavior of atmospheric particles, 36 which can have irregular morphologies. Combining scanning electron microscopy with energy 37 dispersive X-ray analysis (SEM/EDX), scanning transmission X-ray microscopy (STXM) 38 analysis, and in situ STXM humidification experiments, this method was validated using 39 laboratory-generated, atmospherically relevant particles. Then, the hygroscopicity and elemental 40 composition of 15 complex atmospheric particles were analyzed by leveraging quantification of 41 C, N, and O from STXM, and complementary elemental quantification from SEM/EDX. We 42 found three types of hygroscopic responses, and correlated high hygroscopicity with Na and Cl 43 content. The mixing state of 158 other particles from the sample broadly agreed with those of the 44

The effect of hydrophobic glassy organic material on the cloud condensation nuclei activity of particles with different morphologies

“…where k represents the steepness, T is the measured temperature of the conditioning loop, and T r is the relaxation temperature representative of the midpoint of the logistic curve. The shape factor is converted to viscosity, η, via a lookup table of modified Frenkel sintering theory (Pokluda et al, 1997;Rothfuss and Petters, 2016). Conditioner residence time, monomer diameter, and surface tension assumed in the conversion are t = 5 s, D mono = 50 nm, and σ = 0.034 J m −2 , respectively.…”

Anthropogenic influences on the physical state of submicron particulate matter over a tropical forest

“…Spatially resolved NEXAFS spectra were obtained from a set of images recorded at different photon energies. The NEXAFS spectra provided chemical bonding information and quantitative elemental ratios (Moffet et al, 2010a, b;Piens et al, 2016). Section S2 of the Supplement presents further technical information concerning the TEM and STXM/NEXAFS analyses.…”

Response to Reviewer 1

“…A notable feature of the NEXAFS spectrum of the rebounded particles is the strong double bond. Pöhlker et al (2012) previously collected NEXAFS spectra for samples collected at a background site in central Amazonia, and the strong feature of a double bond was absent. The spectra instead resembled those of different types of reference biogenic secondary organic material.…”

“…The line in the region of 286.5 to 286.7 eV can have contributions from ketones, carbonyl-substituted aromatics, and phenolic species. For comparison, spectra are shown for carbonaceous particles collected in other field and laboratory studies: soil organic particles from the central USA (Wang et al, 2016), soot from the ambient environment, atmospheric particles collected at a background site in central Amazonia (Pöhlker et al, 2012), and three laboratory samples of secondary organic material. Data sources: isoprene-derived SOM produced under HO 2dominant conditions (O'Brien et al, 2014); isoprene-derived SOM produced under NO-dominant conditions (O'Brien et al, 2014), and toluene-derived SOM produced under NO-dominant conditions (this study).…”