The Environmental Molecular Sciences Laboratory (EMSL, pronounced em-zul) is a Department of Energy, Office of Science facility at Pacific Northwest National Laboratory in Richland, Washington, United States..
Ambient soot particles significantly impact Earth's radiative balance, human health, and atmospheric visibility. Their microstructural properties depend on formation and aging mechanisms, which vary by emission source and atmospheric processes. Hence, accurately identifying sources of soot enhances our understanding of their physicochemical properties and atmospheric implications. This study used a multi-modal approach to characterize and attribute sources of sub-micron soot particles collected in Israel during new particle formation events, biomass burning episodes, and background atmospheric conditions. Synchrotron-based X-ray microscopy was used to map soot (elemental carbon), organic carbon, and inorganic species. Implemented atomic force microscopy showed highly diverse phase states, with soot consistently exhibiting a solid-like phase. Automated mu-Raman analysis was subsequently performed on similar to 690 particles, identifying three soot classes based on spectral features corresponding to the "Defect" (D) and "Graphite" (G) bands of soot. We applied two-peak and five-peak fitting approaches to deconvolute the "Defect" peaks (D1, D2, D3, and D4) and G band from average Raman spectra, revealing varying degrees of graphitic order. The degree of graphitic order was determined from metrics such as the D3 peak area, often observed when soot was internally mixed with organic material. Raman spectral features, along with temporal variations in particle classes contributions, suggest that Particle Type 1 corresponds to traffic related soot and Particle Type 2 to less graphitic soot from biomass burning, while Particle Type 3 is associated with mixed soot-organic carbon particles observed during urban new particle formation episodes.Copyright (c) 2025 American Association for Aerosol Research
Ice fog is a common form of air pollution that forms at low temperatures and poses extreme hazards for aircraft and automobile travel, particularly in high-latitude environments. Despite its severe dangers, urban ice fog formation is not well understood, mainly because of the paucity of measurements of the particles that form ice fog. Here, we investigate the chemical composition and sources of atmospheric particles forming ice fog in Fairbanks, Alaska. Ice fog crystals were collected and sublimed, leaving behind residual particles, likely corresponding to the ice nucleating particles (INPs), which were examined in detail through single-particle analytical methods. Non-exhaust vehicular emissions were the dominant source of ice fog residual particles, in the forms of road dust (66–69%, by number) and microplastics (13–16%), such as tire wear. Biological particles (e.g., lichens) comprised 6–10%, highlighting their importance as INPs in wintertime urban and boreal environments. While mineral dust and primary biological particles are well-known INPs, their importance in wintertime cities was not known until recently. The observation of road dust reveals an unintended air quality impact of gravel application for traction on roads. These observations demonstrate microplastics acting as INPs in the urban atmosphere, corroborating recent laboratory experiments. Since most ice fog nuclei are from anthropogenic sources, their emissions, and subsequently, their impacts on ice fog formation, are controllable and addressable by technical and policy interventions.
Ice fog is common across high latitudes, with hazardous visibility reductions causing automobile accidents and aviation delays, yet the particles responsible for nucleating ice fog crystals remain a mystery. During winter in Fairbanks, Alaska, ice fog crystals were collected and sublimed, leaving behind residual particles likely corresponding to the ice nucleating particles (INPs). Non-exhaust vehicular emissions were the dominant source of ice fog residual particles, in the forms of road dust (66–69%, by number) and microplastics (e.g., tire wear, 13–16%). Biological particles (e.g., lichens) comprised 6–10%, highlighting their importance as INPs in wintertime urban and boreal environments. These observations demonstrate microplastics acting as INPs in the urban atmosphere, corroborating previous laboratory experiments. The observation of road dust reveals an unintended air quality impact of gravel application for traction on roads. Therefore, developing methods and policies to reduce road wear aerosol may mitigate hazardous ice fog formation.
Hybrid chemical and biological processes are promising strategies to valorize recalcitrant plastic waste streams by generating soluble oxygenates that can be biologically converted into a single product. Here, we show that acetic acid-mediated autoxidation in the absence of metal catalysts can deconstruct high-density polyethylene (HDPE) to soluble oxygenates at 80 C-mol% carbon yield. These yields are a major improvement over metal-catalyzed autoxidation, and the chemistry readily translates to post-consumer substrates. Multiple analytical approaches enabled identification of major product classes, including dicarboxylic acids (DCAs), 2-oxocarboxylic acids (ketoacids), and -lactone acids. An industrially relevant bacterium, Pseudomonas putida, was engineered to efficiently utilize ketoacids via a unique β-oxidation pathway discovered via barcoded transposon insertion libraries and transcriptomics. P. putida was then engineered to convert HDPE-derived DCAs and ketoacids into mevalonate, an exemplary high-value chemical. Overall, this study demonstrates a carbon-efficient, catalyst-free process for solubilizing HDPE to mixed oxygenates and highlights the need to improve the bioavailability of polyolefin-derived intermediates from oxidation.
