Nga Lee Ng

Urban fire smoke is chemically distinct from wildland fire smoke yet remains poorly understood. Using real-time airborne trace element measurements during the 2025 Los Angeles Eaton urban firestorm, we show that the plume evolved rapidly as fire transitioned from structures to wildland, tracked hourly by the potassium-to-lead ratio. Compared to wildfire smoke, the urban plume was enriched more than 50-fold in lead, 7-fold in halogens, and 3-fold in arsenic, a toxic mixture linked to burning vehicles, electronics, and building materials, a fundamentally different fuel from conventional wildland vegetation. During peak structural burning, we estimate that approximately 7 million residents (range, 4.3 to 8.0 million) experienced 24-hour lead concentrations exceeding 50 nanograms per cubic meter, over 80 times background levels. Unlike wildfire smoke that has been the focus of decades of air quality research, this plume represents an emerging class of urban fire air pollution that demands revised exposure frameworks and emergency response protocols as fires increasingly burn into cities.

1. Urban areas often suffer from unhealthy air quality with high concentrations of aerosol particles and high ozone (O3) levels (Valavanidis et al. 2008; Pope et al. 2020). In urban areas, organic ...

Furanoids are a major compound class emitted during biomass burning and are highly reactive toward hydroxyl radicals (OH), suggesting their oxidation may contribute to secondary organic aerosol (SOA) formation. Previous furanoid studies focused on gas-phase kinetics, leaving SOA formation poorly understood. Here, we investigate the gas-phase oxidation and SOA formation from furfural, 2-methylfuran, and 3-methylfuran reactions with OH radicals in the presence of nitrogen oxides at RH2, whereas methylfuran oxidation proceeds via peroxy radical (RO₂)+NO channel to form alkoxy radicals. Methylfuran isomers also differ in oxidation product speciation, with 2-methylfuran generating C₄ and C₅ compounds, whereas 3-methylfuran predominantly forms C₅ compounds. C₄H₂O₃, potentially maleic anhydride, increases continuously during all furanoid oxidations, supporting its potential as an aged biomass burning marker. Furfural produces the highest SOA mass and yield (66.3 µg⋅m⁻³, 9.8 %), followed by 2-methylfuran (10.3 µg⋅m⁻³, 1.4 %) and 3-methylfuran (7.2 µg⋅m⁻³, 1.1 %). Compared with methylfuran SOA, furfural SOA shows stronger signatures of lower-volatility oligomers, with higher contributions from large m/z fragments, a greater degree of unsaturation, broader thermograms, and more reduced CHON species (O/N<3). Accordingly, estimated particulate organic nitrate fraction is highest for 2-methylfuran SOA (~45 %), followed by 3-methylfuran (~36 %) and furfural (~11 %). These results show that both substituent type and position should be considered when representing furanoid oxidation in atmospheric models.

Furanoids are a major compound class emitted during biomass burning and are highly reactive toward hydroxyl radicals (OH), suggesting their oxidation may contribute to secondary organic aerosol (SOA) formation. Previous furanoid studies focused on gas-phase kinetics, leaving SOA formation poorly understood. Here, we investigate the gas-phase oxidation and SOA formation from furfural, 2-methylfuran, and 3-methylfuran reactions with OH radicals in the presence of nitrogen oxides at RH2, whereas methylfuran oxidation proceeds via peroxy radical (RO₂)+NO channel to form alkoxy radicals. Methylfuran isomers also differ in oxidation product speciation, with 2-methylfuran generating C₄ and C₅ compounds, whereas 3-methylfuran predominantly forms C₅ compounds. C₄H₂O₃, potentially maleic anhydride, increases continuously during all furanoid oxidations, supporting its potential as an aged biomass burning marker. Furfural produces the highest SOA mass and yield (66.3 µg⋅m⁻³, 9.8 %), followed by 2-methylfuran (10.3 µg⋅m⁻³, 1.4 %) and 3-methylfuran (7.2 µg⋅m⁻³, 1.1 %). Compared with methylfuran SOA, furfural SOA shows stronger signatures of lower-volatility oligomers, with higher contributions from large m/z fragments, a greater degree of unsaturation, broader thermograms, and more reduced CHON species (O/N<3). Accordingly, estimated particulate organic nitrate fraction is highest for 2-methylfuran SOA (~45 %), followed by 3-methylfuran (~36 %) and furfural (~11 %). These results show that both substituent type and position should be considered when representing furanoid oxidation in atmospheric models.

Furanoids are a major compound class emitted during biomass burning and are highly reactive toward hydroxyl radicals (OH), suggesting their oxidation may contribute to secondary organic aerosol (SOA) formation. Previous furanoid studies focused on gas-phase kinetics, leaving SOA formation poorly understood. Here, we investigate the gas-phase oxidation and SOA formation from furfural, 2-methylfuran, and 3-methylfuran reactions with OH radicals in the presence of nitrogen oxides at RH<5 %. Furfural exhibits distinct oxidation chemistry compared with methylfurans: furfural alkyl radical preferentially reacts with NO2, whereas methylfuran oxidation proceeds via peroxy radical (RO2)+NO channel to form alkoxy radicals. Methylfuran isomers also differ in oxidation product speciation, with 2-methylfuran generating C4 and C5 compounds, whereas 3-methylfuran predominantly forms C5 compounds. C4H2O3, potentially maleic anhydride, increases continuously during all furanoid oxidations, supporting its potential as an aged biomass burning marker. Furfural produces the highest SOA mass and yield (66.3 µg⋅m⁻³, 9.8 %), followed by 2-methylfuran (10.3 µg⋅m⁻³, 1.4 %) and 3-methylfuran (7.2 µg⋅m⁻³, 1.1 %). Compared with methylfuran SOA, furfural SOA shows stronger signatures of lower-volatility oligomers, with higher contributions from large m/z fragments, a greater degree of unsaturation, broader thermograms, and more reduced CHON species (O/N<3). Accordingly, estimated particulate organic nitrate fraction is highest for 2-methylfuran SOA (~45 %), followed by 3-methylfuran (~36 %) and furfural (~11 %). These results show that both substituent type and position should be considered when representing furanoid oxidation in atmospheric models.

Chemical characterization of atmospheric organic aerosols using gas chromatography with 70 eV electron ionization mass spectrometry (GC/EI-MS) has been used for decades in advancing molecular marker detection and identification, though primarily through suspect screening and/or targeted analyses. To advance non-targeted analyses of environmental samples, we have catalogued approximately 27 000 mass spectra (MS) of the trimethylsilyl derivatives of semi-volatile organic aerosol (OA) analytes in the open-access University of California Berkeley Goldstein Library of Organic Biogenic Environmental Spectra (UCB-GLOBES). Analytes were observed in ambient samples from the U.S. and the Central Amazon and/or laboratory simulations of secondary OA (SOA) formation. These samples are representative of OA under urban and biomass burning influences as well as SOA derived from biogenic precursors (e.g., isoprene, monoterpenes, sesquiterpenes) and biomass burning intermediates. MS are documented in UCB-GLOBES without regard to known chemical identity, annotated with extensive metadata such as sample source/experimental conditions, any structural information gained from MS analyses, and predicted chemical properties such as average carbon oxidation state and carbon number. UCB-GLOBES MS are compatible for importing into the NIST MS Search program, and we have also provided a Jupyter Notebook for MS visualization and comparisons. We demonstrate the utility of UCB-GLOBES through MS reanalyses of prior analytes observed in ambient data, finding a 20 % reduction in the number of analytes assigned to OA source categories reliant solely on time series correlation and an overall 11 % increase in new MS-based OA source categorization for the Southeast U.S. For 1513 analytes observed previously in the Central Amazon, we found 375 MS matches using UCB-GLOBES vs. 136 MS matches during prior analyses, representing a 14 % gain in newly confirmed or newly categorized OA species. While OA from laboratory oxidation experiments in UCB-GLOBES are highly diverse chemically, on average only 29 % of UCB-GLOBES MS have a mass spectral match to another MS entry in UCB-GLOBES and/or in databases of known compounds (i.e. NIST MS Database, Adams Essential Oil, MANE Flavor and Fragrance Company). This indicates that roughly 70 % of UCB-GLOBES MS are unique thus far, not observed more than once among the laboratory oxidation samples and ambient data in UCB-GLOBES MS. Further, only 18 % can be positively identified using these databases or known authentic standards. This points to a large gap between these laboratory simulations and ambient OA. Overall, the UCB-GLOBES database can be utilized for improving confidence in OA source categorization and/or identification, novel chemical marker discovery, tracking chemical diversity, de novo structure and properties prediction, and improving MS search and matching algorithms. This can ultimately inform future research priorities for the chemical characterization of atmospheric organic samples.

Urban fire smoke is chemically distinct from wildland fire smoke, yet remains poorly understood. Using real-time airborne trace element measurements during the 2025 Los Angeles Eaton urban firestorm, we show that the plume evolved rapidly as fire transitioned from structures to wildland, tracked hourly by the potassium-to-lead ratio. Compared to wildfire smoke, the urban plume was enriched more than 50-fold in lead, 7-fold in halogens, and 3-fold in arsenic, a toxic mixture linked to burning vehicles, electronics, and building materials, a fundamentally different fuel from conventional wildland vegetation. During peak structural burning, we estimate approximately 5 million residents experienced 24-hour lead concentrations exceeding 50 ng m ⁻³ , over 80 times background levels. Unlike wildfire smoke that has been the focus of decades of air quality research, this plume represents an emerging class of urban fire air pollution that demands revised exposure frameworks and emergency response protocols as fires increasingly burn into cities.