Abigail Koss

Plants emit substantial amounts of biogenic volatile organic compounds (VOCs) that link plant physiological activity to ecological interactions and atmospheric chemistry. However, the processes regulating VOC emissions within the forest air and at the interface directly above the canopy remain poorly characterized. In this study, we investigated forest-scale VOC dynamics in a cool-temperate deciduous forest dominated by Quercus crispula using high-time- and high-mass-resolution proton-transfer-reaction time-of-flight mass spectrometry (PTR-ToF-MS) integrated with positive matrix factorization (PMF). This non-targeted, process-oriented framework was applied to forest-interior and canopy-top atmospheres during rain-free summer days in 2024 and 2025 to extract dominant modes of VOC emissions. The PMF consistently resolved two recurring modes characterized by the daytime and nighttime enhancement patterns. The daytime mode was dominated by isoprene and its oxidation products and demonstrated strong light- and temperature-dependence, whereas the nighttime mode was enriched in mono- and sesquiterpenes. The daytime contribution exhibited a pronounced morning–afternoon asymmetry, indicating non-linear physiological and canopy-scale controls. These patterns were reproducible across the years. This study demonstrates that combining PTR-ToF-MS with PMF enables robust, top-down identification of recurring modes of forest VOC variability within and above forest canopies, linking leaf-level physiology and ecosystem-scale atmospheric exchange. Highlight: Forest-scale VOC emissions were resolved into recurring daytime and nighttime modes using a non-targeted PTR-ToF-MS and PMF framework.

The continually evolving drug landscape, with novel synthetic drugs and unique compositions, necessitates the need to advance technologies, data analysis methods, and data accessibility for compound detection and identification. Providing public health, first responder, and law enforcement communities with critical information in near real-time will aid emergency response and public awareness, and direct overdose prevention and interdiction efforts. A major component of this framework is the progression of accurate drug screening and preliminary identifications from a more rigid laboratory-based arrangement to an agile point-of-need paradigm. We investigated drug detection and identification of a field deployable high-resolution time-of-flight mass spectrometer, employing both acetone-assisted vacuum ultraviolet (VUV) photoionization and dielectric barrier discharge ionization (DBDI) schemes. This preliminary fit-for-purpose exploration was conducted under laboratory conditions, building toward deployment in a mobile laboratory setting. The chromatography-free measurements enabled rapid analysis of neat drug solutions and multi-component mixtures. Characterization and optimization of system parameters demonstrated sensitive performance, with limits of detection in the tens to hundreds of picograms for a range of drug classes from multiple-component mixtures. The system’s high mass resolution was calibrated with a polyethylene glycol calibrant, enabling accurate matching with spectral library entries. Integrating compound identification with the NIST DART-MS Forensics Database and NIST/NIJ DART-MS Data Interpretation Tool provided a solid foundation for transition to the point-of-need. The overarching framework seeks to support technology advancement and adoption, as well as the development of novel data analysis tools, processes, and management for public access and utilization.

Source attribution of volatile organic compounds (VOCs) can be challenging in urban areas, which have many point sources. Mobile laboratories using time-of-flight mass spectrometers (TOF-MS) can take measurements throughout areas of concern, resulting in data with high spatial resolution that can be used to more easily identify these sources. However, emissions in heavily polluted areas still undergo significant mixing over short distances, making source attribution of some compounds challenging. Positive matrix factorization (PMF) has been widely used for attributing pollutants to different sources when taking stationary measurements due to its ability to process large amounts of data into generally interpretable results. However, some limitations of PMF can impact its usefulness to mobile data; PMF is a computationally intensive process, requires some user choices in attributing factors to emissions sources, and results can be significantly impacted by chemical transformations after emission. Here, both PMF and a simpler comparative analysis method are evaluated in analyzing measurements taken in the Elyria Swansea neighborhood of Commerce City, CO. This neighborhood is located near an oil refinery, a wastewater treatment plant, local industrial shops, and major highways. PMF failed to differentiate between oil refinery emissions and traffic emissions, and had difficulties recognizing other key sources. A simpler comparative analysis showed that the refinery contributed significantly to VOC concentrations throughout the neighborhood, including air toxics such as benzene. A wastewater treatment plant contributed to methanethiol and dimethyl sulfide. Finally, a small woodshop was identified as a hyperlocal VOC source, and contributed high amounts of some VOCs, such as toluene and other solvents, in its immediate surroundings.Implications Statement: This work discusses mobile measurements of VOCs around Commerce City, CO, a heavily polluted urban area north of Denver, using a PTR-TOF-MS. Two different source attribution methods, positive matrix factorization (PMF) and comparative analysis, were evaluated in the context of mobile measurements. The results show that an oil refinery and a woodshop contributed greatly to many VOC concentrations in the Elyria Swansea residential area of Commerce City. Additional sources, such as a wastewater treatment plant, also contributed to some odorous VOCs. PMF was unable to fully describe sources based on the mobile data. Comparative analysis was useful in attributing more VOCs to different sources, but quantitative results were influenced by how the analysis is set up. These findings are relevant to the residents of Denver and regulatory bodies to better understand Denver air pollution, as well as to other mobile studies doing source attribution of VOCs.

Decades of air quality improvements have substantially reduced the motor vehicle emissions of volatile organic compounds (VOCs). Today, volatile chemical products (VCPs) are responsible for half of the petrochemical VOCs emitted in major urban areas. We show that VCP emissions are ubiquitous in US and European cities and scale with population density. We report significant VCP emissions for New York City (NYC), including a monoterpene flux of 14.7 to 24.4 kg ⋅ d⁻¹ ⋅ km⁻² from fragranced VCPs and other anthropogenic sources, which is comparable to that of a summertime forest. Photochemical modeling of an extreme heat event, with ozone well in excess of US standards, illustrates the significant impact of VCPs on air quality. In the most populated regions of NYC, ozone was sensitive to anthropogenic VOCs (AVOCs), even in the presence of biogenic sources. Within this VOC-sensitive regime, AVOCs contributed upwards of ∼20 ppb to maximum 8-h average ozone. VCPs accounted for more than 50% of this total AVOC contribution. Emissions from fragranced VCPs, including personal care and cleaning products, account for at least 50% of the ozone attributed to VCPs. We show that model simulations of ozone depend foremost on the magnitude of VCP emissions and that the addition of oxygenated VCP chemistry impacts simulations of key atmospheric oxidation products. NYC is a case study for developed megacities, and the impacts of VCPs on local ozone are likely similar for other major urban regions across North America or Europe. Significance Recent work in Los Angeles has shown that urban volatile organic compound (VOC) emissions from consumer and industrial products—termed volatile chemical products (VCPs)—are now an important source of ozone precursors. Using advancements in VOC instrumentation, we show that VCP emissions are ubiquitous in urban regions and can be identified via unique VOC fingerprints. Through detailed modeling, we show that VCPs are as important to ozone production as fossil fuel VOCs and that the chemistry of VCPs can have significant impacts on model simulations of key atmospheric processes. Consequently, air quality models must be updated to account for both the emissions and atmospheric chemistry of VCPs in order to capture their full impact on urban air quality.

Decamethylcyclopentasiloxane (D₅) is a cyclic volatile methyl siloxane (cVMS) that is widely used in consumer products and commonly observed in urban air. This study quantifies the ambient mixing ratios of D₅ from ground sites in two North American cities (Boulder, CO, USA and Toronto, ON, CA). From these data, we estimate the diurnal emission profile of D₅ in Boulder, CO. Ambient mixing ratios were consistent with those measured at other urban locations; however, the diurnal pattern exhibited similarities with those of traffic-related compounds such as benzene. Mobile measurements and vehicle experiments demonstrate that emissions of D₅ from personal care products are coincident in time and place with emissions of benzene from motor vehicles. During peak commuter times, the D₅/benzene ratio (wt/wt) is in excess of 0.3, suggesting that the mass emission rate of D₅ from personal care product usage is comparable to that of benzene due to traffic. The diurnal emission pattern of D₅ is estimated using the measured D₅/benzene ratio and inventory estimates of benzene emission rates in Boulder. The hourly D₅ emission rate is observed to peak between 6:00 -- 7:00 AM and subsequently follow an exponential decay with a time constant of 9.2 hr. This profile could be used by models to constrain temporal emission patterns of personal care products.

Volatile and intermediate-volatility non-methane organic gases (NMOGs) released from biomass burning were measured during laboratory-simulated wildfires by proton-transfer-reaction time-of-flight mass spectrometry (PTR-ToF). We identified NMOG contributors to more than 150 PTR ion masses using gas chromatography (GC) pre-separation with electron ionization, H₃O⁺ chemical ionization, and NO⁺ chemical ionization, an extensive literature review, and time series correlation, providing higher certainty for ion identifications than has been previously available. Our interpretation of the PTR-ToF mass spectrum accounts for nearly 90 % of NMOG mass detected by PTR-ToF across all fuel types. The relative contributions of different NMOGs to individual exact ion masses are mostly similar across many fires and fuel types. The PTR-ToF measurements are compared to corresponding measurements from open-path Fourier transform infrared spectroscopy (OP-FTIR), broadband cavity-enhanced spectroscopy (ACES), and iodide ion chemical ionization mass spectrometry (I⁻ CIMS) where possible. The majority of comparisons have slopes near 1 and values of the linear correlation coefficient, R², of > 0.8, including compounds that are not frequently reported by PTR-MS such as ammonia, hydrogen cyanide (HCN), nitrous acid (HONO), and propene. The exceptions include methylglyoxal and compounds that are known to be difficult to measure with one or more of the deployed instruments. The fire-integrated emission ratios to CO and emission factors of NMOGs from 18 fuel types are provided. Finally, we provide an overview of the chemical characteristics of detected species. Non-aromatic oxygenated compounds are the most abundant. Furans and aromatics, while less abundant, comprise a large portion of the OH reactivity. The OH reactivity, its major contributors, and the volatility distribution of emissions can change considerably over the course of a fire.

Surface ozone concentrations are observed to increase with rising temperatures, but the mechanisms responsible for this effect in rural and remote continental regions remain uncertain. Better understanding of the effects of temperature on ozone is crucial to understanding global air quality and how it may be affected by climate change. We combine measurements from a focused ground campaign in summer 2013 with a long-term record from a forested site in the rural southeastern United States, to examine how daily average temperature affects ozone production. We find that changes to local chemistry are key drivers of increased ozone concentrations on hotter days, with integrated daily ozone production increasing by 2.3 ppb °C⁻¹. Nearly half of this increase is attributable to temperature-driven increases in emissions of nitrogen oxides (NO_x), most likely by soil microbes. The increase of soil NO_x emissions with temperature suggests that ozone will continue to increase with temperature in the future, even as direct anthropogenic NO_x emissions decrease dramatically. The links between temperature, soil NO_x, and ozone form a positive climate feedback.

Significance: Atmospheric fine organic aerosol impacts air quality, climate, and human health. Speciating and quantifying the sources of organic aerosol on the molecular level improves understanding of their formation chemistry and hence the resulting impacts. Such study, however, has not been possible due to the chemical complexity of atmospheric organic aerosol. Here, we provide comprehensive molecular characterization of atmospheric organic aerosol samples from the southeastern United States by combining state-of-the-art high-resolution mass spectrometry techniques. We find that monoterpene secondary organic aerosol accounts for approximately half of total fine organic aerosol. More importantly, the monoterpene secondary organic aerosol mass increases with enhanced nitrogen oxide processing, indicating anthropogenic influence on biogenic secondary organic aerosol formation.

Alkenes are reactive hydrocarbons that influence local and regional atmospheric chemistry by playing important roles in the photochemical production of tropospheric ozone and in the formation of secondary organic aerosols. The simplest alkene, ethene (ethylene), is a major plant hormone and ripening agent for agricultural commodities. The group of light alkenes (C₂-C₄) originates from both biogenic and anthropogenic sources, but their biogenic sources are poorly characterized, with limited field-based flux observations. Here we report net ecosystem fluxes of light alkenes and isoprene from a semiarid ponderosa pine forest in the Rocky Mountains of Colorado, USA using the relaxed eddy accumulation (REA) technique during the summer of 2014. Ethene, propene, butene and isoprene emissions have strong diurnal cycles, with median daytime fluxes of 123, 95, 39 and 17 µg m⁻² h⁻¹, respectively. The fluxes were correlated with each other, followed general ecosystem trends of CO₂ and water vapor, and showed similar sunlight and temperature response curves as other biogenic VOCs. The May through October flux, based on measurements and modeling, averaged 62, 52, 24 and 18 µg m⁻² h⁻¹ for ethene, propene, butene and isoprene, respectively. The light alkenes contribute significantly to the overall biogenic source of reactive hydrocarbons: roughly 18 % of the dominant biogenic VOC, 2-methyl-3-buten-2-ol. The measured ecosystem scale fluxes are 40–80 % larger than estimates used for global emissions models for this type of ecosystem.