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1. Relationship between the molecular composition, visible light absorption, and health-related properties of smoldering woodsmoke aerosols

   https://doi.org/10.5194/acp-20-539-2020  

   Chan, Lam Kam; Nguyen, Khanh Q.; Karim, Noreen; Yang, Yatian; Rice, Robert H.; He, Guochun; Denison, Michael S.; Nguyen, Tran B. (January 2020, Atmospheric Chemistry and Physics)

   Abstract. Organic aerosols generated from the smoldering combustion of woodcritically impact air quality and health for billions of people worldwide;yet, the links between the chemical components and the optical or biologicaleffects of woodsmoke aerosol (WSA) are still poorly understood. In thiswork, an untargeted analysis of the molecular composition of smoldering WSA,generated in a controlled environment from nine types of heartwood fuels(African mahogany, birch, cherry, maple, pine, poplar, red oak, redwood, andwalnut), identified several hundred compounds using gas chromatography massspectrometry (GC-MS) and nano-electrospray high-resolution mass spectrometry(HRMS) with tandem multistage mass spectrometry (MSn). The effects ofWSA on cell toxicity as well as gene expression dependent on the aryl hydrocarbon receptor (AhR) and estrogen receptor(ER) were characterized with cellular assays, andthe visible mass absorption coefficients (MACvis) of WSA were measuredwith ultraviolet–visible spectroscopy. The WSAs studied in this work have significantlevels of biological and toxicological activity, with exposure levels inboth an outdoor and indoor environment similar to or greater than those ofother toxicants. A correlation between the HRMS molecular composition andaerosol properties found that phenolic compounds from the oxidativedecomposition of lignin are the main drivers of aerosol effects, while thecellulose decomposition products play a secondary role; e.g., levoglucosanis anticorrelated with multiple effects. Polycyclic aromatic hydrocarbons(PAHs) are not expected to form at the combustion temperature in this work,nor were they observed above the detection limit; thus, biological and opticalproperties of the smoldering WSA are not attributed to PAHs. Syringylcompounds tend to correlate with cell toxicity, while the more conjugatedmolecules (including several compounds assigned to dimers) have higher AhRactivity and MACvis. The negative correlation between cell toxicity andAhR activity suggests that the toxicity of smoldering WSA to cells is notmediated by the AhR. Both mass-normalized biological outcomes have astatistically significant dependence on the degree of combustion of thewood. In addition, our observations support the fact that the visible lightabsorption of WSA is at least partially due to charge transfer effects inaerosols, as previously suggested. Finally, MACvis has no correlationwith toxicity or receptor signaling, suggesting that key chromophores inthis work are not biologically active on the endpoints tested. 

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2. Measurement report: Leaf-scale gas exchange of atmospheric reactive trace species (NO₂, NO, O₃) at a northern hardwood forest in Michigan

   https://doi.org/10.5194/acp-20-11287-2020  

   Wang, Wei; Ganzeveld, Laurens; Rossabi, Samuel; Hueber, Jacques; Helmig, Detlev (January 2020, Atmospheric Chemistry and Physics)

   null (Ed.)

   Abstract. During the Program for Research on Oxidants: PHotochemistry, Emissions, and Transport (PROPHET) campaign from 21 July to 3 August 2016,field experiments on leaf-level trace gas exchange of nitric oxide (NO), nitrogen dioxide (NO2), and ozone (O3) were conducted for thefirst time on the native American tree species Pinus strobus (eastern white pine), Acer rubrum (redmaple), Populus grandidentata (bigtooth aspen), and Quercus rubra (red oak) in a temperate hardwood forest inMichigan, USA. We measured the leaf-level trace gas exchange rates andinvestigated the existence of an NO2 compensation point, hypothesizedbased on a comparison of a previously observed average diurnal cycle ofNOx (NO2+NO) concentrations with that simulated using amulti-layer canopy exchange model. Known amounts of trace gases wereintroduced into a tree branch enclosure and a paired blank referenceenclosure. The trace gas concentrations before and after the enclosures weremeasured, as well as the enclosed leaf area (single-sided) and gas flow rate to obtain the trace gas fluxes with respect to leaf surface. There was nodetectable NO uptake for all tree types. The foliar NO2 and O3uptake largely followed a diurnal cycle, correlating with that of the leafstomatal conductance. NO2 and O3 fluxes were driven by theirconcentration gradient from ambient to leaf internal space. The NO2 loss rate at the leaf surface, equivalently the foliar NO2 deposition velocity toward the leaf surface, ranged from 0 to 3.6 mm s−1 for bigtooth aspen and from 0 to 0.76 mm s−1 for red oak, both of which are∼90 % of the expected values based on the stomatalconductance of water. The deposition velocities for red maple and white pineranged from 0.3 to 1.6 and from 0.01 to 1.1 mm s−1, respectively, and were lower than predicted from the stomatal conductance, implying amesophyll resistance to the uptake. Additionally, for white pine, theextrapolated velocity at zero stomatal conductance was 0.4±0.08 mm s−1, indicating a non-stomatal uptake pathway. The NO2compensation point was ≤60 ppt for all four tree species andindistinguishable from zero at the 95 % confidence level. This agrees withrecent reports for several European and California tree species butcontradicts some earlier experimental results where the compensation pointswere found to be on the order of 1 ppb or higher. Given that the sampledtree types represent 80 %–90 % of the total leaf area at this site, theseresults negate the previously hypothesized important role of a leaf-scaleNO2 compensation point. Consequently, to reconcile these findings,further detailed comparisons between the observed and simulated in- and above-canopy NOx concentrations and the leaf- and canopy-scaleNOx fluxes, using the multi-layer canopy exchange model withconsideration of the leaf-scale NOx deposition velocities as well asstomatal conductances reported here, are recommended. 

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3. Modeling and Monitoring of Wood Moisture Content Using Time-Domain Reflectometry

   https://doi.org/10.3390/f11040479  

   Dahlen, Joseph; Schimleck, Laurence; Schilling, Erik (April 2020, Forests)

   null (Ed.)

   Time-domain reflectometry (TDR) can monitor the moisture content (MC) of water saturated logs stored in wet-decks where the MC exceeds the range that can be measured using traditional moisture meters (>50%). For this application to become routine, it is required that TDR monitoring of wet-decks occurs after establishment, and tools are needed that automate data collection and analysis. We developed models that predict wood MC using three-rod epoxy encased TDR probes inserted into the transverse surface of bolts (prior wet-deck studies were installed on the tangential surface). Models were developed for southern pine, sweetgum, yellow poplar, hickory, red oak, and white oak using a Campbell Scientific TDR100. For each species, at least 37 bolts were soaked for a minimum of three months and then air dried with TDR waveforms, and MC was periodically recorded. Calibrations were developed between MC and the TDR signal using nonlinear mixed effects models. Fixed effects ranged from excellent (southern pine R2 = 0.93) to poor (red oak R2 = 0.36, hickory R2 = 0.38). Independent of wood species, random effects all had a R2 greater than 0.80, which indicates that TDR detects changes in MC at the individual sample level. Use of TDR combined with a datalogger was demonstrated in an operational wet-deck that monitored changes in MC over 12 months, and in a laboratory trial where bolts were exposed to successive wet-dry cycles over 400 days. Both applications demonstrated the utility of TDR to monitor changes in wood MC in high MC environments where periodic measurement is not feasible due to operational safety concerns. Because a saturated TDR reading indicates a saturated MC, and because of the relatively accurate random effects found here, developing individual species models is not necessary for monitoring purposes. Therefore, application of TDR monitoring can be broadly applied for wet-decks, regardless of the species stored. 

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4. Coarse Woody Debris Decomposition Assessment Tool: Model validation and application

   https://doi.org/10.1371/journal.pone.0254408  

   Dai, Zhaohua; Trettin, Carl C.; Burton, Andrew J.; Jurgensen, Martin F.; Page-Dumroese, Deborah S.; Forschler, Brian T.; Schilling, Jonathan S.; Lindner, Daniel L. (July 2021, PLOS ONE)

   Hui, Dafeng (Ed.)

   Coarse woody debris (CWD) is a significant component of the forest biomass pool; hence a model is warranted to predict CWD decomposition and its role in forest carbon (C) and nutrient cycling under varying management and climatic conditions. A process-based model, CWDDAT (Coarse Woody Debris Decomposition Assessment Tool) was calibrated and validated using data from the FACE (Free Air Carbon Dioxide Enrichment) Wood Decomposition Experiment utilizing pine ( Pinus taeda ), aspen ( Populous tremuloides ) and birch ( Betula papyrifera ) on nine Experimental Forests (EF) covering a range of climate, hydrology, and soil conditions across the continental USA. The model predictions were evaluated against measured FACE log mass loss over 6 years. Four widely applied metrics of model performance demonstrated that the CWDDAT model can accurately predict CWD decomposition. The R 2 (squared Pearson’s correlation coefficient) between the simulation and measurement was 0.80 for the model calibration and 0.82 for the model validation ( P <0.01). The predicted mean mass loss from all logs was 5.4% lower than the measured mass loss and 1.4% lower than the calculated loss. The model was also used to assess the decomposition of mixed pine-hardwood CWD produced by Hurricane Hugo in 1989 on the Santee Experimental Forest in South Carolina, USA. The simulation reflected rapid CWD decomposition of the forest in this subtropical setting. The predicted dissolved organic carbon (DOC) derived from the CWD decomposition and incorporated into the mineral soil averaged 1.01 g C m -2 y -1 over the 30 years. The main agents for CWD mass loss were fungi (72.0%) and termites (24.5%), the remainder was attributed to a mix of other wood decomposers. These findings demonstrate the applicability of CWDDAT for large-scale assessments of CWD dynamics, and fine-scale considerations regarding the fate of CWD carbon. 

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5. Constructing a measurement-based spatially explicit inventory of US oil and gas methane emissions (2021)

   https://doi.org/10.5194/essd-16-3973-2024  

   Omara, Mark; Himmelberger, Anthony; MacKay, Katlyn; Williams, James P; Benmergui, Joshua; Sargent, Maryann; Wofsy, Steven C; Gautam, Ritesh (October 2024, Earth System Science Data)

   Abstract. Accurate and comprehensive quantification of oil and gas methane emissions is pivotal in informing effective methane mitigation policies while also supporting the assessment and tracking of progress towards emissions reduction targets set by governments and industry. While national bottom-up source-level inventories are useful for understanding the sources of methane emissions, they are often unrepresentative across spatial scales, and their reliance on generic emission factors produces underestimations when compared with measurement-based inventories. Here, we compile and analyze previously reported ground-based facility-level methane emissions measurements (n=1540) in the major US oil- and gas-producing basins and develop representative methane emission profiles for key facility categories in the US oil and gas supply chain, including well sites, natural-gas compressor stations, processing plants, crude-oil refineries, and pipelines. We then integrate these emissions data with comprehensive spatial data on national oil and gas activity to estimate each facility's mean total methane emissions and uncertainties for the year 2021, from which we develop a mean estimate of annual national methane emissions resolved at 0.1° × 0.1° spatial scales (∼ 10 km × 10 km). From this measurement-based methane emissions inventory (EI-ME), we estimate total US national oil and gas methane emissions of approximately 16 Tg (95 % confidence interval of 14–18 Tg) in 2021, which is ∼ 2 times greater than the EPA Greenhouse Gas Inventory. Our estimate represents a mean gas-production-normalized methane loss rate of 2.6 %, consistent with recent satellite-based estimates. We find significant variability in both the magnitude and spatial distribution of basin-level methane emissions, ranging from production-normalized methane loss rates of < 1 % in the gas-dominant Appalachian and Haynesville regions to > 3 %–6 % in oil-dominant basins, including the Permian, Bakken, and the Uinta. Additionally, we present and compare novel comprehensive wide-area airborne remote-sensing data and results for total area methane emissions and the relative contributions of diffuse and concentrated methane point sources as quantified using MethaneAIR in 2021. The MethaneAIR assessment showed reasonable agreement with independent regional methane quantification results in sub-regions of the Permian and Uinta basins and indicated that diffuse area sources accounted for the majority of the total oil and gas emissions in these two regions. Our assessment offers key insights into plausible underlying drivers of basin-to-basin variabilities in oil and gas methane emissions, emphasizing the importance of integrating measurement-based data when developing high-resolution spatially explicit methane inventories in support of accurate methane assessment, attribution, and mitigation. The high-resolution spatially explicit EI-ME inventory is publicly available at https://doi.org/10.5281/zenodo.10734299 (Omara, 2024). 

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