ACS ES&T Air最新文献

Prescribed burning is an effective land management tool that provides a range of benefits, including ecosystem restoration and wildfire risk reduction. However, prescribed fires, just like wildfires, introduce smoke that degrades air quality. Furthermore, while prescribed fires help manage wildfire risk, they do not eliminate the possibility of wildfires. It is therefore important to also evaluate fire and smoke impacts from wildfires that may occur after a prescribed burn. In this study, we developed a framework for understanding the air quality and health related trade-offs between wildfires and prescribed fires by simulating a set of counterfactual scenarios including wildfires, prescribed fires, and postprescribed burn wildfires. We applied this framework to the case of the Gatlinburg wildfire and found that emissions from prescribed burns and subsequent wildfire were slightly lower than those from the wildfire itself. This reduction resulted in lower daily average concentrations and exposures of PM_2.5, O₃, and NO₂. Even considering the possibility of a postprescribed burn wildfire, prescribed fires reduced population-weighted daily average PM_2.5, daily maximum 8-h average O₃, and 1-h maximum NO₂ concentrations. In Sevier County, Tennessee where the wildfire occurred, these reductions reached 5.28 μg/m³, 0.18 ppb, and 1.68 ppb, respectively. The prescribed fires also reduced the person-days smoke exposures from the wildfire. Our results suggest that although prescribed fires cannot eliminate the air quality impacts of wildfires, they can greatly reduce smoke exposure in downwind areas distant from the burn sites.

Prescribed burning is an effective land management tool that provides a range of benefits, including ecosystem restoration and wildfire risk reduction. However, prescribed fires, just like wildfires, introduce smoke that degrades air quality. Furthermore, while prescribed fires help manage wildfire risk, they do not eliminate the possibility of wildfires. It is therefore important to also evaluate fire and smoke impacts from wildfires that may occur after a prescribed burn. In this study, we developed a framework for understanding the air quality and health related trade-offs between wildfires and prescribed fires by simulating a set of counterfactual scenarios including wildfires, prescribed fires, and postprescribed burn wildfires. We applied this framework to the case of the Gatlinburg wildfire and found that emissions from prescribed burns and subsequent wildfire were slightly lower than those from the wildfire itself. This reduction resulted in lower daily average concentrations and exposures of PM_2.5, O₃, and NO₂. Even considering the possibility of a postprescribed burn wildfire, prescribed fires reduced population-weighted daily average PM_2.5, daily maximum 8-h average O₃, and 1-h maximum NO₂ concentrations. In Sevier County, Tennessee where the wildfire occurred, these reductions reached 5.28 μg/m³, 0.18 ppb, and 1.68 ppb, respectively. The prescribed fires also reduced the person-days smoke exposures from the wildfire. Our results suggest that although prescribed fires cannot eliminate the air quality impacts of wildfires, they can greatly reduce smoke exposure in downwind areas distant from the burn sites.

The work proposes a modeling framework which considers emissions from prescribed fires, wildfires, and postprescribed burn wildfires for understanding the air quality trade-offs between wildfires and prescribed fires.

The Community Multiscale Air Quality (CMAQ) model simulates atmospheric phenomena, including advection, diffusion, gas-phase chemistry, aerosol physics and chemistry, and cloud processes. Gas-phase chemistry is often a major computational bottleneck due to its representation as large systems of coupled nonlinear stiff differential equations. We leverage the parallel computational performance of graphics processing unit (GPU) hardware to accelerate the numerical integration of these systems in CMAQ’s CHEM module. Our implementation, dubbed CMAQ-CUDA, in reference to its use in the Compute Unified Device Architecture (CUDA) general purpose GPU (GPGPU) computing solution, migrates CMAQ’s Rosenbrock solver from Fortran to CUDA Fortran. CMAQ-CUDA accelerates the Rosenbrock solver such that simulations using the chemical mechanisms RACM2, CB6R5, and SAPRC07 require only 51%, 50%, or 35% as much time, respectively, as CMAQv5.4 to complete a chemistry time step. Our results demonstrate that CMAQ is amenable to GPU acceleration and highlight a novel Rosenbrock solver implementation for reducing the computational burden imposed by the CHEM module.

We accelerate CMAQ’s gas-phase chemistry module using GPUs, saving compute resources during intensive simulations.

The Community Multiscale Air Quality (CMAQ) model simulates atmospheric phenomena, including advection, diffusion, gas-phase chemistry, aerosol physics and chemistry, and cloud processes. Gas-phase chemistry is often a major computational bottleneck due to its representation as large systems of coupled nonlinear stiff differential equations. We leverage the parallel computational performance of graphics processing unit (GPU) hardware to accelerate the numerical integration of these systems in CMAQ's CHEM module. Our implementation, dubbed CMAQ-CUDA, in reference to its use in the Compute Unified Device Architecture (CUDA) general purpose GPU (GPGPU) computing solution, migrates CMAQ's Rosenbrock solver from Fortran to CUDA Fortran. CMAQ-CUDA accelerates the Rosenbrock solver such that simulations using the chemical mechanisms RACM2, CB6R5, and SAPRC07 require only 51%, 50%, or 35% as much time, respectively, as CMAQv5.4 to complete a chemistry time step. Our results demonstrate that CMAQ is amenable to GPU acceleration and highlight a novel Rosenbrock solver implementation for reducing the computational burden imposed by the CHEM module.

The interfacial properties of the organic fraction of biomass burning aerosols (BBA), such as the critical micelle concentration (CMC) and surfactant composition, may vary based on the origin and moisture content of the fuel and the resulting combustion conditions. Surfactant composition, fraction of total particle mass, surface tension minimums, and CMC values of organics extracted from fresh and aged BBA produced using fuel beds from Georgia ecoregions (Piedmont, Coastal Plain, and Blue Ridge) and with fuel moisture contents representative of prescribed fires or drought-induced wildfires were measured using high resolution mass spectrometry, UV–vis spectroscopy, and pendant drop tensiometry. Surface tension minimums of organics extracted from all BBA were low (<45 mN m^–1), and surfactants were ∼2% of the total particle mass. The surfactant fraction was tied to combustion conditions, with the highest fractions present in BBA produced from the most efficient (highest temperature) combustion. Aging of BBA using a potential aerosol mass oxidative flow reactor resulted in an increase in the surfactant fractions of total BBA mass. The dependence of the surfactant fraction on combustion conditions may have implications for the microphysics of BBA from wildfires and prescribed fires.

Understanding the chemical and physical characteristics of surfactants in biomass burning aerosols is important for understanding their influence on the climate. The concentration, composition, and surface tension of surface-active organics in biomass burning aerosol varied based on the fuel-bed composition and moisture content.

Measuring initial volatile organic compound (VOC) concentrations (c₀) is an important first step in the development of mass-transport models in diverse fields, including indoor air quality, food packaging, and biocompatibility. Here, we highlight a previously overlooked methodological issue with techniques employing a re-equilibration step and present an improved experiment based on selected ion flow tube mass spectrometry (SIFT-MS). Specifically, the overlooked aspect of these techniques is unaccounted for VOC loss from the sample during the headspace flushing step. Diffusion modeling indicates that this loss can be significant even when the flushing time is a fraction of the diffusion time. To experimentally demonstrate the impact of mass loss during flushing, we compare the initial concentrations of several volatile methyl siloxanes in Sylgard 184 obtained from multiple headspace extraction (MHE) and a real-time extraction method: TD-SIFT-MS. We find that the TD-SIFT-MS method reports higher c₀ values than MHE with a lower temperature dependence. A technique like TD-SIFT-MS is advantageous because it does not require numerous lengthy equilibration steps and offers full awareness of the system dynamics over the course of the experiment.

The interfacial properties of the organic fraction of biomass burning aerosols (BBA), such as the critical micelle concentration (CMC) and surfactant composition, may vary based on the origin and moisture content of the fuel and the resulting combustion conditions. Surfactant composition, fraction of total particle mass, surface tension minimums, and CMC values of organics extracted from fresh and aged BBA produced using fuel beds from Georgia ecoregions (Piedmont, Coastal Plain, and Blue Ridge) and with fuel moisture contents representative of prescribed fires or drought-induced wildfires were measured using high resolution mass spectrometry, UV-vis spectroscopy, and pendant drop tensiometry. Surface tension minimums of organics extracted from all BBA were low (<45 mN m^-1), and surfactants were ∼2% of the total particle mass. The surfactant fraction was tied to combustion conditions, with the highest fractions present in BBA produced from the most efficient (highest temperature) combustion. Aging of BBA using a potential aerosol mass oxidative flow reactor resulted in an increase in the surfactant fractions of total BBA mass. The dependence of the surfactant fraction on combustion conditions may have implications for the microphysics of BBA from wildfires and prescribed fires.

Electricity generation units (EGUs) emit a mix of health- and climate-relevant air emissions through coal combustion, with the potential to impact multiple emissions. Previous studies have focused on evaluating the cobenefits of climate policies on air quality, studies that consider how air pollution controls affect carbon emissions remain relatively sparse. To evaluate different emission reduction strategies’ impacts on multiple air pollutants and carbon dioxide (CO₂), here we apply a multi-pollutant analysis framework, focused on sulfur dioxide (SO₂) controls on coal-fired EGUs in the United States (U.S.). Eighty-nine EGUs without SO₂ controls in the contiguous U.S. as of 2020 are identified and investigated. Results show that add-on pollution controls like flue gas desulfurization (FGD) reduce SO₂ emissions from coal combustion, but increase emissions of nitrogen oxides (NOx), fine particulate matter (PM_2.5), volatile organic compounds (VOCs), and CO₂. A coal-to-natural gas transition reduces all pollutants except VOCs. A coal-to-renewable transition reduces all studied pollutants. We find that add-on SO₂ controls could generate a total annual net benefit of $13.4 billion nationwide when considering a multi-pollutant portfolio of emissions, as compared with $32.9 billion total annual net benefits from coal-to-natural gas transition and $40.5 billion from coal-to-renewable transition. Our results highlight the potential of implementing the multi-pollutant analysis framework to evaluate multi-pollutant emission reduction strategies.

The impact of detailed spatial and temporal allocation of unconventional oil and gas development (UOGD) NOx emissions on predicted ozone formation was examined using hydraulic fracturing emissions in the Eagle Ford Shale region of Texas as a case study. Hydraulic fracturing occurs at specific well sites, lasting only 1-2 weeks prior to production. Four scenarios for spatial and temporal allocation of hydraulic fracturing NOx emissions were developed. In one scenario, NOx emissions were evenly distributed to all active wells in the Eagle Ford region, with continuous emissions throughout the year. In other scenarios, NOx emissions from hydraulic fracturing engines in Karnes County were allocated only to fractured wells, with durations ranging from 2 days to 2 weeks. In the month of August, predicted daily maximum of 8 h average (MDA8) O₃ concentrations were consistently 6, 8, and 10 ppb higher over wide regions for the two-week, one-week, and two-day emission periods, respectively, compared to the annual county level distribution, demonstrating that detailed spatial and temporal allocation of NOx emissions in regions like the Eagle Ford Shale, with abundant biogenic VOCs, impacts predicted ozone formation.