A process-based fire parameterization of intermediate complexity in a Dynamic Global Vegetation Model
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Abstract. A process-based fire parameterization of intermediate complexity has been developed for global simulations in the framework of a Dynamic Global Vegetation Model (DGVM) in an Earth System Model (ESM). Burned area in a grid cell is estimated by the product of fire counts and average burned area of a fire. The scheme comprises three parts: fire occurrence, fire spread, and fire impact. In the fire occurrence part, fire counts rather than fire occurrence probability are calculated in order to capture the observed high burned area fraction in areas of high fire frequency and realize parameter calibration based on MODIS fire counts product. In the fire spread part, post-fire region of a fire is assumed to be elliptical in shape. Mathematical properties of ellipses and some mathematical derivations are applied to improve the equation and assumptions of an existing fire spread parameterization. In the fire impact part, trace gas and aerosol emissions due to biomass burning are estimated, which offers an interface with atmospheric chemistry and aerosol models in ESMs. In addition, flexible time-step length makes the new fire parameterization easily applied to various DGVMs. Global performance of the new fire parameterization is assessed by using an improved version of the Community Land Model version 3 with the Dynamic Global Vegetation Model (CLM-DGVM). Simulations are compared against the latest satellite-based Global Fire Emission Database version 3 (GFED3) for 1997–2004. Results show that simulated global totals and spatial patterns of burned area and fire carbon emissions, regional totals and spreads of burned area, global annual burned area fractions for various vegetation types, and interannual variability of burned area are reasonable, and closer to GFED3 than CLM-DGVM simulations with the commonly used Glob-FIRM fire parameterization and the old fire module of CLM-DGVM. Furthermore, average error of simulated trace gas and aerosol emissions due to biomass burning is 7% relative to GFED3. Results suggest that the new fire parameterization may improve the global performance of ESMs and help to quantify fire-vegetation-climate interactions on a global scale and from an Earth system perspective.Keywords:
Trace gas
Fire regime
A monoethanolamine (MEA) aerosol growth model was developed to quantify the aerosol growth factor in an amine-based CO2 capture absorber that considers the gas-liquid interactions, and it is empirically validated by measuring the aerosol particle size and concentration. The aerosol growth model, using sucrose as the aerosol nuclei instead of sulfuric acid to prevent the corrosion of the test equipment, accurately predicted that the outlet aerosol size increased to the same level regardless of the sucrose concentration. It also found that particle concentration was the primary factor affecting aerosol growth and amine emissions. We found an inverse relationship between aerosol particle concentration and the aerosol size, while the MEA emissions were proportional to particle concentration.
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Trend analyses of satellite and ground-based observations clearly indicate that temperatures and ozone concentrations in the upper stratosphere are undergoing long-term changes. Variations in solar ultraviolet radiation during the 11-year solar cycle are influencing stratospheric temperatures and photochemistry from above. Forcings from below result from the increasing atmospheric concentrations of long-lived trace constituents, such as carbon dioxide, methane, nitrous oxide, several chlorofluorocarbons and other halocarbons. Using the LLNL two-dimensional chemical-radiative-transport model of the global atmosphere, we evaluate the influences of these external forcings on the middle atmosphere. Our calculations include recent estimates of the variations in solar ultraviolet radiation since 1974. Model results for the solar cycle effects on total ozone, upper stratospheric ozone and temperature are within the uncertainty (in some cases, large) range of observational data analyses. The model calculations including both solar variability and the effects of changing trace gas emissions can explain much of the observed trends in upper stratospheric ozone and temperature from 1979 to 1986.
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Abstract. We introduce and evaluate aerosol simulations with the global aerosol–climate model ECHAM6.3–HAM2.3, which is the aerosol component of the fully coupled aerosol–chemistry–climate model ECHAM–HAMMOZ. Both the host atmospheric climate model ECHAM6.3 and the aerosol model HAM2.3 were updated from previous versions. The updated version of the HAM aerosol model contains improved parameterizations of aerosol processes such as cloud activation, as well as updated emission fields for anthropogenic aerosol species and modifications in the online computation of sea salt and mineral dust aerosol emissions. Aerosol results from nudged and free-running simulations for the 10-year period 2003 to 2012 are compared to various measurements of aerosol properties. While there are regional deviations between the model and observations, the model performs well overall in terms of aerosol optical thickness, but may underestimate coarse-mode aerosol concentrations to some extent so that the modeled particles are smaller than indicated by the observations. Sulfate aerosol measurements in the US and Europe are reproduced well by the model, while carbonaceous aerosol species are biased low. Both mineral dust and sea salt aerosol concentrations are improved compared to previous versions of ECHAM–HAM. The evaluation of the simulated aerosol distributions serves as a basis for the suitability of the model for simulating aerosol–climate interactions in a changing climate.
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A general purpose aerosol conditioning device called the Universal Aerosol Conditioner (UAC) has been designed and tested. The device may be used to condition an aerosol in multiple ways: dilute the entire aerosol (gas- and particle-phase), dilute only a gas-phase component of the aerosol without diluting the particle concentration, denude the aerosol by removing semi-volatile material from the particle phase, and humidify or dehumidify an aerosol. The UAC accomplishes these processes by bringing the aerosol into contact with sheath air and allowing enough time for gas-phase components of the aerosol to diffuse into the sheath flow. A model was developed to assess the theoretical performance of the UAC and was solved numerically. From the model it was determined that two parameters dictated the rate of diffusion between the two flows: the Péclet number and the ratio of sheath-to-aerosol flow rates. A prototype was designed and built and the theory of operation was experimentally validated by measuring the particle penetration efficiency and the gas dilution factor at various particle sizes and flow conditions. The results showed that at low aerosol and sheath flows, the prototype behaved closely to the theoretical model but diverged from the theory once the sheath flows were increased, presumably due to mixing between the two flows.Copyright © 2022 American Association for Aerosol Research
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The HALOE (Halogen Occultation Experiment) dataset is used to study the relation of stratospheric aerosols with trace gases (O3, H2O, HCl, NOx, CH4, and HF) and temperature in a period of relative volcanic quiescence. The lag-correlation analysis shows trace gases and temperature are significantly related to aerosol surface area density. Characteristics of the relevance vary with different components. Temperature is negatively correlated with aerosol for 70-20 hPa over low-and mid-latitudes. Standardized multiple linear regression demonstrates that greenhouse gases are the primary direct contributor for temperature change, and the direct contribution of aerosols is much less. The impact of aerosols on the stratosphere is simulated with the two-dimensional model SOCRATES (Simulation of Chemistry, Radiation, and Transport of Environmentally important Species). The response of trace gases and temperature coincides with the analysis of the HALOE. The rangeability of temperature is much less than that of aerosols. The result suggests that the stratospheric heterogeneous processes on aerosol surfaces are important for the relation between aerosols and trace gases in the aerosol-enriched layers. The radiation effect of aerosols is cooling in the period of relative volcanic quiescence, which is different from the warming effect after volcanic eruptions. The phenomenon depends on the aerosol contents. The indirect radiation effect via heterogeneous processes is stronger than the direct effect of aerosols themselves, but the total radiation effect makes little impact on temperature.
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ABSTRACT Aim The purpose of the study was to determine aerosol exposure generated by coughing in operation room environments to create a quantitative limit value for high-risk aerosol-generating medical procedures. Background Coughing is known to produce a significant amount of aerosols and is thus commonly used as a best reference for high-risk aerosol-generation. Accordingly, procedures during which aerosol generation exceeds the amount of aerosol generated in instances of coughing are seen as high-risk aerosol generating procedures. However, no reliable quantitative values are available for high-risk aerosol-generation. Methods Coughing was measured from 37 healthy volunteers in the operating room environment. Aerosol particles generated during coughing within the size range of 0.3–10 µm were measured with Optical Particle Sizer from 40cm, 70cm, and 100cm distances. The distances reflected potential exposure distances where personnel are during surgeries. Results A total of 306 coughs were measured. Average aerosol concentration during coughing was 1.580 ± 13.774 particles/cm 3 (range 0.000 – 195.528). Discussion The aerosol concentration measured in this study can be used as a limit for high-risk aerosol generation in the operating room environment when assessing the aerosol generating procedures and the risk of operating room staff’s exposure for aerosol particles.
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In this study, a monoethanolamine aerosol growth model was developed to investigate the aerosol growth factor. Interactions among the internal conditions in an absorber were considered in this aerosol model. Additionally, an experiment was conducted to measure aerosol particle size, for collecting in-house validation data. Sucrose was used as the aerosol nuclei instead of sulfuric acid to prevent the corrosion of equipment used in the experiment. Experimental results showed that the outlet aerosol sizes increased to the same size regardless of the sucrose concentrations. The aerosol growth model was validated using the in-house experimental data. The aerosol growth model efficiently predicted the aerosol size. For investigating aerosol growth effects, particle number concentration was determined to be the primary factor affecting aerosol growth and amine emissions. When the particle number concentration increased, the aerosol size decreased, whereas the MEA emission increased.
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Abstract. We introduce and evaluate the aerosol simulations with the global aerosol-climate model ECHAM6.3-HAM2.3, which is the aerosol component of the fully coupled aerosol-chemistry-climate model ECHAM-HAMMOZ. Both the host atmospheric climate model ECHAM6.3 and the aerosol model HAM2.3 were updated from previous versions. The updated version of the HAM aerosol model contains improved parameterizations of aerosol processes such as cloud activation, as well as updated emission fields for anthropogenic aerosol species and modifications in the online computation of sea salt and mineral dust aerosol emissions. Aerosol results from nudged and free running simulations for the 10-year period 2003 to 2012 are compared to various measurements of aerosol properties. While there are regional deviations between model and observations, the model performs well overall in terms of aerosol optical thickness, but may underestimate coarse mode aerosol concentrations to some extent, so that the modeled particles are smaller than indicated by the observations. Sulfate aerosol measurements in the US and Europe are reproduced well by the model, while carbonaceous aerosol species are biased low. Both mineral dust and sea salt aerosol concentrations are improved compared to previous versions of ECHAM-HAM. The evaluation of the simulated aerosol distributions serves as a basis for the suitability of the model for simulating aerosol-climate interactions in a changing climate.
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We present a method to assess the behavior of aerosol nanoparticles as a function of time and of selected aerosol chamber and environmental conditions upon exposure to polydisperse silicon dioxide (SiO2) aerosol nanoparticles (NPs). Through synthesis of SiO2 aerosol NPs, a well-controlled, stable source of aerosol NPs was used to probe aerosol behavior in an enclosed aerosol chamber. This paper describes a procedure to interface an aerosol chamber downstream of a SiO2 aerosol NP reactor that is capable of synthesizing SiO2 NPs with particle diameters from 10 to 100 nm at particle concentrations of approximately 10(4) to 10(7) particles/cm3. This paper also describes the relative impact on aerosol and aerosol chamber variables, such as chamber volume, the entering aerosol NP size distribution, and environmental parameters, such as relative humidity and ambient particle concentrations, on the observed changes in aerosol NPs over time under unmixed conditions. These findings provide insights into aerosol NP behavior under ideal, well-controlled conditions which can be further refined to include more occupationally relevant conditions that would be important for establishing guidance on suitable workplace containment and controls.
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Changes to the frequency of fire due to management decisions and climate change have the potential to affect the flammability of vegetation, with long-term effects on the vegetation structure and composition. Frequent fire in some vegetation types can lead to transformational change beyond which the vegetation type is radically altered. Such feedbacks limit our ability to project fuel loads under future climatic conditions or to consider the ecological tradeoffs associated with management burns. We present a “pathway modelling” approach to consider multiple transitional pathways that may occur under different fire frequencies. The model combines spatial layers representing current and future fire danger, biomass, flammability, and sensitivity to fire to assess potential future fire activity. The layers are derived from a dynamically downscaled regional climate model, attributes from a regional vegetation map, and information about fuel characteristics. Fire frequency is demonstrated to be an important factor influencing flammability and availability to burn and therefore an important determinant of future fire activity. Regional shifts in vegetation type occur in response to frequent fire, as the rate of change differs across vegetation type. Fire-sensitive vegetation types move towards drier, more fire-adapted vegetation quickly, as they may be irreversibly impacted by even a single fire, and require very long recovery times. Understanding the interaction between climate change and fire is important to identify appropriate management regimes to sustain fire-sensitive communities and maintain the distribution of broad vegetation types across the landscape.
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