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  • × National Center for Atmospheric Research, Boulder, CO, USA
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来源:Biogeosciences

作者:C. L. Goodale, G. B. Bonan, R. Q. Thomas

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In many forest ecosystems, nitrogen (N) deposition enhances plant uptake ofcarbon dioxide, thus reducing climate warming from fossil fuel emissions.Therefore, accurately modeling how forest carbon (C) sequestration respondsto N deposition is critical for understanding how future changes in Navailability will influence climate. Here, we use observations of forest Cresponse to N inputs along N deposition gradients and at five temperateforest sites with fertilization experiments to test and improve a globalbiogeochemical model (CLM-CN 4.0). We show that the CLM-CN plant C growthresponse to N deposition was smaller than observed and the modeled responseto N fertilization was larger than observed. A set of modifications to theCLM-CN improved the correspondence between model predictions andobservational data (1) by increasing the aboveground C storage in responseto historical N deposition (1850–2004) from 14 to 34 kg C per additional kg N added through deposition and (2) by decreasing the aboveground net primaryproductivity response to N fertilization experiments from 91 to 57 g C m−2 yr−1. Modeled growth response to N deposition was mostsensitive to altering the processes that control plant N uptake and thepathways of N loss. The response to N deposition also increased with a moreclosed N cycle (reduced N fixation and N gas loss) and decreased whenprioritizing microbial over plant uptake of soil inorganic N. The net effectof all the modifications to the CLM-CN resulted in greater retention of Ndeposition and a greater role of synergy between N deposition and risingatmospheric CO2 as a mechanism governing increases in temperate forestprimary production over the 20th century. Overall, testing models with boththe response to gradual increases in N inputs over decades (N deposition)and N pulse additions of N over multiple years (N fertilization) allows forgreater understanding of the mechanisms governing C–N coupling.

    来源:Biogeosciences

    作者:C. L. Goodale, G. B. Bonan, R. Q. Thomas

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    In many forest ecosystems, nitrogen (N) deposition enhances plant uptake ofcarbon dioxide, thus reducing climate warming from fossil fuel emissions.Therefore, accurately modeling how forest carbon (C) sequestration respondsto N deposition is critical for understanding how future changes in Navailability will influence climate. Here, we use observations of forest Cresponse to N inputs along N deposition gradients and at five temperateforest sites with fertilization experiments to test and improve a globalbiogeochemical model (CLM-CN 4.0). We show that the CLM-CN plant C growthresponse to N deposition was smaller than observed and the modeled responseto N fertilization was larger than observed. A set of modifications to theCLM-CN improved the correspondence between model predictions andobservational data (1) by increasing the aboveground C storage in responseto historical N deposition (1850–2004) from 14 to 34 kg C per additional kg N added through deposition and (2) by decreasing the aboveground net primaryproductivity response to N fertilization experiments from 91 to 57 g C m−2 yr−1. Modeled growth response to N deposition was mostsensitive to altering the processes that control plant N uptake and thepathways of N loss. The response to N deposition also increased with a moreclosed N cycle (reduced N fixation and N gas loss) and decreased whenprioritizing microbial over plant uptake of soil inorganic N. The net effectof all the modifications to the CLM-CN resulted in greater retention of Ndeposition and a greater role of synergy between N deposition and risingatmospheric CO2 as a mechanism governing increases in temperate forestprimary production over the 20th century. Overall, testing models with boththe response to gradual increases in N inputs over decades (N deposition)and N pulse additions of N over multiple years (N fertilization) allows forgreater understanding of the mechanisms governing C–N coupling.

      来源:Biogeosciences

      作者:C. L. Goodale, G. B. Bonan, R. Q. Thomas

      使用许可:署名(BY)

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      来源:Biogeosciences

      作者:T. M. VanReken;B. K. Lamb;S. H. Chung;等

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      Exposure to bioaerosol allergens such as pollen can cause exacerbations ofallergenic airway disease (AAD) in sensitive populations, and thus causeserious public health problems. Assessing these health impacts by linking theairborne pollen levels, concentrations of respirable allergenic material, andhuman allergenic response under current and future climate conditions is akey step toward developing preventive and adaptive actions. To that end, aregional-scale pollen emission and transport modeling framework was developedthat treats allergenic pollens as non-reactive tracers within the coupledWeather Research and Forecasting Community Multiscale Air Quality (WRF/CMAQ)modeling system. The Simulator of the Timing andMagnitude of Pollen Season (STaMPS) model was usedto generate a daily pollen pool that can then be emitted into the atmosphereby wind. The STaMPS is driven by species-specific meteorological (temperatureand/or precipitation) threshold conditions and is designed to be flexiblewith respect to its representation of vegetation species and plant functionaltypes (PFTs). The hourly pollen emission flux was parameterized byconsidering the pollen pool, friction velocity, and wind threshold values.The dry deposition velocity of each species of pollen was estimated based onpollen grain size and density. An evaluation of the pollen modeling frameworkwas conducted for southern California (USA) for the period from March to June2010. This period coincided with observations by the University of SouthernCalifornia's Children's Health Study (CHS), which included O3,PM2.5, and pollen count, as well as measurements of exhaled nitric oxidein study participants. Two nesting domains with horizontal resolutions of 12and 4 km were constructed, and six representative allergenic pollen generawere included: birch tree, walnut tree, mulberry tree, olive tree, oak tree,and brome grasses. Under the current parameterization scheme, the modelingframework tends to underestimate walnut and peak oak pollen concentrations,and tends to overestimate grass pollen concentrations. The model showsreasonable agreement with observed birch, olive, and mulberry tree pollenconcentrations. Sensitivity studies suggest that the estimation of the pollenpool is a major source of uncertainty for simulated pollen concentrations.Achieving agreement between emission modeling and observed pattern of pollenreleases is the key for successful pollen concentration simulations.

        来源:Atmospheric Chemistry and Physics

        作者:H. Schlager;A. Roiger;A. Weinheimer;等

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        来源:Atmospheric Chemistry and Physics

        作者:H. Schlager;A. Roiger;A. Weinheimer;等

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        Ozone pollution transported to the Arctic is a significant concernbecause of the rapid, enhanced warming in high northern latitudes,which is caused, in part, by short-lived climate forcers, such asozone. Long-range transport of pollution contributes to backgroundand episodic ozone levels in the Arctic. However, the extent towhich plumes are photochemically active during transport,particularly during the summer, is still uncertain. In this study,regional chemical transport model simulations are used to examinephotochemical production of ozone in air masses originating fromboreal fire and anthropogenic emissions over North America andduring their transport toward the Arctic during early July2008. Model results are evaluated using POLARCAT aircraft datacollected over boreal fire source regions in Canada (ARCTAS-B) andseveral days downwind over Greenland (POLARCAT-France andPOLARCAT-GRACE). Model results are generallyin good agreement with the observations, except for certain tracegas species over boreal fire regions, in some cases indicating thatthe fire emissions are too low. Anthropogenic and biomass burningpollution (BB) from North America was rapidly uplifted duringtransport east and north to Greenland where pollution plumes wereobserved in the mid- and upper troposphere during POLARCAT. A modelsensitivity study shows that CO levels are in better agreement withPOLARCAT measurements (fresh and aged fire plumes) upon doubling COemissions from fires. Analysis of model results, usingΔO3/ΔCO enhancement ratios, showsthat pollution plumes formed ozone during transport towards theArctic. Fresh anthropogenic plumes have average ΔO3/ΔCO enhancement ratios of 0.63increasing to 0.92 for aged anthropogenic plumes, indicatingadditional ozone production during aging. Fresh fire plumes are onlyslightly enhanced in ozone(ΔO3/ΔCO=0.08), but form ozonedownwind with ΔO3/ΔCO of 0.49 foraged BB plumes (model-based run). We estimate that aged anthropogenic and BB pollutiontogether made an important contribution to ozone levels with anaverage contribution for latitudes >55° N of up to6.5 ppbv (18%) from anthropogenic pollution and 3 ppbv(5.2%) from fire pollution in the model domain in summer 2008.