Simulation of tropospheric chemistry and aerosols with the climate model EC-Earth
Noije, T.P.C. van; Sager, P. Le; Segers, A.J. ; Velthoven, P.F.J. van; Krol, M.C. ; Hazeleger, W. ; Williams, A.G. ; Chambers, S.D. - \ 2014
Geoscientific Model Development 7 (2014)5. - ISSN 1991-959X - p. 2435 - 2475.
intercomparison project accmip - general-circulation model - dry deposition parameterization - modified band approach - atmospheric chemistry - global-models - transport models - boundary-layer - stratospheric ozone - sulfur emissions
We have integrated the atmospheric chemistry and transport model TM5 into the global climate model EC-Earth version 2.4. We present an overview of the TM5 model and the two-way data exchange between TM5 and the IFS model from the European Centre for Medium-Range Weather Forecasts (ECMWF), the atmospheric general circulation model of EC-Earth. In this paper we evaluate the simulation of tropospheric chemistry and aerosols in a one-way coupled configuration. We have carried out a decadal simulation for present-day conditions and calculated chemical budgets and climatologies of tracer concentrations and aerosol optical depth. For comparison we have also performed offline simulations driven by meteorological fields from ECMWF's ERA-Interim reanalysis and output from the EC-Earth model itself. Compared to the offline simulations, the online-coupled system produces more efficient vertical mixing in the troposphere, which reflects an improvement of the treatment of cumulus convection. The chemistry in the EC-Earth simulations is affected by the fact that the current version of EC-Earth produces a cold bias with too dry air in large parts of the troposphere. Compared to the ERA-Interim driven simulation, the oxidizing capacity in EC-Earth is lower in the tropics and higher in the extratropics. The atmospheric lifetime of methane in EC-Earth is 9.4 years, which is 7% longer than the lifetime obtained with ERA-Interim but remains well within the range reported in the literature. We further evaluate the model by comparing the simulated climatologies of surface radon-222 and carbon monoxide, tropospheric and surface ozone, and aerosol optical depth against observational data. The work presented in this study is the first step in the development of EC-Earth into an Earth system model with fully interactive atmospheric chemistry and aerosols.
Off-line algorithm for calculation of vertical tracer transport in the troposphere due to deep convection
Belikov, D.A. ; Maksyutov, S. ; Krol, M.C. ; Fraser, A. ; Rigby, M. ; Bian, H. ; Agusti-Panareda, A. ; Bergmann, D. ; Bousquet, P. ; Cameron-Smith, P. ; Chipperfield, M.P. ; Fortems-Cheiney, A. ; Gloor, E. ; Haynes, K. ; Hess, P. ; Houweling, S. ; Kawa, S.R. ; Law, R.M. ; Loh, Z. ; Meng, L. ; Palmer, P.I. ; Patra, P.K. ; Prinn, R.G. ; Saito, R. ; Wilson, C. - \ 2013
Atmospheric Chemistry and Physics 13 (2013)3. - ISSN 1680-7316 - p. 1093 - 1114.
general-circulation model - observed radon profiles - cumulus convection - atmospheric transport - climate simulations - meteorological data - cloud ensemble - precipitation - rn-222 - parameterization
A modified cumulus convection parametrisation scheme is presented. This scheme computes the mass of air transported upward in a cumulus cell using conservation of moisture and a detailed distribution of convective precipitation provided by a reanalysis dataset. The representation of vertical transport within the scheme includes entrainment and detrainment processes in convective updrafts and downdrafts. Output from the proposed parametrisation scheme is employed in the National Institute for Environmental Studies (NIES) global chemical transport model driven by JRA-25/JCDAS reanalysis. The simulated convective precipitation rate and mass fluxes are compared with observations and reanalysis data. A simulation of the short-lived tracer Rn-222 is used to further evaluate the performance of the cumulus convection scheme. Simulated distributions of Rn-222 are evaluated against observations at the surface and in the free troposphere, and compared with output from models that participated in the TransCom-CH4 Transport Model Intercomparison. From this comparison, we demonstrate that the proposed convective scheme in general is consistent with observed and modeled results.
Reassessing the variability in atmospheric H2 using the two-way nested TM5 model
Pieterse, G. ; Krol, M.C. ; Batenburg, A.M. ; Brenninkmeijer, C.A. ; Popa, M.E. ; O'Doherty, S. ; Grant, A. ; Steele, L.P. ; Krummel, P.B. ; Langenfelds, R.L. ; Wang, H.J. ; Vermeulen, A.T. ; Schmidt, M. ; Yver, C. ; Jordan, A. ; Engel, A. ; Fisher, R.E. ; Lowry, D. ; Nisbet, E.G. ; Reimann, S. ; Vollmer, M.K. ; Steinbacher, M. ; Hammer, S. ; Forster, G. ; Sturges, W.T. ; Rockmann, T. - \ 2013
Journal of Geophysical Research: Atmospheres 118 (2013)9. - ISSN 2169-897X - p. 3764 - 3780.
dry deposition parameterization - stable isotopic composition - general-circulation model - global hydrogen economy - molecular-hydrogen - trace gases - environmental-impact - dissolved hydrogen - seasonal-variation - data assimilation
This work reassesses the global atmospheric budget of H2 with the TM5 model. The recent adjustment of the calibration scale for H2 translates into a change in the tropospheric burden. Furthermore, the ECMWF Reanalysis-Interim (ERA-Interim) data from the European Centre for Medium-Range Weather Forecasts (ECMWF) used in this study show slower vertical transport than the operational data used before. Consequently, more H2 is removed by deposition. The deposition parametrization is updated because significant deposition fluxes for snow, water, and vegetation surfaces were calculated in our previous study. Timescales of 1-2h are asserted for the transport of H2 through the canopies of densely vegetated regions. The global scale variability of H2 and [DH2] is well represented by the updated model. H2 is slightly overestimated in the Southern Hemisphere because too little H2 is removed by dry deposition to rainforests and savannahs. The variability in H2 over Europe is further investigated using a high-resolution model subdomain. It is shown that discrepancies between the model and the observations are mainly caused by the finite model resolution. The tropospheric burden is estimated at 165 +/- 8TgH2. The removal rates of H2 by deposition and photochemical oxidation are estimated at 53 +/- 4 and 23 +/- 2TgH2/yr, resulting in a tropospheric lifetime of 2.2 +/- 0.2year.
Impact of transport model errors on the global and regional methane emissions estimated by inverse modelling
Locatelli, R. ; Bousquet, P. ; Chevallier, F. ; Fortems-Cheney, A. ; Szopa, S. ; Saunois, M. ; Agusti-Panareda, A. ; Bergmann, D. ; Bian, H. ; Cameron-Smith, P. ; Chipperfield, M.P. ; Gloor, E. ; Houweling, S. ; Kawa, S.R. ; Krol, M.C. ; Patra, P.K. ; Prinn, R.G. ; Rigby, M. ; Saito, R. ; Wilson, C. - \ 2013
Atmospheric Chemistry and Physics 13 (2013)19. - ISSN 1680-7316 - p. 9917 - 9937.
general-circulation model - atmospheric transport - tracer transport - co2 inversions - boundary-layer - vertical profiles - data assimilation - climate-change - growth-rate - part i
A modelling experiment has been conceived to assess the impact of transport model errors on methane emissions estimated in an atmospheric inversion system. Synthetic methane observations, obtained from 10 different model outputs from the international TransCom-CH4 model inter-comparison exercise, are combined with a prior scenario of methane emissions and sinks, and integrated into the three-component PYVAR-LMDZ-SACS (PYthon VARiational-Laboratoire de Meteorologie Dynamique model with Zooming capability-Simplified Atmospheric Chemistry System) inversion system to produce 10 different methane emission estimates at the global scale for the year 2005. The same methane sinks, emissions and initial conditions have been applied to produce the 10 synthetic observation datasets. The same inversion set-up (statistical errors, prior emissions, inverse procedure) is then applied to derive flux estimates by inverse modelling. Consequently, only differences in the modelling of atmospheric transport may cause differences in the estimated fluxes. In our framework, we show that transport model errors lead to a discrepancy of 27 Tg yr(-1) at the global scale, representing 5% of total methane emissions. At continental and annual scales, transport model errors are proportionally larger than at the global scale, with errors ranging from 36 Tg yr(-1) in North America to 7 Tg yr(-1) in Boreal Eurasia (from 23 to 48 %, respectively). At the model grid-scale, the spread of inverse estimates can reach 150% of the prior flux. Therefore, transport model errors contribute significantly to overall uncertainties in emission estimates by inverse modelling, especially when small spatial scales are examined. Sensitivity tests have been carried out to estimate the impact of the measurement network and the advantage of higher horizontal resolution in transport models. The large differences found between methane flux estimates inferred in these different configurations highly question the consistency of transport model errors in current inverse systems. Future inversions should include more accurately prescribed observation covariances matrices in order to limit the impact of transport model errors on estimated methane fluxes.
The use of forest stand age information in an atmospheric CO2 inversion applied to North America
Deng, F. ; Chen, J.M. ; Pan, Y. ; Peters, W. ; Birdsey, R. ; McCullough, K. ; Xiao, J. - \ 2013
Biogeosciences 10 (2013)8. - ISSN 1726-4170 - p. 5335 - 5348.
terrestrial carbon metabolism - conterminous united-states - general-circulation model - ponderosa pine - interannual variability - disturbance history - satellite imagery - flux inversion - climate-change - transport
Atmospheric inversions have become an important tool in quantifying carbon dioxide (CO2) sinks and sources at a variety of spatiotemporal scales, but associated large uncertainties restrain the inversion research community from reaching agreement on many important subjects. We enhanced an atmospheric inversion of the CO2 flux for North America by introducing spatially explicit information on forest stand age for US and Canada as an additional constraint, since forest carbon dynamics are closely related to time since disturbance. To use stand age information in the inversion, we converted stand age into an age factor, and included the covariances between subcontinental regions in the inversion based on the similarity of the age factors. Our inversion results show that, considering age factors, regions with recently disturbed or old forests are often nudged towards carbon sources, while regions with middle-aged productive forests are shifted towards sinks. This conforms to stand age effects observed in flux networks. At the subcontinental level, our inverted carbon fluxes agree well with continuous estimates of net ecosystem carbon exchange (NEE) upscaled from eddy covariance flux data based on MODIS data. Inverted fluxes with the age constraint exhibit stronger correlation to these upscaled NEE estimates than those inverted without the age constraint. While the carbon flux at the continental and subcontinental scales is predominantly determined by atmospheric CO2 observations, the age constraint is shown to have potential to improve the inversion of the carbon flux distribution among subcontinental regions, especially for regions lacking atmospheric CO2 observations
Application of the CALIOP layer product to evaluate the vertical distribution of aerosols estimated by global models: AeroCom phase I results
Koffi, B. ; Schulz, M. ; Breon, F.M. ; Griesfeller, J. ; Winker, D. ; Balkanski, Y. ; Bauer, S. ; Berntsen, T. ; Chin, M.A. ; Collins, W.D. ; Dentener, F. ; Diehl, T. ; Easter, R. ; Ghan, S. ; Ginoux, P. ; Gong, S.L. ; Horowitz, L.W. ; Iversen, T. ; Kirkevag, A. ; Koch, D. ; Krol, M.C. ; Myhre, G. ; Stier, P. ; Takemura, T. - \ 2012
Journal of Geophysical Research: Atmospheres 117 (2012). - ISSN 2169-897X
general-circulation model - sun photometer measurements - optical-properties - satellite-observations - goddard-institute - north-atlantic - calipso lidar - gocart model - mineral dust - emission inventories
The CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) layer product is used for a multimodel evaluation of the vertical distribution of aerosols. Annual and seasonal aerosol extinction profiles are analyzed over 13 sub-continental regions representative of industrial, dust, and biomass burning pollution, from CALIOP 2007-2009 observations and from AeroCom (Aerosol Comparisons between Observations and Models) 2000 simulations. An extinction mean height diagnostic (Z(alpha)) is defined to quantitatively assess the models' performance. It is calculated over the 0-6 km and 0-10 km altitude ranges by weighting the altitude of each 100 m altitude layer by its aerosol extinction coefficient. The mean extinction profiles derived from CALIOP layer products provide consistent regional and seasonal specificities and a low inter-annual variability. While the outputs from most models are significantly correlated with the observed Z(alpha) climatologies, some do better than others, and 2 of the 12 models perform particularly well in all seasons. Over industrial and maritime regions, most models show higher Z(alpha) than observed by CALIOP, whereas over the African and Chinese dust source regions, Za is underestimated during Northern Hemisphere Spring and Summer. The positive model bias in Z(alpha) is mainly due to an overestimate of the extinction above 6 km. Potential CALIOP and model limitations, and methodological factors that might contribute to the differences are discussed.
TransCom model simulations of CH4 and related species: linking transport, surface flux and chemical loss with CH4 variability in the troposphere and lower stratosphere
Patra, P.K. ; Houweling, S. ; Krol, M.C. ; Bousquet, P. ; Belikov, D. - \ 2011
Atmospheric Chemistry and Physics 11 (2011)24. - ISSN 1680-7316 - p. 12813 - 12837.
general-circulation model - biomass burning emissions - atmospheric methane - growth-rate - interannual variability - methyl chloroform - tracer transport - sf6 - gases - co2
A chemistry-transport model (CTM) intercomparison experiment (TransCom-CH4) has been designed to investigate the roles of surface emissions, transport and chemical loss in simulating the global methane distribution. Model simulations were conducted using twelve models and four model variants and results were archived for the period of 1990–2007. All but one model transports were driven by reanalysis products from 3 different meteorological agencies. The transport and removal of CH4 in six different emission scenarios were simulated, with net global emissions of 513±9 and 514±14 TgCH4 yr-1 for the 1990s and 2000s, respectively. Additionally, sulfur hexafluoride (SF6) was simulated to check the interhemispheric transport, radon (222Rn) to check the subgrid scale transport, and methyl chloroform (CH3CCl3) to check the chemical removal by the tropospheric hydroxyl radical (OH). The results are compared to monthly or annual mean time series of CH4, SF6 and CH3CCl3 measurements from 8 selected background sites, and to satellite observations of CH4 in the upper troposphere and stratosphere. Most models adequately capture the vertical gradients in the stratosphere, the average long-term trends, seasonal cycles, interannual variations (IAVs) and interhemispheric (IH) gradients at the surface sites for SF6, CH3CCl3 and CH4. The vertical gradients of all tracers between the surface and the upper troposphere are consistent within the models, revealing vertical transport differences between models. An average IH exchange time of 1.39±0.18 yr is derived from SF6 time series. Sensitivity simulations suggest that the estimated trends in exchange time, over the period of 1996–2007, are caused by a change of SF6 emissions towards the tropics. Using six sets of emission scenarios, we show that the decadal average CH4 growth rate likely reached equilibrium in the early 2000s due to the flattening of anthropogenic emission growth since the late 1990s. Up to 60% of the IAVs in the observed CH4 concentrations can be explained by accounting for the IAVs in emissions, from biomass burning and wetlands, as well as meteorology in the forward models. The modeled CH4 budget is shown to depend strongly on the troposphere-stratosphere exchange rate and thus on the model’s vertical grid structure and circulation in the lower stratosphere. The 15-model median CH4 and CH3CCl3 atmospheric lifetimes are estimated to be 9.99±0.08 and 4.61±0.13 yr, respectively, with little IAV due to transport and temperature.
Global modelling of H2 mixing ratios and isotopic compositions with the TM5 model
Pieterse, G. ; Krol, M.C. ; Batenburg, A.M. ; Steele, L.P. ; Krummel, P.B. ; Langenfelds, R.L. ; Röckmann, T. - \ 2011
Atmospheric Chemistry and Physics 11 (2011)14. - ISSN 1680-7316 - p. 7001 - 7026.
dry deposition parameterization - european photoreactor facility - tropospheric photolysis rates - general-circulation model - molecular-hydrogen - atmospheric chemistry - lowermost stratosphere - photochemical data - transport - impact
The isotopic composition of molecular hydrogen (H2) contains independent information for constraining the global H2 budget. To explore this, we have implemented hydrogen sources and sinks, including their isotopic composition, into the global chemistry transport model TM5. For the first time, a global model now includes a simplified but explicit isotope reaction scheme for the photochemical production of H2. We present a comparison of modelled results for the H2 mixing ratio and isotope composition with available measurements on the seasonal to inter annual time scales for the years 2001–2007. The base model results agree well with observations for H2 mixing ratios. For dD[H2], modelled values are slightly lower than measurements. A detailed sensitivity study is performed to identify the most important parameters for modelling the isotopic composition of H2. The results show that on the global scale, the discrepancy between model and measurements can be closed by adjusting the default values of the isotope effects in deposition, photochemistry and the stratosphere-troposphere exchange within the known range of uncertainty. However, the available isotope data do not provide sufficient information to uniquely constrain the global isotope budget. Therefore, additional studies focussing on the isotopic composition near the tropopause and on the isotope effects in the photochemistry and deposition are recommended.
Global dust model intercomparison in AeroCom phase I
Huneeus, N. ; Schulz, M. ; Balkanski, Y. ; Griesfeller, J. ; Krol, M.C. - \ 2011
Atmospheric Chemistry and Physics 11 (2011)15. - ISSN 1680-7316 - p. 7781 - 7816.
general-circulation model - atmospheric iron deposition - last glacial maximum - mineral dust - aerosol direct - tropospheric chemistry - optical-properties - goddard-institute - north-atlantic - sulfur cycle
This study presents the results of a broad intercomparison of a total of 15 global aerosol models within the AeroCom project. Each model is compared to observations related to desert dust aerosols, their direct radiative effect, and their impact on the biogeochemical cycle, i.e., aerosol optical depth (AOD) and dust deposition. Additional comparisons to Angström exponent (AE), coarse mode AOD and dust surface concentrations are included to extend the assessment of model performance and to identify common biases present in models. These data comprise a benchmark dataset that is proposed for model inspection and future dust model development. There are large differences among the global models that simulate the dust cycle and its impact on climate. In general, models simulate the climatology of vertically integrated parameters (AOD and AE) within a factor of two whereas the total deposition and surface concentration are reproduced within a factor of 10. In addition, smaller mean normalized bias and root mean square errors are obtained for the climatology of AOD and AE than for total deposition and surface concentration. Characteristics of the datasets used and their uncertainties may influence these differences. Large uncertainties still exist with respect to the deposition fluxes in the southern oceans. Further measurements and model studies are necessary to assess the general model performance to reproduce dust deposition in ocean regions sensible to iron contributions. Models overestimate the wet deposition in regions dominated by dry deposition. They generally simulate more realistic surface concentration at stations downwind of the main sources than at remote ones. Most models simulate the gradient in AOD and AE between the different dusty regions. However the seasonality and magnitude of both variables is better simulated at African stations than Middle East ones. The models simulate the offshore transport of West Africa throughout the year but they overestimate the AOD and they transport too fine particles. The models also reproduce the dust transport across the Atlantic in the summer in terms of both AOD and AE but not so well in winter-spring nor the southward displacement of the dust cloud that is responsible of the dust transport into South America. Based on the dependency of AOD on aerosol burden and size distribution we use model bias with respect to AOD and AE to infer the bias of the dust emissions in Africa and the Middle East. According to this analysis we suggest that a range of possible emissions for North Africa is 400 to 2200 Tg yr-1 and in the Middle East 26 to 526 Tg yr-1.
The European aerosol budget in 2006
Brugh, J.M.J. Aan de; Schaap, M. ; Vignati, E. ; Dentener, F. ; Kahnert, M. ; Sofiev, M. ; Huijnen, V. ; Krol, M.C. - \ 2011
Atmospheric Chemistry and Physics 11 (2011)3. - ISSN 1680-7316 - p. 1117 - 1139.
general-circulation model - evaluation program emep - light absorbing carbon - air-pollution - sulfuric-acid - sea-salt - tropospheric aerosols - 3-dimensional model - size distributions - particulate matter
This paper presents the aerosol budget over Europe in 2006 calculated with the global transport model TM5 coupled to the size-resolved aerosol module M7. Comparison with ground observations indicates that the model reproduces the observed concentrations quite well with an expected slight underestimation of PM10 due to missing emissions (e.g. resuspension). We model that a little less than half of the anthropogenic aerosols emitted in Europe are exported and the rest is removed by deposition. The anthropogenic aerosols are removed mostly by rain (95%) and only 5% is removed by dry deposition. For the larger natural aerosols, especially sea salt, a larger fraction is removed by dry processes (sea salt: 70%, mineral dust: 35%). We model transport of aerosols in the jet stream in the higher atmosphere and an import of Sahara dust from the south at high altitudes. Comparison with optical measurements shows that the model reproduces the Ångström parameter very well, which indicates a correct simulation of the aerosol size distribution. However, we underestimate the aerosol optical depth. Because the surface concentrations are close to the observations, the shortage of aerosol in the model is probably at higher altitudes. We show that the discrepancies are mainly caused by an overestimation of wet-removal rates. To match the observations, the wet-removal rates have to be scaled down by a factor of about 5. In that case the modelled ground-level concentrations of sulphate and sea salt increase by 50% (which deteriorates the match), while other components stay roughly the same. Finally, it is shown that in particular events, improved fire emission estimates may significantly improve the ability of the model to simulate the aerosol optical depth. We stress that discrepancies in aerosol models can be adequately analysed if all models would provide (regional) aerosol budgets, as presented in the current study
The global chemistry transport model TM5: description and evaluation of the tropospheric chemistry version 3.0
Huijnen, V. ; Williams, J. ; Weele, M. van; Noije, T. van; Krol, M.C. ; Dentener, F. ; Segers, A. ; Houweling, S. ; Peters, W. - \ 2010
Geoscientific Model Development 3 (2010)2. - ISSN 1991-959X - p. 445 - 473.
general-circulation model - dry deposition parameterization - organic-compound emissions - mozaic airborne program - gas-phase reactions - air-quality models - interannual variability - atmospheric chemistry - photochemical data - tracer transport
We present a comprehensive description and benchmark evaluation of the tropospheric chemistry version of the global chemistry transport model TM5 (Tracer Model 5, version TM5-chem-v3.0). A full description is given concerning the photochemical mechanism, the interaction with aerosol, the treatment of the stratosphere, the wet and dry deposition parameterizations, and the applied emissions. We evaluate the model against a suite of ground-based, satellite, and aircraft measurements of components critical for understanding global photochemistry for the year 2006. The model exhibits a realistic oxidative capacity at a global scale. The methane lifetime is ~8.9 years with an associated lifetime of methyl chloroform of 5.86 years, which is similar to that derived using an optimized hydroxyl radical field. The seasonal cycle in observed carbon monoxide (CO) is well simulated at different regions across the globe. In the Northern Hemisphere CO concentrations are underestimated by about 20 ppbv in spring and 10 ppbv in summer, which is related to missing chemistry and underestimated emissions from higher hydrocarbons, as well as to uncertainties in the seasonal variation of CO emissions. The model also captures the spatial and seasonal variation in formaldehyde tropospheric columns as observed by SCIAMACHY. Positive model biases over the Amazon and eastern United States point to uncertainties in the isoprene emissions as well as its chemical breakdown. Simulated tropospheric nitrogen dioxide columns correspond well to observations from the Ozone Monitoring Instrument in terms of its seasonal and spatial variability (with a global spatial correlation coefficient of 0.89), but TM5 fields are lower by 25–40%. This is consistent with earlier studies pointing to a high bias of 0–30% in the OMI retrievals, but uncertainties in the emission inventories have probably also contributed to the discrepancy. TM5 tropospheric nitrogen dioxide profiles are in good agreement (within ~0.1 ppbv) with in situ aircraft observations from the INTEX-B campaign over (the Gulf of) Mexico. The model reproduces the spatial and seasonal variation in background surface ozone concentrations and tropospheric ozone profiles from the World Ozone and Ultraviolet Radiation Data Centre to within 10 ppbv, but at several tropical stations the model tends to underestimate ozone in the free troposphere. The presented model results benchmark the TM5 tropospheric chemistry version, which is currently in use in several international cooperation activities, and upon which future model improvements will take place
The impact of Future Land Use and Land Cover Changes on Atmospheric Chemistry-Climate Interactions
Ganzeveld, L.N. ; Bouwman, L. - \ 2010
Journal of Geophysical Research: Atmospheres 115 (2010)D23. - ISSN 2169-897X - 18 p.
general-circulation model - organic-compound emissions - isoprene emissions - technical note - dry deposition - sres scenarios - ozone - surface - echam5/messy1 - exchanges
To demonstrate potential future consequences of land cover and land use changes beyond those for physical climate and the carbon cycle, we present an analysis of large-scale impacts of land cover and land use changes on atmospheric chemistry using the chemistry-climate model EMAC (ECHAM5/MESSy Atmospheric Chemistry) constrained with present-day and 2050 land cover, land use, and anthropogenic emissions scenarios. Future land use and land cover changes are expected to result in an increase in global annual soil NO emissions by ~1.2 TgN yr-1 (9%), whereas isoprene emissions decrease by ~50 TgC yr-1 (-12%). The analysis shows increases in simulated boundary layer ozone mixing ratios up to ~9 ppbv and more than a doubling in hydroxyl radical concentrations over deforested areas in Africa. Small changes in global atmosphere-biosphere fluxes of NOx and ozone point to compensating effects. Decreases in soil NO emissions in deforested regions are counteracted by a larger canopy release of NOx caused by reduced foliage uptake. Despite this decrease in foliage uptake, the ozone deposition flux does not decrease since surface layer mixing ratios increase because of a reduced oxidation of isoprene by ozone. Our study indicates that the simulated impact of land cover and land use changes on atmospheric chemistry depends on a consistent representation of emissions, deposition, and canopy interactions and their dependence on meteorological, hydrological, and biological drivers to account for these compensating effects. It results in negligible changes in the atmospheric oxidizing capacity and, consequently, in the lifetime of methane. Conversely, we expect a pronounced increase in oxidizing capacity as a consequence of anthropogenic emission increases
Sources of uncertainties in modelling black carbon at the global scale
Vignati, E. ; Karl, M. ; Krol, M.C. ; Wilson, J. ; Stier, P. ; Cavalli, F. - \ 2010
Atmospheric Chemistry and Physics 10 (2010)6. - ISSN 1680-7316 - p. 2595 - 2611.
general-circulation model - aerosol-climate model - elemental carbon - atmospheric aerosols - optical characterization - hygroscopic properties - marine atmosphere - chemistry models - soot particles - mt. sonnblick
Our understanding of the global black carbon (BC) cycle is essentially qualitative due to uncertainties in our knowledge of its properties. This work investigates two source of uncertainties in modelling black carbon: those due to the use of different schemes for BC ageing and its removal rate in the global Transport-Chemistry model TM5 and those due to the uncertainties in the definition and quantification of the observations, which propagate through to both the emission inventories, and the measurements used for the model evaluation. The schemes for the atmospheric processing of black carbon that have been tested with the model are (i) a simple approach considering BC as bulk aerosol and a simple treatment of the removal with fixed 70% of in-cloud black carbon concentrations scavenged by clouds and removed when rain is present and (ii) a more complete description of microphysical ageing within an aerosol dynamics model, where removal is coupled to the microphysical properties of the aerosol, which results in a global average of 40% in-cloud black carbon that is scavenged in clouds and subsequently removed by rain, thus resulting in a longer atmospheric lifetime. This difference is reflected in comparisons between both sets of modelled results and the measurements. Close to the sources, both anthropogenic and vegetation fire source regions, the model results do not differ significantly, indicating that the emissions are the prevailing mechanism determining the concentrations and the choice of the aerosol scheme does not influence the levels. In more remote areas such as oceanic and polar regions the differences can be orders of magnitude, due to the differences between the two schemes. The more complete description reproduces the seasonal trend of the black carbon observations in those areas, although not always the magnitude of the signal, while the more simplified approach underestimates black carbon concentrations by orders of magnitude. The sensitivity to wet scavenging has been tested by varying in-cloud and below-cloud removal. BC lifetime increases by 10% when large scale and convective scale precipitation removal efficiency are reduced by 30%, while the variation is very small when below-cloud scavenging is zero. Since the emission inventories are representative of elemental carbon-like substance, the model output should be compared to elemental carbon measurements and if known, the ratio of black carbon to elemental carbon mass should be taken into account when the model is compared with black carbon observations
Atmosphere-Ocean Ozone Exchange – A Global Modeling Study of Biogeochemical, Atmospheric and Water-Side Turbulence Dependencies
Ganzeveld, L.N. ; Helmig, D. ; Fairall, C.W. ; Hare, J. ; Pozzer, A. - \ 2009
Global Biogeochemical Cycles 23 (2009). - ISSN 0886-6236 - 16 p.
general-circulation model - dry deposition parameterization - marine boundary-layer - nonmethane hydrocarbons - iodide distribution - tropospheric ozone - dissolved iodine - aqueous-solution - south atlantic - technical note
The significance of the removal of tropospheric ozone by the oceans, covering ~2/3 of the Earth's surface, has only been addressed in a few studies involving water tank, aircraft, and tower flux measurements. On the basis of results from these few observations of the ozone dry deposition velocity (VdO3), atmospheric chemistry models generally apply an empirical, constant ocean uptake rate of 0.05 cm s-1. This value is substantially smaller than the atmospheric turbulent transport velocity for ozone. On the other hand, the uptake is higher than expected from the solubility of ozone in clean water alone, suggesting that there is an enhancement in oceanic ozone uptake, e.g., through a chemical destruction mechanism. We present an evaluation of a global-scale analysis with a new mechanistic representation of atmosphere-ocean ozone exchange. The applied atmosphere chemistry-climate model includes not only atmospheric but also waterside turbulence and the role of waterside chemical loss processes as a function of oceanic biogeochemistry. The simulations suggest a larger role of biogeochemistry in tropical and subtropical ozone oceanic uptake with a relative small temporal variability, whereas in midlatitude and high-latitude regions, highly variable ozone uptake rates are expected because of the stronger influence of waterside turbulence. Despite a relatively large range in the explicitly calculated ocean uptake rate, there is a surprisingly small sensitivity of simulated Marine Boundary Layer ozone concentrations compared to the sensitivity for the commonly applied constant ocean uptake approach. This small sensitivity points at compensating effects through inclusion of the process-based ocean uptake mechanisms to consider variability in oceanic O3 deposition consistent with that in atmospheric and oceanic physical, chemical, and biological processes
Flux estimates of isoprene, methanol and acetone from airborne PTR-MS measurements over the tropical rainforest during the GABRIEL 2005 campaign
Eerdekens, G. ; Ganzeveld, L.N. ; Vilà-Guerau de Arellano, J. ; Klüpfel, T. ; Sinha, V. - \ 2009
Atmospheric Chemistry and Physics 9 (2009). - ISSN 1680-7316 - p. 4207 - 4227.
volatile organic-compounds - methyl vinyl ketone - reaction mass-spectrometry - convective boundary-layer - general-circulation model - chemistry-climate model - atmospheric chemistry - shallow cumulus - initiated oxidation - monoterpene fluxes
Tropical forests are a strong source of biogenic volatile organic compounds (BVOCs) to the atmosphere which can potentially impact the atmospheric oxidation capacity. Here we present airborne and ground-based BVOC measurements representative for the long dry season covering a large area of the northern Amazonian rainforest (6-3° N, 50-59° W). The measurements were conducted during the October 2005 GABRIEL (Guyanas Atmosphere-Biosphere exchange and Radicals Intensive Experiment with the Learjet) campaign. The vertical (35 m to 10 km) and diurnal (09:00-16:00) profiles of isoprene, its oxidation products methacrolein and methyl vinyl ketone and methanol and acetone, measured by PTR-MS (Proton Transfer Reaction Mass Spectrometry), have been used to empirically estimate their emission fluxes from the forest canopy on a regional scale. The mixed layer isoprene emission flux, inferred from the airborne measurements above 300 m, is 5.7 mg isoprene m-2 h-1 after compensating for chemistry and ~6.9 mg isoprene m-2 h-1 taking detrainment into account. This surface flux is in general agreement with previous tropical forest studies. Inferred methanol and acetone emission fluxes are 0.5 mg methanol m¿2 h¿1 and 0.35 mg acetone m-2 h-1, respectively. The BVOC measurements were compared with fluxes and mixing ratios simulated with a single-column chemistry and climate model (SCM). The inferred isoprene flux is substantially smaller than that simulated with an implementation of a commonly applied BVOC emission algorithm in the SCM.
Surface and boundary layer exchanges of volatile organic compounds, nitrogen oxides and ozone during the GABRIEL campaign
Ganzeveld, L.N. ; Eerdekens, G. ; Feig, G. ; Vilà-Guerau de Arellano, J. - \ 2008
Atmospheric Chemistry and Physics 8 (2008). - ISSN 1680-7316 - p. 6223 - 6243.
general-circulation model - chemistry-climate model - gaseous dry deposition - simple biosphere model - tropical rain-forest - coniferous forest - isoprene - emissions - amazonia - aerosols
We present an evaluation of sources, sinks and turbulent transport of nitrogen oxides, ozone and volatile organic compounds (VOC) in the boundary layer over French Guyana and Suriname during the October 2005 GABRIEL campaign by simulating observations with a single-column chemistry and climate model (SCM) along a zonal transect. Simulated concentrations of O3 and NO as well as NO2 photolysis rates over the forest agree well with observations when a small soil-biogenic NO emission flux was applied. This suggests that the photochemical conditions observed during GABRIEL reflect a pristine tropical low-NOx regime. The SCM uses a compensation point approach to simulate nocturnal deposition and daytime emissions of acetone and methanol and produces daytime boundary layer mixing ratios in reasonable agreement with observations. The area average isoprene emission flux, inferred from the observed isoprene mixing ratios and boundary layer height, is about half the flux simulated with commonly applied emission algorithms. The SCM nevertheless simulates too high isoprene mixing ratios, whereas hydroxyl concentrations are strongly underestimated compared to observations, which can at least partly explain the discrepancy. Furthermore, the model substantially overestimates the isoprene oxidation products methlyl vinyl ketone (MVK) and methacrolein (MACR) partly due to a simulated nocturnal increase due to isoprene oxidation. This increase is most prominent in the residual layer whereas in the nocturnal inversion layer we simulate a decrease in MVK and MACR mixing ratios, assuming efficient removal of MVK and MACR. Entrainment of residual layer air masses, which are enhanced in MVK and MACR and other isoprene oxidation products, into the growing boundary layer poses an additional sink for OH which is thus not available for isoprene oxidation. Based on these findings, we suggest pursuing measurements of the tropical residual layer chemistry with a focus on the nocturnal depletion of isoprene and its oxidation products.
Global reactive nitrogen deposition from lightning NOx
Shepon, A. ; Gildor, H. ; Labrador, L.J. ; Butler, T. ; Ganzeveld, L.N. ; Lawrence, M.G. - \ 2007
Journal of Geophysical Research: Atmospheres 112 (2007). - ISSN 2169-897X - 14 p.
general-circulation model - dry deposition - atmospheric chemistry - organic nitrogen - climate-change - trace gases - distributions - parameterization - cycle - emissions
We present results of the deposition of nitrogen compounds formed from lightning (LNO x ) using the global chemical transport Model of Atmospheric Transport and Chemistry¿Max Planck Institute for Chemistry version. The model indicates an approximately equal deposition of LNO x in both terrestrial and oceanic ecosystems, primarily in the tropics and midlatitudes open ocean, despite much higher intensities of lightning flashes above landmasses. The highest values of deposition are due to wet convective deposition, with highest values concentrated in the tropical continents. Nonconvective wet deposition, associated with large-scale weather patterns, occurs over large areas of the ocean amid lower values per square meter, manifesting the long-range transport of NO y , including long-lived species such as HNO3 at high altitudes and PAN. Dry deposition is concentrated primarily above landmasses, yet oceanic deposition over wide areas is still observed. Combined together, the total LNO x deposition exhibits maximal influx values over land, whereas oceanic deposition over wider areas renders the integrated deposition over both ecosystems almost identical. Peaks of terrestrial deposition values (located in Africa, South America, and Asia) show seasonal variability by meridionally penetrating the northern or southern midlatitude following the corresponding summer hemisphere, in accordance with the migration of LNO x production sites. On land, wet and dry deposition rates are more or less equal with a small bias toward wet deposition, whereas above the ocean, wet deposition is markedly higher because of a small water uptake efficiency and relatively small surface roughness. Further work of modeling additional species and obtaining more information on different compounds is required
The role of ozone atmosphere-snow gas exchange on polar, boundaru-layer tropospheric ozone - a review sensitivity analysis
Helmig, D. ; Ganzeveld, L.N. ; Butler, T. ; Oltmans, S. - \ 2007
Atmospheric Chemistry and Physics 7 (2007). - ISSN 1680-7316 - p. 15 - 30.
general-circulation model - dry deposition parameterization - chemical-transport model - sunrise experiment 1992 - spruce-fir forest - art. no. 4683 - surface ozone - south-pole - photochemical production - antarctic snow
Recent research on snowpack processes and atmosphere-snow gas exchange has demonstrated that chemical and physical interactions between the snowpack and the overlaying atmosphere have a substantial impact on the composition of the lower troposphere. These observations also imply that ozone deposition to the snowpack possibly depends on parameters including the quantity and composition of deposited trace gases, solar irradiance, snow temperature and the substrate below the snowpack. Current literature spans a remarkably wide range of ozone deposition velocities (vdO3); several studies even reported positive ozone fluxes out of the snow. Overall, published values range from ~¿3
The effect of harmonized emissions on aerosol properties in global models - an AeroCom experiment
Textor, C. ; Schulz, M. ; Krol, M.C. - \ 2007
Atmospheric Chemistry and Physics 7 (2007)17. - ISSN 1680-7316 - p. 4489 - 4501.
general-circulation model - ground measurements - optical-properties - sulfate aerosols - transport model - wet deposition - mineral dust - simulation - climate - size
The effects of unified aerosol sources on global aerosol fields simulated by different models are examined in this paper. We compare results from two AeroCom experiments, one with different (ExpA) and one with unified emissions, injection heights, and particle sizes at the source (ExpB). Surprisingly, harmonization of aerosol sources has only a small impact on the simulated inter-model diversity of the global aerosol burden, and consequently global optical properties, as the results are largely controlled by model-specific transport, removal, chemistry (leading to the formation of secondary aerosols) and parameterizations of aerosol microphysics (e.g., the split between deposition pathways) and to a lesser extent by the spatial and temporal distributions of the (precursor) emissions. The burdens of black carbon and especially sea salt become more coherent in ExpB only, because the large ExpA diversities for these two species were caused by a few outliers. The experiment also showed that despite prescribing emission fluxes and size distributions, ambiguities in the implementation in individual models can lead to substantial differences. These results indicate the need for a better understanding of aerosol life cycles at process level (including spatial dispersal and interaction with meteorological parameters) in order to obtain more reliable results from global aerosol simulations. This is particularly important as such model results are used to assess the consequences of specific air pollution abatement strategies
Technical Note: An implementation of the dry removal processesDRY DEPosition and SEDImentation in the Modular EarthSubmodel System (MESSy)
Kerkweg, A. ; Buchholz, J. ; Ganzeveld, L.N. ; Pozzer, A. ; Tost, H. ; Jöckel, P. - \ 2006
Atmospheric Chemistry and Physics 6 (2006)12. - ISSN 1680-7316 - p. 4617 - 4632.
general-circulation model - parameterization - chemistry
We present the submodels DRYDEP and SEDI for the Modular Earth Submodel System (MESSy). Dry deposition of gases and aerosols is calculated within DRYDEP, whereas SEDI deals with aerosol particle sedimentation. Dry deposition velocities depend on the near-surface turbulence and the physical and chemical properties of the surface cover (e.g. the roughness length, soil pH or leaf stomatal exchange). The dry deposition algorithm used in DRYDEP is based on the big leaf approach and is described in detail within this Technical Note. The sedimentation submodel SEDI contains two sedimentation schemes: a simple upwind zeroth order scheme and a first order approach