Drastic increase of isoprene fluxes in the future climate
Isoprene is the dominant biogenic hydrocarbon emitted into the atmosphere. It plays a key role in the atmospheric composition because of its influence on tropospheric ozone and its contribution to fine particle formation. Isoprene emissions respond strongly to changes in temperature and solar radiation, and are therefore strongly dependent on the warming climate. Here we use the MEGAN-MOHYCAN biogenic emission model to estimate high-resolution isoprene fluxes over Europe in the past 35 years and in different projection scenarios for the end-of-the-century climate.
In this study we used the MEGAN (Model of Emissions of Gases and Aerosols from Nature) emission model coupled with the MOHYCAN (Model of HYdrocarbon emissions by the CANopy) canopy model to calculate the isoprene fluxes emitted by vegetation in the recent past (1979–2014), and in the future (2070–2099) over Europe. As a result of the changing climate, modeled isoprene fluxes increased by 1.1% per year on average in Europe over 1979–2014, with the strongest trends found over eastern Europe and European Russia. For the 1979–2014 period the model used ECMWF meteorology, whereas for the comparison of current with projected emissions, the meteorology was simulated by the ALARO climate model. Depending on the climate scenario, isoprene fluxes were found to increase between 7% and 83% compared to the control run, and even stronger increases were found when considering the potential impact of CO2 fertilization. However, the inhibitory CO2 effect goes a long way towards canceling these increases.
Fig. 1. Relative differences in isoprene emissions between the control (CTRL) run and three climate scenarios considering the effect of (A) climate, (B) climate and fertilization, (C, D) climate and moderate or strong inhibition, (E) climate, fertilization, and strong inhibition, from Bauwens et al. Recent past (1979–2014) and future (2070–2099) isoprene fluxes over Europe simulated with the MEGAN–MOHYCAN model. Biogeosciences, 15, 3673-3690, 2018.
New assessment of the global carbon monoxide source
The hydroxyl radical (OH) is the main detergent in the atmosphere and its abundance controls the concentrations of carbon monoxide (CO), a primary pollutant gas. As a result, the carbon monoxide emissions determined through inverse modeling constrained by satellite data depend crucially upon the OH levels simulated with models. Here we have combined observation-based constraints on OH levels, satellite CO data from the IASI sensor, and the IMAGES atmospheric model to provide improved global estimates of CO emissions.
The sources of CO include direct emissions and photochemical production due to the oxidation of hydrocarbons. The dominant CO sink is its reaction with OH, CO has therefore a strong influence on the oxidative capacity of the atmosphere and on the removal of air pollutants. However, most chemistry transport models fall short of reproducing constraints on OH levels derived from methyl chloroform (MCF) observations. In this study, we prescribe different OH fields compatible with MCF data in the IMAGES global model to infer CO fluxes constrained by IASI CO data. Each OH field leads to a different set of optimized emissions. Differences of 40% in the top‐down global anthropogenic CO emissions are found when varying the OH levels, and even larger differences are found regionally, e.g. in China and the United States. Comparisons with independent surface and aircraft observations indicate that the inversion adopting the lowest average OH level in the Northern Hemisphere (18% lower than the best estimate based on MCF measurements) provides the best overall agreement with all tested observation datasets.
Fig.1. Mean annual updates (optimized/prior) of anthropogenic, biomass burning, and biogenic emissions in the optimization HN and LN, assuming either very high and very low OH in the Northern Hemisphere, from Müller et al. Top‐Down CO Emissions Based On IASI Observations and Hemispheric Constraints on OH Levels. Geophys. Res. Lett., https://doi.org/10.1002/2017GL076697, 2018.
Vapour pressure of Pure Liquid Organic Compounds
Estimation by EVAPORATION
The vapour pressure of an organic compound is one of the main factors controlling its equilibrium partitioning between the gas and condensed (aerosol) phases.
Here we present the method EVAPORATION of Compernolle et al. (1), which calculates the vapour pressure of an organic molecule from molecular structure. Functional groups within its scope are: aldehyde, ketone, ether, ester, alcohol, nitrate, acid, peroxide, hydroperoxide, peracid and peroxy acyl nitrate. Aromatics are not treated.
The empirical factor for functionalized diacids was introduced to accommodate data like those of Booth et al., (Atmos. Chem. Phys. 2010) . However, more recent data of Huisman et al., (Atmos. Chem. Phys. 2013) are in clear disagreement with such a factor. Therefore, the user can choose to turn it off.
Use empirical factor for functionalized diacids:
Compernolle, S., K. Ceulemans, and J.-F. Müller, EVAPORATION: a new vapor pressure estimation method for organic molecules including non-additivity and intramolecular interactions, Atmos. Chem. Phys., 19431-9450, 2011. [abstract][pdf]
Clarification about EVAPORATION. [pdf]
11 May 2014. Concerning descriptor 19. Number of functional groups in alpha of alcohol was not always counted correctly. Thanks to Dr. William Carter for spotting this bug.
11 May 2014. Concerning descriptor 12. 'Ester in ring' was sometimes not counted for this descriptor. Thanks to Dr. William Carter for spotting this bug.
MAGRITTE : Model of Atmospheric Composition at Global and Regional scales using Inversion Techniques for Trace Gas Emissions
- Chemical mechanism
The chemical mechanism is described in Müller, J.-F. et al.: Chemistry and deposition in the Model of Atmospheric composition at Global and Regional scales using Inversion Techniques for Trace Gas Emissions (MAGRITTE v1.0). Part A: Chemical mechanism, Geosci. Model Dev., 12, 2307-2356, https://doi.org/10.5194/gmd-2018-316, 2019.
Download the mecanism in KPP format
Last modified : 14 June 2019
Absorption cross sections used in MAGRITTEv1.1 (hydroperoxycarbonyls, nitroxycarbonyls, keto-enols)
- Dry deposition velocity calculation
The dry deposition velocities are calculated as described in
Müller, J.-F. et al.: Chemistry and deposition in the Model of Atmospheric composition at Global and Regional scales using Inversion Techniques for Trace Gas Emissions (MAGRITTE v1.0). Part B: Dry deposition, Geosci. Model Dev. Discuss., https://doi.org/10.5194/gmd-2018-317, in review, 2018.
The code is divided in two parts :
1) The package
Last modified : 20/12/2018
includes Fortran code and input files for calculation of stomatal resistances for H2O.
2) The package
Last modified : 20/12/2018
includes Fortran code and input files for the general calculation of dry deposition velocities.
Last modified : 20/12/2018
Resolution is 0.5x0.5 degree. The user should provide meteorological fields. Typical values of those variables are assumed in the code.
- Dry deposition velocity measurements
The dry deposition velocity measurements used in Müller et al. (GMDD) can be found below.
Last modified : 20/12/2018
- Müller, J.-F., T. Stavrakou, J. Peeters: Chemistry and deposition in the Model of Atmospheric composition at Global and Regional scales using Inversion Techniques for Trace Gas Emissions (MAGRITTE v1.0). Part A: Chemical mechanism, Geosci. Model Dev. Dissuss., https://doi.org/10.5194/gmd-2018-316, in review, 2018.
- Müller, J.-F., T. Stavrakou, Maite Bauwens, S. Compernolle, J. Peeters: Chemistry and deposition in the Model of Atmospheric composition at Global and Regional scales using Inversion Techniques for Trace Gas Emissions (MAGRITTE v1.0). Part B: Dry deposition, Geosci. Model Dev. Dissuss., https://doi.org/10.5194/gmd-2018-317, in review, 2018.
This scheme shows the general lines in the oxidation of a VOC. Extremely reactive alkyl radicals reacts almost instantly with O2 to produce peroxy radicals. Many reactions are possible for these peroxy radicals, yielding various stable compounds (hydroperoxides, nitrates, etc.) and/or very reactive alkoxy radicals. The product distribution therefore depends on the abundance of the different sorts of radicals (NO, HO2, other RO2 radicals) which can react with the RO2. The fate of alkoxy radicals is often difficult to predict from our current knowledge, due to the scarcity of direct measurements and the complexity of theoretical methods. Note that the "stable "compounds themselves (indicated by ellipses on this Figure) are oxidized by OH or by photolysis. It is easy to imagine the enormous number of different compounds that will be generated in the oxidation of complex hydrocarbons (e.g. monoterpenes).