Biogenic Reactive Compounds in ORCHIDEE

1. Context

The terrestrial biosphere is the main source of volatile organic compounds (VOCs) into the atmosphere, contributing to more than 80% of global annual emissions of VOCs. About 1000 TgC/yr are therefore emitted by vegetation, mainly from leaves, into the low regions of the atmosphere. In comparison, anthropogenic emissions of VOCs, mostly related to fossil fuel and biomass burning, do not exceed 100 TgC/yr. Isoprene (alkene: C5H8, global emissions: 400-600 TgC/yr) and monoterpenes (C10H16, global emissions ~130 TgC/yr) emissions dominate biogenic VOC emissions but several campaigns brought to light significant biogenic emissions of methanol, acetone, acetaldehyde as well as formic and acetic acids. Nitrification and denitrification processes in soils are also a significant source of nitrogen oxides (NOx). Biogenic compounds such as BVOCs and NOx are usually very reactive molecules, with lifetime ranging from a few minutes to hours for most of them in the troposphere, and are several crucial for atmospheric chemistry processes (ozone cycle, secondary organic aerosol formation, etc.). The vegetation type (boreal forests, tropical forests, grasses…), climatic conditions (temperature, radiation, humidity) as well as human activities (land-use change, deforestation, reforestation) strongly determine the biogenic emission level of those compounds. Having parameterizations directly implemented in a vegetation model to calculate biogenic emissions of VOCs and NOx is therefore of strong interest, giving the possibility to quantify and study the evolution of those emissions in relation with changes in climate, vegetation distribution and ecosystem growth.

2. Implementation in ORCHIDEE (PhD Juliette Lathière, LSCE, 2005)

For more information, especially for a detailed description of parameterizations, see the following references:

10. Lathière (2005), Evolution des émissions de composés organiques et azotés par la biosphère continentale dans le modèle LMDz-INCA-ORCHIDEE, Thèse de doctorat, Université Paris VI.

10. Lathière, D.A. Hauglustaine, N. De Noblet-Ducoudré, G. Krinner et G.A. Folberth (2005), Past and future changes in biogenic volatile organic compound emissions simulated with a global dynamic vegetation model, Geophysical Research Letters, 32, doi: 10.1029/2005GL024164.

10. Lathière, D.A. Hauglustaine, A. Friend, N. De Noblet-Ducoudré, N. Viovy, et G. Folberth (2006), Impact of climate variability and land use changes on global biogenic volatile organic compound emissions, Atmospheric Chemistry and Physics, 6, 2129-2146.

2.1: General code description and location in ORCHIDEE

The core of the code for biogenic VOC and NOx emissions is located in ‘diffuco_inca’, a new subroutine created for this purpose in ORCHIDEE.

2.2: Related flags

Several flags have been created to activate the different options available for biogenic emissions. By default, all those flags are set to FALSE.

• DIFFUCO_OK_INCA: if ‘TRUE’, allow calculation of VOCs and NOx biogenic emissions, using the subroutine diffuco_inca.

• LEAFAGE_OK_INCA: if ‘TRUE’, the impact of leaf age on isoprene and methanol emissions is considered, otherwise, related impact functions set to 1.

• CANOPY_EXTINCTION: if ‘TRUE’, the extinction of radiation inside the canopy is considered by splitting the leaf area between sunlit and shaded leaves. Radiation received by sunlit leaves on one hand, and sunlit leaves on the other hand, is then estimated and used to calculate isoprene emissions (isoprene being the only BVOC considered to vary with radiation). Otherwise, all leaves are considered to receive the same radiation, and no partition between sunlit and shaded leaves is done.

• CANOPY_MULTILAYER: if ‘TRUE’, a vertical distribution of leaves and extinction of radiation through the canopy is taken into account to calculate isoprene emissions

• NOx_RAIN_PULSE: if ‘TRUE’, the increase in NOx emissions from soils, occurring when a dry surface receives a sufficient amount of precipitation, is considered (or so-called ‘pulse’ of emissions). Otherwise, the related pulse function is set to 1.

• NOx_BBG_FERTIL: if ‘TRUE’, the impact of biomass burning on NOx soil emission increase is taken into account, based on the ‘…’ map, read and interpolated at the beginning of the run.

• NOx_FERTILIZERS_USE: if ‘TRUE’, the impact of fertilizers use on NOx soil emission increase is considered, and the related map ‘…’ is read and interpolated at the beginning of the run. Otherwise, the related function ‘…’ is set to 1 and the map…

3. Merge in the trunk version (Nicolas Vuichard and Didier Solyga, LSCE, June 2012)

4. Perspective

• So far the different flags for biogenic emissions are described in orchidee.default, and should be also included in the ‘run.card’ file so that any user can set them depending on the run purposes.

• The code related to biogenic VOC and NOx emissions is currently mainly located in diffuco.f90. It could be suitable to gather all developments performed in ORCHIDEE, and dealing with biosphere-atmospheric chemistry interactions, in one new module. To be discussed.

• This work is the first step dealing with the interactions between the terrestrial biosphere and the atmospheric chemical composition. The next step, in progress, will be the coupling between ORCHIDEE and the chemistry-transport model LMDzINCA: see the page ‘…’.