Emission inventory of the main natural methane sources in ...€¦ · fires, and the Non Methanic...

Emission inventory of the main natural methane sources in a Mediterranean area

V. Simon, L. Dumergues & L.Torres Laboratoire Chimie Energie et Environnement, Ecole Nationale Supérieure des Ingénieurs en Arts Chimiques et Technologiques de Toulouse, France

Abstract

A natural emission inventory of methane (CH4), one of the main greenhouse gases, was carried out in the frame of the ESCOMPTE project. The algorithms used for calculation are mainly based on the CORINAIR [1] and the IPCC methodology [2]. Methane emission is estimated for the year 1999 at 10.3Tg in the ESCOMPTE area which represents one of the main natural sources of emissions with dimethylsulfide (DMS) from the sea, carbon dioxide (CO2) from forest fires, and the Non Methanic Volatile Organic Compounds from vegetation. Natural methane emissions, around 43% of the total CH4 emission, are dominated mainly by the animals and wetlands contribution. They are located in the west of the area. Soils constitute a sink (about 1Tg) that does not compensate the emissions. Despite the important amount of data collected, additional information would be needed to determine a more detailed evolution of emissions throughout the year.

1 Introduction

The present work, carried out in the frame of the European ESCOMPTE (FiEld experimentS to COnstrain Models of atmospheric Pollution and Transport of Emissions) project, is a part of the emission inventory of biogenic sources in a Mediterranean area. The methane, an atmospheric greenhouse gas, is a heat absorbent 21 times more powerful than a molecule of carbon dioxide. Its relative contribution to the additive greenhouse effect is around 15-20% according to Dautray [3].

Air Pollution XII, C. A. Brebbia (Editor)© 2004 WIT Press, www.witpress.com, ISBN 1-85312-722-1

During ages, air temperatures have shown an evolution pattern similar to those of atmospheric methane concentrations [4]. For the 200 last year, the atmospheric methane concentration has doubled [5] to reach nowadays a concentration range from around 1.7 to 1.8 ppmV [6]. The increase rate is estimated around 0.5 – 0.7% yearly. Methane can be removed from the troposphere by exchanges with the stratosphere or by soil deposition. The main elimination process of atmospheric methane, is the reaction with the hydroxyl radical OHh. As many NMVOC (including ozone destructive substances) are typically removed from the troposphere by reaction with OHh, high methane concentration, by interacting with OHh, can reduce the atmosphere capacity to eliminate greenhouse gases. About 30% of the increase of CH4 concentration is due to the limited capability of atmosphere to absorb it. The methane atmospheric life is estimated to be around 10 years. This paper presents the methodology, used to produce an inventory from natural methane emissions through the atmosphere, and the results obtained for the ESCOMPTE area during 1999.

2 Escompte project

The ESCOMPTE project takes place in one of the most air polluted place in France: the Mediterranean area. The main goal of ESCOMPTE project is to co-ordinate emission inventory (3D data base of primary pollutants), meso-scale model of atmospheric reactivity and transport, coupled with intensive experimental measurement [7]. Concerning emission inventory, the ESCOMPTE area is a gridded square (140km x 140km) centred on the Marignane airport and with a 1km² resolution (Figure 1).

3 Sources

Methane emissions come from both anthropogenic (gas and oil production, waste decomposition, fossil and fuel extraction) and biogenic sources (anaerobic fermentation in wetlands, rice cultivation, digestive processes (enteric fermentation) from ruminants, deforestation like biomass forest fire and decomposition of organic matter. Most of these emissions are originated by anaerobic bacteria. It is estimated that around 37 millions tonnes of methane are emitted yearly in the world [8]. In the present inventory, are taken in consideration the main natural sources: water (wetlands), animals, and forest fire for emission, and soils for deposition. Other natural sources like termites or gas seeps have not been inventoried because of, in one hand, their minor impact guessed in the area, and in the other hand, the lack of knowledge of quantification and localisation.

464 Air Pollution XII


Figure 1: Main characteristics of the ESCOMPTE area considering CH4 sources (Circles give examples of low, medium and high CH4 emitters).

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Cattles (14441), Sheeps (13523)Horses (9386), Deers (130)

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Goats (369499), Wild boars (37256)Pigs (13554), Sows (1065), Roebuck (#130)

ESCOMPTE AREA (19600km²)Sea: 7770km² (= 40%)Low vegetation: 5875km² (30%), Forest: 3976 km² (20%)Wetlands: 400km² (2%)Population: 2,738 million, Main City in the area: Marseille

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Cattles (14441), Sheeps (13523)Horses (9386), Deers (130)

Medium CH4 emitter (1 to 10 kg CH4.yr-1)

Goats (369499), Wild boars (37256)Pigs (13554), Sows (1065), Roebuck (#130)

ESCOMPTE AREA (19600km²)Sea: 7770km² (= 40%)Low vegetation: 5875km² (30%), Forest: 3976 km² (20%)Wetlands: 400km² (2%)Population: 2,738 million, Main City in the area: Marseille

Air Pollution XII 465


4 Methodology

In the following, the calculation procedures and the sources of activity data are described. We compiled a spatially explicit inventory of CH4 emissions from the ESCOMPTE area, based upon the both methodology, CORINAIR 1999 [1] and the IPCC guidebook (1997) [2], and on the 1999 statistical data from CRIGE.

4.1 Animals and human

Methane is released from ruminants as well as from manure management. Both sources are considered here. Due to intensive research efforts during the last decades, the quantification of CH4 release from enteric fermentation by the Intergovernmental Panel on Climate Change (IPCC) methodology is already detailed and well established [2], [9]. Two methods are used to calculate methane emission according to the contained pertinence of obtained information.

Method 1: algorithm applied according to the animal type [1]: EM = Σ Fi . ni. (1)

EM: annual methane weight emission from animals and human origin (g.yr-1), i: animal specie, ni: amount of animal (type (i)), Fi: animal specific emission (gCH4.animal-1.yr-1).

Method 2: algorithm applied according to both animal type and animal weight [1]:

EM = Σ Fi .ni. mi. (2) EM: annual methane weight emission from animals and human origin (g.yr-1), i: animal specie, ni: amount of animal (type i), Fi: animal specific emission (gCH4.animal-1.yr-1), mi: average weight of animal (type i). Because of the lack of data concerning the emission factor variation throughout the year specific to Mediterranean bovines, year coefficients have been used [1], [10] and [11].

4.2 Wetlands

Methanogenesis is restricted to completely anaerobic soil conditions as occur in rice paddies when the soils are flooded. These CH4 emissions are calculated by the IPCC (1997) [2] methodology. Many other types of wetlands exist: bog, fen, swamps, flood plain, marsh, swallow lake. Definition and references are given in [1]. The methane is the main product emitted from wetlands. Methane fluxes are calculated according to the CORINAIR methodology (1999) [1].



∑→

=n1

it.F.AEM ii . (3)

EM: daily weight emission (gCH4.d-1), i: wetland type, A: area of each wetland type (m²), Fi: seasonal average flux (gCH4.m-2.d-1), t: length of the emission period taken in consideration. This period corresponds to the wetland « flooded ». Average data used came from [1] and personal communication [12], [13].

4.3 Forest fire

The methane emission from forest fire is determined in two steps: first, carbon emission is estimated according to the nature of the burnt biomass, and second, methane emission is deduced from an emission factor applied to the carbon emissions. [14]. The carbon weight emitted during a forest fire M (C) (kg), is calculated from a methodology developed by Seiler and Crutzen (1980) [15]:

M (C) = 0,45 . A . B . α . γ. (4) 0,45: average fraction of carbon in fuel wood, A: area burnt (m2), B: average total biomass of fuel material per unit area (kg m-2), α: fraction of the average aboveground biomass relative to the total average biomass B (dimensionless), γ: burning efficiency (fraction burnt) of the aboveground biomass (dimensionless). In the Mediterranean ESCOMPTE area, we distinguished 3 vegetation classes with the following factors (table 1). The nature of the burnt area is known using GIS (Arcview 8.2) by superposition between fire localisation (PROMETHEE data [16]) and vegetal land cover (CRIGE 1999). The methane emission is then determined by multiplication between the carbon weight emitted (M (C)) by an emission factor [14]:

Table 1: Coefficient relative to Mediterranean ecosystem [1] and methane emission factor during a vegetation burning [14].

B (kg.m-2) α

γ

Derived emission factor (g.m-2), assuming default B, α, γ values (Andreae 1991)

Mediterranean forest 15 0.75 0.25 18,98 Grassland 2 0.36 0.5 2,43 Scrubland 7.5 0.64 0.5 16,20



4.4 Soils consumption

All other agricultural soils (except rice land) take up CH4 through oxidation by methanotrophic bacteria except for poorly drained sites. Fertilised and cultivated soils consume CH4 at rates of 40% or less of those in undisturbed forest soils as a result of complex short-term and long-term adverse effects of soil disturbance, shift in microbial species diversity and ammonium inhibition of methanotrophic activity [17]. The emission factor of -0.5 (±0.5) kg.ha-1.yr-1 relies on a set of 66 long-term measurements in Europe analysed by [18] and agrees well with the log–mean oxidation rate of -0.65 kg.ha-1.yr-1 CH4 of agricultural soils in Northern Europe given by [19]. To estimate the methane flux (kg.yr-1) deposited by the Mediterranean forest soils and grassland, the Simpson’s (1999) approach was used.

FCH4 = - Σ Ai . Fi. (5) Ai: area of forest or grassland (ha), Fi: seasonal average flux (kg CH4. ha-1.yr-1) (Table 2).

Table 2: Methane soil consumption (Simpson [20]).

Fi Forest

Grassland Grazing, meadows

(-) 0.14 (-) 0.07 (-) 0.07

.

4.5 Other emitted pollutants

The main other pollutants emitted by animals (NH3, NO, N2O), and wetlands (sulfur compounds, NMHC and NO) are calculated following the IPCC methodology (1997).

5 Data base

The inventory conception requires the use of appropriate algorithms and the knowledge of specific data such as the geographic coverage, emission factors, and the different local compositions. The main databases used are from different order: geographic (CRIGE land cover database as the map support, PROMETHEE map for forest fire, RGA map for farming), inventory (INSEE for human, ONC for wild animals and RGA for livestock data, AFIRAC for pet), and statistic (emission rates, wetland and fire composition…etc),



6 Results

Methane natural emission for 1999 is estimated around 10.3 Tg in the ESCOMPTE area what is about 43% of the global methane emission (anthropogenic sources: 12.7 Tg and transport: 0.8 Tg). The amount emitted represents the fourth natural emission source after DMS (sea), CO2 (forest fire), and Non Methanic Volatile Organic Compounds (vegetation). Methane soils deposition is about 1Tg. The main results of CH4 emission, geographically and quantitatively are shown in the figure 2 and 3 respectively.

Figure 2: Methane emissions and sinks (kg.km-2) from natural sources – 1999.

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CH4 Emission in the ESCOMPTE area (1999)ktonnes

Animals Wetlands Forest fires Soils

Figure 3: Detail of contribution of the natural sources and sinks.

NO1%

NH330%

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CH462%

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Total : 8,2 tonnes

Animal emission - year 1999

Figure 4: Proportion of the annual animal emission.

6.1 Animals

Even if normally, the Mediterranean area is not an intensive farming zone, the CH4 animal emission ranks first like in most methane inventories with a total of 5,1 kt for 1999. The methane represents more than 60% of all animal emissions (figure 4).

6.2 Wetlands

The West of the ESCOMPTE zone is particularly « rich » in wetland because it is flooded by the Rhone delta and it is a rice cultivation area. As consequence,



wetlands constitute the second natural source of methane emission with a total of 4.7 kt for 1999 and that represents about ¾ of the wetland emission (figure 5).

76%

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CH4

Sulfur compounds

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Proportion of the w etland emission - ESCOMPTE area - 1999

Total = 6,1ktonnes

Figure 5: Proportion of the annual wetland emission.

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Figure 6: Evolution of methane emission from forest fires – 1999 – ESCOMPTE area.

6.3 Forest fires

Around 34.9 km² of burnt vegetation have been taken in account. Methane emission from forest fire is highly dependant of the period of the year. In 1999, for example, almost all forest fires took place in July (figure 6).



With a total of 0.5 kt in 1999, the methane emissions represent a minor part of the natural emission of CH4. These emissions represent less than 0,4% of the total emission from forest fire, dominated by CO2 (93%) and CO (6%)

6.4 Soil deposition

Soil deposition represents around 10% of the methane natural emission (animals, wetlands and forest fire) with almost 1kt yearly. The East of the ESCOMPTE zone, a particularly wooded area, constitutes the main “sink”.

7 Uncertainties

Not all sources of uncertainty can be quantified. Uncertainty due to lack of adequate knowledge of processes and dependencies between emissions and their natural and human controls inherently limits the adequacy and accuracy of any model approach. An uncertainty of about ±50% is consistent with the methodology recommendation (e.g.: 30% for animal emission factor and 10% for animal inventory [9]), and the other inventories estimations [23], [25].

8 Methane inventories

Some proportions of methane emitted, from different inventories, table 3 are consistent with the proportions found for ESCOMPTE. Such emissions are highly dependant of the geographic location. In boreal region, it is frequent that emission be dominated by wetland emissions. In Europe, emissions are generally shared between anthropogenic and animal emission. That is the case for the ESCOMPTE area which has also the characteristic to own many wetlands and to be subject every year to random forest fire that can be important.

Table 3: Proportion (%) of methane emitted from other inventories (Soil deposition not taken in consideration).

Inventory Anthropogenic part

Animal Wetlands Forest fire

year ref

ESCOMPTE 56,6 21,5 19,8 2,1 1999 [21] Europe (15) ≈ 50 48,1 1,1 0,6 2000 [22]

World (NASA)

20,2 13,5 31,7 16,3 1991 [23]

Belgium ≈ 40 60 1996 [24] Australia 33,6 48 3 4,7 1997 [25]

9 Conclusions

The methane emission from biogenic sources has been determined according to several algorithmic approaches [1], [2], [9], [10], [14], [15] and [20]. The main



natural emissions in the ESCOMPTE area are from animals (5,1 kt), wetlands (4.7 kt). They are completed by the forest fire source (0,5 kt). Such emissions are highly dependant of the geographic location. In European countries for example, it is typical that soil deposition compensates wetland emission [20]. This is not the case here as the West of the ESCOMPTE area is particularly rich in wetland and as the soil deposition is around 1 kt. This methane estimation, part of the total ESCOMPTE inventory that regroup both anthropogenic sources and other pollutants, show that natural emission represent around 44% of the CH4 emissions behind the anthropogenic fixed sources (53%) and far ahead transports (3%). Although the amount of data collected, it remains difficult to estimate precisely the CH4 emission variation all along the year due to the lack of data.

Acknowledgements

We acknowledge the financial support from the ADEME (Agence de l’Environnement et de la Maîtrise de l’Energie-France) and the technical collaboration from the LPCA (Strasbourg).

References

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[2] IPCC, IPCC Guidelines for National Greenhouse Gas Inventories. Workbook, Intergovernmental Panel on Climate Change, Paris, 1997.

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[4] Raynaud, D., Barnola, J-M., Chappellaz, J., Blunier., T. Indermühle A. & Stauffer B., The ice record of greenhouse gases: a view in the context of future changes, Quaternary Science Reviews, 19, (1-5), pp. 9-17, 2000.

[5] http://www.univ-lemans.fr/~trouve/climat/anthrop.html [6] Blieffert C., Perraud R., Chimie de l'environnement, De Boeck Université,

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Atmospheric Inventory Guidebook, second ed., CD-ROM. EEA, Copenhagen, 2000.

[10] Crutzen, P. J., et al., Methane production by domestic animals, wild ruminant, other herbivorous fauna and humans., Tellus Ser.B, 38, pp. 271-284, 1986.

[11] Vermorel, M., INRA Prod. Anim., 10, pp. 153-161, 1997. [12] http://www.inra.fr/Internet/Produits/PA/an1997/num972/vermo

/mv972.htm Centre Français du riz – Arles - France



[13] Compagnie des Salins du Midi - France . [14] Andreae, M. O, Biomass burning: Its history, use and distribution and its

impact on environmental quality and global climate. Global Biomass Burning: Atmospheric, Climate, and Biospheric implications. Cambridge, Massachusetts, MIT Press, pp 3-21, 1991.

[15] Seiler, W. and P. J. and Crutzen, “Estimates of gross and net fluxes of carbon between the biosphere and the atmosphere form biomass burning.” Climatic Change, 2, pp 207-247, 1980.

[16] PROMETHEE Database, (www.promethee.com) [17] Hütsch, B., Methane oxidation in non-flooded soils as affected by crop

production - invited paper., European Journal of Agronomy, 14, pp. 237–260, 2001.

[18] Freibauer, A., Kaltschmitt, M. (Eds.), Emission rates and emission factors of greenhouse gas fluxes from arable and animal agriculture., European Summary Report of the EU Concerted Action Biogenic Emissions of Greenhouse Gases Caused by Arable and Animal Agriculture (FAIR3-CT96-1877), Project Report Task 1. University of Stuttgart, Institute of Energy Economics and the Rational Use of Energy, 2000.

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[24] http://www.environment.fgov.be/Root/tasks/atmosphere/atmopol/Cijfers/ChiffresF/atmopolCF.html . Belgian national inventory (CORINE)

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