Carboxylic monoacids in the air of mayombe forest (Congo): Role of the forest as a source or sink
- 397 Downloads
In the tropical rain forests of the Congo during the dry season, from June to September 1987, carboxylic acid partial pressures (Pgas) in the air above the canopy, at ground level, and at the boundary layer, were estimated from water samples such as fog and rainwater. The concentrations of these acids were also measured in the sap of tree leaves. Tree leaves act as a sink or as a source if the acid Pgas is greater of lower than the acid concentrations in molecular form in sap. For each of these soluble gases, there is a value of Pgas where the exchange is nul. This is called the compensation point. Values of the compensation point for some tree leaves were evaluated according to Henry's law. Henry's law coefficients at ppm levels were redetermined for formic (HCOOH), acetic (CH3COOH), propionic (CH3CH2COOH), and isobutyric (CH3CH(CH3)COOH) acids.
By comparison of Pgas and compensation points, it is concluded that the forest was a potential source for these acids. The soil-or the litter-acts as a significant source of a carboxylic acid of C3 or C4 atoms in the aliphatic chain. This carboxylic acid, not yet fully characterized, could play an important role in the rain acidity in forested zones of the equatorial areas.
The direct emission of these carboxylic acids by vegetation was the main source in the boundary layer above the forest. The average emissions were 3.1×109, 7.8×109, and 8.4×109 molecules cm-2 s-1 for HCOOH, CH3COOH, and CH3CH2COOH, respectively. The savanna is an exogenous source of HCOOH and CH3CH2COOH during moderately rainy days for 30% of the time. The ozonolysis of isoprene seems to be a small source of HCOOH.
Key wordsEquatorial forest carboxylic acids emission compensation point
Unable to display preview. Download preview PDF.
- Andreae, M. O., Talbot, R. W., and Li, S. M., 1987, Atmospheric measurement of pyruvic acid, J. Geophys. Res. 92, 6635–6641.Google Scholar
- Andreae, M. O., Talbot, R. W., Andreae, T. W., and Harris, R. C., 1988, Formic and acetic over the central Amazon region, Brazil 1. Dry season, J. Geophys. Res. 93, 1616–1624.Google Scholar
- Chameides, W. L. and Davis, D. D., 1983, Aqueous-phase source of formic acid in clouds, Nature 304, 427–429.Google Scholar
- Chameides, W. L., 1984, The photochemistry of a remote marine stratiform cloud, J. Geophys. Res. 89, 427–429.Google Scholar
- Clairac, B., 1986, L'aérosol en forêt tropicale humide d'Afrique. Application aux échanges entre la forêt et son environnment, Thèse d'Etat-Université Paul Sabatier (Sciences Toulouse) no d'ordre 1266.Google Scholar
- Graedel, T. E. and Weschler, C. J., 1981, Chemistry within aqueous atmospheric aerosols and raindrops, Rev. Geophys. Space Res. 19, 505–539.Google Scholar
- Graedel, T. E., Hawkins, D. T., and Claxton, L. D., 1986, Atmospheric Chemical Compounds: Sources, Occurrence and Bioassay, Academic Press, Orlando, Fla.Google Scholar
- Jacob, D. J., Wang, R. F. T. and Flagan, R. C., 1984, Fogwater collector design and characterization, Environ. Sci. Technol. 18, 827–833.Google Scholar
- Jacob, D. J., 1986, The chemistry of OH in remote clouds and its role in the production of formic acid and peroxymonosulfate. J. Geophys. Res. 91, 9807–9826.Google Scholar
- Jacob, D. J. and Wofsy, S. C., 1988, Photochemistry of biogenic emissions over the Amazon forest, J. Geophys. Res. 93, 1477–1486.Google Scholar
- Jacob, D. J. and Wofsy, S. C., 1990, Budgets of reactive nitrogen, hydrocarbons, and ozone over the Amazon forest during the wet season, J. Geophys. Res. 95, 16737–16754.Google Scholar
- Keene, W. C., Galloway, J. N., and Holden, J. N., 1983, Measurement of weak organic acidity in precipitation from remote areas of the world, J. Geophys. Res. 88, 5122–5130.Google Scholar
- Keene, W. C. and Galloway, J. N., 1986, Considerations regarding sources for formic and acetic acids in the troposphere, J. Geophys. Res. 91, 14466–14474.Google Scholar
- Lacaux, J. P. and Warburton, J. A., 1980, The deposition of silver released from Soviet Oblako rockets in precipitation during the hail suppression experiment Grossversuch IV. Part I: Measurement of background and preliminary seeding test. J. Appl. Meteorol. 19, 771–778.Google Scholar
- Lelieveld, J., 1990, The role of clouds in tropospheric photochemistry, Thesis, Rijksuniversiteit Utrecht.Google Scholar
- Mackay, D., Shiu, W. Y., and Sutherland, R. P., 1979, Determination of air-water Henry's law constants for hydrophobic pollutants, Environ. Sci. Technol. 13, 333–337.Google Scholar
- Moortgat, G. K., Veyret, B., and Lesclaux, R., 1989a, Absorption spectrum and kinetics of the acetylperoxy radical, J. Phys. Chem. 93, 2362–2368.Google Scholar
- Moortgat, G. K., Veyret, B., and Lesclaux, R., 1989b, Kinetics of the reaction of HO2 with CH3C(O)O2 in the temperature range 253–368 K, Chem. Phys. Lett. 160, 443–447.Google Scholar
- Nicholas, H. J., 1973, Miscellaneous volatile plant products, in L. P.Miller (ed.), Phytochemistry, Vol. 2, Van Nostrand Reinhold, New York, pp. 381–399.Google Scholar
- Stryer, L., 1981, Biochemistry, W. H. Freeman, New York, pp. 449.Google Scholar
- Talbot, R. W., Andreae, M. O., Berresheim, H., Jacob, D. J., and Beecher, K. M., 1990, Sources and sinks of formic, acetic, and pyruvic acids over Central Amazonia: 2. Wet season, J. Geophys. Res. 95, 16 799–16 811.Google Scholar
- Zahn, B. C., Horie, O., and Moortgat, G. K., 1990, Ozonolysis of isoprene and butadiene under atmospheric conditions. Abstracts of the symposium ‘Chemistry of the Global Atmosphere’, September, Chamrousse, France.Google Scholar