Halogenated organic species over the tropical South American rainforest S. Gebhardt1, A. Colomb2, R. Hofmann1, J. Williams1, and J. Lelieveld1 1Max Planck Institute for Chemistry, Mainz, Germany 2Laboratoire Interuniversitaire des Systèmes Atmosphériques (LISA), Paris, France
Abstract. Airborne measurements of the halogenated trace gases methyl chloride, methyl
bromide and chloroform were conducted over the Atlantic Ocean and about
1000 km of pristine tropical rainforest in Suriname and French Guyana (3–6° N,
51–59° W) in October 2005. In the boundary layer (0–1.4 km), maritime air
masses, advected over the forest by southeasterly trade winds, were measured
at various distances from the coast. Since the organohalogens presented here
have relatively long atmospheric lifetimes (0.4–1.0 years) in comparison to
the advection times from the coast (1–2 days), emissions will accumulate in
air traversing the rainforest. The distributions of methyl chloride, methyl
bromide and chloroform were analyzed as a function of time the air spent
over land and the respective relationship used to determine net fluxes from
the rainforest for one week within the long dry season.
Net fluxes from the rainforest ecosystem have been calculated for methyl
chloride and chloroform as 9.5 (±3.8 2σ) and 0.35 (±0.15
2σ)μg m-2 h−1, respectively. No significant flux was
observed for methyl bromide within the limits of these measurements.
The global budget of methyl chloride contains large uncertainties, in
particular with regard to a possible source from tropical vegetation. Our
measurements are used in a large-scale approach to determine the net flux
from a tropical ecosystem to the planetary boundary layer. The obtained
global net flux of 1.5 (±0.6 2σ) Tg yr-1 for methyl
chloride is at the lower end of current estimates for tropical vegetation
sources, which helps to constrain the range of tropical sources and sinks
(0.82 to 8.2 Tg yr-1 from tropical plants, 0.03 to 2.5 Tg yr-1 from senescent/dead leaves and a sink of 0.1 to 1.6 Tg yr-1 by soil
uptake). Nevertheless, these results show that the contribution of the
rainforest ecosystem is the major source in the global budget of methyl
For chloroform, the extrapolated global net flux from tropical ecosystems is
56 (±23 2σ) Gg yr−1, which is of minor importance
compared to the total global sources and might be already contained in the
soil emission term.
Citation: Gebhardt, S., Colomb, A., Hofmann, R., Williams, J., and Lelieveld, J.: Halogenated organic species over the tropical South American rainforest, Atmos. Chem. Phys., 8, 3185-3197, doi:10.5194/acp-8-3185-2008, 2008.