Regional N₂O fluxes in Amazonia derived from aircraft vertical profiles

• Main Authors: P. Tans, J. B. Miller, M. T. S. D'Amelio, L. V. Gatti
• Format: Article
• Language: English
• Published: Copernicus Publications 2009-11-01
• Series: Atmospheric Chemistry and Physics
• Online Access: http://www.atmos-chem-phys.net/9/8785/2009/acp-9-8785-2009.pdf

Nitrous oxide (N₂O) is the third most important anthropogenic greenhouse gas. Globally, the main sources of N₂O are nitrification and denitrification in soils. About two thirds of the soil emissions occur in the tropics and approximately 20% originate in wet rainforest ecosystems, like the Amazon forest. The work presented here involves aircraft vertical profiles of N₂O from the surface to 4 km over two sites in the Eastern and Central Amazon: Tapajós National Forest (SAN) and Cuieiras Biologic Reserve (MAN), and the estimation of N₂O fluxes for regions upwind of these sites. To our knowledge, these regional scale N₂O measurements in Amazonia are unique and represent a new approach to looking regional scale emissions. The fluxes upwind of MAN exhibited little seasonality, and the annual mean was 2.1±1.0 mg N₂O m^−2 day^−1, higher than that for fluxes upwind of SAN, which averaged 1.5±1.6 mg N₂O m^−2 day^−1. The higher rainfall around the MAN site could explain the higher N₂O emissions, as a result of increased soil moisture accelerating microbial nitrification and denitrification processes. For fluxes from the coast to SAN seasonality is present for all years, with high fluxes in the months of March through May, and in November through December. The first peak of N₂O flux is strongly associated with the wet season. The second peak of high N₂O flux recorded at SAN occurs during the dry season and can not be easily explained. However, about half of the dry season profiles exhibit significant correlations with CO, indicating a larger than expected source of N₂O from biomass burning. The average CO:N₂O ratio for all profiles sampled during the dry season is 94±77 mol CO:mol N₂O and suggests a larger biomass burning contribution to the global N₂O budget than previously reported.