Abstract ID: 237

Implications of observed surprisingly high atmospheric oxidizing capacity over tropical forest: the GABRIEL Campaign

In October 2005 the GABRIEL intensive field campaign, including ground-based and airborne measurements, was conducted over the Guyana’s to study the atmospheric oxidizing capacity and role of atmosphere-biosphere exchanges in this region. One key new component of this particular campaign compared to previous LBA atmospheric chemistry studies was the measurement of hydroxyl (OH) and hydroperoxy (HO2) radicals. OH is also called the atmospheric “detergent” since it determines through the oxidation of many reactive compounds, including methane and volatile organic compounds (VOC), the lifetime and, consequently, the role of these compounds in atmospheric chemistry and climate. Previously, it was thought that in unpolluted air over the Amazon rainforest, biogenic VOC consume OH and reduce the atmospheric oxidation capacity. However, the observations revealed unexpectedly high OH concentrations. Further analysis including model simulations as well as laboratory experiments have indicated that the oxidation of natural VOC, notably of isoprene, might efficiently recycle OH radicals in the unpolluted tropical atmosphere through reactions possibly involving organic peroxy radicals. Although further analysis is still needed to corroborate these results, it demonstrates that the tropical biosphere maintains a remarkable balance with its atmospheric environment. We will discuss the key findings of the GABRIEL campaign and their implications for assessments of the impact of tropical deforestation on atmospheric chemistry and climate. In addition, we will discuss the need for follow-up activities, e.g., observations of tropical residual layer chemistry, to optimally address remaining challenges in tropical atmospheric chemistry-climate interactions.

Session:  Biogeochemistry - Sources, sinks, and atmospheric chemistry of trace gases.

Presentation Type:  Oral