Natural and Human Emissions in the Tropical Canopy
In addition to being hotbeds of biodiversity, tropical forests are important to Earth’s water, energy, and carbon cycles—but they are increasingly impacted by climate change and human activities. Atmospheric chemistry in the once-pristine Amazon Basin, for example, is rapidly changing with deforestation, biomass burning, and pollution related to development in the region.
Like other forests, tropical forests naturally generate and emit volatile organic compounds that can react with other elements to form aerosols, or fine particles suspended in the atmosphere. A multi-year observational campaign was recently deployed in the Amazon Basin to study interactions between tropical ecosystems, aerosols, clouds, and precipitation under clean conditions, as well as how such interactions are influenced by pollutant outflow from the tropical megacity of Manaus, Brazil. The observational campaign, which is jointly sponsored by DOE, NSF, and two Brazilian organizations, used ground-based and aircraft platforms to gather extensive environmental observations. A Fourier transform spectrometer deployed for the experiment will serve a double purpose as an important Southern Hemisphere validation point for measurements from NASA’s OCO-2 satellite.
A surprising early result from the campaign is that organic aerosols appear to partially shift between liquid and solid phases with the extent of the pollution, potentially affecting both cloud formation and atmospheric chemistry. Longer-term expected results include better models of fast-reacting atmospheric chemistry within the tropical forest canopy; deeper knowledge and improved modeling of interactions between biogenic emissions, human-generated pollutants, and meteorological factors; and a better understanding of how these interactions affect cloud and precipitation lifecycles.
The observational campaign in the Amazon Basin measures key environmental variables, including light and temperature, that drive biogenic emissions of volatile organic compounds from the canopy. (Source: NASA/JPL-Caltech)