Scientists Find Mostly Liquid Particulates over Amazon Rainforest
When it comes to particles in the atmosphere, state matters.
Recent observations reveal that aerosol particles in the Amazon are mostly liquid, in contrast to previous studies.
The properties and size distribution of aerosol particles influence Earth’s “energy balance” either directly, by altering or absorbing sunlight, or indirectly, by affecting cloud formation. Whether organic particulate matter exists in a liquid, semi-solid, or solid state can affect particle growth and reactivity and hence particle number, size, composition, optical properties, and ability to nucleate clouds.
Research conducted during the Department of Energy’s (DOE) GOAmazon field campaign provides a new twist to a recently proposed theory about atmospheric particulates and paints a clearer picture of how these particles behave. The research found that atmospheric particles tied to plant life can be either solid or liquid, depending on the environment in which they form. These findings expand on a previous study that posited such particles favor a solid state. The previous research, which found that atmospheric particles over forests are in a solid or semi-solid state, was conducted in a boreal (pine) forest in Finland. There, pine trees release alpha-pinene, an organic building block that reacts with other substances such as ozone to produce atmospheric organic particulate matter. The research team decided to test that theory in the Amazon rainforest, which has about 80 percent humidity, compared to the pine forest’s 30 percent. In the Amazon, the reaction products of the compound isoprene provide the basic building block for atmospheric organic particulate matter. The team found that 80 percent of the time, the atmospheric organic particles that formed in the Amazon were in a liquid state. Liquid particles absorb molecules from the gas phase and grow. Semi-solid particles, on the other hand, grow layer by layer and remain smaller, which affects the types of clouds that form and their propensity to rain. The results of the present study highlight a biome-dependent distribution of liquid and non-liquid particulate matter over forested regions. These differences arise both because of intrinsic differences related to emissions of volatile organic compounds and oxidation pathways, as well as extrinsic differences in climatology of relative humidity and temperature, among other possible factors. Climate models must be able to treat aerosol particles as either liquid or solid, depending on the region, to accurately model their climate impacts.
This project was funded by DOE’s Office of Science, Office of Biological and Environmental Research, Atmospheric Radiation Measurement and Atmospheric System Research programs; São Paulo (Brazil) Research Foundation (FAPESP); Amazonas State Research Foundation (FAPEAM); and Brazil Scientific Mobility Program (CsF/CAPES).
Bateman, A. P., Z. Gong, P. Liu, B. Sato, G. Cirino, Y. Zhang, P. Artaxo, A. K. Bertram, A. O. Manzi, L. V. Rizzo, R. A. F. Souza, R. A. Zaveri , and S. T. Martin. 2015. “Sub-Micrometre Particulate Matter is Primarily in Liquid Form over Amazon Rainforest,” Nature Geoscience 9, 34-37. DOI: 10.1038/ngeo2599.