Impacts of an Amazon Pollution Plume on the Microphysical Properties of Warm-Phase Clouds in the Wet Season

The ARM Climate Research Facility’s G-1 aircraft collected data to distinguish background versus in-plume properties of wet season urban and biomass plumes.

The Science

Scientists examined the impact of urban and biomass emissions on the microphysical properties of warm-phase clouds in the Amazon basin within and around the city of Manaus, Brazil, in which the wet season presents a relatively clean background atmosphere characterized by frequent rain showers.

The Impact

This study shows that the pollution produced by Manaus, Brazil, significantly affects warm-phase microphysical properties of the surrounding clouds by changing the initial droplet size distribution (DSD).


A field study team of Brazilian and U.S. scientists analyzed microphysical properties of warm-phase clouds in the Amazon during the wet season, with a specific emphasis on interactions with urban and biomass plumes emitted by the city of Manaus and the surrounding basin. A statistical approach was used to compare several clouds probed in different flights on different days. A Gulfstream 1 (G-1) aircraft was used, instrumented mainly with a condensational particle counter and fast cloud droplet probe to obtain aerosol number concentration and particle size and concentration, respectively. The G-1 was from the Department of Energy’s Atmospheric Radiation Measurement (ARM) Climate Research Facility. Sixteen flights were conducted between February and March of 2014 as part of the Green Ocean Amazon (GoAmazon2014/5) field experiment supported by the ARM Climate Research Facility.

The most discernable observable difference between a polluted and background atmosphere is the number concentration of aerosol particles per unit volume. Urban activities such as traffic emit large quantities of particles to the atmosphere that are then transported by atmospheric motion and can contribute to cloud formation, becoming effective droplet activators through growth and aging.

Results show that higher droplet number concentrations are more likely to be found under polluted conditions than in background air. Based on the statistical approach to compare data collected during the 16 G-1 flights, a polluted environment with a high particle count presents favorable conditions for condensation, implying higher bulk liquid water on DSDs. Despite the lower amount of water condensed in the background DSDs, larger droplets readily form due to the early start of the collision-coalescence process. Given that aerosols alter the properties of the entire warm-phase process, impacts on the initial formation of the cloud mixed layer process can be assumed. The mixed and frozen portions of the upper cloud layers will be addressed in future work.

The wet season scenario described is responsible for transporting hydrometeors beyond the freezing level, activating the cold processes. Those processes are known to be associated with thunderstorms and intense precipitation. Nevertheless, the main feature that determines warm-phase DSD shapes seems to be the aerosol conditions, with the vertical velocities playing a role in the modulation of the distributions.

Principal Investigator(s)

Micael Cecchini
Center for Weather Forecasting and Climate Research (CPTEC)

Jennifer Comstock
Atmospheric Science and Global Change Division, Pacific Northwest National Laboratory


Sao Paulo Research Foundation (FAPESP; project grant 2014/08615-7 and 2009/15235-8); U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research Atmospheric Radiation Measurement (ARM) Climate Research Facilityand Atmospheric System Research program; Central Office of the Large Scale Biosphere Atmosphere Experiment in Amazonia (LBA); Instituto Nacional de Pesquisas da Amazonia (INPA); and Instituto Nacional de Pesquisas Espaciais (INPE).


Cecchini, M. A., L. A. T. Machado, J. M. Comstock, F. Mei, J. Wang, J. Fan, J. M. Tomlinson, B. Schmid, R. Albrecht, S. T. Martin, and P. Artaxo. 2016. “Impacts of the Manaus Pollution Plume on the Microphysical Properties of Amazonian Warm-Phase Clouds in the Wet Season,” Atmospheric Chemistry and Physics 16, 7029-41. DOI: 10.5194/acp-16-7029-2016.