Journal Article

Amazon boundary layer aerosol concentration sustained by vertical transport during rainfall

Pöhlker, Christopher, Petäjä, Tuukka, Comstock, Jennifer, Kuang, Chongai, Smith, James N., Pöhlker, Mira L., Toto, Tami, Moran-Zuloaga, Daniel, Souza, Rodrigo A. F., Barbosa, Henrique M. J., Wimmer, Daniela, Mei, Fan, Walter, David, Andreae, Meinrat O., Martin, Scot T., Schmid, Beat, Wang, Jian, Brito, Joel, Tomlinson, Jason M., Giangrande, Scott, Chi, Xuguang, Artaxo, Paulo, Carbone, Samara, Machado, Luiz A. T., Saturno, Jorge, Manninen, Hanna E., Kulmala, Markku, Krejci, Radovan, Ditas, Florian, Lavric, Jost, Springston, Stephen R.

2016

Overview

Rapid vertical transport of small aerosol particles from the free troposphere to the atmospheric boundary layer occurs during precipitation and maintains the population of aerosol particles over Amazonia. Aerosol particles over Amazonia The Amazon rainforest is one of the few continental regions where atmospheric aerosol processes can be studied under near-natural conditions, but the origin of small aerosol particles that grow into cloud condensation nuclei in the Amazon boundary layer remains poorly understood. This paper reports rapid vertical transport of small aerosol particles from the free troposphere into the boundary layer during precipitation events by strong convective downdrafts and weaker downward motions in the trailing stratiform region. This effect can help to maintain the population of aerosol particles in the pristine Amazon boundary layer, so may influence cloud properties and climate under natural conditions. The nucleation of atmospheric vapours is an important source of new aerosol particles that can subsequently grow to form cloud condensation nuclei in the atmosphere 1 . Most field studies of atmospheric aerosols over continents are influenced by atmospheric vapours of anthropogenic origin (for example, ref. 2 ) and, in consequence, aerosol processes in pristine, terrestrial environments remain poorly understood. The Amazon rainforest is one of the few continental regions where aerosol particles and their precursors can be studied under near-natural conditions 3 , 4 , 5 , but the origin of small aerosol particles that grow into cloud condensation nuclei in the Amazon boundary layer remains unclear 6 , 7 , 8 . Here we present aircraft- and ground-based measurements under clean conditions during the wet season in the central Amazon basin. We find that high concentrations of small aerosol particles (with diameters of less than 50 nanometres) in the lower free troposphere are transported from the free troposphere into the boundary layer during precipitation events by strong convective downdrafts and weaker downward motions in the trailing stratiform region. This rapid vertical transport can help to maintain the population of particles in the pristine Amazon boundary layer, and may therefore influence cloud properties and climate under natural conditions.

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: 704/106/35 / 704/106/47 / 704/172 / Aerosols / Aerosols - analysis / Aerosols - chemistry / Altitude / Anthropogenic factors / Atmospheric aerosols / Atmospheric and Oceanic Physics / Atmospheric boundary layer / Atoms & subatomic particles / Biomass / Boundary layers / Brazil / Condensation / Distribution / Environmental aspects / ENVIRONMENTAL SCIENCES / Fires / Global Changes / Humanities and Social Sciences / letter / multidisciplinary / Ocean, Atmosphere / Particle Size / Physics / Rain / Rainforests / Rainy season / Science / Sciences of the Universe / Terrestrial environments / Troposphere / Volatile Organic Compounds - analysis / Volatile Organic Compounds - chemistry