Aerosol characteristics and particle production in the upper troposphere over the Amazon Basin

Abstract

Observations over the Amazon Basin showed high aerosol particle concentrations in the upper troposphere (UT) between 8 and 15 km altitude, with number densities (normalized to standard temperature and pressure) often exceeding those in the planetary boundary layer (PBL) by one or two orders of magnitude. The measurements were made during the German-Brazilian cooperative aircraft campaign ACRIDICON-CHUVA on the German High Altitude and Long Range Research Aircraft (HALO). The campaign took place over the Amazon Basin in September/October 2014, with the objective of studying tropical deep convective clouds over the Amazon rainforest and their interactions with atmospheric trace gases, aerosol particles, and atmospheric radiation. Aerosol enhancements were observed consistently on all flights during which the UT was probed, using several aerosol metrics, including condensation nuclei (CN), cloud condensation nuclei (CCN), and chemical species mass concentrations. The enhanced UT particles differed in their composition and size distribution from the aerosol in the BL, ruling out convective transport of combustion-derived particles from the BL as a source. The air in the immediate outflow of deep convective clouds was depleted in aerosol particles, whereas strongly enhanced number concentrations of small particles (<90 nm diameter) were found in UT regions that had experienced outflow from deep convection in the preceding 5-72 hours. We also found elevated concentrations of larger (>90 nm) particles in the UT, which consisted mostly of organic matter and nitrate and were very effective CCN.