Oxidized organic molecules in the tropical free troposphere over Amazonia

TL;DR

This study provides the first direct chemical evidence of oxidized organic molecules in the tropical free troposphere over Amazonia, linking biogenic emissions to aerosol formation and particle growth.

Contribution

It offers novel in-situ molecular-level measurements of OOMs in the tropical FT, demonstrating their presence in both gas and particulate phases and their role in particle growth.

Findings

Presence of OOMs mainly with 4-5 carbon atoms in gas and particulate phases

OOMs linked to isoprene emissions from Amazonian rainforests

OOMs contribute to particle growth and new particle formation

Abstract

New particle formation (NPF) in the tropical free troposphere (FT) is a globally important source of cloud condensation nuclei, affecting cloud properties and climate. Oxidized organic molecules (OOMs) produced from biogenic volatile organic compounds are believed to contribute to aerosol formation in the tropical FT, but without direct chemical observations. We performed in-situ molecular-level OOMs measurements at the Bolivian station Chacaltaya at 5240 meters above sea level, on the western edge of Amazonia. For the first time, we demonstrate the presence of OOMs, mainly with 4-5 carbon atoms, simultaneously in both gas and particulate phases in tropical FT air from Amazonia. These observations, combined with air mass history analyses, indicate that the observed OOMs are linked to isoprene emitted from the rainforests hundreds of kilometers away. Based on particle-phase measurements, we find that these compounds can contribute to the growth of newly formed particles, and are potentially crucial for new particle formation in the tropical free troposphere on a continental scale. Our study will thus improve the understanding of aerosol formation process in the tropics.