Using the Amazon as a natural laboratory to understand anthropogenic enhancement of biogenic SOA

 

Authors

Manishkumar Shrivastava — Pacific Northwest National Laboratory
Meinrat Andreae — Max Planck Institute of Chemistry
Paulo Artaxo — University of Sao Paulo
Henrique de Melo Jorge Barbosa — University of Maryland, Baltimore County
Larry Berg — Pacific Northwest National Laboratory
Joel Brito —
Joseph Ching — Pacific Northwest National Laboratory
Dick C Easter — Pacific Northwest National Laboratory
Jiwen Fan — Pacific Northwest National Laboratory
Jerome D Fast — Pacific Northwest National Laboratory
Zhe Feng — Pacific Northwest National Laboratory
Jose D Fuentes — Pennsylvania State University
Allen Goldstein — University of California, Berkeley
Helber Gomes — National Institute for Space Research (INPE)
Dasa Gu — University of California Irvine
Alex B Guenther — University of California - Irvine
Shantanu Jathar — Colorado State University
Saewung Kim — University of California, Irvine
Ying Liu — Pacific Northwest National Laboratory
Scot T. Martin — Harvard University
V. Faye McNeill — Columbia University
Adan Sady Medeiros — Amazonas State University
Suzane Simoes deSa — Harvard University
John E Shilling — Pacific Northwest National Laboratory
Stephen R. Springston — Brookhaven National Laboratory
Rodrigo Augusto Souza — Universidade do Estado do Amazonas
Thornton Joel — University of Washington
Gabriel IsaacmanVanWertz — Virginia Polytechnic Institute and State University
Lindsay Yee — University of California Berkeley
Rahul Zaveri — Pacific Northwest National Laboratory
Alla ZelenyukImre — Pacific Northwest National Laboratory
Chun Zhao — Pacific Northwest National Laboratory

Category

Secondary organic aerosol

Description

Understanding how anthropogenic emissions have modified natural biogenic secondary organic aerosol (SOA) formation constitutes one of the largest uncertainties in our understanding of the radiative forcing of climate. Due to ubiquitous influence of anthropogenic emissions over most terrestrial locations in the Northern Hemisphere, it is difficult to establish baseline biogenic SOA formation i.e. biogenic SOA that would be formed in the absence of anthropogenic perturbations. The vast Amazon rainforest during its wet season is one of the few remaining places on Earth where atmospheric chemistry transitions between preindustrial-like and present-day polluted conditions and serves as a unique natural laboratory to study anthropogenic-biogenic interactions. We develop insights from several laboratory measurements to simulate SOA formation in the wet-season Amazon using a high-resolution regional model (at 2 km grid spacing) and develop mechanistic insights about the role of anthropogenic emissions in biogenic SOA formation. We perform model simulations using the community regional Weather Research and Forecasting Model coupled to chemistry (WRF-Chem) at cloud-, chemistry-, and emissions-resolving scales i.e. at 2 km grid spacing. Sensitivity simulations that turn the urban emissions on/off are performed to quantify the impacts of anthropogenic-biogenic interactions on SOA formation. We evaluate WRF-Chem simulations using aircraft-based field measurements of SOA during the Green Ocean Amazon (GoAmazon 2014/5) field campaign. Our results show that urban emissions increase concentrations of nitrogen-oxides (NOx), which cause increase in oxidant (ozone and OH radical) concentrations within the otherwise pristine Amazon. Increased oxidant concentrations catalyzed by NOx substantially increase reactions of forest organic carbon, emitted as volatile organic compounds (VOCs include isoprene, monoterpene and sesquiterpene compound classes), and thereby enhance biogenic SOA formation by 60-200% on average in plume-influence regions. Model simulated enhancements agree with those observed by the aircraft which rapidly and concomitantly measures organic aerosols in background and plume-influenced locations using the Aerosol Mass Spectrometer (AMS). Our results provide a clear picture of how anthropogenic emissions might have substantially enhanced natural biogenic SOA formation since preindustrial times on Earth.