Growth of urban ultrafine aerosols and their impact on shallow clouds and precipitation in the Amazon rainforest

 

Authors

Rahul Zaveri — Pacific Northwest National Laboratory
Jian Wang — Washington University in St. Louis
Jiwen Fan — Pacific Northwest National Laboratory
Yuwei Zhang — Pacific Northwest National Laboratory
John E Shilling — Pacific Northwest National Laboratory
Alla ZelenyukImre — Pacific Northwest National Laboratory
Fan Mei — Pacific Northwest National Laboratory
Mikhail S. Pekour — Pacific Northwest National Laboratory
Jason Tomlinson — Pacific Northwest National Laboratory
John Hubbe — Pacific Northwest National Laboratory
Manishkumar Shrivastava — Pacific Northwest National Laboratory
Ed Fortner — Aerodyne Research, Inc.
Stephen R. Springston — Brookhaven National Laboratory
Karla Longo — National Institute for Space Research (INPE)
Courtney Schumacher — Texas A&M University
Saewung Kim — University of California, Irvine
Luiz Augusto Toledo Machado — INPE-CPTEC
Paulo Artaxo — University of Sao Paulo
Scot T. Martin — Harvard University

Category

Secondary organic aerosol

Description

As part of the Green Ocean Amazon (GoAmazon) field campaign in Brazil, the DOE G-1 aircraft was deployed to make semi-Lagrangian measurements of aerosols and trace gases over and downwind of Manaus, with the objective of investigating the interactions between urban and biogenic emissions. Here we focus on the rapid growth of anthropogenic ultrafine aerosols observed in the Manaus plume on March 13th, 2014. Observations indicate that the ultrafine particles rapidly grew from about 20 nm to 50 nm at a sustained average rate of 11 nm h-1 largely due to secondary organic aerosol (SOA) formation from oxidation of biogenic volatile organic compounds. Lagrangian box model analysis of the evolving number and volume size distributions indicate that SOA growth kinetics was dominated by condensation of semivolatile organic compounds (SVOCs). Although SVOCs are conventionally assumed to equilibrate with organic aerosol mass and thereby promote the growth of large particles, our analysis shows that dynamic partitioning of SVOCs, with hindered uptake by large semisolid particles, facilitates the growth of small particles. We further demonstrate, via cloud-resolving model simulations, that the grown ultrafine particles can enhance the vertical development of shallow warm clouds early in the cloud lifecycle, then augment the transition of shallow to deep convective clouds, with appreciable reductions in the effective cloud droplet sizes and rain rates. These findings have important implications for representing SOA formation and phase-dependent particle growth mechanisms in aerosol-climate models.