Particle production in the upper troposphere over the Amazon Basin

Particle production in the upper troposphere has been reported as an important source of aerosol particles and cloud condensation nuclei in pristine environment and tropical regions and exerts significant climate effects. In this work, we develop a new organic nucleation scheme to the WRF-Chem model with extended particle size bins from 1nm to 10μm. We improve on previous coarse-resolution global simulations that approximate the highly oxygenated multifunctional organic compounds (HOMs) in a thermodynamic state by implementing kinetic calculation of HOMs and using fine-grid regional simulations. Sensitivity studies are conducted over the Amazon Basin during the dry season in 2014 to characterize the HOMs-induced new particle formation and identify its key controlling factors in Amazon. The model simulations are evaluated using aircraft observations of profiles of aerosol particles during the 2014 ACRIDICON-CHUVA campaign. We show that the new particle formation occurs mostly at the upper troposphere and modestly in the planetary boundary layer, driven by low temperature and high concentration of biogenic precursors, respectively. Including the HOMs-induced biogenic new particle formation mechanism decreases the model prediction bias of the particle number concentration in the upper troposphere by over 50%, suggesting an important role of the HOMs-induced biogenic new particle formation in the dry season over the Amazon region.