Seasonal Investigation of the Factors and Sources Contributing to Ultrafine Particles in the Eastern Amazon Rainforest

ADAM THOMAS, Deanna Myers, Hayley Glicker, Alex Guenther, James Smith, University of California, Irvine

     Abstract Number: 370
     Working Group: Remote and Regional Atmospheric Aerosol

Abstract
The Amazon basin serves as one of our planet’s largest aerosol reservoirs, but the factors and species driving new particle formation in the region are nevertheless not fully understood. Given what is known of the basin’s renowned biodiversity as well as the seasonality of its biogenic emissions, it is reasonable to suspect that the sources contributing to particle formation and growth may vary considerably across different subregions and times of the year. Herein we present observations of ultrafine particles (<100 nm in diameter) from studies conducted at the Tapajós National Forest located within the Eastern Amazon, a region with emission profiles and wet/dry seasonality patterns distinct from the more highly studied Central Amazon. We observe that during the transition between the wet and dry season the frequency of new particle growth events decreased, as did the concentrations of particles within these events. Boundary layer height tightly correlated with ultrafine particle concentrations in the wet season (May), but less so into the dry season (July), suggesting different factors are contributing to new particle growth in this period. The molecular composition of ultrafine particles collected in three distinct seasonal periods was analyzed with a high resolution Orbitrap mass spectrometer. With this data, we provide chemical evidence that isoprene organosulfate and monoterpene oxidation chemistries are likely key drivers of ultrafine particle growth in each period observed. In addition, biomass burning likely contributes significantly to ultrafine particle concentrations in drier months (September and December) and biological spore emissions may be an unaccounted secondary source of ultrafine particles in this region during the late wet season (June). Overall, our findings highlight the complexity of factors contributing to particle formation and growth in the Eastern Amazon and suggest that anthropogenic perturbations such as wildfires likely already have a profound influence on these processes.