AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Ultrafine Particle Composition and Growth in the Amazon Basin: Observations from Two Surface Sites
HAYLEY GLICKER, Sarah Batalha, Julio Tota, Alex Guenther, James Smith, University of California, Irvine
Abstract Number: 538 Working Group: Remote and Regional Atmospheric Aerosol
Abstract The Amazon Basin serves as an interesting location to study atmospheric particle formation since it often represents natural, pre-industrial conditions but can also experience periods of anthropogenic influence due to emissions from large agricultural and urban areas. Ultrafine (sub-100 nm diameter) particles are often observed in this region, although new particle formation events seldom occur near the ground despite being readily observed in other forested regions with similar emissions. This study presents measurements of the physical and chemical properties of ultrafine particles and related measurements such as meteorology, bulk particle composition, and key gas phase compounds obtained at two sites in the Amazon Basin: the T3 site from the GoAmazon2014/5 campaign, located 70 km southwest of Manaus, Brazil, and the Tapajós KM67 Mature Forest site located 600 km east of Manaus near Santarém, Brazil. We use these observations to infer possible factors that influence the formation and growth of ultrafine particles in this region. Measurements at the T3 site were performed during the wet season during GoAmazon2014/5, and featured a Thermal Desorption Chemical Ionization Mass Spectrometer (TDCIMS), which measured the concentrations of the most abundant compounds detected in ultrafine particles. Measurements at the KM67 site were performed during the transition between the wet and dry season in 2014 and periodically during a 12-month period in 2016-17, and included size distribution, volatile organic compounds measurements, and ultrafine particle collection followed by offline chemical analysis. The latter was performed using a Sequential Spot Sampler (Aerosol Devices, Inc.) located downstream of a size-selecting nanometer Differential Mobility Analyzer. Comparisons between particle size distributions at each location, supported by air mass back trajectories using the HYSPLIT model, provide insights into the potential influences on particle composition. Each region highlights specific differences in regional chemistry, as anthropogenic influence is seen to a larger extent at the T3 site and agricultural influence is observed more at KM67. The anthropogenic influence at the T3 site is manifested in enhanced levels of particulate sulfate in a background composition consisting largely of organics with significant amounts of nitrogen-containing organic compounds. During times of direct Manaus influence, higher number concentrations of particles over the diameter range of 10-200 nm were observed at T3, while times of background influence had lower number concentrations of these particles with minimal formation and growth events. In contrast, regional ultrafine particle formation and growth events were observed in particles at KM67 during evening hours, starting at particle diameters of ~20 nm with characteristic growth rates of 8 nm/hr. Offline chemical analysis of ultrafine particles collected at KM67 will be compared to TDCIMS measurements performed at T3, and differences relative to the suspected emission sources are discussed.