Brazil-USA collaborative research: modifications by anthropogenic pollution of the natural atmospheric chemistry and particle microphysics of the tropical rain forest during GoAmazon intensive operating periods

Abstract

Manaus, a city of nearly two rnillion people, represents an isolated urban area having a distinct urban pollution plume within the otherwise pristine Amazon Basin. The plume has high concentrations of oxides ofnitrogen and sulfur, carbon monoxide, particle concentrations, and soot, among other pollutants. Critically, the distinct plume in the setting ofthe surrounding tropical rain forest serves as a natural laboratory to allow direct comparisons between periods ofpollution influence to those ofpristine conditions. For this purpose, here we propose a Brazil-USA collaborative project during the two Intensive Operating Periods (wet season, 1 Feb - 31 Mar 2014; dry season, 15 Aug - 15 Oct 2014) ofGoAmazon. The project addresses key science questions regarding the modification of the natural atmospheric chemistry and particle microphysics of the forest by present and future anthropogenic pollution. The first objective ofthe proposed project is to understand and quantify the interactions ofbiogenic and anthropogenic ernissions with respect to the production of secondary organic aerosol (SOA). In clean conditions in the Amazon basin, SOA dominates the diameter distribution of the subrnicron particles. How and why is the diameter distribution shifted by pollution? The second objective follows from the first in that, although the diameter distribution is dominated by SOA, the actual source of new particle production remains uncertain (i.e., the number concentration). The second objective is to test the hypothesis that new particles under natural conditions are produced as a result of evaporation of primary particles emitted by fungaI spores as well as to investigate any shifts in this mechanism under pollution conditions, e.g., in consequence to the high concentrations of SO2 in the pollution plume, Combined, the number-diarneter distribution is the key connection to upscaling to the effects of aerosol particles on clouds and climate. Understanding this upscaling under c1ean and pollution conditions, including differences, is the third objective. The objectives will be addressed both by data sets obtained by to-the-purpose instrumentation deployed only during the IOPs as well as by baseline data sets ofthe ARM Mobile Facility in Amazonia (AMFA; specifically, MAOS) and the Intensive Airborne Research in Amazonia (lARA; AAF G1). The additional IOP instrurnentation will include a chernical ionization mass spectrometer for OH, H2SO4, and HO2 + RO2 concentrations, an oxidation flow reactor and temperature profiler in front of an aerosol mass spectrometer as well as a proton-transfer gas mass spectrometer to define mechanisms of SOA production and VOC chemistry, and a therrnal desorption chernical ionization mass spectrometer to study the chernical composition of freshly nucleated particles. The data sets will be put to use in several different upscaling analyses. The implications of the more accurate understanding ofthe number-diameter distribution, including anthropogenic influences, will be implemented in a rnicrophysical treatment of cloud-aerosol-precipitations interactions tailored to the Manaus region. Satellite tools will be used to expand the regional representativeness of the ground and aircraft measurements, including the associated implications ofthe Manaus plume on climate-relevant quantities. The proposed activities and associated three objectives, when taken together as a whole, respond to the Thematic Area of Atmospheric System Research (ASR) of DOE DE-FOA-0000919, FAPESP Chamada FAPESP 21/2013, and FAPEAM EDITAL N. 013/2013. With respect to Science Areas of those calls, the proposal will "improve understanding of the life cycle of aerosols ... including the interaction of pristine and polluted air masses" (80% of proposed effort) as well as "improve understanding of the interaction of aerosols and clouds over the Amazon basin, including aerosol impacts on precipitation ... as well as cloud impacts on aerosoI transport, chemistry, and removal" (20% ofproposed effort). (AU)