GOAMAZON-SRIPTRTOFMS

Observations and Modeling of the Green Ocean Amazon: SRI-PTR-ToFMS

1 January 2014 - 31 October 2014

Lead Scientist: Alex Guenther

Observatory: AMF , MAO

One of the major uncertainties in climate model simulations is the effects of aerosols on radiative forcing and a better understanding of the factors controlling aerosol distributions and life cycle is urgently needed. Aerosols contribute directly to the Earth’s radiation balance by scattering or absorbing light as a function of their physical properties and indirectly through particle-cloud interactions that lead to cloud formation and the modification of cloud properties. On a global scale, the dominant source of organic aerosol is biogenic volatile organic compounds (BVOC) emitted from terrestrial ecosystems. These organic aerosols are a major part of the total mass of all airborne particles and are currently not sufficiently represented in climate models. To incorporate quantitatively the effects of BVOCs and their oxidation products on biogenic organic aerosol (BOA) requires parameterization of their production in terrestrial ecosystems and their atmospheric transformations. This project reduced the gaps in our understanding of how these processes control BVOCs and BOAs, and their impact on climate. This was accomplished by wet and dry season measurements at the DOE ARM T3 site along with a comprehensive suite of complementary measurements. The specific goals were to (i) to measure and mechanistically understand the factors affecting aerosol distributions over a tropical rain forest, especially the effects of anthropogenic pollution as a perturbation to natural state, and (ii) to develop and implement an upscaling analysis from this new data set and knowledge of aerosol distributions to prognosticate possible climatic impacts of present-day urban pollution and possibly greater pollution in the future. The SRI-PTR-TOFMS measured a wide range of BVOC and oxidation products in support of the following specific objectives: 1) Understand and quantify the interactions of biogenic and anthropogenic emissions with respect to the production of secondary organic aerosol. Hypotheses to be tested are that (i) a shift takes place under anthropogenic conditions in the fate of organic peroxy radicals from HO2 to NO pathways (to be tested by gas-phase analysis by CIMS and SRI-PTR-TOFMS leading to altered rates of particle growth (to be tested by number-diameter distribution measurement of MAOS and AAF, (ii) a significant increase occurs under anthropogenic conditions in the total potential material that can ultimately condense after atmospheric aging to the particle phase (to be tested by the data set of the oxidation flow reactor as well as in chemical composition that can influence optical properties and CCN activity (to be tested by the data sets of MAOS and AAF, and (iii) these significant changes in the atmospheric particle population can be monitored regionally by satellite. 2) Understand and quantify the mechanisms of new particle production over the tropical rain forest, both for natural and anthropogenically influenced conditions. Hypotheses to be tested are that (i) new particle formation occurs above the boundary layer (to be tested by aircraft observations of number-diameter distributions), (ii) new particles are produced from the evaporation of the jet droplets from fungal spore emission (to be tested by nanoparticle analysis for potassium by the TDCIMS, and (iii) an absence of sufficient H2SO4 concentration in the gas phase explains the differences for Amazonia compared to other observational sites worldwide (to be tested by gas phase analysis for H2SO4 by CIMS; §3.1.5). These hypotheses will be separately evaluated for conditions when the research site T3 is under influence or not of the plume from Manaus (i.e., natural compared to anthropogenically influenced conditions).