CCN activity of Amazonian aerosols during GoAmazon 2014/5

During the Green Ocean Amazon (GoAmazon) 2014/5 campaign, size-resolved cloud condensation nuclei (CCN) spectra were characterized at a research site (T3) 70-km downwind of the city of Manaus (pop. 2 million) from March 12, 2014 to March 3, 2015. Air masses arriving at the T3 site ranged from near natural conditions to strongly impacted by urban pollution and/or biomass burning. Particle hygroscopicity and chemical mixing state were derived from the size resolved CCN spectra, and the hygroscopicity of the organic component of the aerosol was then calculated from the particle hygroscopicity and composition concurrently measured by an Aerosol Mass Spectrometer (AMS) or an Aerosol Chemical Speciation Monitor (ACSM). On average, particle hygroscopicity increased with increasing particle diameter, mainly due to an increasing sulfate volume fraction. The diel variations of particle hygroscopicity, mixing state, and organic hygroscopicity were strongly influenced by a combination of emissions, photochemical oxidation, and the development of boundary layer. The diel variations are examined for different air masses during both wet and dry seasons. The impact of urban pollution and biomass burning on both organic and particle hygroscopicities will be presented. The organic hygroscopicity is investigated against its sources and the oxidation levels (e.g., O:C atomic ratio) for improved understanding of its variations and parameterizations in global models.