10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Evaluation and Comparison of Aerosol Properties at Two Background Sites in the Central Amazon Rainforest
MARCO AURÉLIO FRANCO, Luciana Rizzo, Paulo Artaxo, University of São Paulo
Abstract Number: 71 Working Group: Aerosol Physics
Abstract The Amazon rainforest is the largest tropical forest in the world and occupies approximately half of the Brazilian territory. Its huge ecosystem interacts directly with the atmosphere, making the forest a biogeochemical reactor with capacity of regulation of climatic processes on a continental scale. The Amazon is one of the few continental regions of the Earth where the atmosphere in the rainy season is considered in pristine conditions, allowing for detailed studies of natural processes that controls generation and influence of aerosols on climate. In particular two sites, ATTO and ZF2, are of great relevance in the study of background aerosols properties in the Central Amazon, both sites located upwind the pollution plume of the Manaus city. The ATTO and ZF2 sites are located 160 and 60 km from the city, respectively, both surrounded by undisturbed forests. Due to the proximity, it is possible that the ZF2 is occasionally affected by the Manaus plume.
In this study it was evaluated the distribution of natural aerosols at the ZF2 and ATTO sites based on their physico-chemical properties. The data used in this analyzes were taken simultaneously at the sites between 2014 and 2016 , including particle light scattering and absorption coefficients, number concentration, number size distribution and chemical composition with nephelometer, MultiAngle Absorption Photometry, Scanning Mobility Particle Sizer and Aerosol Chemical Speciation Monitor. The analysis showed that both in dry and rainy seasons the aerosol scattering coefficients at 525 nm has differences between the sites. In the dry season of 2014 there were two events, probably regional fires, one in August and another in September, in which the scattering coefficient reached values greater than 200 Mm-1 at the ZF2 site and 140 Mm-1 at the ATTO site, respectively. Analyzes of the single scattering albedo (SSA) in 637 nm using boxplots showed that the median value in August at the ATTO site was 0.81 and at the ZF2 site the median was 0.91.
In September, the median SSA in the ATTO site was 0.83, while at the ZF2 site the median SSA was 0.87, what indicate predominance of more light scattering particles in ZF2 site in comparison of those at the ATTO site. In the rainy season of 2014, other two aerosol events occurred in March and April, raised the scattering coefficient to approximately 60 Mm-1 at the ATTO site, while at the ZF2 site its values remained at approximately 40 Mm-1.Analyzes of SSA in these months showed that in the ATTO site the median was 0.93 for both March and April, while in the ZF2 site the median was 0.81, showing predominance of light absorbing particles at the ZF2 site. Monthly boxplots for SSA showed opposite behaviors at both sites. While in the ZF2 the monthly median of SSA increases between January and August and decreases between October and December, in the ATTO there are very clear oscillations, with values of medians higher in the rainy season and lower in the dry season, with predominance of more light scattering particles at this site. Those results indicate unexpected inhomogeneity in the optical properties of the aerosols between both sites, and can be caused by the presence of different types of particles in both sites, probably by pollutants from Manaus that reach ZF2 site.