Extended Elemental Mixing State of Amazonian Aerosols During GoAmazon 2014/2015 IOP2

Description

The extent of aging of aerosol particles as they travel over time and distance is complex and not well understood. During GoAmazon2014/15 IOP2, aerosol samples were collected around the industrial city of Manaus in the Amazon basin during a dry season. Three aerosol sampling sites were investigated here: the pristine Amazon Tall Tower Observatory (ATTO), the Terrestrial Ecosystem Center (site ZF2), and the Atmospheric Radiation Measurement (ARM) site in Manacapuru (site T3). The ATTO site serves as a clean background for sites ZF2 and T3. Meteorological data puts site ZF2 downwind of ATTO whereas site T3 is directly downwind of Manaus, providing a way to evaluate anthropogenic effects on the mixing state of aerosols. The anthropogenic effects on composition changes specific to individual particles are characterized by calculating a quantitative mixing state index for nine samples collected around Manaus during the GoAmazon campaign. These samples were initially analyzed with scanning transmission x-ray microscopy (STXM) to obtain mass information for C, N, and O. The same particles were then analyzed by scanning transmission electron microscopy coupled with energy dispersive-rays spectroscopy (STEM/EDX) to obtain masses of the higher Z elements Na, Mg, P, S, Cl, K, Ca, Mn, Fe, Ni, and Zn. The two data sets were overlapped manually using pattern matching to combine the techniques on a per-particle basis. With this, previously established techniques to determine the mixing state parameter (χ) were applied. We found the mixing state at T3 was generally smaller than either ATTO or ZF2, potentially due to fresh emission of black carbon. Assuming a conservative 5% error, however, makes all mixing state indices indistinguishable. K-means clustering was also performed, allowing potential sources to be assigned to clusters of particles.