Elemental Mixing State of Dry Season Aerosols in Central Amazonia During GoAmazon2014/15

The extent of aerosol aging as they travel over time and distance is complex and not well understood. To better understand this process, particle samples from three sites in Central Amazonia were collected as part of the Observations and Modeling of the Green Ocean Amazon (GoAmazon2014/5) field campaign during the dry season of 2014. The sites are as follows: site T3 (near Manacapuru, downwind from metropolitan Manaus), site ZF2 (also TT34, T0t, 80 km north of T3), and the Amazon Tall Tower Observatory (ATTO, also T0a, 170 km northwest of T3). With these samples, two techniques were used on the exact same region on each sample. First, Scanning Transmission X-ray Microscopy/Near Edge Fine Structure spectroscopy (STXM/NEXAFS) was used to quantify elemental masses of C, N, and O, followed by Scanning Electron Microscopy/Energy Dispersive X-ray spectroscopy (SEM/EDX) to quantify elemental masses for Na, Mg, P, S, Cl, K, Ca, Mn, Fe, Ni, and Zn. K-means cluster analysis was conducted on data set, which identified 12 particle clusters based on size, and elemental composition. Samples from the ATTO site had the least cluster diversity whereas the other two sampling sites showed an increase in the number of particle classes present. This data also allowed for individual particle diversity and mixing state parameters to be calculated. From this, mixing state parameters were universally high (χ > 0.8) and had a large uncertainty due to the varied particle types identified in clustering. Two diversity populations were also observed, one at 2.4 and another at 3.6 suggesting a distinction between fresh and aged aerosol. The high diversity population wasn't observed at site T3 due to the large number of fresh emissions from Manaus.