Individual particle morphology, coatings, and impurities of black carbon aerosols in Antarctic ice and tropical rainfall

Abstract

Black carbon (BC) aerosols are a large source of climate warming, impact atmospheric chemistry, and are implicated in large‐scale changes in atmospheric circulation. Inventories of BC emissions suggest significant changes in the global BC aerosol distribution due to human activity. However, little is known regarding BC's atmospheric distribution or aged particle characteristics before the twentieth century. Here we investigate the prevalence and structural properties of BC particles in Antarctic ice cores from 1759, 1838, and 1930 Common Era (C.E.) using transmission electron microscopy and energy‐dispersive X‐ray spectroscopy. The study revealed an unexpected diversity in particle morphology, insoluble coatings, and association with metals. In addition to conventionally occurring BC aggregates, we observed single BC monomers, complex aggregates with internally, and externally mixed metal and mineral impurities, tar balls, and organonitrogen coatings. The results of the study show BC particles in the remote Antarctic atmosphere exhibit complexity that is unaccounted for in atmospheric models of BC.

Mass and Number Size Distributions of rBC in Snow and Firn Samples From Pine Island Glacier, West Antarctica

“…The NMD observed in the Antarctic samples in this work (<80 nm) is similar to the NMD observed in Greenland snow (~90 nm—Mori et al, 2019) and in East Antarctica (~70 nm—Kinase et al, 2019). This is also in agreement to previous qualitative observations that found abundant small rBC spherules with D BC ~ 30 nm in Antarctic snow and ice (Ellis et al, 2016). An NMD in the Aitken mode (less than 100 nm diameter) is commonly related to fresh, high temperature BC emissions, originated from efficient fuel burning (Bond et al, 2013), although we consider unlikely that this NMD is related to fossil‐fuel combustion or to fresh emissions.…”

“…Khan et al (2018) presented rBC volume distributions (rather than MMD) showing large rBC particles of 300–400 nm in a shallow snow pit in McMurdo Dry Valleys. Ellis et al (2016) observed a substantial fraction of small particles ( D BC < 90 nm) in East Antarctica snow and ice, although only qualitatively. Thus, further studies of Antarctic BC mass size distributions are necessary.…”

Author Response to RC2

“…Second, the physical lower bound on BC core size makes log-normal fitting reasonable in the Aitken range, even if it is below the SP2 detection limit. Single BC nanospheres (i.e., individual spherules) have been observed to be~20-30 nm in diameter by using TEM imaging techniques (Ellis et al, 2016;Wentzel et al, 2003). Although the de-C6…”

A Review of the Representation of Aerosol Mixing State in Atmospheric Models

“…Aerosol particles are assumed in most modelling studies to be spherical. However, particles can exhibit several morphologies [2][3][4][5][6][7][8][9][10], for example uncoated black carbon (BC) particles are known to have fractal-like structures, and dry sea salt or mineral dust particles can have crystalline structures. The distribution of chemical species within a single particle includes the distinction between a homogeneously-mixed particle and one where a hydrophobic core is coated by a layer or layers of more hydrophilic material (a core-shell configuration).…”

“…Uncoated BC generally has an aciniform (grape-like) fractal structure, consisting of chains of spherules around 30 nm in diameter (e.g., [9]). Each chain typically has tens of spherules per particle, resulting in a volume-equivalent diameter of around 120 nm (e.g., [2]), although single spheres have been observed as well [3]. As the BC particle takes up more hydrophilic species, these fractal chains collapse and become more sphere-like.…”