Natural oxidation of black carbon in soils: Changes in molecular form and surface charge along a climosequence

Submitted by Erin Rasmussen on

Publication Type:

Journal Article

Authors:

Cheng, Chih-Hsin; Johannes Lehmann; Engelhard, Mark H.

Source:

Geochimica et Cosmochimica Acta, Volume 72, p.1598 (2008)

URL:

http://www.css.cornell.edu/faculty/lehmann/publ/GeochimCosmochimActa%2072,%201598-1610,%202008%20Cheng.pdf

Abstract:

The aim of this work was to investigate changes in molecular form and surface charge of black carbon (BC) due to longtermnatural oxidation and to examine how climatic and soil factors affect BC oxidation. Black C was collected from 11 historicalcharcoal blast furnace sites with a geographic distribution from Quebec, Canada, to Georgia, USA, and compared toBC that was newly produced (new BC) using rebuilt historical kilns. The results showed that the historical BC samples weresubstantially oxidized after 130 years in soils as compared to new BC or BC incubated for one year. The major alterations bynatural oxidation of BC included: (1) changes in elemental composition with increases in oxygen (O) from 7.2% in new BC to24.8% in historical BC and decreases in C from 90.8% to 70.5%; (2) formation of oxygen-containing functional groups, particularlycarboxylic and phenolic functional groups, and (3) disappearance of surface positive charge and evolution of surfacenegative charge after 12 months of incubation. Although time of exposure significantly increased natural oxidation of BC, asignificant positive relationship between mean annual temperature (MAT) and BC oxidation (O/C ratio with r = 0.83;P < 0.01) explained that BC oxidation was increased by 87 mmole kg C