Effects of Production Conditions and Environmental Aging on Solid-Phase and Dissolvable Pyrogenic Organic Matter Characteristics

Pyrogenic organic matter (PyOM, aka ‘black carbon’) generated via the incomplete combustion of biomass or fossil fuels is an important component in soil, atmospheric, sedimentary, and aquatic environments. In particular, the condensed aromatic compounds (ConAC) in PyOM are slow-cycling rendering them important to global carbon cycles and the sequestration of carbon in soils. Recently, the dissolvable component of PyOM (PyDOM) has received interest because of Py-DOM’s higher mobility and potential to be transferred through watersheds to rivers, estuaries, and the ocean. An understanding of the processes governing the cycling of this mobile PyDOM pool is thus important for PyOM carbon budgets and cycles. Despite the association of ConAC with PyOM, PyOM and PyDOM molecular composition and physical properties vary along a combustion continuum thought to be largely controlled by the temperature of production. The varying composition and physical properties have consequences for PyOM cycling, and a thorough understanding of PyOM and PyDOM chemical composition is thus critical. In this work, I discuss the results of multiple complementary analyses on PyOM (¹³C NMR spectroscopy, benzenepolycarboxylic acid biomarkers (BPCAs)) and PyDOM (¹H NMR, BPCAs, Fourier transform ion cyclotron resonance mass spectrometry) from oak and grass biochars produced at temperatures ranging from 250°C to 650°C as well as wildfire chars aged in place for <1 to 30 years. Our results demonstrate dynamic and heterogeneous PyOM and PyDOM pools controlled initially by production conditions then by environmental processes.