Stable polycyclic aromatic carbon (SPAC) formation in wildfire chars and engineered biochars

Area of Science:

• Environmental Science
• Carbon Cycling
• Biogeochemistry

Background:

• Pyrogenic carbon (PyC), particularly stable polycyclic aromatic carbon (SPAC), is a long-term carbon sink.
• Accurate quantification of SPAC is vital for global carbon cycle models.
• Current SPAC characterization methods are often specialized and may not reflect real-world formation conditions.

Purpose of the Study:

• To investigate the relationship between SPAC formation and easily measurable physicochemical metrics.
• To develop predictive models for SPAC content based on mass loss and elemental ratios.
• To compare SPAC content in wildfire chars versus engineered biochars.

Main Methods:

• Utilized hydrogen pyrolysis (HyPy) to accurately measure SPAC content.
• Correlated SPAC content with mass loss and molar H:C and O:C ratios.
• Analyzed chars from both wildfires and engineered biochar production.

Main Results:

• SPAC formation showed a linear correlation with increased mass loss, indicating higher pyrolysis severity.
• Wildfire chars contained <30 wt% SPAC, suggesting a large labile fraction.
• Engineered biochars exhibited a range of SPAC content, up to approximately 75 wt%.

Conclusions:

• Physicochemical metrics (mass loss, elemental ratios) can reliably predict SPAC content.
• Developed predictive models can enhance accuracy in global carbon accounting.
• The study provides a more accessible method for characterizing SPAC in diverse char types.