Evidence for multi-decadal fuel buildup in a large California wildfire from smoke radiocarbon measurements

Over the past several decades, the annual burned area in California's Sierra Nevada mountains has increased considerably, with significant social, economic, and ecosystem impacts that provide motivation for understanding how the history of forest management influences the composition of fuels and emissions in wildfires. Here, we measured the carbon concentration and radiocarbon abundance (∆14C) of fire-emitted particulate matter from the KNP Complex Fire, which burned through several groves of giant sequoia trees in the southern Sierra Nevada mountains during California’s 2021 wildfire season. Over a 26-hour sampling period, we measured the concentration of fine airborne particulate matter (PM2.5) along with carbon monoxide (CO) and methane (CH4) dry air mole fractions using a ground-based mobile laboratory. Filter samples of PM2.5 were also collected and later analyzed for carbon concentration and ∆14C. Covariation of PM2.5, CO, and CH4 time series data confirmed that our PM2.5 samples..., PM2.5 concentrations were collected using a PurpleAir PA-II air quality sensor with laser particle counting (PurpleAir, Draper, UT, USA).
PM2.5 filter samples were analyzed for total carbon (TC) concentration and ∆14C at the W. M. Keck Carbon Cycle Accelerator Mass Spectrometry laboratory at the University of California, Irvine.
Carbon monoxide (CO) and methane (CH4) dry air mole fractions were measured using a wavelength-scanned cavity ring-down spectrometer (G2401, Picarro, Santa Clara, CA, USA)., ,