Impact of fuel moisture on chaparral emissions under flaming and smoldering conditions.

Fourier-transform infrared (FTIR) spectroscopy was used to quantify gas and particulate emissions from flaming and smoldering combustion of four dominant chaparral species (eucalyptus, coastal live oak, manzanita, and toyon) with different fuel moisture content from California, USA under controlled laboratory conditions. Results show that the higher fuel moisture content enhanced the production of incomplete combustion products, mostly CO and hydrocarbons. Smoldering combustion consistently produced 10-70 times higher particulate matter emission factors compared to flaming across all species, and this amplification ratio varied substantially depending on both fuel type and moisture content. Live eucalyptus exhibited the highest hydrocarbon emissions under smoldering conditions at 37.18 ± 0.65 g/kg. Cross-ecosystem comparisons revealed that chaparral emission profiles were broadly similar to western shrubland and grassland fuels, with notable differences primarily in nitrogen-containing species, highlighting the influence of combustion scale and mixing conditions on emission profiles. These findings provide important emission factor data on chaparral fuels, demonstrating the impact of fuel moisture, combustion mode, and fuel-specific properties on emissions, contributing to wildfire emission inventories and air quality modeling.