Chemical Speciation of Flaming and Smoldering Combustion from Sagebrush Ecosystem Vegetation

BIANCA MARTINEZ, Chiranjivi Bhattarai, Andrey Khlystov, Desert Research Institute

     Abstract Number: 540
     Working Group: Burning Questions of Aerosol Emissions, Chemistry, and Impacts from Wildland-Urban Interface (WUI) Fires

Abstract
Wild and prescribed fires are prevalent across the western and central United States, where shrubland and grassland vegetation cover over 60% of the landscape, including the wildland-urban interface (WUI). Biomass burning can occur under varying efficiencies, leading to different burning conditions. This study aims to determine the emission factors (EFs) from the burning of sagebrush ecosystem vegetation under flaming and smoldering, as few studies have explored the various chemical species associated with these conditions. Two common fuels from the sagebrush ecosystem, sagebrush (SB) and rabbitbrush (RB), were used. The experiments were conducted at the Desert Research Institute courtyard. Samples were collected for analysis of various chemical classes, including carbonyls, terpenes, volatile organic compounds (VOCs), polycyclic aromatic hydrocarbons (PAHs), carbonaceous aerosols, and particulate matter (PM). Carbonaceous aerosols were collected from both fresh and aged biomass burning smoke. The collected samples for carbonyls were extracted and analyzed using high-performance liquid chromatography coupled with a photodiode array detector (HPLC-PDA). For the other classes, the collected samples were extracted and analyzed using gas chromatography coupled with mass spectrometry (GC-MS). Online instruments, such as carbon monoxide and carbon dioxide sensors, were used to calculate the modified combustion efficiency and to obtain carbon-based EFs. The emissions of total carbonyl compounds were higher for SB in both smoldering (2.7±0.3 g/kgC) and flaming (2.5±0.4 g/kgC) conditions. RB showed lower emissions but followed a similar trend. For carbonaceous emissions, RB had higher emission factors compared to SB. Organic carbon concentrations increased after aging for smoldering of SB but not for RB. Regarding VOCs, smoldering conditions resulted in higher emissions, especially for RB (2737±834 g/kgC). SB followed a similar trend but lower (777±1087 g/kgC). For individual VOCs, such as isoprene, smoldering of RB (605±174 g/kgC) produced 1.8 times more emissions than flaming (328±218 g/kgC).