Parameterization of Volatile Organic Compound Emissions from Western US Wildfires

Abstract:

Biomass burning is a large source of volatile organic compounds (VOCs) and many other trace species to the atmosphere, which can act as precursors to secondary pollutants. Some VOCs can also have direct effects on human and ecosystem health. Multiple different and complex processes take place in biomass burning, e.g., distillation, flaming, and smoldering combustion processes. In a given fire, most of these processes occur simultaneously, but the relative importance of each can change over the course of a fire. This gives rise to some of the variability in VOC emissions between different fires. Despite the complexity and variability of emissions, it was found using a proton-transfer reaction time-of-flight mass spectrometer (PTR-ToF-MS) in 2016 FireLab measurements that VOC emissions from western US wildfire fuels can be described by just two emission profiles, i.e., high-temperature pyrolysis profile and low-temperature pyrolysis profile (K. Sekimoto et al., Atmos. Phys. Chem., 18 9263-9281, 2018). To parameterize the VOC emissions from real-world wildfires, measurements performed with the PTR-ToF-MS on board the NASA DC-8 during the FIREX-AQ project were analyzed with positive matrix factorization (PMF) constrained by high- and low-temperature pyrolysis profiles. We found here that a solution including just three emission profiles, i.e., (i) high-temperature profile, (ii) low-temperature profile, and (iii) a profile for secondary produced compounds and compounds with low reactivity with OH radicals, explained on average 80% of the VOC emissions across various wildfires. In this presentation, we will discuss how VOC emissions from real-world wildfires can be parameterized.