Volatile organic compound (VOC) emissions during FIREX-AQ: Distributions, emission ratios, and comparison with ARCTAS and SEAC4RS

Abstract:

Biomass burning is a major source of trace gases to the global atmosphere, which impacts air quality and human health. The summer 2019 FIREX-AQ mission sampled wildfires in the northwest United States and agricultural fires in the southeast, using research platforms including the NASA DC-8 aircraft. During FIREX-AQ, the University of California, Irvine whole air sampling group (UCI-WAS) collected 2637 samples that were analyzed for 130 C₁-C₁₁ volatile organic compounds (VOCs) using multi-column gas chromatography. The compounds include alkanes (C₁-C₁₁), alkenes (C₁-C₁₀), alkynes (C₁-C₈), aromatics (C₆-C₉), halocarbons (C₁-C₂), alkyl nitrates (C₁-C₅), sulfur compounds (C₁-C₂), nitrogen compounds (C₁-C₃), and oxygenated VOCs (OVOCs, C₃-C₈). Samples were collected into evacuated 2-L stainless steel canisters and pressurized to 2.7 atm during 23 DC-8 research flights from July 22 to September 5, 2019. The average canister fill time was 35 s and the average interval between samples was 2.5 minutes. Here we present VOC abundances, distributions, and emission ratios during FIREX-AQ based on WAS data and selected measurements from other teams. For example, as in previous airborne missions in North America (ARCTAS, SEAC⁴RS), OVOCs and simple VOCs (e.g., ethene, ethane, propene, ethyne, benzene) were abundant in the fire plumes, while halogenated species such as C₂Cl₄ and H-1211 were good urban tracers during FIREX-AQ. n-Pentane was preferentially emitted from the wildfires compared to i-pentane, and the ratio of i-pentane to n-pentane was a sensitive tracer of different VOC source influences during FIREX-AQ. These and other results will be presented.