Emissions of Reactive Nitrogen From Western U.S. Wildfires During Summer 2018

Abstract

Reactive nitrogen (N r) within smoke plumes plays important roles in the production of ozone, the formation of secondary aerosols, and deposition of fixed N to ecosystems. The Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption, and Nitrogen (WE-CAN) field campaign sampled smoke from 23 wildfires throughout the western U.S. during summer 2018 using the NSF/NCAR C-130 research aircraft. We empirically estimate N r normalized excess mixing ratios and emission factors from fires sampled within 80 min of estimated emission and explore variability in the dominant forms of N r between these fires. We find that reduced N compounds comprise a majority (39%-80%; median = 66%) of total measured reactive nitrogen (ΣN r) emissions. The smoke plumes sampled during WE-CAN feature rapid chemical transformations after emission. As a result, within minutes after emission total measured oxidized nitrogen (ΣNO y) and measured total ΣNH x (NH 3 + pNH 4) are more robustly correlated with modified combustion efficiency (MCE) than NO x and NH 3 by themselves. The ratio of ΣNH x /ΣNO y displays a negative relationship with MCE, consistent with previous studies. A positive relationship with total measured ΣN r suggests that both burn conditions and fuel N content/volatilization differences contribute to the observed variability in the distribution of reduced and oxidized N r. Additionally, we compare our in situ field estimates of N r EFs to previous lab and field studies. For similar fuel types, we find ΣNH x EFs are of the same magnitude or larger than lab-based NH 3 EF estimates, and ΣNO y EFs are smaller than lab NO x EFs. Plain Language Summary Smoke from large wildfires in the western U.S. degrades air quality across the whole U.S. Smoke contains a mixture of many different gases and particles, including carbon compounds like carbon dioxide and carbon monoxide, as well as nitrogen compounds such as ammonia and nitrogen oxides. Gases containing nitrogen are important for the production of ozone and the formation of more or larger particles as the smoke moves downwind. During the summer of 2018, we used the National Science Foundation/National Center for Atmospheric Research C130 research aircraft to fly through smoke across the western U.S. and measure many of the most abundant nitrogen compounds. We find that the smoke plumes we sampled emitted more nitrogen in a reduced form than in an oxidized form, and chemical reactions change the form and phase of nitrogen very quickly in the smoke. We compare our field measurements with laboratory measurements with the goal of using them together to improve our forecasts of how and where wildfire smoke will impact air quality. LINDAAS ET AL.

Emissions of Trace Organic Gases From Western U.S. Wildfires Based on WE‐CAN Aircraft Measurements

“…The WE‐CAN field campaign was based on Boise, ID, from July 24 to August 31 and Broomfield, CO from September 1 to 13, 2018. Nineteen flights were conducted by the NSF/NCAR C‐130 research aircraft approximately every 1–3 days and sampled smoke from fires across seven western states (Juncosa Calahorrano et al., 2021; Lindaas et al., 2021). Smoke plumes were typically sampled between 14:00 and 19:00 local time when burning conditions were most active.…”

Daytime Oxidized Reactive Nitrogen Partitioning in Western U.S. Wildfire Smoke Plumes

“…Particulate nitrate ( p NO 3 ) was measured using the CSU high‐resolution time‐of‐flight aerosol mass spectrometer (HR‐TOF‐AMS). C 1 –C 5 alkyl nitrates have been quantified by the NCAR Advanced Whole Air Sampler (AWAS) for the transects closest to the fires (Lindaas et al., 2020). They contribute a small fraction of the ΣNO y and are not yet quantified for all smoke‐impacted samples, so they are not included here.…”

“…Of the two example plumes shown here, the Taylor Creek Fire produced larger emissions of ΣNO y relative to CO (0.030 ppbv ppbv −1 ), more than twice that of the Bear Trap Fire (0.012 ppbv ppbv −1 ). We calculated the MCE for each fire following Lindaas et al (2020). The Bear Trap Fire had an average MCE of 0.88 (±0.017, standard deviation) indicating that the plume contained emissions produced from both smoldering and flaming conditions.…”

“…Peng et al (2020) document the emissions and evolution of HONO in fresh smoke plumes sampled during WE-CAN. Lindaas et al (2020) describe the emissions of all the N-compounds measured during WE-CAN. Lindaas et al (under review) discuss the evolution of reduced nitrogen (i.e., NH 3 and pNO 4 ) in the fresh plumes sampled during WE-CAN.…”

Biomass burning nitrogen dioxide emissions derived from space with TROPOMI: methodology and validation

“…The WE-CAN campaign, coordinated with the BB-FLUX campaign, also took place in the summer of 2018 in Northwestern US (based in Boise, Idaho), in many cases covering the same fires as the BB-FLUX campaign (Lindaas et al, 2021). The NCAR/NSF C-130 research aircraft was equipped with numerous instruments, including a NOyO3 chemiluminescence instrument, which measured the NO and NO 2 concentrations at 1 Hz.…”