skip to main content

Search for: All records

Award ID contains: 1652688

Note: When clicking on a Digital Object Identifier (DOI) number, you will be taken to an external site maintained by the publisher. Some full text articles may not yet be available without a charge during the embargo (administrative interval).
What is a DOI Number?

Some links on this page may take you to non-federal websites. Their policies may differ from this site.

  1. Abstract

    We present emission measurements of volatile organic compounds (VOCs) for western U.S. wildland fires made on the NSF/NCAR C‐130 research aircraft during the Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption, and Nitrogen (WE‐CAN) field campaign in summer 2018. VOCs were measured with complementary instruments onboard the C‐130, including a proton‐transfer‐reaction time‐of‐flight mass spectrometer (PTR‐ToF‐MS) and two gas chromatography (GC)‐based methods. Agreement within combined instrument uncertainties (<60%) was observed for most co‐measured VOCs. GC‐based measurements speciated the isomeric contributions to selected PTR‐ToF‐MS ion masses and generally showed little fire‐to‐fire variation. We report emission ratios (ERs) and emission factors (EFs) for 161 VOCs measured in 31 near‐fire smoke plume transects of 24 specific individual fires sampled in the afternoon when burning conditions are typically most active. Modified combustion efficiency (MCE) ranged from 0.85 to 0.94. The measured campaign‐average total VOC EF was 26.1 ± 6.9 g kg−1, approximately 67% of which is accounted for by oxygenated VOCs. The 10 most abundantly emitted species contributed more than half of the total measured VOC mass. We found that MCE alone explained nearly 70% of the observed variance for total measured VOC emissions (r2 = 0.67) and >50% for 57 individual VOC EFs representing more than half themore »organic carbon mass. Finally, we found little fire‐to‐fire variability for the mass fraction contributions of individual species to the total measured VOC emissions, suggesting that a single speciation profile can describe VOC emissions for the wildfires in coniferous ecosystems sampled during WE‐CAN.

    « less
  2. Abstract

    The Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption, and Nitrogen (WE‐CAN) deployed the NSF/NCAR C‐130 aircraft in summer 2018 across the western U.S. to sample wildfire smoke during its first days of atmospheric evolution. We present a summary of a subset of reactive oxidized nitrogen species (NOy) in plumes sampled in a pseudo‐Lagrangian fashion. Emissions of nitrogen oxides (NOx = NO + NO2) and nitrous acid (HONO) are rapidly converted to more oxidized forms. Within 4 h, ∼86% of the ΣNOyis in the form of peroxy acyl nitrates (PANs) (∼37%), particulate nitrate (pNO3) (∼27%), and gas‐phase organic nitrates (Org N(g)) (∼23%). The averagee‐folding time and distance for NOxare ∼90 min and ∼40 km, respectively. Nearly no enhancements in nitric acid (HNO3) were observed in plumes sampled in a pseudo‐Lagrangian fashion, implying HNO3‐limited ammonium nitrate (NH4NO3) formation, with one notable exception that we highlight as a case study. We also summarize the observed partitioning of NOyin all the smoke samples intercepted during WE‐CAN. In smoke samples intercepted above 3 km above sea level (ASL), the contributions of PANs andpNO3to ΣNOyincrease with altitude. WE‐CAN also sampled smoke from multiple fires mixed with anthropogenic emissions over the California Central Valley. We distinguish samples where anthropogenic NOxemissions appear to leadmore »to an increase in NOxabundances by a factor of four and contribute to additional PAN formation.

    « less
  3. Abstract

    Reactive nitrogen (Nr) 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 estimateNrnormalized excess mixing ratios and emission factors from fires sampled within 80 min of estimated emission and explore variability in the dominant forms ofNrbetween these fires. We find that reduced N compounds comprise a majority (39%–80%; median = 66%) of total measured reactive nitrogen (ΣNr) 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 (ΣNOy) and measured totalΣNHx(NH3 + pNH4) are more robustly correlated with modified combustion efficiency (MCE) than NOxand NH3by themselves. The ratio of ΣNHx/ΣNOydisplays a negative relationship with MCE, consistent with previous studies. A positive relationship with total measuredΣNrsuggests that both burn conditions and fuel N content/volatilization differences contribute to the observed variability in the distribution of reduced and oxidizedNr. Additionally, we compare our in situ field estimates ofNrEFs to previous lab and field studies. Formore »similar fuel types, we findΣNHxEFs are of the same magnitude or larger than lab‐based NH3EF estimates, andΣNOyEFs are smaller than lab NOxEFs.

    « less
  4. Abstract. Chemical ionization mass spectrometry (CIMS) techniques have becomeprominent methods for sampling trace gases of relatively low volatility.Such gases are often referred to as being “sticky”, i.e., havingmeasurement artifacts due to interactions between analyte molecules andinstrument walls, given their tendency to interact with wall surfaces viaabsorption or adsorption processes. These surface interactions can impactthe precision, accuracy, and detection limits of the measurements. Weintroduce a low-pressure ion–molecule reaction (IMR) region primarily builtfor performing iodide-adduct ionization, though other adduct ionizationschemes could be employed. The design goals were to improve upon previouslow-pressure IMR versions by reducing impacts of wall interactions at lowpressure while maintaining sufficient ion–molecule reaction times. Chambermeasurements demonstrate that the IMR delay times (i.e., magnitude of wallinteractions) for a range of organic molecules spanning 5 orders ofmagnitude in volatility are 3 to 10 times lower in the new IMR compared toprevious versions. Despite these improvements, wall interactions are stillpresent and need to be understood. To that end, we also introduce aconceptual framework for considering instrument wall interactions and ameasurement protocol to accurately capture the time dependence of analyteconcentrations. This protocol uses short-duration, high-frequencymeasurements of the total background (i.e., fast zeros) during ambientmeasurements as well as during calibration factor determinations. Thisframework and associatedmore »terminology applies to any instrument andionization technique that samples compounds susceptible to wallinteractions.« less