Volatile and intermediate-volatility non-methane organic gases (NMOGs) released from biomass burning were measured during
laboratory-simulated wildfires by proton-transfer-reaction time-of-flight ...mass spectrometry (PTR-ToF). We identified NMOG
contributors to more than 150 PTR ion masses using gas chromatography (GC) pre-separation with electron ionization,
H3O+ chemical ionization, and NO+ chemical ionization, an extensive literature review, and
time series correlation, providing higher certainty for ion identifications than has been previously available. Our
interpretation of the PTR-ToF mass spectrum accounts for nearly 90 % of NMOG mass detected by PTR-ToF across all fuel
types. The relative contributions of different NMOGs to individual exact ion masses are mostly similar across many fires
and fuel types. The PTR-ToF measurements are compared to corresponding measurements from open-path Fourier transform
infrared spectroscopy (OP-FTIR), broadband cavity-enhanced spectroscopy (ACES), and iodide ion chemical ionization mass
spectrometry (I− CIMS) where possible. The majority of comparisons have slopes near 1 and values of the linear
correlation coefficient, R2, of > 0.8, including compounds that are not frequently reported by PTR-MS such as
ammonia, hydrogen cyanide (HCN), nitrous acid (HONO), and propene. The exceptions include methylglyoxal and compounds that
are known to be difficult to measure with one or more of the deployed instruments. The fire-integrated emission ratios to
CO and emission factors of NMOGs from 18 fuel types are provided. Finally, we provide an overview of the chemical
characteristics of detected species. Non-aromatic oxygenated compounds are the most abundant. Furans and aromatics, while
less abundant, comprise a large portion of the OH reactivity. The OH reactivity, its major contributors, and the
volatility distribution of emissions can change considerably over the course of a fire.
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 such as ozone and fine ...particles.
Measurements performed with a proton-transfer-reaction time-of-flight mass
spectrometer during the FIREX 2016 laboratory intensive were analyzed with
positive matrix factorization (PMF), in order to understand the
instantaneous variability in VOC emissions from biomass burning, and to
simplify the description of these types of emissions. Despite the complexity
and variability of emissions, we found that a solution including just two
emission profiles, which are mass spectral representations of the relative
abundances of emitted VOCs, explained on average 85 % of the VOC emissions
across various fuels representative of the western US (including various
coniferous and chaparral fuels). In addition, the profiles were remarkably
similar across almost all of the fuel types tested. For example, the
correlation coefficient r2 of each profile between ponderosa pine
(coniferous tree) and manzanita (chaparral) is higher than 0.84. The
compositional differences between the two VOC profiles appear to be related
to differences in pyrolysis processes of fuel biopolymers at high and low
temperatures. These pyrolysis processes are thought to be the main source of
VOC emissions. “High-temperature” and “low-temperature” pyrolysis
processes do not correspond exactly to the commonly used “flaming” and
“smoldering” categories as described by modified combustion efficiency
(MCE). The average atmospheric properties (e.g., OH reactivity, volatility,
etc) of the high- and low-temperature profiles are significantly different.
We also found that the two VOC profiles can describe previously reported VOC
data for laboratory and field burns.
Atmospheric black carbon (BC) warms Earth's climate, and its reduction has been targeted for near-term climate change mitigation. Models that include forcing by BC assume internal mixing with non-BC ...aerosol components that enhance BC absorption, often by a factor of ∼2; such model estimates have yet to be clearly validated through atmospheric observations. Here, direct in situ measurements of BC absorption enhancements (E abs ) and mixing state are reported for two California regions. The observed E abs is small—6% on average at 532 nm—and increases weakly with photochemical aging. The E abs is less than predicted from observationally constrained theoretical calculations, suggesting that many climate models may overestimate warming by BC. These ambient observations stand in contrast to laboratory measurements that show substantial E abs for BC are possible.
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Volatile organic compounds (VOCs) emitted from residential wood and crop residue burning were measured in Colorado, U.S. When compared to the emissions from crop burning, residential wood burning ...exhibited markedly lower concentrations of acetonitrile, a commonly used biomass burning tracer. For both herbaceous and arboraceous fuels, the emissions of nitrogen‐containing VOCs (NVOCs) strongly depend on the fuel nitrogen content; therefore, low NVOC emissions from residential wood burning result from the combustion of low‐nitrogen fuel. Consequently, the emissions of compounds hazardous to human health, such as HNCO and HCN, and the formation of secondary pollutants, such as ozone generated by NOx, are likely to depend on fuel nitrogen. These results also demonstrate that acetonitrile may not be a suitable tracer for domestic burning in urban areas. Wood burning emissions may be best identified through analysis of the emissions profile rather than reliance on a single tracer species.
Key Points
The emissions of nitrogen‐containing VOCs from biomass burning smoke is strongly dependent on fuel composition
Common biomass burning markers, such as acetonitrile, are weakly associated with emissions from residential wood burning
The emissions of hazardous nitrogen‐containing compounds, such as HNCO and HCN, will depend on fuel nitrogen content
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The magnitude and sources of chlorine atoms in marine air remain highly uncertain but have potentially important consequences for air quality in polluted coastal regions. We made continuous ...measurements of ambient ClNO2 and Cl2 concentrations from May 15 to June 8 aboard the Research Vessel Atlantis during the CalNex 2010 field study. In the Los Angeles region, ClNO2 was more ubiquitous than Cl2 during most nights of the study period. ClNO2 and Cl2 ranged from detection limits at midday to campaign maximum values at night reaching 2100 and 200 pptv, respectively. The maxima were observed in Santa Monica Bay when sampling the Los Angeles urban plume. Cl2 at times appeared well correlated with ClNO2, but at other times, there was little to no correlation implying distinct and varying sources. Well-confined Cl2 plumes were observed, largely independent of ClNO2, providing support for localized industrial emissions of reactive chlorine. Observations of ClNO2, Cl2, and HCl are used to constrain a simple box model that predicts their relative importance as chlorine atom sources in the polluted marine boundary layer. In contrast to the emphasis in previous studies, ClNO2 and HCl are dominant primary chlorine atom sources for the Los Angeles basin.
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Tropospheric O3 has been decreasing across much of the eastern U.S. but has remained steady or even increased in some western regions. Recent increases in VOC and NOx emissions associated with the ...production of oil and natural gas (O&NG) may contribute to this trend in some areas. The Northern Front Range of Colorado has regularly exceeded O3 air quality standards during summertime in recent years. This region has VOC emissions from a rapidly developing O&NG basin and low concentrations of biogenic VOC in close proximity to urban‐Denver NOx emissions. Here VOC OH reactivity (OHR), O3 production efficiency (OPE), and an observationally constrained box model are used to quantify the influence of O&NG emissions on regional summertime O3 production. Analyses are based on measurements acquired over two summers at a central location within the Northern Front Range that lies between major regional O&NG and urban emission sectors. Observational analyses suggest that mixing obscures any OPE differences in air primarily influenced by O&NG or urban emission sector. The box model confirms relatively modest OPE differences that are within the uncertainties of the field observations. Box model results also indicate that maximum O3 at the measurement location is sensitive to changes in NOx mixing ratio but also responsive to O&NG VOC reductions. Combined, these analyses show that O&NG alkanes contribute over 80% to the observed carbon mixing ratio, roughly 50% to the regional VOC OHR, and approximately 20% to regional photochemical O3 production.
Key Points
Modeled photochemical O3 production is Nox‐sensitive at a central location in the Colorado Northern Front Range
Oil and natural gas VOC emissions contribute over 80% to the observed carbon mixing ratio and 17.4% to maximum modeled photochemical O3
Observed O3 production efficiencies are variable but show an influence of less than 1.8 ppbv/ppbv from oil and natural gas VOC emissions
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Dry deposition of ozone (O3) to the ocean surface and the ozonolysis of organics in the sea surface microlayer (SSML) are potential sources of volatile organic compounds (VOCs) to the marine ...atmosphere. We use a gas chromatography system coupled to a Vocus proton-transfer-reaction time-of-flight mass spectrometer to determine the chemical composition and product yield of select VOCs formed from ozonolysis of coastal seawater collected from Scripps Pier in La Jolla, California. Laboratory-derived results are interpreted in the context of direct VOC vertical flux measurements made at Scripps Pier. The dominant products of laboratory ozonolysis experiments and the largest non-sulfur emission fluxes measured in the field correspond to Vocus CxHy+ and CxHyOz+ ions. Gas chromatography (GC) analysis suggests that C5–C11 oxygenated VOCs, primarily aldehydes, are the largest contributors to these ion signals. In the laboratory, using a flow reactor experiment, we determine a VOC yield of 0.43–0.62. In the field at Scripps Pier, we determine a maximum VOC yield of 0.04–0.06. Scaling the field and lab VOC yields for an average O3 deposition flux and an average VOC structure results in an emission source of 10.7 to 167 Tg C yr−1, competitive with the DMS source of approximately 20.3 Tg C yr−1. This study reveals that O3 reactivity to dissolved organic carbon can be a significant carbon source to the marine atmosphere and warrants further investigation into the speciated VOC composition from different seawater samples and the reactivities and secondary organic aerosol (SOA) yields of these molecules in marine-relevant, low NOx conditions.
Nighttime reaction of nitrate radicals (NO3) with biogenic volatile organic compounds (BVOC) has been proposed as a potentially important but also highly uncertain source of secondary organic aerosol ...(SOA). The southeastern United States has both high BVOC and nitrogen oxide (NOx) emissions, resulting in a large model-predictedNO3-BVOC source of SOA. Coal-fired power plants in this region constitute substantial NOx emissions point sources into a nighttime atmosphere characterized by high regionally widespread concentrations of isoprene. In this paper, we exploit nighttime aircraft observations of these power plant plumes, in which NO3 radicals rapidly remove isoprene, to obtain field-based estimates of the secondary organic aerosol yield from NO3 + isoprene. Observed in-plume increases in nitrate aerosol are consistent with organic nitrate aerosol production from NO3 + isoprene, and these are used to determine molar SOA yields, for which the average over nine plumes is 9 % (±5 %). Corresponding mass yields depend on the assumed molecular formula for isoprene-NO3-SOA, but the average over nine plumes is 27 % (±14 %), on average larger than those previously measured in chamber studies (12 %–14 % mass yield as ΔOA / ΔVOC after oxidation of both double bonds). Yields are larger for longer plume ages. This suggests that ambient aging processes lead more effectively to condensable material than typical chamber conditions allow. We discuss potential mechanistic explanations for this difference, including longer ambient peroxy radical lifetimes and heterogeneous reactions ofNO3-isoprene gas phase products. More in-depth studies are needed to better understand the aerosol yield and oxidation mechanism of NO3 radical + isoprene, a coupled anthropogenic–biogenic source of SOA that may be regionally significant.
The exchange of trace gases between the biosphere and the atmosphere is an important process that controls both chemical and physical properties of the atmosphere with implications for air quality ...and climate change. The terrestrial biosphere is a major source of reactive biogenic volatile organic compounds (BVOCs) that govern atmospheric concentrations of the hydroxy radical (OH) and ozone (O3) and control the formation and
growth of secondary organic aerosol (SOA). Common simulations of BVOC
surface–atmosphere exchange in chemical transport models use parameterizations derived from the growing season and do not consider
potential changes in emissions during seasonal transitions. Here, we use
observations of BVOCs over a mixed temperate forest in northern Wisconsin
during broadleaf senescence to better understand the effects of the seasonal changes in canopy conditions (e.g., temperature, sunlight, leaf area, and leaf stage) on net BVOC exchange. The BVOCs investigated here include the terpenoids isoprene (C5H8), monoterpenes (MTs; C10H16), a monoterpene oxide (C10H16O), and sesquiterpenes (SQTs; C15H24), as well as a subset of other monoterpene oxides and dimethyl sulfide (DMS). During this period, MTs were primarily composed of α-pinene, β-pinene, and camphene, with α-pinene and camphene dominant during the first half of September and β-pinene thereafter. We observed enhanced MT and monoterpene oxide emissions following the onset of leaf senescence and suggest that senescence has the potential to be a significant control on late-season MT emissions in this ecosystem. We show that common parameterizations of BVOC emissions cannot reproduce the fluxes of MT, C10H16O, and SQT during the onset and continuation of senescence but can correctly simulate isoprene flux. We also describe the impact of the MT emission enhancement on the potential to form highly oxygenated organic molecules (HOMs). The calculated production rates of HOMs and H2SO4, constrained by terpene and DMS concentrations, suggest that biogenic aerosol formation and growth in this region should be dominated by secondary organics rather than sulfate. Further, we show that models using parameterized MT emissions likely underestimate HOM production, and thus aerosol growth and formation, during early autumn in this region. Further measurements of forest–atmosphere BVOC exchange during seasonal transitions as well as measurements of DMS in temperate regions are needed to effectively predict the effects of canopy changes on reactive carbon cycling and aerosol production.
Emissions of methane (CH4) and volatile organic compounds (VOCs) from oil and gas production may have large impacts on air quality and climate change. Methane and VOCs were measured over the ...Haynesville and Marcellus shale gas plays on board the National Center for Atmospheric Research C‐130 and NOAA WP‐3D research aircraft in June–July of 2013. We used an eddy covariance technique to measure in situ fluxes of CH4 and benzene from both C‐130 flights with high‐resolution data (10 Hz) and WP‐3D flights with low‐resolution data (1 Hz). Correlation (R = 0.65) between CH4 and benzene fluxes was observed when flying over shale gas operations, and the enhancement ratio of fluxes was consistent with the corresponding concentration observations. Fluxes calculated by the eddy covariance method show agreement with a mass balance approach within their combined uncertainties. In general, CH4 fluxes in the shale gas regions follow a lognormal distribution, with some deviations for relatively large fluxes (>10 µg m−2 s−1). Statistical analysis of the fluxes shows that a small number of facilities (i.e., ~10%) are responsible for up to ~40% of the total CH4 emissions in the two regions. We show that the airborne eddy covariance method can also be applied in some circumstances when meteorological conditions do not favor application of the mass balance method. We suggest that the airborne eddy covariance method is a reliable alternative and complementary analysis method to estimate emissions from oil and gas extraction.
Key Points
Airborne eddy covariance flux measurements over oil and gas extraction regions
Estimates of CH4 emissions agree with the mass balance method
Airborne eddy covariance is a powerful method to estimate oil and gas emissions
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