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  • 1
    Publication Date: 2019-07-13
    Description: Recent laboratory experiments have shown that a first generation isoprene oxidation product, ISOPOOH, can decompose to methyl vinyl ketone (MVK) and methacrolein (MACR) on instrument surfaces, leading to overestimates of MVK and MACR concentrations. Formaldehyde (HCHO) was suggested as a decomposition co-product, raising concern that in situ HCHO measurements may also be affected by an ISOPOOH interference. The HCHO measurement artifact from ISOPOOH for the NASA In Situ Airborne Formaldehyde instrument (ISAF) was investigated for the two major ISOPOOH isomers, (1,2)-ISOPOOH and (4,3)-ISOPOOH, under dry and humid conditions. The dry conversion of ISOPOOH to HCHO was 3+/-2% and 6+/-4% for (1,2)-ISOPOOH and (4,3)-ISOPOOH, respectively. Under humid (RH= 40-60%) conditions, conversion to HCHO was 6+/-4% for (1,2)-ISOPOOH and 10+/-5% for (4,3)-ISOPOOH. The measurement artifact caused by conversion of ISOPOOH to HCHO in the ISAF instrument was estimated for data obtained on the 2013 September 6 flight of the Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS) campaign. Prompt ISOPOOH conversion to HCHO was the source for 〈4% of the observed HCHO, including in the high-isoprene boundary layer. Time-delayed conversion, where previous exposure to ISOPOOH affects measured HCHO later in flight, was conservatively estimated to be 〈 10% of observed HCHO and is significant only when high ISOPOOH sampling periods immediately precede periods of low HCHO.
    Keywords: Environment Pollution
    Type: GSFC-E-DAA-TN41602 , Atmospheric Measurement Techniques (ISSN 1867-1381) (e-ISSN 1867-8548); 9; 9; 4561-4568
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  • 2
    Publication Date: 2019-07-13
    Description: Isoprene oxidation schemes vary greatly among gas-phase chemical mechanisms, with potentially significant ramifications for air quality modeling and interpretation of satellite observations in biogenic-rich regions. In this study, in situ observations from the 2013 SENEX mission are combined with a constrained O-D photochemical box model to evaluate isoprene chemistry among five commonly used gas-phase chemical mechanisms: CBO5, CB6r2, MCMv3.2, MCMv3.3.1, and a recent version of GEOS-Chem. Mechanisms are evaluated and inter-compared with respect to formaldehyde (HCHO), a high-yield product of isoprene oxidation. Though underestimated by all considered mechanisms, observed HCHO mixing ratios are best reproduced by MCMv3.3.1 (normalized mean bias = -15%), followed by GEOS-Chem (-17%), MCMv3.2 (-25%), CB6r2 (-32%) and CB05 (-33%). Inter-comparison of HCHO production rates reveals that major restructuring of the isoprene oxidation scheme in the Carbon Bond mechanism increases HCHO production by only approx. 5% in CB6r2 relative to CBO5, while further refinement of the complex isoprene scheme in the Master Chemical Mechanism increases HCHO production by approx. 16% in MCMv3.3.1 relative to MCMv3.2. The GEOS-Chem mechanism provides a good approximation of the explicit isoprene chemistry in MCMv3.3.1 and generally reproduces the magnitude and source distribution of HCHO production rates. We analytically derive improvements to the isoprene scheme in CB6r2 and incorporate these changes into a new mechanism called CB6r2-UMD, which is designed to preserve computational efficiency. The CB6r2-UMD mechanism mimics production of HCHO in MCMv3.3.1 and demonstrates good agreement with observed mixing ratios from SENEX (-14%). Improved simulation of HCHO also impacts modeled ozone: at approx. 0.3 ppb NO, the ozone production rate increases approx. 3% between CB6r2 and CB6r2-UMD, and rises another approx. 4% when HCHO is constrained to match observations.
    Keywords: Environment Pollution
    Type: GSFC-E-DAA-TN47241 , Atmospheric Environment (ISSN 1352-2310); 164; 325-336
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  • 3
    Publication Date: 2019-07-13
    Description: VOCs (Volatile Organic Compounds) related to oil and gas extraction operations in the United States were measured by H3O (sup plus) chemical ionization time-of-flight mass spectrometry (H3O (sup plus) ToFCIMS/PTR-ToF-MS (Time of Flight Chemical Ionization Mass Spectrometry/Proton Transfer Reaction-Time of Flight-Mass Spectroscopy) from aircraft during the Shale Oil and Natural Gas Nexus (SONGNEX) campaign in March-April 2015. This work presents an overview of major VOC species measured in nine oil- and gas-producing regions, and a more detailed analysis of H3O (sup plus) ToF-CIMS measurements in the Permian Basin within Texas and New Mexico. Mass spectra are dominated by small photochemically produced oxygenates and compounds typically found in crude oil: aromatics, cyclic alkanes, and alkanes. Mixing ratios of aromatics were frequently as high as those measured downwind of large urban areas. In the Permian, the H3O (sup plus) ToF-CIMS measured a number of underexplored or previously unreported species, including aromatic and cycloalkane oxidation products, nitrogen heterocycles including pyrrole (C4H5N) and pyrroline (C4H7N), H2S, and a diamondoid (adamantane) or unusual monoterpene. We additionally assess the specificity of a number of ion masses resulting from H3O (sup plus) ion chemistry previously reported in the literature, including several new or alternate interpretations.
    Keywords: Environment Pollution
    Type: GSFC-E-DAA-TN47232 , Atmospheric Measurement Techniques (e-ISSN 1867-8548); 10; 8; 2941-2968
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  • 4
    Publication Date: 2019-07-13
    Description: We use a 0-D photochemical box model and a 3-D global chemistry-climate model, combined with observations from the NOAA Southeast Nexus (SENEX) aircraft campaign, to understand the sources and sinks of glyoxal over the Southeast United States. Box model simulations suggest a large difference in glyoxal production among three isoprene oxidation mechanisms (AM3ST, AM3B, and Master Chemical Mechanism (MCM) v3.3.1). These mechanisms are then implemented into a 3-D global chemistry-climate model. Comparison with field observations shows that the average vertical profile of glyoxal is best reproduced by AM3ST with an effective reactive uptake coefficient gamma(sub glyx) of 2 x 10(exp -3) and AM3B without heterogeneous loss of glyoxal. The two mechanisms lead to 0-0.8micrograms m(exp -3) secondary organic aerosol (SOA) from glyoxal in the boundary layer of the Southeast U.S. in summer. We consider this to be the lower limit for the contribution of glyoxal to SOA, as other sources of glyoxal other than isoprene are not included in our model. In addition, we find that AM3B shows better agreement on both formaldehyde and the correlation between glyoxal and formaldehyde (RGF[GLYX]/[HCHO]), resulting from the suppression of delta-isoprene peroxy radicals (delta-ISOPO2). We also find that MCM v3.3.1 may underestimate glyoxal production from isoprene oxidation, in part due to an underestimated yield from the reaction of isoprene epoxydiol (IEPOX) peroxy radicals with HO2. Our work highlights that the gas-phase production of glyoxal represents a large uncertainty in quantifying its contribution to SOA.
    Keywords: Environment Pollution
    Type: GSFC-E-DAA-TN41635 , Journal of Geophysical Research: Atmospheres (ISSN 2169-897X) (e-ISSN 2169-8996); 121; 16; 9849-9861
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  • 5
    Publication Date: 2019-08-09
    Description: We report enhancements of glyoxal relative to carbon monoxide and formaldehyde from biomass burning plumes intercepted from the NOAA WP-3D aircraft during the 2013 Southeast Nexus and 2015 Shale Oil and Natural Gas Nexus field campaigns. The intercepted biomass burning plumes were from small agricultural fires. Since the plume ages were not known, these values are normalized excess mixing ratios, instead of the more common emission ratio, which is used only for fresh emissions. Glyoxal was measured using broadband cavity enhanced spectroscopy, which provides a sensitive and highly selective measurement of glyoxal. Emissions of other species such as methane, formaldehyde, and nitrous acid agreed with previous laboratory and field measurements, but the glyoxal emissions relative to CO were on average a factor of 4 lower than previously reported. Several glyoxal loss processes such as aerosol uptake were examined to determine if they could affect the observed glyoxal concentrations, but they were insufficient to explain the lower measured values of glyoxal relative to other biomass burning trace gases, indicating that glyoxal emissions from biomass burning may be significantly overestimated.
    Keywords: Environment Pollution
    Type: NF1676L-27262 , GSFC-E-DAA-TN47723 , Environmental Science and Technology (ISSN 0013-936X) (e-ISSN 1520-5851); 51; 20; 11761-11770
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  • 6
    Publication Date: 2019-10-05
    Description: Recent studies suggest overestimates in current U.S. emission inventories of nitrogen oxides (NOx=NO+NO2). Here, we expand a previously developed Fuel-based Inventory of motor-Vehicle Emissions (FIVE) to the continental U.S. for the year 2013, and evaluate our estimates of mobile source emissions with the U.S. Environmental Protection Agency's National Emissions Inventory (NEI) interpolated to 2013. We find that mobile source emissions of NOx and carbon monoxide (CO) in the NEI are higher than FIVE by 28% and 90%, respectively. Using a chemical transport model, we model mobile source emissions from FIVE, and find consistent levels of urban NOx and CO as measured during the Southeast Nexus (SENEX) Study in 2013. Lastly, we assess the sensitivity of ozone (O3) over the Eastern U.S. to uncertainties in mobile source NOx emissions and biogenic volatile organic compound (VOC) emissions. The ground-level O3 is sensitive to reductions in mobile source NOx emissions, most notably in the Southeastern U.S. and during O3 exceedance events, under the revised standard proposed in 2015 (〉70 ppb, 8-hr maximum). This suggests that decreasing mobile source NOx emissions could help in meeting more stringent O3 standards in the future.
    Keywords: Environment Pollution
    Type: GSFC-E-DAA-TN61544 , Environmental Science and Technology (ISSN 0013-936X) (e-ISSN 1520-5851); 52; 13; 7360–7370
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