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  • 1
    Electronic Resource
    Electronic Resource
    Distribution of222Rn over the north Pacific: Implications for continental influences (1992)
    Springer
    Journal of atmospheric chemistry 14 (1992), S. 353-374 
    Details
    ISSN: 1573-0662
    Keywords: North Pacific ; global atmospheric chemistry ; modeling ; radon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The atmospheric distribution of222Rn over the north Pacific is simulated with a three-dimensional chemical tracer model using meteorological input from the NASA-GISS general circulation model (4°×5° resolution). Radon-222 (half-life 3.8 days) is a tracer of continental air. Model results are in good agreement with measurements from ships and aircraft. Strong Asian influence is found throughout the tropospheric column over the north Pacific in spring, reflecting a combination of frequent convection over the continent, strong westerly winds at altitude, and subsidence over the ocean. In summer, the upper troposphere over the north Pacific is heavily affected by deep convection over China; however, Asian influences at the surface are then at their yearly minimum. In winter, strong Asian influence is found near the surface but not at high altitudes. Transport of American air over the Pacific is important only at low latitudes. American sources account for 11% of total222Rn in the model at Midway, 30% at Mauna Loa and 59% at Oahu. Results for Hawaii indicate two seasonal peaks of American influence, one in summer and one in winter. The tropical western Pacific is particularly remote from continental influences year round.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00115244
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  • 2
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    Simulation of summertime ozone over North America (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-08-27
    Description: The concentrations of O3 and its precursors over North America are simulated for three summer months with a 3D, continental-scale photochemical model using meteorological input from the Goddard Institute for Space Studies (GISS) GCM. The model has 4 x 5 deg grid resolution and represents nonlinear chemistry in urban and industrial plumes with a subgrid nested scheme. Simulated median afternoon O3 concentrations at rural U.S. sites are within 5 ppb of observations in most cases, except in the south central U.S., where concentrations are overpredicted by 15-20 ppb. The model captures successfully the development of regional high-O3 episodes over the northeastern United States on the back side of weak, warm, stagnant anticyclones. Simulated concentrations of CO and nonmethane hydrocarbons are generally in good agreement with observations, concentrations of NO(x) are underpredicted by 10-30 percent, and concentrations of PANs are overpredicted by a factor of 2 to 3. The overprediction of PANs is attributed to flaws in the photochemical mechanism, including excessive production from oxidation of isoprene, and may also reflect an underestimate of PANs deposition. Subgrid nonlinear chemistry as captured by the nested plumes scheme decreases the net O3 production computed in the U.S. boundary layer by 8 percent on average.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 98; D8; p. 14,797-14,816.
    Format: text
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  • 3
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    Chemistry of a polluted cloudy boundary layer (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: A one-dimensional photochemical model for cloud-topped boundary layers has been developed to include descriptions of gas- and aqueous-phase chemistry and the radiation field in and below the cloud. The model is applied to the accumulation of pollutants during a wintertime episode with low stratus over Bakersfield, CA. The mechanisms of sulfate production and the balance between the concentrations of acids and bases are examined. It is shown that most of the sulfate production may be explained by the Fe(III)-catalyzed autoxidation of S(IV). Another source of sulfate is the oxidation of SO2 by OH in both the gas and the aqueous phase. It is shown that the sulfate production in the model is controlled by the availability of NH3. It is suggested that this explains the balance observed between total concentration of acids and bases.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 94; 12975-13
    Format: text
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  • 4
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    Photochemistry of biogenic emissions over the Amazon forest (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The boundary layer chemistry over the Amazon forest during the dry season is simulated with a photochemical model. Results are in good agreement with measurements of isoprene, NO, ozone, and organic acids. Photochemical reactions of biogenic isoprene and NOx can supply most of the ozone observed in the boundary layer. Production of ozone is very sensitive to the availability of NOx, but is insensitive to the isoprene source strength. High concentrations of total odd nitrogen (NOy) are predicted for the planetary boundary layer, about 1 ppb in the mixed layer and 0.75 ppb in the convective cloud layer. Most of the odd nitrogen is present as PAN-type species, which are removed by dry deposition to the forest. The observed daytime variations of isoprene are explained by a strong dependence of the isoprene emission flux on sun angle. Nighttime losses of isoprene exceed rates of reaction with NO3 and O3 and appear to reflect dry-deposition processes. The 24-hour averaged isoprene emission flux is calculated to be 38 mg/sq m per day. Photooxidation of isoprene could account for a large fraction of the CO enrichment observed in the boundary layer under unpolluted conditions and could constitute an important atmospheric source of formic acid, methacrylic acid, and pyruvic acid.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 1477-148
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  • 5
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    Budgets of reactive nitrogen, hydrocarbons, and ozone over the Amazon forest during the wet season (1990)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The atmospheric composition over the Amazon forest during the wet season is simulated with a one-dimensional photochemical model for the planetary boundary layer (PBL) extending from the ground to 2000-m altitude. The model is constrained and evaluated using observations from the Amazon Boundary Layer Experiment 2B field expedition. Results indicate that only about 20 percent of NO(x) emitted by soils is exported to the atmosphere above the forest canopy. The balance is deposited to vegetation before leaving the canopy layer. The small NO(x) flux that escapes from the canopy is nevertheless sufficient to account for the low NO concentrations observed in the PBL. Soil emission can account for only a portion of NO(y) observed over the forest. Organic nitrates of nonbiogenic origin likely account for the balance of NO(y). Enhancements of CO observed in the PBL appear to reflect direct emission of CO by the forest ecosystem. Concentrations of O3 in the PBL are regulated largely by transport from aloft and deposition to the canopy, with little net influence from photochemistry. Ozone is photochemically produced immediately above the forest where NO concentrations are relatively high, but is photochemically consumed in the upper portion of the PBL.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 16737-16
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  • 6
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    BrO and Inferred Bry Profiles over the Western Pacific: Relevance of Inorganic Bromine Sources and a Bry Minimum in the Aged Tropical Tropopause Layer (2017)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: We report measurements of bromine monoxide (BrO) and use an observationally constrained chemical box model to infer total gas-phase inorganic bromine (Br(sub y)) over the tropical western Pacific Ocean (tWPO) during the CONTRAST field campaign (January-February 2014). The observed BrO and inferred Bry profiles peak in the marine boundary layer (MBL), suggesting the need for a bromine source from sea-salt aerosol (SSA), in addition to organic bromine (CBry ). Both profiles are found to be C-shaped with local maxima in the upper free troposphere (FT). The median tropospheric BrO vertical column density (VCD) was measured as 1.6 x 10(exp 13) molec cm(exp -2), compared to model predictions of 0.9 x 10(exp 13) molec cm(exp -2) in GEOS-Chem (CBr(sub y) but no SSA source), 0.4 x 10(exp 13) molec cm(exp -2) in CAM-Chem (CBr(sub y) and SSA), and 2.1 x 10(exp 13) molec cm(exp -2) in GEOS-Chem (CBry and SSA). Neither global model fully captures the Cshape of the Br(sun y) profile. A local Br(sub y) maximum of 3.6 ppt (2.9-4.4 ppt; 95% confidence interval, CI) is inferred between 9.5 and 13.5 km in air masses influenced by recent convective outflow. Unlike BrO, which increases from the convective tropical tropopause layer (TTL) to the aged TTL, gas-phase Br(sub y) decreases from the convective TTL to the aged TTL. Analysis of gas-phase Br(sub y) against multiple tracers (CFC-11, H2O/O3 ratio, and potential temperature) reveals a Br(sub y) minimum of 2.7 ppt (2.3-3.1 ppt; 95% CI) in the aged TTL, which agrees closely with a stratospheric injection of 2.6 +/- 0.6 ppt of inorganic Br(sub y) (estimated from CFC-11 correlations), and is remarkably insensitive to assumptions about heterogeneous chemistry. Bry increases to 6.3 ppt (5.6-7.0 ppt; 95% CI) in the stratospheric "middleworld" and 6.9 ppt (6.5-7.3 ppt; 95% CI) in the stratospheric "overworld". The local Br(sub y) minimum in the aged TTL is qualitatively (but not quantitatively) captured by CAM-Chem, and suggests a more complex partitioning of gas-phase and aerosol Br(sub y) species than previously recognized. Our data provide corroborating evidence that inorganic bromine sources (e.g., SSA-derived gas-phase Br(sub y) ) are needed to explain the gas-phase Br(sub y) budget in the upper free troposphere and TTL. They are also consistent with observations of significant bromide in Upper Troposphere-Lower Stratosphere aerosols. The total Br(sub y) budget in the TTL is currently not closed, because of the lack of concurrent quantitative measurements of gas-phase Br(sub y) species (i.e., BrO, HOBr, HBr, etc.) and aerosol bromide. Such simultaneous measurements are needed to (1) quantify SSA-derived Br(sub y) in the upper FT, (2) test Br(sub y) partitioning, and possibly explain the gas-phase Br(sub y) minimum in the aged TTL, (3) constrain heterogeneous reaction rates of bromine, and (4) account for all of the sources of Br(sub y) to the lower stratosphere.
    Keywords: Geosciences (General)
    Type: GSFC-E-DAA-TN55227 , Atmospheric Chemistry and Physics (ISSN 1680-7316) (e-ISSN 1680-7324); 17; 24; 15245-15270
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