Earth and Atmospheric Science

We apply an inverse method to estimate the carbon monoxide emissions in Atlanta, Georgia. The resultant carbon monoxide inventory is unrealistically characterized by temporal oscillations on the frequency of 1 hour. We suspect that the difficulty in deducing the emissions is due to inhomogeneities in the spatial distribution of the emissions. In several controlled experiments we reproduce the oscillations by introducing relatively small errors into the spatial distribution of the emission inventory. In similar experiments with isoprene in which the emissions are more homogeneous, we do not find this problem. These results are discussed in the context of previous inverse studies of carbon monoxide and isoprene. these variables are difficult to determine. To build an emission inventory for mobile sources, a variety of parameters must be known, for example, number of vehicles, makes and models, miles traveled, operating speeds, rates of acceleration, ambient and vehicle operating temperatures, emission control efficiencies, and rates of emission given the previous factors. Spatially allocating the emissions can introduce further uncertainty.

The concentrations of ozone, nitrogen oxides, and nonmethane hydrocarbons measured near the surface in a variety of urban, suburban, rural, and remote locations are analyzed and compared in order to elucidate the relationships between ozone, its photochemical precursors, and the sources of these precursors. While a large gradient is found among remote, rural, and urban/suburban nitrogen oxide concentrations, the total hydrocarbon reactivity in all continental locations is found to be comparable. Apportionment of the observed hydrocarbon species to mobile and stationary anthropogenic sources and biogenic sources suggests that present-day emission inventories for the United States underestimate the size of mobile emissions. The analysis also suggests a significant role for biogenic hydrocarbon emissions in many urban/suburban locations and a dominant role for these sources in rural areas of the eastern United States. As one moves from remote locations to rural locations and then from rural to urban/suburban locations, ozone and nitrogen oxide concentrations tend to increase in a consistent manner while total hydrocarbon reactivity does not.

Data obtained in Hong Kong during the Hong Kong and the Pearl River Delta (PRD) Pilot Air Monitoring Study in autumn 2002 are analyzed to unravel the relationship between ground-level ozone (O 3 ), pollution precursors, and cross-border transport. Ten ozone episodes, during which the hourly O 3 concentration exceeded 100 ppbv in 9 cases and 90 ppbv in one case, are subject to detailed analysis, including one case with hourly O 3 of 203 ppbv, which is the highest concentration on record to date in Hong Kong. Combined with high-resolution back trajectories, dCO/dNO y (the ratio of enhancement of CO concentration above background to that of NO y ) is used to define whether O 3 is locally or regionally produced. Five out of the ten Hong Kong O 3episodes studied show a "pollution signature" that is indicative of impact from Guangdong Province. Examination of speciated volatile organic compounds (VOCs) shows that the reactivity of VOCs is dominated by anthropogenic VOCs, of which the reactive aromatics dominate, in particular xylenes and toluene. Calculations using a photochemical box model indicate that between 50-100% of the O 3 increase observed in Hong Kong during the O 3 episodes can be explained by photochemical generation within the Hong Kong area, provided that nitrous acid (HONO) is present at the concentrations derived from this study. An Observation-Based Model (OBM) is used to calculate the sensitivity of the O 3 production to changes in the concentrations of the precursor compounds. Generally the production of O 3 throughout much of the Hong Kong area is limited by VOCs, while high nitric oxide (NO) concentrations suppress O 3 concentration.

The recent recognition of the detrimental impacts ofnear-surface ozone concentrations has led to the establishment of regionwide monitoring networks. The size of the collected data sets, as well as the presence of pseudorandom patterns in measured ozone concentrations, has motivated the use of advanced techniques for data analysis and presentation. In this work, a series of geostatistical and visualization procedures are applied to the analysis of hourly ozone measurements collected from 29 stations in the southeastern United States. The exploratory data analysis and variography clearly confirm the diurnal pattern of ozone fluctuations, and suggest that during daytime hours, local factors are dominant over the ozone production process. In contrast; during evening hours, regional factors and small-scale uneven variations become more dominant in the ozone depletion process. Using the geostatistical technique of cross-validation, results are generated in order to evaluate the rural classification of investigated stations. The findings of these studies indicate that: (1) the non-rural status of near-urban or presumably downwind stations is an hour-specific condition; (2) prevailing wind directions on each day can significantly alter the rural status of presumably upwind sites; and (3) local topography of a site can be an important factor in influencing its rural status during different hours of the day. Geostatistical techniques are shown to be not only useful for optimal mapping and network design, but also can be coupled with visualization tools to generate animated pseudocolored sequential maps. These maps are an efficient means for analysing spatial and temporal patterns of ozone concentrations.

Seven years of daily gas chromatographic measurements of CC14 at the five globally distributed ALE/GAGE surface sites are reported. It is determined that CCI 4 has been accumulating in the atmosphere at a rate of 1.3 ±0.1%/yr over the period 1978-1985 and that the releases of CC14 into the atmosphere have remained fairly constant, with the smallest releases in 1981-1982. Using an inversion scheme based on a nine box model of the atmosphere, we infer a CCI 4 lifetime of approximately 40 yr, an inventory on 1 July 1978 of (2.08±0.07)× 109 kg and an average rate of release over the period 1978-1985 of(9.0 ± 0.9) × 107 kg/yr. These results produce excellent agreement with a release scenario derived from global production estimates for CC14 and the major CC14 byproduct, the chlorofluorocarbons. However, to obtain this consistency, it is necessary that our current ALE/GAGE absolute calibration standard be reduced approximately 25% thus bringing it into agreement with measurements by Yokohata et al. (1985) and Hanst et al. (1975).

Observations of the chlorofluorocarbon CFCl3 obtained several times daily over the period July 1978 to June 1981 at Adrigole, Ireland (52°N, 10°W); Ragged Point, Barbados (13°N, 59°W); Point Matatula, American Samoa (14°S, 171°W); and Cape Grim, Tasmania (41°S, 145°E) are reported. In addition, observations at Cape Meares, Oregon (45°N, 124°W) are given for the period January 1980 to June 1981. On January 1, 1980, the average mixing ratio of CFCl3 in the lower troposphere is estimated to have been 168 pptv, and this is calculated to have been increasing 5.7% annually. An optimal estimation procedure for deriving the atmospheric lifetime of CFCl3 by using a nine‐box two‐dimensional model of the atmosphere is described. In this procedure, model parameters are estimated based upon minimizing the differences between the temporal trends observed and those calculated in the two‐dimensional model. Assuming that the only destruction of CFCl3 occurs in the stratosphere, the lifetime, on Janu...

Observations of dichlorodifluoromethane obtained several times daily over the period July 1978 to June 1981 at Adrigole, Ireland (52øN, 10øW), Ragged Point, Barbados (13øN, 59øW), Point Matatula, American Samoa (14øS, 171øW), and Cape Grim, Tasmania (41øS, 145øE), are reported. Observations at Cape Meares, Oregon (45øN, 124øW), are also given for the period November 1980 to June 1981. On January 1, 1980, the average mixing ratio of dichlorodifluoromethane in the lower troposphere is estimated to have been 285 pptv and to have been increasing at 6.0%/year. The atmospheric lifetime of this compound is estimated from this data by adjusting its destruction rate in a two-dimensional model of the atmosphere so as to provide the best fit to the observations. Assuming destruction of CF2C12 in the stratosphere only, the lifetime estimate for January 1 1980, by the inventory technique is •:c•+36 , •-18 years. The trend technique principally provides a lower limit to the lifetime of 81 years. The results suggest a need for further assessment of dichlorodifluoromethane release estimates, particularly those from the U SSR and eastern Europe.

The automated electron capture gas chromatographic determination of the atmospheric concentrations of CCl4 are reported for the period July 1978 to June 1981 at five coastal monitoring stations, Adrigole (Ireland), Cape Meares (Oregon), Ragged Point (Barbados, West Indies), Point Matatula (American Samoa), and Cape Grim (Tasmania). Daily measurements at approximately 6‐hourly intervals are always complimented by an equivalent number of on‐site calibration measurements. Estimates of CCl4 emissions to the atmosphere from known industrial sources are compared with the measured trends and the absolute values of the observed concentrations. A globally averaged atmospheric lifetime for CCl4 is calculated by using an optimal estimation technique incorporating a nine‐box model of the atmosphere. The average global concentration of CCl4 from July 1978 to June 1981 in the lower troposphere was 118 pptv, and it was increasing 2.1 pptv/year over this period. Both the absolute concentration obse...

Atmospheric Lifetime Experiment measurements of CFCl3 and CF2Cl2 several times per day at five remote surface sites from July 1978 to June 1983 are reported. For January 1, 1981, the mean latitudinally averaged mixing ratios were 177.5 parts per trillion by volume (pptv) and 300.4 pptv for CFCl3 and CF2Cl2, respectively. The atmospheric content at that time is estimated to have been 3,960 million kg of CFCl3 and 6,000 million kg of CF2Cl2. The mixing ratios exhibited an annual rate of increase of 9.0 and 15.3 pptv/yr for CFCl3 and CF2Cl2, respectively. Trend lifetime estimates for January 1, 1981 from this 5‐year data set are 74−17+31 years for CFCl3 and 111−44+222 years for CF2Cl2. On the basis of a comparison of CFCl3 data on two different chromatographic columns, it is shown that the spectrum of measurement errors maximizes at low frequencies but may be relatively flat at periods longer than approximately 3 years. The uncertainties in the trend lifetime estimates are, however, do...

1 EXECUTIVE SUMMARY Guided by the Endangered Species Act (ESA), the DOI through the Fish and Wildlife Service mandates that most army and air force bases in the South-Eastern US use prescribed burning to maintain the health of its native long leaf pine forest and thus protecting the habitat of the endangered red-cockaded woodpecker. Other installations across the Nation utilize prescribed burning to control invasive plants, which would otherwise endanger the habitat of other creatures. Due to the direct benefits of ...

Continuous measurements of 03, CO, NOy, and SO2 and twice a day samples of hydrocarbons were made over a 40 day period in June and July 1995 at the downtown Nashville Southern Oxidants Study (SOS) site located on the rooftop of the Polk office building, 106 m above ground level, in the urban center. This site experiences elevated concentrations of VOCs, CO, and NOy due to local emissions from the Nashville urban area. High 03 concentrations were also observed and are discussed with reference to violations of the existing air quality standard and the much harder task of meeting the proposed 8 hour average standard. A comparison between the VOC measurements made from the Department of Energy G-1 aircraft with those measured downtown indicates a preferential loss of reactive ingredients in the samples taken outside of the city. The concentration ratios, VOC/CO (ppbC/ppb), VOC/NOx (ppbC/ppb), and CO/NOx (ppb/ppb) were calculated to be 0.32, 2.9, and 9.3, respectively, from morning samples. These ratios agree to within 35% with estimates from Nashville emissions. 1. Introduction The Southern Oxidants Study (SOS) Nashville/Mid Tennessee Ozone Study had as one of its objectives an analysis of 0 3 formation in the Nashville urban plume. In support of this objective trace gas and meteorology measurements were made by the Tennessee Valley Authority (TVA) from on top of the James K. Polk office building in downtown Nashville [Meagher et al., 1996; K. J. Olszyna et al., unpublished manuscript, 1997]. Hydrocarbon samples were analyzed by researchers from the University of Miami. The intent of these observations was to characterize the chemical composition of the urban air mixture before extensive processing had occurred. Aircraft observations were used to determine the composition of the urban plume in later stages of its evolution [Hiibler et al., this issue]. In this study we are concerned with the chemical content of the air in downtown Nashville. This air, as it is advected downwind from Nashville, is subject to dilution and chemical reactions leading to the disappearance of primary pollutants and the formation of 03. The downtown measurements provide the initial conditions for that process (L. J. Nunnermacker et al., unpublished manuscript, 1998). A second objective of this study is to compare ratios of ambient concentrations observed downtown with the corre

The structural, electronic, and thermochemical properties of indium compounds which are of interest in halide transport and organometallic chemical vapor deposition processes have been studied by ab initio and statistical thermodynamic methods. The compounds reported include: indium halides and hydrides (InF, InCl, InCl 3 , InH, InH 2 , InH 3); indium clusters (In 2 , In 3); methylindium, dimethylindium, and their hydrogen derivatives [In(CH 3), In(CH 3)H, In(CH 3)H 2 , In(CH 3) 2 , In(CH 3) 2 H]; dimethylindium dimer [In 2 (CH 3) 4 ] and trimethylindium [In(CH 3) 3 ]; dehydrogenated methyl-, dimethyl-, and trimethylindium [In(CH 3) 2 CH 2 , In(CH 3)CH 2 , In(CH 2)]; trimethylindium adducts with ammonia, trimethylamine and hydrazine [(CH 3) 3 In:NH 3 , (CH 3) 3 In:N(CH 3) 3 , (CH 3) 3 In:N(H 2)N(H 2)]; dimethylamino-indium and methylimino-indium [In(CH 3) 2 (NH 2), In(CH 3)(NH)]; indium nitride and indium nitride dimer (InN, In 2 N 2); indium phosphide,-arsenide, and-antimonide (InP, InAs, InSb). The predicted electronic properties are based on density functional theory calculations; the calculated thermodynamic properties are reported following the format of the JANAF (Joint Army, Navy, NASA, Air Force) Tables. Equilibrium compositions at two temperatures (298 and 1000K) have been analyzed for groups of competing simultaneous reactions.

Since the zero-point energy was selected as a reference value, the electronic partition function q el was expressed as g el,0 + i g el,i exp {-E el,i /(kT)}. Because of the relatively large energy separation between electronic states, q el can usually be assumed to be equal to the degeneracy of the ground state, except at high temperatures. In this work, the expression for q el was truncated after the first excited state and its energy was approximated with the HOMO-LUMO (highest occupied and lowest unoccupied molecular orbital) difference. The molecular partition function of translation q tr was calculated as a function of temperature and molar volume as (2 M R T h-2) 1.5 L-4 V, where M is the molar mass, h is Planck's constant, and L is Avogadro's number. Assuming harmonicity, the molecular vibrational partition function q v was calculated as the product of the [1exp {-h j /(kT) } ]-1 terms. The parameter j varies from 1 to 3n-5 in linear molecules and from 1 to 3n-6 in nonlinear molecules, where n is the number of atoms in the molecule, and j is the harmonic vibrational frequency of the j th vibrational state. The molecular partition function for external rotation q r was calculated assuming the rigid rotor approximation. The expression of q r for linear molecules was (8 2 I k)/h 2 , and for nonlinear molecules is (1/2 / r) [(8 2 k)/h 2 ] 3/2 (I A I B I C) 1/2 , where I A , I B , I C are the moments of inertia in the three directions and r is the symmetry number of the external rotation. Assuming free internal rotations, the corresponding molecular partition function q ir was calculated as (1/ ir) (8 3 I rir k T / h 2) 1/2 , where ir is the symmetry number of the internal rotation. The reduced moment of inertia of the rotating group I rir was obtained from: I ir [ 1-I ir (cos 2 /I A + cos 2 /I B + cos 2 /I C)], where I ir is the moment of inertia of the rotating

ABSTRACTThe purpose of this paper is to review modeling and real-time monitoring by robust methods of reflectance spectroscopy of organometallic chemical vapor deposition processes in extreme regimes of pressure. The merits of p-polarized reflectance spectroscopy under the conditions of chemical beam epitaxy (CBE) and of internal transmission spectroscopy and principal angle spectroscopy at high pressure are assessed. In order to extend OMCVD to materials that exhibit large thermal decomposition pressure at their optimum growth temperature we have designed and built a differentially-pressure-controlled (DCP) OMCVD reactor for use at pressures ≤ 6 atm. We also describe a compact hard-shell (CHS) reactor for extending the pressure range to 100 atm. At such very high pressure the decomposition of source vapors occurs in the vapor phase, and is coupled to flow dynamics and transport. Rate constants for homogeneous gas phase reactions can be predicted based on a combination of first prin...

A numerical model was developed to simulate vapor deposition in high-pressure chemical vapor-deposition reactors, under different conditions of pressure, temperature, and flow rates. The model solved for steady-state gas-phase and heterogeneous chemical kinetic equations coupled with fluid dynamic equations within a three-dimensional grid simulating the actual reactor. The study was applied to indium nitride (InN) epitaxial growth. The steady-state model showed that at 1050-1290 K average substrate temperatures and 10 atm of total pressure, atomic indium (In) and monomethylindium [In(CH 3)] were the main group III gaseous species, and undissociated ammonia (NH 3) and amidogen (NH 2) the main group V gaseous species. The results from numerical models with an inlet mixture of 0.73:0.04:0.23 mass fraction ratios for nitrogen gas (N 2), NH 3 and trimethylindium [In(CH 3) 3 ], respectively, and an initial flow rate of 0.17 m s-1 , were compared with experimental values. Using a simple four-path surface reaction scheme, the numerical models yielded a growth rate of InN film of 0.027 µm per hour when the average substrate temperature was 1050 K and 0.094 µm per hour when the average substrate temperature was 1290 K. The experimental growth rate under similar flow ratios and reactor pressure, with a reactor temperature between 800 and 1150 K yielded an average growth rate of 0.081 µm per hour, comparing very well with the computed values.

The April 29, 2003, earthquake centered near Fort Payne, in DeKalb County, Alabama, was, perhaps, the largest historical event in the southeastern Tennessee Seismic Zone. The focal mechanism and aftershocks for this earthquake suggest a north-south striking near-vertical strike-slip fault. Other earthquakes in the seismic zone consistently suggest north-south or east-west striking near-vertical faults. The strike of the fault is discordant with the average northeast strike of most near-surface geologic structures. However, the seismic zone is parallel to regional basement structures. These earthquakes may represent the response of a weak zone to the current direction of plate stress. More local seismic stations and detailed investigations of east-west and north-south surface structures are needed to understand the cause of these earthquakes.

The objective of differential surface-wave interpretation is to identify temporal perturbations in the shear-wave velocity. Perturbations in phase velocity are measured by computing the Fourier transform of the difference of normalized traces. The perturbed structure can then be computed relative to a reference structure that need only approximate the actual structure.