Gerald E. Streit

Beyond acid rain

This paper discussed the effects of the interactions of soluble oxidants and organic toxins with sulfur dioxide and nitrogen dioxide. It suggested that these chemical reactions in the atmosphere produced a more potent acid rain which was harmful not only because it had a low pH but because it contained oxidants and organic toxins which were harmful to surface vegetation and the organisms found in surface waters. It was stressed that air pollution is a global problem and that is is necessary to develop a better fundamental understanding of how air pollution is causing damage to the streams and forests of the world. 50 references.

Negative ion chemistry and the electron affinity of SF6

An extensive study of negative ion–molecule chemistry involving SF6 and SF−6 utilizing the room temperature flowing afterglow technique is reported. Based on a series of limit determinations, the recommended value of E.A.(SF6) is 1.0±0.2 eV. The discrepancy between this value and several previous determinations of E.A. (SF6) is discussed in terms of systematic experimental conditions and the formation of an excited state of SF−6. A large number of reaction rate coefficients as well as qualitative observations of reaction mechanisms are presented.

Motorization of China implies changes in Pacific air chemistry and primary production

The Peoples Republic of China, the worlds most populous nation, is considering extensive development of its automotive transportation infrastructure. Upper limits to the associated pollution increases can be defined through scenarios with Western style vehicles and vehicle-to-person ratios. Here we construct estimates of fundamental changes to chemistry of the Pacific ocean/atmosphere system through simple budgeting procedures. Regional increases in tropospheric ozone could reach tens of parts per billion. Observations/experiments suggest that enhanced nitrogen oxides will react with sea salt aerosols to yield chlorine atoms in the marine boundary layer. Nitrate deposition onto the open sea surface would support several percent of exported North Pacific carbon production. Transport of biologically active iron to surface waters may follow from increases in mineral dust and acid sulfate aerosols. Altered plankton ecodynamics will feed back into climate processes through sea to air flux of reduced sulfur gases and through carbon dioxide drawdown.

Mexico City Air quality: Progress of an international collaborative project to define air quality management options

Abstract The Mexico City Air Quality Research Initiative was a 3-yr international collaborative project to develop or adapt a set of air quality management decision analysis tools for Mexico City and make them available to Mexican policy makers. The project comprised three tasks: modeling and simulation, characterization and measurement, and strategic evaluation. A prognostic, mesoscale meteorological model was adapted to the region of Mexico City and linked to a 3-D airshed model. These were extensively tested against data from the air quality monitoring network and from three intensive field campaigns. The interaction between policy and science was promoted through the development of a formal multiattribute decision analysis model to evaluate alternative control strategies. The project benefited by having researchers from both nations working side by side as peers, by having both nations investing resources and having an interest in the success of the project, and by having an objective, not of advocacy, but of the application of science to problem solving.

Negative ion–molecule reactions of SF4

A study of some negative ion–molecule reactions involving SF4 has been carried out by the flowing afterglow technique at ambient temperature. By examining a series of charge exchange reactions of SF4 and SF4−, the electron affinity of SF4 has been determined to be 2.35±0.1 eV. Rate coefficients for the charge exchange reactions of HS−, S−, OH−, and O− with SF4 and of SF4− with Cl2 and NO2 are reported. In addition, the fluoride transfer reactions of SF4− and SF6− with SF4 to produce SF5− have been examined. That both reactions proceed indicates that the fluoride affinity of SF4 is greater than that of SF3 or SF5. A lower limit of 3.7 eV for the electron affinity of SF5 may also be deduced from the fluoride transfer reactions. The two body addition of halide ions (X−) to SF4 to form the adduct SF4X− proceeds at near the collision limit (k = 9.7×10−10 cm3 molecule−1 s−1) for F−, very slowly (k = 2.6×10−11 cm3 molecule−1 s−1) for Cl−, and not at all within experimental limits (k<2×10−12 cm3 molecule−1 s−1) f...

Ion–molecule reactions of SF6: Determination of I.P.(SF5), A.P.(SF5+/SF6), and D(SF5–F)

SF6 reacts with CF3+ to produce SF5+ and CF4. Under conditions of large amounts of CF4, an equilibrium is established. From flowing afterglow data, not only is a forward rate constant kf = (2.5±0.2)×10−10 cm3 molecule−1 s−1 determined, but also an equilibrium constant of 5.9×103 (±50%) is deduced. Using this equilibrium constant and standard entropies for the various species, ΔH°298 = −0.17±0.02 eV is calculated. A thermochemical cycle then yields a value of A.P.(SF5+/SF6) = 14.62±0.09 eV. An examination of charge exchange reactions of SF5+ leads to establishment of the ionization potential of SF5 at 10.5±0.1 eV. Combining this with A.P.(SF5+/SF6) allows a calculation of the bond dissociation energy D°298(SF5–F) = 4.1±0.13 eV. In addition to these new values of A.P.(SF5+/SF6), I.P.(SF5), and D°298(SF5–F), the fragmentation pattern of SF6 reacting with He+ as well as rates of reaction of SF6 with several positive ions are reported.

Modeling the atmospheric deposition and stormwater washoff of nitrogen compounds

Abstract We investigated the suitability of integrating deterministic models to estimate the relative contributions of atmospheric dry and wet deposition onto an urban surface and the subsequent amounts removed by stormwater runoff. The CIT airshed model and the United States Environmental Protection Agency Storm Water Management Model (SWMM) were linked in order to simulate the fate and transport of nitrogen species through the atmosphere and storm drainage system in Los Angeles, California, USA. Coupling CIT and SWMM involved defining and resolving five critical issues: (1) reconciling the different modeling domain sizes, (2) accounting for dry deposition due to plant uptake, (3) estimating the fraction of deposited contaminant available for washoff, (4) defining wet deposition inputs to SWMM, and (5) parameterizing the SWMM washoff algorithm. The CIT–SWMM interface was demonstrated by simulating dry deposition, wet deposition, and stormwater runoff events to represent the time period from November 18, 1987 to December 4, 1987 for a heavily urbanized Los Angeles watershed discharging to Santa Monica Bay. From November 18th to December 3rd the simulated average dry deposition flux of nitrogen was 0.195 kg N/ha-day to the watershed and 0.016 kg N/ha-day to Santa Monica Bay. The simulated rainfall concentrations during the December 4th rainfall event ranged from 3.76 to 8.23 mg/l for nitrate and from 0.067 to 0.220 mg/l for ammonium. The simulated stormwater runoff event mean concentrations from the watershed were 4.86 mg/l and 0.12 mg/l for nitrate and ammonium, respectively. Considering the meteorology during the simulation period, the CIT and SWMM predictions compare well with observations in the Los Angeles area and in other urban areas in the United States.

Development and testing of meteorology and air dispersion models for Mexico City

Abstract Los Alamos National Laboratory and Instituto Mexicano del Petroleo are completing a joint study of options for improving air quality in Mexico City. We have modified a three-dimensional, prognostic, higher-order turbulence model for atmospheric circulation (HOTMAC) and a Monte Carlo dispersion and transport model (RAPTAD) to treat domains that include an urbanized area. We used the meteorological model to drive models which describe the photochemistry and air transport and dispersion. The photochemistry modeling is described in a separate paper. We tested the model against routine measurements and those of a major field program. During the field program, measurements included: (1) lidar measurements of aerosol transport and dispersion, (2) aircraft measurements of winds, turbulence, and chemical species aloft, (3) aircraft measurements of skin temperatures, and (4) Tethersonde measurements of winds and ozone. We modified the meteorological model to include provisions for time-varying synoptic-scale winds, adjustments for local wind effects, and detailed surface-coverage descriptions. We developed a new method to define mixing-layer heights based on model outputs. The meteorology and dispersion models were able to provide reasonable representations of the measurements and to define the sources of some of the major uncertainties in the model-measurement comparisons.

Atmospheric Effects of the Emerging Mainland Chinese Transportation System at and Beyond the Regional Scale

Abstract Local surface travel needs in the People‘s Republic of China (mainlandChina) have traditionally been met largely by nonpolluting bicycles. A majorautomobile manufacturing/importing effort has begun in the country over thelast decade, and planning documents indicate that the Chinese may strive toacquire more than 100 million vehicles early in the next century. By analogywith large automotive fleets already existing in the western world, bothregional and global scale pollution effects are to be expected from theincrease. The present work adopts the latest projections of Chinese automobilemanufacture and performs some quantitative assessments of the extent ofpollution generation.Focus for the investigation is placed upon the oxidant ozone. Emissions of theprecursor species nitrogen oxides and volatile organics are constructed basedon data for the current automotive sector in the eastern portion of the UnitedStates. Ozone production is first estimated from measured values forcontinental/oceanic scale yields relative to precursor oxidation. Theestimates are then corroborated through idealized two dimensional modeling ofthe photochemistry taking place in springtime air flow off the Asian land massand toward the Pacific Ocean. The projected fleet sizes could increase coastaland remote oceanic ozone concentrations by tens of parts per billion (ppb)in the lower troposphere. Influences on the tropospheric aerosol system andon the major greenhouse gas carbon dioxide are treated peripherally. Nitrogenoxides created during the vehicular internal combustion process willcontribute to nitrate pollution levels measured in the open Pacific. Thepotential for soot and fugitive dust increases should be considered as theautomotive infrastructure develops. Since the emerging Chinese automotivetransportation system will represent a substantial addition to the globalfleet and all the carbon in gasoline is eventually oxidized completely, asignificant rise in global carbon dioxide inputs will ensue as well.Some policy issues are treated preliminary. The assumption is made thatalterations to regional oxidant/aerosol systems and to terrestrial climate areconceivable. The likelihood that the Chinese can achieve the latest vehiclefleet goals is discussed, from the points of view of new production, positivepollution feedbacks from a growing automobile industry, and known petroleumreserves. Vehicular fuel and maintenance options lying before the Chinese areoutlines and compared. To provide some perspective on the magnitude of theenvironmental changes associated with an Asian automotive buildup, recentestimates of the effects of future air traffic over the Pacific Rim aredescribed.

Ventilation of liquefied petroleum gas components from the Valley of Mexico

The saturated hydrocarbons propane and the butane isomers are both indirect greenhouse gases and key species in liquefied petroleum gas (LPG). Leakage of LPG and its component alkanes/alkenes is now thought to explain a significant fraction of the volatile organic burden and oxidative potential in the basin which confines Mexico City. Propane and the butanes, however, are stable enough to escape from the basin. The gas Chromatographie measurements which have drawn attention to their sources within the urban area are used here to estimate rates of ventilation into the free troposphere. The calculations are centered on several well studied February/March pollution episodes. Carbon monoxide observations and emissions data are first exploited to provide a rough time constant for the removal of typical inert pollutant species from the valley. The timescale obtained is validated through an examination of meteorological simulations of three-dimensional flow. Heuristic arguments and transport modeling establish that propane and the butanes are distributed through the basin in a manner analogous to CO despite differing emissions functions. Ventilation rates and mass loadings yield outbound fluxes in a box model type computation. Estimated in this fashion, escape from the Valley of Mexico constitutes of the order of half of 1% of the northern hemispheric inputs for both propane and n-butane. Uncertainties in the calculations are detailed and include factors such as flow into the basin via surface winds and the size of the polluted regime. General quantification of the global propane and butane emissions from large cities will entail studies of this type in a variety of locales.