David F. Miller

Ozone Formation Related to Power Plant Emissions

A curious and unambiguous event of excess ozone formation downwind of a power plant has been analyzed. A kinetic model used to simulate the event indicates that the excess ozone can be reconciled entirely on the basis of excess nitrogen oxides in the polluted air.

Measurement of Nitric Acid in Smog

The formation of nitric acid (HONO2) in the polluted atmosphere has been monitored using a newly developed analyzer. The analytical method, the operation and performance of the analyzer and some results of recent applications are described. The analysis consists of sample conditioning in combination with a Mast micro-coulomb detection cell adapted for sensing acids rather than oxi-dants. Results of calibration and interference testing are presented. The sensitivity of the instrument to HONO2 is about 2 ppb. Application of the analyzer for smog chamber and atmospheric studies is demonstrated. In simulated smog experiments with synthetic auto exhaust, the pattern of HONO2 formation parallels that of ozone formation. A similar formation pattern was observed during ambient sampling. Evidence is presented which suggest that these reactions, may both contribute to HONO2 formation in smog, but the relative importance of the two is yet uncertain. Atmospheric sampling in the Los Angeles area indicated 24 hour aver...

Nitrogen Balance in Smog Chamber Studies

The nitrogen-containing products of smog chamber reactions have been the subject of much controversy. Concern has arisen over nitrogen products because of the almost universally poor nitrogen balance reported for irradiated mixtures of hydrocarbons and nitrogen oxides. Some possible nitrogen-containing products, such as molecular nitrogen, nitrous oxide, and nitroolefins have been investigated and shown to be unimportant. The nitrogen products most often measured are peroxyacetyl nitrate and residual nitrogen dioxide. These two products rarely comprise more than 70% of the initial nitrogen at the end of an experiment, and often account for less than 50%. Previous experiments in which total nitrate was determined in the gas phase and on the vessel walls at the end of irradiation have shown very good nitrogen balances. The assumption has been made that the nitrate arises from nitric acid formed on the walls by adsorbed N2O5. In the work reported here, all major nitrogen-containing compounds have been monito...

Combustion and Photochemical Aerosols Attributable to Automobiles

An aerosol size analyzing system developed at the University of Minnesota was used to measure in situ primary aerosols produced by operation of automobiles on a chassis dynamometer and secondary aerosols produced by photochemical reactions of exhaust vapors in a 610 cu ft smog chamber. The total automotive contribution to urban aerosol concentrations is estimated using the volume emission rate of primary aerosol together with the relative concentrations of primary and secondary aerosols. The size distributions and primary aerosol concentrations determined in the laboratory agreed quite well with results obtained alongside roadways using a similar aerosol analyzer. For exhaust dilution ratios of 20/1 and 40/1 in a laboratory dilution tunnel, the predominant mode in the aerosol size distributions occurred at about 0.03 μm diameter. This size is substantially smaller than that reported in other laboratory studies. The size distribution of the diluted exhaust is sensitive to the rate of dilution at the tailpi...

AEROSOL FORMATION IN URBAN PLUMES OVER LAKE MICHIGAN

Results are reported for field measurements of sulfate aerosol formation in urban plumes from Milwaukee, Wis., that were transported over Lake Michigan by westerly winds. Various types of airborne measurements were made of, for example, light scattering, particles larger than 0.01 micron, the total concentration of condensation nuclei, total hydrocarbons, and concentrations of O/sub 3/, SO/sub 2/, NO, NO/sub x/, SO/sub 4/(-), trace metals, nitrate, and ammonium. Data on derived SO/sub 2/ oxidation rates are compared with the results of a chemical kinetics model that simulated the pollutant conditions. It is concluded that rates of SO/sub 2/ oxidation in isolated urban plumes appear to be quite variable, that kinetics modeling is hindered by an inadequate understanding of the free-radical chemistry that is strongly coupled to the NO/sub x/ cycles, and that the free-radical (HO/sub 2/, RO/sub 2/, O/sub H/) concentrations should be measured in real time so that instantaneous rates may be determined for SO/sub 2/ oxidation.

The Effect of Fuel Composition on Atmospheric Aerosol Due to Auto Exhaust

Aerosols attributable to automobile exhaust can be classified as two types—primary aerosol (initially present in the exhaust) and secondary aerosol (generated photochemically from hydrocarbons and nitrogen oxides in the exhaust). In this study, investigation was made of possible effects of motor-fuel composition on the formation of these aerosols. Secondary aerosol, of principal interest in this work, was produced by irradiating auto exhaust in Battelle-Columbus’ 610 ft3 environmental chamber. A limited number of determinations of primary aerosol in diluted auto exhaust was made at the exit of a 36 ft dilution runnel. Determination of both primary and secondary aerosol was based on light-scattering measurements. Exhaust was generated with seven full-boiling motor gasolines, both leaded and nonleaded, in a 1967 Chevrolet which was not equipped with exhaust-emission control devices. Changes in fuel composition produced a maximum factor of three difference in light scattering due to primary aerosol. Aerosol ...

Semicontinuous method for monitoring SO2 at low parts-per-trillion concentrations

A technique is described for low parts-per-trillion (ppt) detection of SO 2 with high temporal resolution compared to current filter sampling methods. A sulfur chemiluminescence detector, equipped with a quartz burner chamber and a sample probe with a critical orifice, was used as a single detector to analyze SO 2 in ambient air by alternately cycling the sample airstream through a SO 2 denuder. The method provides one SO 2 concentration reading every 10 min. The limits of detection and quantitation were found to be 20 and 70 pptv, respectively. Results from field measurements at a remote site on the south rim of the Grand Canyon during November 1991 are presented, and they indicate a highly variable distribution of SO 2 from the limit of detection to near 2 ppbv

A Versatile Electrochemical Monitor for Air-Quality Measurements

An electrochemical instrument of the type commonly used to monitor total oxidants was adapted to measure acid gases such as SO2, HCI, and HCO2H. By using chemical methods of treating the air sample prior to absorption, it is possible to monitor for specific oxidants and acids. Measurements of NO, NOx, and SO2 during smog-chamber experiments were found to be in good agreement with measurements made by other methods.

Exhaust Hydrocarbon Relationships with Photochemical Aerosol Formation

The formation of photochemically derived aerosols from auto exhaust vapors has been studied in the Battelle-Columbus smog chamber for several years, and this paper summarizes our principal findings on the subject. In leading up to conclusions regarding exhaust composition effects on aerosol formation, salient features of secondary aerosol growth and the measurement of these aerosols by light scattering methods are discussed. Inclusion of primary exhaust aerosols during the irradiation of exhaust influences the ultimate size distribution of the secondary aerosols and may therefore have sizeable effects on light scattering. With unleaded fuel, relatively little primary aerosol is present, and the effect is minimal. In the absence of primary aerosols, substantial concentrations of secondary aerosols might be produced before aerosol growth extends into the light scattering size range. When the smog chamber data are considered entirely, a significant correlation exists between the percent aromatic content of t...

Size characterization of sulfuric acid aerosol emissions

In the course of a vehicle dynamometer study of sulfur emissions from an automobile equipped with oxidation catalysts, aerosol size distribution measurements were made while the exhaust was rapidly mixed with 10 parts of filtered air in a dilution tube. Results obtained with an electrical aerosol analyzer show that, under these dilution conditions, the sulfuric acid aerosols are consistently smaller than 0.3 ..mu..m in diameter. The distribution of aerosol volume (or mass) is slightly bimodal with maxima near 0.03 and 0.09 ..mu..m particle diameters. When a light-scattering effect is computed from theory using the observed particle size distributions good agreement is obtained between theory and measured light scattering. Within a reasonable margin of error, consistency is found between cascade impactor data, nephelometer light-scattering data, electrical analyzer data, and chemical analyses for sulfate.