Nelson A. Kelly

Nitric acid and ammonia in urban and rural locations

Abstract Measurements of ammonia, nitric acid and particulate nitrate were made at urban sites in Commerce City, Colorado, and Warren, Michigan and at rural locations near Abbeville, Louisiana and Luray, Virginia. The average ammonia and nitric acid concentrations over all sites were 1.7 ppb and 0.7 ppb, respectively. Diurnal patterns, determined at the Abbeville site, suggested a photochemical mechanism for the production of nitric acid and local sources for ammonia. Seasonal data collected in Warren, Michigan showed ammonia concentrations were lowest in the winter. This appears to be caused by the temperature dependence of the ammonium nitrate equilibrium constant. Ammonia and nitric acid concentrations at the other sites were not in agreement with the concentrations predicted from the ammonium nitrate equilibrium constant.

Sources and sinks of ozone in rural areas

Abstract Based on data collected at rural sites in South Dakota, Louisiana and Virginia during the summers of 1978–1980, the factors controlling the diurnal behavior of O3 near the surface were determined. At all three sites, the diurnal O3 profile consisted of a period of O3 increase from sunrise until mid-afternoon, and a period of O3 decrease from late afternoon until sunrise. The daily O3 increase was comprised of two approximately equal portions: one due to downmixing of O3 from aloft (0600–1000 h), and the other due to photochemistry and possibly some further downmixing (1000–1400 h). Even assuming that all of the O3 increase during the 1000–1400 h period was due to local photochemistry, only very small amounts of O3 were formed i.e. about 6 ppb of O3 per ppb of nitrogen oxides (NOx). Both bag irradiation and photochemical modeling studies suggested similar, but slightly higher O3 formation. Comparing the ambient data with the bag irradiation and modeling results, it was concluded that rural photochemistry was not controlled exclusively by NOx, but depended on hydrocarbons as well. The O3 decrease (1800 to 0600 h) generally occurred while nocturnal inversions isolated the lower 50 m of the atmosphere from the air aloft. Since the O3 loss-rate could be parameterized equally well by either zero- or first-order rate laws, we could not distinguish between the two mechanisms. However, concentrations of gaseous species such as terpenes and NOx that might lead to pseudo zero-order O3 loss were generally of minor significance. Consequently, it is concluded that O3 loss was controlled by surface deposition with deposition velocities ranging from 0.06 to 0.34cms−1 at the three sites.

Real-World Emissions from a Modern Production Vehicle Driven in Los Angeles

The emissions of hydrocarbons, nitric oxide, and carbon monoxide from one modern vehicle were measured using on-board instrumentation during about 350 miles of driving in Los Angeles, California. Emissions during on-road driving were compared to those obtained on dynamometers using the urban dynamometer driving schedule (UDDS). Although this study only used one driver and vehicle, tested over a relatively short distance, the analysis technique may be useful for a larger evaluation of off-cycle emissions. The test vehicle had low warmed-up running emissions over the UDDS and for most of the on-road testing where the air-to-fuel ratio was maintained at the stoichiometric point. However, occasional heavily-loaded conditions during the on-road testing led to richerthan-stoiehiometric operation. During these brief enrichment events, which lasted up to 29 seconds, CO emissions were increased by a factor of 2500 and HC by a factor of 40 over closed-loop stoichiometric operation. Nitrogen oxide emissions were sim...

The Nature and Sources of Haze in the Shenandoah Valley/Blue Ridge Mountains Area

In order to investigate the nature and sources of regional haze, the General Motors mobile Atmospheric Research Laboratory was used in the summer of 1980 to monitor ambient air quality in the Shenandoah Valley of northern Virginia. On the average, 92% of the total light extinction was due to scattering by particles; the remainder was due to scattering by gases and absorption by gases and particles. Sulfate aerosols were the most Important visibility-reducing species. Averaging 55% of the fine participate mass, sulfates (and associated water) accounted for 78% of the total light extinction. The second most abundant fine particulate, accounting for 29% of the fine mass, was carbon—most of which was organic. Most of the remaining particulate mass and extinction were due to crustal materials. It is estimated that 78–86% of the total light extinction was caused by anthropogenic aerosol, most of which originated in major source areas of the midwest.

The relationships between the chemical composition of fine particles and visibility in the Detroit metropolitan area

During July 1981, a one week intensive study was conducted to determine the identity of the major visibility-reducing species in Detroits summertime atmosphere. To accomplish this goal, fine particulate samples were collected every 4 h and analyzed for sulfates, nitrates, ammonium, elemental and organic carbon, and trace metals. These species were then related statistically to the light scattering and absorption components of the extinction coefficient. The chemical composition of the aerosol during the study appeared to be representative of the summertime aerosol. The fine particle mass, which accounted for 64% of the total mass less than 15 ..mu..m in diameter, was dominated by ammonium sulfate which comprised 50% of the fine mass. The contributors to the observed light extinction were: sulfate and its associated water, 65%; carbon, 20%; Rayleigh scattering, 7%; NO/sub 2/, 4%; and other fine particulate species, 4%. The regression coefficients used to derive these percentages are in excellent agreement with the coefficients derived for other locations. In addition, the results support our previous finding that sulfates are the most efficient light-scattering species per unit mass of dry weight.

Measurements of sulfur oxides, nitrogen oxides, haze and fine particles at a rural site on the Atlantic coast

During August, 1982 and January and February, 1983, General Motors Research Laboratories operated air monitoring sites on the Atlantic Coast near Lewes, Delaware and 1250 km to the east on the southwest coast of Bermuda. The overall purpose of this project was to study the transformations of the principal acid precipitation precursors, NO x and SO x species, as they transport under conditions not complicated by emissions from local sources. In this paper, the measurements of gas and particulate species from Lewes are described and the composition and sources of sulfate aerosol, which is the most important haze-producing species, are investigated. On the average, the total suspended particulate (TSP) concentration was 27.9 μg/m3 while the PM10 (mass of particles with a diameter less than or equal to 10 μm) concentration was 22.0 μg/m3 or 79 percent of the TSP. The PM10 consisted of 6.1 μg/m3 of coarse particles (CPM, diameter = 2.5 − 10μm) and 15.9 μg/m3 of fine particles (FPM, diameter < 2.5 μm). On a mas...

Relationships between fine particulate species, gaseous pollutants and meteorological parameters in detroit

Abstract During June, July and August 1981, General Motors Research Laboratories operated a comprehensive air-quality monitoring site in Detroit. Parameters monitored included the criteria pollutants, meteorological variables and the organic carbon, elemental carbon and sulfate content of the fine and coarse fractions of inhalable particulates (diameter ⩽ 15 μm). In addition, air parcel trajectories were used to compute the length of time air parcels spent in various upwind emission-source areas before arriving in Detroit. The data were analyzed using varimax-rotated principal component analysis. The results show that midwestern sources upwind of southeastern (SE) Michigan are responsible for most of the observed sulfate, which accounted for about 50% of the fine particle fraction. Significant amounts of ozone, particulate organic carbon and sulfur dioxide are also transported in from upwind sources. Local emissions dominate the concentrations of coarse particulate mass, elemental carbon, carbon monoxide and non-methane hydrocarbons. Important local sources exist for nitrogen oxides, sulfur dioxide and particulate organic carbon.

The Chemical and Meteorological Conditions Associated with High and Low Ozone Concentrations in Southeastern Michigan and Nearby Areas of Ontario

This analysis represents the first characterization of the photochemistry and transport of ozone in the Detroit metropolitan area and provides a basis for comparing data for Detroit to that for other cities. The characterization is based on a comprehensive set of meteorological and chemical measurements obtained at a site in the urban core of Detroit during the summer of 1981, together with measurements of O3, nitrogen oxides (NO X ), and nonmethane organic compounds (NMOC) from rural, suburban, and urban areas in southeastern Michigan and adjacent areas of Ontario. For the quartile (23 days) with highest ozone maxima (97-180 ppb), the maxima occurred 10-70 km north-northeast of the city on days that were warm and hazy with light southsouthwest winds. On such days there was a marked accumulation of ozone precursors (NMOC and NOX) in the early morning, as well as a rapid chemical removal of NO X (NO X half-life of ∼5 h) from morning to midday. The timing of the daily ozone increase across the study region ...

SOURCE REGIONS OF SUMMERTIME OZONE AND HAZE EPISODES IN THE EASTERN UNITED STATES

During the summer of 1979, the mobile Atmospheric Research Laboratory (ARL) was sited near the Louisiana Gulf Coast to monitor the concentrations of air contaminants in air masses moving northward from the Gulf. Using the ARL data in conjunction with O3 and visibility measurements across the entire eastern United States as well as synoptic meteorological data and satellite photographs, major source areas were identified. The haze which was observed on the Louisiana Gulf Coast appears to be primarily due to aged sulfate aerosols. The evidence presented strongly suggests that the sulfates were largely due to SO2 emissions in the northeastern and midwestern United States. The haze initially formed over and downwind of these source areas and was transported to the Gulf Coast area. In the last two episodes, the haze was subsequently transported back to the Midwest source region. Elevated levels of O3 were also associated with the haze. Again, the Northeast and Midwest appear to be the most significant source areas for the regional O3 episodes. Occasionally, O3 formed from emissions in the east Texas area also appear to affect a large portion of the Gulf Coast. In addition, each episode appeared to have a significant stratospheric air component based on 7Be measurements. All three episodes followed the passage of upper levels troughs which produce stratospheric intrusions due to tropopause folding.

Response of ozone to changes in hydrocarbon and nitrogen oxide concentrations in outdoor smog chambers filled with Los Angeles air

Abstract During the summer portion of the 1987 Southern California Air Quality Study (SCAQS), outdoor smog chamber experiments were performed on Los Angeles air to determine the response of maximum ozone levels, O 3 (max), to changes in the initial concentrations of hydrocarbons, HC, and nitrogen oxides, NO x . These captive-air experiments were conducted in downtown Los Angeles and in the downwind suburb of Claremont. Typically, eight chambers were filled with LA air in the morning. In some chambers the initial HC and/or NO x concentrations were changed by 25% to 50% by adding various combinations of a mixture of HC, clean air, or NO x . The O 3 concentration in each chamber was monitored throughout the day to determine O 3 (max). An empirical mathematical model for O 3 (max) was developed from regression fits to the initial HC and NO x concentrations and to the average daily temperature at both sites. This is the first time that a mathematical expression for the O 3 -precursor relationship and the positive effect of temperature on O 3 (max) have been quantified using captive-air experiments. An ozone isopleth diagram prepared from the empirical model was qualitatively similar to those prepared from photochemical mechanisms. This constitutes the first solely empirical corroboration of the O 3 contour shape for Los Angeles. To comply with the Federal Ozone Standard in LA, O 3 (max) must be reduced by approximately 50%. Several strategies for reducing O 3 (max) by 50% were evaluated using the empirical model. For the average initial conditions that we measured in LA, the most efficient strategy is one that reduces HC by 55–75%, depending on the ambient HC/NO x ratio. Any accompanying reduction in NO x would be counter-productive to the benefits of HC reductions. In fact, reducing HC and NO x simultaneously requires larger percentage reductions for both than the reduction required when HC alone is reduced. The HC-reduction strategy is the most efficient on average, but no single strategy is the optimum every day.