Wayne T. Davis

An environmental decision-making tool for evaluating ground-level ozone-related health effects.

Abstract A computer model called the Ozone Risk Assessment Model (ORAM) was developed to evaluate the health effects caused by ground-level ozone (O3) exposure. ORAM was coupled with the U.S. Environmental Protection Agency’s (EPA) Third-Generation Community Multiscale Air Quality model (Models-3/CMAQ), the state-of-the-art air quality model that predicts O3 concentration and allows the examination of various scenarios in which emission rates of O3 precursors (basically, oxides of nitrogen [NOx] and volatile organic compounds) are varied. The principal analyses in ORAM are exposure model performance evaluation, health-effects calculations (expected number of respiratory hospital admissions), economic valuation, and sensitivity and uncertainty analysis through a Monte Carlo simulation. As a demonstration of the system, ORAM was applied to the eastern Tennessee region, and the entire O3 season was simulated for a base case (typical emissions) and three different emission scenarios. The results indicated that a synergism occurs when reductions in NOx emissions from mobile and point sources were applied simultaneously. A 12.9% reduction in asthma hospital admissions is expected when both mobile and point source NOx emissions are reduced (50 and 70%, respectively) versus a 5.8% reduction caused by mobile source and a 3.5% reduction caused by point sources when these emission sources are reduced individually.

THERMAL DECOMPOSITION OF SODIUM BICARBONATE

The thermal decomposition of sodium bicarbonate, a candidate material for Hue gas desulfurization, has been investigated over the temperature range of 225-350°F (380-450K) and over the particle size range of 51 -140 μm. The shrinking core model, with chemical reaction as the rate controlling step, provides a good fit to the data in the temperature range investigated. However, caution should be exercised in extrapolating these results into the range of about 600°F (about 590K) where sintering of this material is reported to occur. The activation energy of the decomposition reaction is 20.5 kcal/mol (85.7 kj/mol)

EFFECT OF COUNTY-LEVEL INCOME ON VEHICLE AGE DISTRIBUTION AND EMISSIONS

In conjunction with a statewide emissions inventory of on-road mobile sources in Tennessee, a county-by-county analysis of vehicle registration data was performed. Several interesting trends were observed in the kinds and ages of vehicles driven in Tennessee counties compared with national statistics and compared with the average personal income of county residents. In particular, median vehicle age correlated strongly with average personal income for each county. Vehicle fleets were oldest in lowestincome counties and newest in the highest-income county; median vehicle age was 10.8 years in the former and only 5.9 years in the latter. This difference in vehicle age results in average mobile-source emissions factors 63% higher for nitrogen oxides, 73% higher for carbon monoxide, and 104% higher for volatile organic compounds in the lowest-income counties than in the highest-income counties, based on the MOBILE6 emissions model run for calendar year 2000. The low-income counties also registered 76% more light-duty trucks per capita than the national average, and these trucks were 5 years older than the national median age. It is concluded that county-level personal income is a good predictor of vehicle age and can be used as a readily obtainable indication of whether local vehicle registration data should be used to improve the accuracy of emissions inventories (instead of national defaults or statewide averages). County-level personal income also can be used as a basis for determining whether more than one vehicle age distribution should be used for modeling mobile-source emissions within a state, a metropolitan area, or an airshed.

Study of the Reaction of SO2 with NaHCO3 and Na2CO3

The results are presented of a study conducted to examine the reactivity of NaHCO3 and its thermally decomposed product, Na2CO3, with SO2 as a function of temperature and particle size in a simulated flue gas. The NaHCO3 reaction was found to be significantly more efficient than the Na2CO3 reaction for temperatures less than 450°F (230°C) with a maximum efficiency of conversion occurring between 250 and 350°F. In the temperature range of 450-650°F, both compounds were observed to behave similarly. The Na2CO3 reaction with SO2 was found to be dependent on particle size in the range of 20-200/tm for temperatures less than 450°F.

Ozone and PM2.5 exposure and acute pulmonary health effects: a study of hikers in the Great Smoky Mountains National Park.

To address the lack of research on the pulmonary health effects of ozone and fine particulate matter (≤ 2.5 μm in aerodynamic diameter; PM2.5) on individuals who recreate in the Great Smoky Mountains National Park (USA) and to replicate a study performed at Mt. Washington, New Hampshire (USA), we conducted an observational study of adult (18–82 years of age) day hikers of the Charlies Bunion trail during 71 days of fall 2002 and summer 2003. Volunteer hikers performed pre- and posthike pulmonary function tests (spirometry), and we continuously monitored ambient O3, PM2.5, temperature, and relative humidity at the trailhead. Of the 817 hikers who participated, 354 (43%) met inclusion criteria (nonsmokers and no use of bronchodilators within 48 hr) and gave acceptable and reproducible spirometry. For these 354 hikers, we calculated the posthike percentage change in forced vital capacity (FVC), forced expiratory volume in 1 sec (FEV1), FVC/FEV1, peak expiratory flow, and mean flow rate between 25 and 75% of the FVC and regressed each separately against pollutant (O3 or PM2.5) concentration, adjusting for age, sex, hours hiked, smoking status (former vs. never), history of asthma or wheeze symptoms, hike load, reaching the summit, and mean daily temperature. O3 and PM2.5 concentrations measured during the study were below the current federal standards, and we found no significant associations of acute changes in pulmonary function with either pollutant. These findings are contrasted with those in the Mt. Washington study to examine the hypothesis that pulmonary health effects are associated with exposure to O3 and PM2.5 in healthy adults engaged in moderate exercise.

A MECHANISTICALLY BASED MATHEMATICAL MODEL OF SULFUR DIOXIDE ABSORPTION INTO A CALCIUM HYDROXIDE SLURRY IN A SPRAY DRYER

A mathematical model has been developed to predict So2 absorption and removal during the constant rate drying period of a spray dryer. The model, based on film theory, treats the atomized slurry droplets as spheres containing discrete sorbent particles of slaked lime with the fluid uniformly distributed around the individual particles. The model includes gas and liquid phase mass transfer coefficients as well as resistance to Ca(OH)2 dissolution. A sensitivity analysis has been conducted and a comparison was made between pilot-scale experimental data and model-predicted values of S02 removal efficiency.

STUDY OF THE ADSORPTION/REMOVAL EFFICIENCY OF WOVEN AND NONWOVEN ACTIVATED CARBON FABRICS FOR MEK

The initial gaseous contaminant removal efficiency and adsorption characteristics for various commercially available activated carbon fabrics were determined at air flow rates, air temperature and pressure drop typical of an indoor air residential or small office environment. Methyl ethyl ketone (MEK) was used as the hazardous air pollutant for the laboratory tests. For the range of MEK concentrations tested, the initial fabric adsorption efficiency decreased as concentration increased, although the total adsorption capacity (g/g) increased. Initial fabric efficiencies were also higher at a lower air flow rate. The pure activated carbon nonwoven felt had higher adsorption capacity as well as higher initial adsorption efficiencies than the woven carbon fabrics tested. In all of the fabrics which were tested, the maximum adsorption efficiency was achieved initially, lasted only momentarily, then steadily decreased until adsorption capacity was reached. It was also observed that fabrics that had reached capacity, but were then subjected to the same air flow conditions as occurred during the adsorption process (except without the MEK present), immediately began to desorb the adsorbed MEK. This raises concern about the application of carbon adsorption systems for indoor environments, if concentrations are highly variable due to the potential of desorption from the fabric.

A Combined Ca(OH)2/NH3 Flue Gas Desulfurization Process for High Sulfur Coal: Results of a Pilot Plant Study

The removal of SO2 with atomization of a slaked lime slurry and supplemental injection of gaseous NH3 were tested in a conventional spray dryer/baghouse system for SO2 concentrations of 2000 ppm and 3000 ppm and a 30° F approach to saturation. Results at 3000 ppm of SO2 showed an average SO2 removal efficiency of 90.3 percent at a combined stoichiometric ratio of 0.95-1.10 and an average overall sorbent utilization of 91.6 percent. The overall molal ratio of NH3/SO2 reaction was found to be 2:1 under the test conditions Particle size analyses, and EP toxicity tests were conducted on the products of the reactions.

The retention of sulfur in fly ash from coal-fired boilers

Graphical and statistical analyses of the study presented showed that the sulfur retention in fly ash emitted from coal-fired boilers is a function of the alkaline metal oxide content of the fly ash. Further, it was shown that the correlations between sulfur retention and the relative concentrations of the specific alkaline metal oxides were improved significantly, when the data sets were reduced to include only those data obtained from coal-fired boilers which had similar combustion characteristics and particulate collection systems. Excellent correlations were obtained for the wide range of fly ashes that were studied, but the range of observed values of sulfur retention at any specific value of alkaline metal content is greater than a factor of two in most cases. This variation is due to the combined effects of many factors including boiler characteristics, particle size effects, and other mass transfer parameters. (JMT)

Air Quality Measurements Inside Diesel Truck Cabs During Long-Term Idling

The overall objective of this study was to measure the air pollutant concentrations inside and outside of diesel truck cabs under conditions of extended idling at a truck stop. The measurements were conducted under different modes of engine and air conditioner operation at different times of day and night. One-hour average concentrations of fine particulate matter, nitrogen oxides, and carbon monoxide were measured. All trucks showed some level of self-contamination of in-cab air quality from engine emissions during idling. Some trucks showed significantly higher in-cab concentrations than outside concentrations, indicating engine compartment leaks into the cab. Other trucks showed in-cab concentrations similar to or even lower than outside concentrations but showed higher outside and in-cab concentrations during engine idling than when the engine was turned off. In these cases, truck emissions raised the outside concentrations, which then migrated into the truck cab. Carbon monoxide concentrations measured in the cab were insignificant compared with relevant air quality standards, but fine particulate matter and nitrogen dioxide concentrations were higher than some U.S. Environmental Protection Agency ambient air quality standards. None of the measurements was higher than Occupational Safety and Health Administration or National Institute for Occupational Safety and Health air quality standards.