Computer Simulation of a Municipal Solid Waste Combustor

A mathematical model has been developed to study the thermal and chemical processes occurring In a municipal solid waste mass combustor. Treating the solids feed as a mixture of pseudo-components, the model determines the Interrelationships between the solids feed rate, grate travel rate and length, amounts and distributions of primary and secondary air, extent of solids burn out, and the bed and flame temperatures. The model Incorporates the kinetics of pyrolysis of solids and simulates heat and mass transfer within the bed.

The temperature and mass flow profiles generated show that much of the grate Is taken up by the heatup and burnout zones. The heatup zone can be reduced by distributing the primary air to maintain minimal air flow In that region, thereby permitting rapid heatup. Increasing the solids feed rate and adjusting the air flow distributions can reduce the length of the burnout zone. The computer program, available on both PCs and mainframe, can be used for different MSW Incinerator dimensions and feed parameters to Investigate the effects of the control variables and optimize the desired output characteristics, e.g., maximize solids throughput.     

An historical experiment: Los Angeles smog evolution observed by blimp

Observations of smog over the Los Angeles Basin (LAB) links high oxidant mixing ratios with poor visibility, sometimes <5 km. By the 1970s, investigators recognized that most of the aerosol affecting visibility was from gaseous oxidation products, sulfate, nitrate, and organic carbon. This led to the 1972–1973 Aerosol Characterization Experiment (ACHEX), which included observations at the ground and from aircraft. Part of ACHEX was the measurement of smog by blimp in a Lagrangian-like format. The experiment on September 6, 1973, demonstrated that a blimp could travel with the wind across the LAB, observing ozone (O₃) and precursors, and particles of different size ranges. These included condensation nuclei (CN) concentrations dominated by particles of ≤ 0.1 µm diameter and light scattering coefficient (b_sc) representing mainly particles of 0.1–2.0 µm diameter. The results indicated a pollutant variation similar to that measured at a fixed site. Ozone was produced in an air mass, reaching a maximum of ~400 ppb in the presence of nitrogen oxides (NO_x) and nonmethane hydrocarbons (NMHCs), then declined. Although the photochemistry was developing, b_sc grew with O₃ mixing ratio to a quasi-steady state at ~9–10 × 10^?4 m^?1, decreasing in value much later with decease in O₃. The light scattering coefficient was found to be positively associated with the O₃ mixing ratio, whereas CN concentrations were negatively proportional to O₃ mixing ratio. The blimp experiment was supported with aircraft vertical profiles and ground-level observations from a mobile laboratory. The blimp flight obtained combined gas and particle changes aloft that could not be obtained by ground or fixed-wing aircraft measurements alone. The experiment was partially successful in achieving a true Lagrangian characterization of smog chemistry in a constrained or defined “open” air mass.

Implications: The Los Angeles experiment demonstrated the use of a blimp as a platform for measurement of air pollution traveling with an air mass across an urban area. The method added unique data showing the relationship between photochemical smog chemistry and aerosol dynamics in smog. The method offers an alternative to reliance on smog chamber and modeling observations to designing air quality management strategies for reactive pollutants.     

Relationships between Aerosol Extinction Coefficients Derived from Airport Visual Range Observations and Alternative Measures of Airborne Particle Mass

Epidemiological assessments of population exposures to airborne particles are often hampered by the scarcity of available fine particle mass measurements. In an attempt to overcome this serious problem, we analyze In this paper methods for predicting fine particle (M ₁) and Inhalable particle (IP) mass concentrations using relative humidity corrected light extinction coefficient (b _ext) estimated from airport visual range (V _r) observations. The analyses presented are based on theoretical determinations as well as statistical investigations utilizing EPA's NASN and Inhalable Particle Monitoring Network (IPMN) data bases and routine airport visual range observations In twelve large U.S. cities. Our results Indicate that, after controlling for certain limitations of airport visual range data, most of the regression models developed in this paper can be applied satisfactorily to predict M _t and IP. Furthermore, our findings Indicate that a more representative formula than the commonly used meteorological range formula to predict atmospheric b _ext values in urban areas may be b _ext = (1.8 ± 0.04)/V _r. Because of known local or regional influences, however, we do suggest calibration of any predictive model which utilizes airport visibility data against site-specific aerometric data on particle mass concentrations or scattering coefficient measurements.     

fluoride concentrations in the ambient air

The body of the information presented in this paper is of general interest to those concerned with air quality. This paper reports data for ambient atmospheric concentrations of water-soluble fluorides determined in samples of suspended particulate matter collected on glass-fiber filters by the National Air Surveillance Network. Data for over 12,000 samples collected in calendar years 1966, 1967, and 1968 are examined. The purpose of the examination of the data is to give an estimation of current air quality with respect to fluoride content.

The samples are extracted with pure boiling water, and the fluoride concentration of the extracts measured using a fluoride-ion selective electrode. The data engendered are tabulated on an annual basis, and a table is presented summarizing the results. Comparative data will be presented showing the distribution of urban and non-urban stations that exhibit various specified fluoride levels. The results show that the fluoride content in the majority of the samples is below the minimum detectable amount of 0.05 µgF/m³. Conclusions that can be drawn include the observations that: few of the urban samples contain over 1.00 µg/m ³ of fluoride, very few of all samples exceeded 1.00 µ/m³ of fluoride, and no non-urban sample contained over 0.16 µg/m³ of fluoride. It was also concluded that only in rare instances would the fluoride concentrations at the sites sampled be in excess of published standards.     

Note on a Method to Estimate Missing Air Pollution Data

An iterative regression procedure is presented to estimate missing air pollution measurements when the data are measured at two or more sampling stations in the same vicinity. The procedure utilizes the measurements taken at other stations, on neighboring days, and of other pollutants.

The procedure is applied to a set of Philadelphia pollution data with from five to seventeen per cent of the observations missing. The method is tested by comparing the known observed pollutant values, with their estimates given by the procedure. Correlations between the observations and their estimates are uniformly high, ranging from 0.87 to 0.91. These correlations compare favorably with those estimates given by a simple linear interpolation. The magnitude of the correlations suggests that estimates given by this iterative regression procedure may be used where missing observations pccur without fear of undesirable effects on subsequent work. Therefore, this procedure may be a valuable tool in handling the problem of missing observations in air pollution data.     

Lagrangian Dispersion Modeling of Vehicular Emissions from a Highway in Complex Terrain

Abstract

Transit traffic through the Austrian Alps is of major concern in government policy. Pollutant burdens resulting from such traffic are discussed widely in Austrian politics and have already led to measures to restrict traffic on transit routes. In the course of an environmental assessment study, comprehensive measurements were performed. These included air quality observations using passive samplers, a differential optical absorption spectroscopy system, a mobile and a fixed air quality monitoring station, and meteorological observations. As was evident from several previous studies, dispersion modeling in such areas of complex terrain and, moreover, with frequent calm wind conditions, is difficult to handle. Further, in the case presented here, different pollutant sources had to be treated simultaneously (e.g., road networks, exhaust chimneys from road tunnels, and road tunnel portals). No appropriate system for modeling all these factors has so far appeared in the literature. A prognostic wind field model coupled with a Lagrangian dispersion model is thus presented here and is designed to treat all these factors. A comparison of the modeling system with results from passive samplers and from a fixed air quality monitoring station proved the ability of the model to provide reasonable figures for concentration distributions along the A10.     

Development and implementation of a remote-sensing and in situ data-assimilating version of CMAQ for operational PM2.5 forecasting. Part 1: MODIS aerosol optical depth (AOD) data-assimilation design and testing

This two-part paper reports on the development, implementation, and improvement of a version of the Community Multi-Scale Air Quality (CMAQ) model that assimilates real-time remotely-sensed aerosol optical depth (AOD) information and ground-based PM_2.5 monitor data in routine prognostic application. The model is being used by operational air quality forecasters to help guide their daily issuance of state or local-agency-based air quality alerts (e.g. action days, health advisories). Part 1 describes the development and testing of the initial assimilation capability, which was implemented offline in partnership with NASA and the Visibility Improvement State and Tribal Association of the Southeast (VISTAS) Regional Planning Organization (RPO). In the initial effort, MODIS-derived aerosol optical depth (AOD) data are input into a variational data-assimilation scheme using both the traditional Dark Target and relatively new “Deep Blue” retrieval methods. Evaluation of the developmental offline version, reported in Part 1 here, showed sufficient promise to implement the capability within the online, prognostic operational model described in Part 2. In Part 2, the addition of real-time surface PM_2.5 monitoring data to improve the assimilation and an initial evaluation of the prognostic modeling system across the continental United States (CONUS) is presented.

Implications: Air quality forecasts are now routinely used to understand when air pollution may reach unhealthy levels. For the first time, an operational air quality forecast model that includes the assimilation of remotely-sensed aerosol optical depth and ground based PM_2.5 observations is being used. The assimilation enables quantifiable improvements in model forecast skill, which improves confidence in the accuracy of the officially-issued forecasts. This helps air quality stakeholders be more effective in taking mitigating actions (reducing power consumption, ride-sharing, etc.) and avoiding exposures that could otherwise result in more serious air quality episodes or more deleterious health effects.     

The effect of variability in industrial emissions on ozone formation in Houston, Texas

Ambient observations have indicated that high concentrations of ozone observed in the Houston/Galveston area are associated with plumes of highly reactive hydrocarbons, mixed with NO_x, from industrial facilities. Ambient observations and industrial process data, such as mass flow rates for industrial flares, indicate that the VOCs associated with these industrial emissions can have significant temporal variability. To characterize the effect of this variability in emissions on ozone formation in Houston, data were collected on the temporal variability of industrial emissions or emission surrogates (e.g., mass flow rates to flares). The observed emissions variability was then used to construct regionwide emission inventories with variable industrial emissions, and the impacts of the variability on ozone formation were examined for two types of meteorological conditions, both of which lead to high ozone concentrations in Houston. The air quality simulations indicate that variability in industrial emissions has the potential to cause increases and decreases of 10–52 ppb (13–316%), or more, in ozone concentration. The largest of these differences are restricted to regions of 10–20 km², but the variability also has the potential to increase regionwide maxima in ozone concentrations by up to 12 ppb.     

Regional climate forcing of aerosol estimated by a box model for a rural site in Central Europe during summer

In the present work, a box model is applied to estimate the direct climate forcing of aerosol particles for rural air in Central Europe during summertime. In the model, the input parameters reflect regional character: data from satellite observations and other surface measurements are used referring to the selected area, Hungary. In the calculation of direct climate forcing of aerosol particles satellite observations serve as the source of incoming solar radiation intensity data and cloudiness, while different aerosol parameters of the model (mass extinction coefficient, chemical composition, scale height, hygroscopic growth factor, etc.) are based on local measurements. Finally, surface albedo of the area studied was determined on the basis of vegetation cover and precipitation amount. As the summary of our calculations, in Central Europe direct climate forcing of ammonium sulfate is equal to –2.4 W m⁻². The climate forcing of total carbon is composed of two terms. The forcings due to scattering and absorption are –1.0 and +0.2 W m⁻², respectively. In spite of the fact that the mass concentrations of ammonium sulfate and total carbon are similar, their contribution to the aerosol direct forcing is different. We conclude that ammonium sulfate plays the major role in this process and organics have an additional impact.     

A note on average vertical profiles of vehicular pollutant concentrations in urban street canyons

Recent observations of air pollutant concentrations measured within and above street canyons were used to study the average vertical profiles of vehicular pollutant concentrations in the urban environment. The idea of an exponential vertical concentration distribution, exp( −Bz^q), resulted from a near ground-level source diffusing over flat terrain, was tentatively extended to the urban street canyons, where the empirical parameters B and q are generally dependent on the atmospheric stability and the aerodynamic characteristics of the canyon.     

The Analysis of PPM Levels of Gases in Air By Photoionization Mass Spectrometry

The body of information in this paper is directed toward individuals involved in the analysis of trace gases in air. The photoionization mass spectrometer has been investigated for a variety of potential inorganic and organic air pollutants at four ionizing wavelengths. The three aspects studied were (a) selective ionization of trace gases eliminating the ionization of the major components of air, (b) simplification of mass spectral fragmentation patterns, and (c) currently feasible sensitivities and detection limits. The results demonstrate that photoionization is superior to electron impact ionization for the first two aspects. The measured sensitivities and calculated detection limits require some improvement. It is shown that the necessary sensitivities can be obtained by eliminating the UV monochromator and using direct ionization with a hydrogen light source.     

Size Distribution of Participates Emitted from a Horizontal Spike Soderberg Aluminum Reduction Cell

Aerosol size distributions were measured in the air exhausted from a horizontal spike Soderberg aluminum reduction cell at the Kaiser Aluminum and Chemical Corporation plant in Tacoma, Wash. The particle size distributions were measured with the University of Washington cascade impactor, developed specifically for source testing. The particle mass concentrations and size distributions were found to vary significantly with changes in the cell process operations. For a typical aerosol size distribution at the exit of the cell hood the mass mean particle diameter was 5.5 microns and the particle size standard geometric deviation was 25.     

The Correlation between Light Scattering and Mass Concentration of Tobacco Smoke

Reports by others^1,2 have pointed to tobacco smoke as a significant source of air pollution in indoor spaces. Studies by Charlson, et al., ³ Kretzschmar,⁴ and Eccleston, et al. ⁵ have yielded mass concentration-light scattering correlations for several natural aerosols. This note presents a value for the mass concentration/ light scattering ratio for tobacco smoke. This ratio provides a means of assessing air quality in indoor spaces using an instrument with a fairly short (?1 min) time constant.     

A Model for Uptake of Pollutants by Vegetation

A mass transfer approach is used in developing a practical mathematical model of gaseous pollutant uptake by leaves in which a series of resistances is summed across a concentration difference. The body of information presented in this paper is directed to plant pathologists or physiologists in the field of vegetal-pollutant effects and to people interested in the natural removal of air pollutants by vegetation. Correlations are given to calculate the aerodynamic and the stomatal resistances to uptake, while both a qualitative investigation and quantitative estimates are made of the mesophyllic resistance. The factors which control the aerodynamic resistance, r_a, are leaf size and wind speed, while the leaf physiology is the determinant of the stomatal resistance, r_s . It is noted that the chemical reaction rate and pollutant diffusivity in the mesophyll control the mesophyllic resistance, r_m, though the overall gas phase mesophyllic resistance, Hr_m, is strongly a function of pollutant solubility in water. Finally, the overall model is compared to earlier experimental work on vegetal uptake of SO₂.     

A New Method for the Rapid Determination of Volatile Organic Compound Breakthrough Times for a Sorbent at Concentrations Relevant to Indoor Air Quality

Abstract

The use of sorbents has been proposed to remove volatile organic compounds (VOCs) present in ambient air at concentrations in the parts-per-billion (ppb) range, which is typical of indoor air quality applications. Sorbent materials, such as granular activated carbon and molecular sieves, are used to remove VOCs from gas streams in industrial applications, where VOC concentrations are typically in the parts-per-million range. A method for evaluating the VOC removal performance of sorbent materials using toluene concentrations in the ppb range is described. Breakthrough times for toluene at concentrations from 2 to 7500 ppb are presented for a hydrophobic molecular sieve at 25% relative humidity. By increasing the ratio of challenge gas flow rate to the mass of the sorbent bed and decreasing both the mass of sorbent in the bed and the sorbent particle size, this method reduces the required experimental times by a factor of up to several hundred compared with the proposed American Society of Heating, Refrigerating, and Air-Conditioning Engineers method, ASHRAE 145P, making sorbent performance evaluation for ppb-range VOC removal more convenient. The method can be applied to screen sorbent materials for application in the removal of VOCs from indoor air.     

Process analysis of a regional air pollution episode over Pearl River Delta Region,China, using the MM5-CMAQ model

This study focuses on the influences of a warm high-pressure meteorological system on aerosol pollutants, employing the simulations by the Models-3/CMAQ system and the observations collected during October 10–12, 2004, over the Pearl River Delta (PRD) region. The results show that the spatial distributions of air pollutants are generally circular near Guangzhou and Foshan, which are cities with high emissions rates. The primary pollutant is particulate matter (PM) over the PRD. MM5 shows reasonable performance for major meteorological variables (i.e., temperature, relative humidity, wind direction) with normalized mean biases (NMB) of 4.5–38.8% and for their time series. CMAQ can capture one peak of all air pollutant concentrations on October 11, but misses other peaks. The CMAQ model systematically underpredicts the mass concentrations of all air pollutants. Compared with chemical observations, SO₂ and O₃ are predicted well with a correlation coefficient of 0.70 and 0.65. PM_2.5 and NO are significantly underpredicted with an NMB of 43% and 90%, respectively. The process analysis results show that the emission, dry deposition, horizontal transport, and vertical transport are four main processes affecting air pollutants. The contributions of each physical process are different for the various pollutants. The most important process for PM₁₀ is dry deposition, and for NO_x it is transport. The contributions of horizontal and vertical transport processes vary during the period, but these two processes mostly contribute to the removal of air pollutants at Guangzhou city, whose emissions are high. For this high-pressure case, the contributions of the various processes show high correlations in cities with the similar geographical attributes. According to the statistical results, cities in the PRD region are divided into four groups with different features. The contributions from local and nonlocal emission sources are discussed in different groups.

Implications: The characteristics of aerosol pollution episodes are intensively studied in this work using the high-resolution modeling system MM5/SMOKE/CMAQ, with special efforts on examining the contributions of different physical and chemical processes to air concentrations for each city over the PRD region by a process analysis method, so as to provide a scientific basis for understanding the formation mechanism of regional aerosol pollution under the high-pressure system over PRD.     

Quantification and Analysis of Airborne Bacterial Characteristics in a Nursing Care Institution

ABSTRACT

Indoor air quality has become a critical issue because people spend most of their time in the indoor environment. The factors that influence indoor air quality are very important to environmental sanitation and air quality improvement. This study focuses on monitoring air quality, colony counts, and bacteria species of the indoor air of a nursing care institution. The regular colony counts in two different wards range from 55 to 600 cfu m^?3. Regression analysis results indicate that the bacterial colony counts have close correlation with relative humidity or carbon dioxide (CO₂) but not with carbon monoxide (CO) or ozone (O₃). Real-time PCR was used to quantify the bacterial pathogens of nosocomial infection, including Acinetobacter baumannii, Citrobacter freundii, Escherichia coli, Klebsiella pneumoniae, and methicillin-sensitive Staphylococcus aureus. The most abundant bacteria species in the air of the nursing care institution is E. coli.

IMPLICATIONS Indoor temperature, humidity, ventilation, accumulation of biological pollutants, and potential infection problems will seriously affect the indoor environments. Studying these factors is important to indoor environmental sanitation and air quality improvements. Results of using real-time PCR to evaluate the bacterial pathogens of nosocomial infection for a nursing care institution in Taiwan reveal that the main bacteria species existing in the indoor air is E. coli.     

Development and field validation of a community-engaged particulate matter air quality monitoring network in Imperial,California, USA

The Imperial County Community Air Monitoring Network was developed as part of a community-engaged research study to provide real-time particulate matter (PM) air quality information at a high spatial resolution in Imperial County, California. The network augmented the few existing regulatory monitors and increased monitoring near susceptible populations. Monitors were both calibrated and field validated, a key component of evaluating the quality of the data produced by the community monitoring network. This paper examines the performance of a customized version of the low-cost Dylos optical particle counter used in the community air monitors compared with both PM_2.5 and PM₁₀ (particulate matter with aerodynamic diameters <2.5 and <10 μm, respectively) federal equivalent method (FEM) beta-attenuation monitors (BAMs) and federal reference method (FRM) gravimetric filters at a collocation site in the study area. A conversion equation was developed that estimates particle mass concentrations from the native Dylos particle counts, taking into account relative humidity. The R² for converted hourly averaged Dylos mass measurements versus a PM_2.5 BAM was 0.79 and that versus a PM₁₀ BAM was 0.78. The performance of the conversion equation was evaluated at six other sites with collocated PM_2.5 environmental beta-attenuation monitors (EBAMs) located throughout Imperial County. The agreement of the Dylos with the EBAMs was moderate to high (R² = 0.35–0.81).

Implications: The performance of low-cost air quality sensors in community networks is currently not well documented. This paper provides a methodology for quantifying the performance of a next-generation Dylos PM sensor used in the Imperial County Community Air Monitoring Network. This air quality network provides data at a much finer spatial and temporal resolution than has previously been possible with government monitoring efforts. Once calibrated and validated, these high-resolution data may provide more information on susceptible populations, assist in the identification of air pollution hotspots, and increase community awareness of air pollution.     

Smog Chamber Simulation of Los Angeles Pollutant Transport

The body of information presented in this paper is directed to those individuals concerned with the effect of urban pollution on downwind areas. In the absence of any evidence, it has been widely assumed that increasing NO _x emissions have caused oxidant levels to increase downwind of Los Angeles, i.e., Riverside and San Bernardino. This smog chamber study simulated pollutant transport from Los Angeles to the downwind areas by irradiating a typical Los Angeles hydrocarbon/NO _x mixture for extended periods of time. The smog chamber experiments were extended to 22 hours to obtain an integrated light intensity equal to that which occurs in the Los Angeles area. The effects of variations of nitrogen oxide emissions on an aged air mass were examined. The results show that downwind oxidant levels are only slightly affected by large changes in NO _x emissions. However, it is clear that reduced nitrogen oxide emissions will lead to an increase in oxidant in downtown Los Angeles.