Laboratory Characterization of Modified Tapered Element Oscillating Microbalance Samplers

Abstract

Laboratory tests with generated aerosols were conducted to test the efficacy of two recent design modifications to the well-established tapered element oscillating microbalance (TEOM) continuous particulate matter (PM) mass monitor. The two systems tested were the sample equilibration system-equipped TEOM monitor operating at 30 °C, which uses a Nafion dryer as part of the sample inlet, and the differential TEOM monitor, which adds a switched electrostatic precipitator and uses a self-referencing algorithm to determine “true PM mass.” Test aerosols included ammonium sulfate, ammonium nitrate, sodium chloride, copper (II) sulfate, and mixed aerosols. Aerosols were generated with an atomizer or a vibrating orifice generator and were equilibrated in a 450-L slow flow chamber before being sampled. Relative humidity in the chamber was varied between 10 and 90%, and step changes in humidity were executed while generating aerosol to test the response of the instruments. The sample equilibration system-equipped TEOM monitor does reduce, but not totally eliminate, the sensitivity of the TEOM mass monitor to changes in humidity. The differential TEOM monitor gives every indication of being a very robust technique for the continuous real-time measurement of ambient aerosol mass, even in the presence of semi-volatile particles and condensable gases.     

Long-Term Field Characterization of Tapered Element Oscillating Microbalance and Modified Tapered Element Oscillating Microbalance Samplers in Urban and Rural New York State Locations

Abstract

Long-term field comparisons of continuous and integrated filter measurements of mass concentrations of par-ticulate matter (PM) with an aerodynamic diameter less than or equal to 2.5 μm (PM_2.5) were performed at rural and urban sites in New York State. Two versions of the continuous tapered element oscillating microbalance (TEOM) mass monitor are deployed at each site, in addition to Federal Reference Method filter samplers. Data are grouped into monthly averages to retain and demonstrate seasonal differences. Strong seasonal dependence is observed—the TEOM monitors with the heated sensors are biased systematically low with respect to the Federal Reference Method measurements during the cold season. For the rural site, the average bias for the sample equilibration system (SES)-equipped and standard TEOM monitors is 14 and 24%, respectively. At this location, the TEOM monitor measurements were biased low for all 34 months. For the urban site, the average bias for the SES and standard TEOM monitors is 8 and 18%, respectively. At this location, the TEOM monitor measurements are as likely to be biased high as low during the warm-season months. The hour averaged data from the two versions of the TEOM monitor are also compared, and also indicate that the SES-equipped version of the TEOM monitor captures 7-11% more PM_2.5 mass at these locations.     

Continuous Measurement of Diesel Particulate Emissions

Evaluation of emerging diesel particulate emissions control technology will require analytical procedures capable of continuous or “real-time” measurement of transient organic and elemental carbon emissions. Procedures based on the flame ionlzation properties of organic carbon and the opacity or light extinction properties of elemental carbon are described, and applied for measurement of particulate emissions from diesel engines. The Instrumentation provided adequate sensitivity and time resolution for observation of the transient emissions associated with typical automobile urban driving conditions. Analytical accuracy is evaluated by comparing Integrated average results to measurements using classical gravimetric filtration and solvent extraction procedures. Mass specifc extinction coefficients are evaluated using the Beer-Lambert law. A simplified linear model relating elemental carbon concentration to opacity is also evaluated.     

Evaluation of a Test Method for Measuring Indoor Air Emissions from Dry-Process Photocopiers

ABSTRACT

A large chamber test method for measuring indoor air emissions from office equipment was developed, evaluated, and revised based on the initial testing of four dry-process photocopiers. Because all chambers may not necessarily produce similar results (e.g., due to differences in sink effects, temperature and humidity control, air exchange, pollutant monitoring, and measurement biases), a preliminary four-laboratory evaluation of the revised test method was conducted. To minimize variability, the evaluation used a single dry-process photocopier that was shipped to each of the four laboratories along with supplies (i.e., toner and paper).

The results of this preliminary four-laboratory evaluation demonstrate that the test method was used successfully in the different chambers to measure emissions from dry-process photocopiers. Differences in chamber design and construction appeared to have had minimal effect on the results for the volatile organic compounds (VOCs). Perhaps more important than the chamber itself is the sample analysis as identified by duplicate samples that were analyzed by a different laboratory. Percent relative standard deviation (%RSD) was used to provide a simplistic view of interlaboratory precision for this evaluation. Excluding problems with suspected analytical bias observed from one of the laboratories, the precision was excellent for the VOCs with RSDs of less than 10% in most cases. Less precision was observed among the laboratories for aldehydes/ketones (RSD of 23.2% for formaldehyde). The precision for ozone emission rates among three of the laboratories was excellent (RSD of 7.9%), but emission rates measured at the fourth laboratory were much higher.     

An Inventory of Particulate Emissions from Open Sources

Open sources are those stationary sources of air pollution too great in extent to be controlled through enclosure or ducting. Open sources of atmospheric particles include: wind erosion, tilling, and prescribed burning of agricultural cropland; surface mining and wind erosion of tailings piles; vehicular travel on both paved and unpaved roads; construction site activity; and forest fires. It is estimated that in 1976 the total open source emissions of particles in the U.S. amounted to over 580 × 10⁶ ton. These estimates indicate that emissions from the two largest open source classes, travel on unpaved roads and agricultural wind erosion, accounted for 86% of this total. The open source emissions in ten states (AZ, CA, KS, MN, MT, NM, ND, OH, SD, TX) contributed 6 2% of the national emissions for 1976.     

An Evaluation of the Semi-VOST Method for Determining Emissions from Hazardous Waste Incinerators

The Semi-Volatile Organic Sampling Train method was investigated to determine its reliability and to determine the bias and precision of the method when used to determine emissions from hazardous waste incinerators. Experiments showed that the matrix and sampling variables usually involved in sampling emissions from a hazardous waste incinerator had no significant effect on the recovery of 11 different organic compounds. Significant losses of the sampled compounds can occur during sample preparation. The degree of loss appears to be directly related to the compounds, vapor pressure. These losses can be corrected for by adding deuterated surrogates to the sample and analyzing the surrogates along with the native compounds.

The bias determination was based on dynamic spiking of the sampling train with five deuterated organic compounds selected from Appendix VIII of the Resource Conservation and Recovery Act regulations. The results show biases of from -1 ± 8 percent to -18 ± 27 percent for chlorinated and nonchlorinated compounds. Pyridine, a water-soluble compound, showed a larger bias of-29 ± 13 percent. Particular attention to the recovery of water soluble compounds is necessary to minimize bias in their determinations. Further work is needed to determine the reliability of laboratory-determined retention volumes that are used to determine sampling conditions.     

Control of Diesel Gaseous and Particulate Emissions with a Tube-Type Wet Electrostatic Precipitator

Abstract

In this study, experiments were performed with a bench-scale tube-type wet electrostatic precipitator (wESPs) to investigate its effectiveness for the removal of mass- and number-based diesel particulate matter (DPM), hydrocarbons (HCs), carbon monoxide (CO), and oxides of nitrogen (NO_x) from diesel exhaust emissions. The concentration of ozone (O₃) present in the exhaust that underwent a nonthermal plasma treatment process inside the wESP was also measured. A nonroad diesel generator operating at varying load conditions was used as a stationary diesel emission source. The DPM mass analysis was conducted by means of isokinetic sampling and the DPM mass concentration was determined by a gravimetric method. An electrical low-pressure impactor (ELPI) was used to quantify the DPM number concentration. The HC compounds, n-alkanes, and polycyclic aromatic hydrocarbons (PAHs) were collected on a moisture-free quartz filter together with a PUF/XAD/PUF cartridge and extracted in dichloromethane with sonication. Gas chromatography (GC)/mass spectroscopy (MS) was used to determine HC concentrations in the extracted solution. A calibrated gas combustion analyzer (Testo 350) and an O₃ analyzer were used for quantifying the inlet and outlet concentrations of CO and NO_x (nitric oxide [NO] + nitrogen dioxide [NO₂]), and O₃ in the diesel exhaust stream. The wESP was capable of removing approximately 67–86% of mass- and number-based DPM at a 100% exhaust volumetric flow rate generated from 0- to 75-kW engine loads. At 75-kW engine load, increasing gas residence time from approximately 0.1 to 0.4 sec led to a significant increase of DPM removal efficiency from approximately 67 to more than 90%. The removal of n-alkanes, 16 PAHs, and CO in the wESP ranged from 31 to 57% and 5 to 38%, respectively. The use of the wESP did not significantly affect NO_x concentration in diesel exhaust. The O₃ concentration in diesel exhaust was measured to be less than 1 ppm. The main mechanisms responsible for the removal of these pollutants from diesel exhaust are discussed.     

A New Alternative Fuel for Reduction of Polycyclic Aromatic Hydrocarbon and Particulate Matter Emissions from Diesel Engines

Abstract

This study investigated the emissions of polycyclic aromatic hydrocarbons (PAHs), carcinogenic potential of PAH and particulate matter (PM), brake-specific fuel consumption (BSFC), and power from diesel engines under transient cycle testing of six test fuels: premium diesel fuel (PDF), B100 (100% palm biodiesel), B20 (20% palm biodiesel + 80% PDF), BP9505 (95% paraffinic fuel + 5% palm biodiesel), BP8020 (80% paraffinic fuel + 20% palm biodiesel), and BP100 (100% paraffinic fuel; Table 1). Experimental results indicated that B100, BP9505, BP8020, and BP100 were much safer when stored than PDF. However, we must use additives so that B100 and BP100 will not gel as quickly in a cold zone. Using B100, BP9505, and BP8020 instead of PDF reduced PM, THC, and CO emissions dramatically but increased CO₂ slightly because of more complete combustion. The CO₂-increased fraction of BP9505 was the lowest among test blends. Furthermore, using B100, B20, BP9505, and BP8020 as alternative fuels reduced total PAHs and total benzo[a]pyrene equivalent concentration (total BaP_eq) emissions significantly. BP9505 had the lowest decreased fractions of power and torque and increased fraction of BSFC. These experimental results implied that BP9505 is feasible for traveling diesel vehicles. Moreover, paraffinic fuel will likely be a new alternative fuel in the future. Using BP9505 instead of PDF decreased PM (22.8%), THC (13.4%), CO (25.3%), total PAHs (88.9%), and total BaP_eq (88.1%) emissions significantly.     

Current Technology for Continuous Monitoring of Particulate Emissions

Particulate matter is characterized by its physical and chemical properties. Federal and state emission standards identify two important physical properties, opacity (visible emissions) and particulate mass concentration. In addition, particle size and particle composition are characteristics that play a significant role in the assessment of health effects, visibility, and control strategy. Systems to monitor these particle characteristics are in various stages of development. Opacity monitors have the longest history of commercial availability and of applicability to various source emissions. Particulate mass monitors have a short history as commercially available systems and are under evaluation in various source applications. Particle size monitors are mainly in the advanced prototype development stage undergoing evaluation. Particle composition monitors are in the early stages of development as research prototypes. Real time size monitoring systems will eventually be wedded to real time particle composition analyzers to give a monitoring system for particle size distributions of chemical constituents.     

Alternatives to the Gravimetric Method for Quantification of Diesel Particulate Matter near the Lower Level of Detection

Abstract

This paper is part of the Journal of the Air & Waste Management Association’s 2010 special issue on combustion aerosol measurements. The issue is a combination of papers that synthesize and evaluate ideas and perspectives that were presented by experts at a series of workshops sponsored by the Coordinating Research Council that aimed to evaluate the current and future status of diesel particulate matter (DPM) measurement. Measurement of DPM is a complex issue with many stakeholders, including air quality management and enforcement agencies, engine manufacturers, health experts, and climatologists. Adoption of the U.S. Environmental Protection Agency 2007 heavy-duty engine DPM standards posed a unique challenge to engine manufacturers. The new standards reduced DPM emissions to the point that improvements to the gravimetric method were required to increase the accuracy and the sensitivity of the measurement. Despite these improvements, the method still has shortcomings. The objectives of this paper are to review the physical and chemical properties of DPM that make gravimetric measurement difficult at very low concentrations and to review alternative metrics and methods that are potentially more accurate, sensitive, and specific. Particle volatility, size, surface area, and number metrics are considered, as well as methods to quantify them. Although the authors believe that an alternative method is required to meet the needs of engine manufacturers, the methods reviewed in the paper are applicable to other areas where the gravi-metric method detection limit is approached and greater accuracy and sensitivity are required. The paper concludes by suggesting a method to measure active surface area, combined with a method to separate semi-volatile and solid fractions to further increase the specificity of the measurement, has potential for reducing the lower detection limit of DPM and enabling engine manufacturers to reduce DPM emissions in the future.     

A Strategy for Reduction of Particulate Emissions in the Boston Area

Initial implementation plans provided for particulate reduction largely through the imposition of emission limitations on industrial processes, large steam generators, and solid waste disposal, requiring, in turn, application of control equipment for compliance. In many urban areas, this approach is not adequate to achieve the secondary air quality standards so that a more general strategy must be employed. Such strategy may include restrictions on fuel burning, combustion equipment, maintenance programs, utility steam distribution, etc. The potential abatement achievable through such strategies is described using Boston as a case study. Cost and technical factors associated with each strategy are discussed.     

Field Measurements of Particulate Matter Emissions,Carbon Monoxide,and Exhaust Opacity from Heavy-Duty Diesel Vehicles

ABSTRACT

Diesel particulate matter (PM) is a significant contributor to ambient air PM₁₀ and PM_2.5 particulate levels. In addition, recent literature argues that submicron diesel PM is a pulmonary health hazard. There is difficulty in attributing PM emissions to specific operating modes of a diesel engine, although it is acknowledged that PM production rises dramatically with load and that high PM emissions occur during rapid load increases on turbocharged engines. Snap-acceleration tests generally identify PM associated with rapid transient operating conditions, but not with high load. To quantify the origin of PM during transient engine operation, continuous opacity measurements have been made using a Wager 650CP full flow exhaust opacity meter. Opacity measurements were taken while the vehicles were operated over transient driving cycles on a chassis dynamometer using the West Virginia University (WVU) Transportable Heavy Duty Vehicle Emissions Testing Laboratories. Data were gathered from Detroit Diesel, Cummins, Caterpillar, and Navistar heavy-duty (HD) diesel engines. Driving cycles used were the Central Business District (CBD) cycle, the WVU 5-Peak Truck cycle, the WVU 5-Mile route, and the New York City Bus (NYCB) cycle. Continuous opacity measurements, integrated over the entire driving cycle, were compared to total integrated PM mass. In addition, the truck was subjected to repeat snap-acceleration tests, and PM was collected for a composite of these snap-acceleration tests. Additional data were obtained from a fleet of 1996 New Flyer buses in Flint, MI, equipped with electronically controlled Detroit Diesel Series 50 engines. Again, continuous opacity, regulated gaseous emissions, and PM were measured. The relationship between continuous carbon monoxide (CO) emissions and continuous opacity was noted. In identifying the level of PM emissions in transient diesel engine operation, it is suggested that CO emissions may prove to be a useful indicator and may be used to apportion total PM on a continuous basis over a transient cycle. The projected continuous PM data will prove valuable in future mobile source inventory prediction.     

An Evaluation of Emissions and Control Technologies for the Metal Decorating Process

A simple but effective sampling and analytical procedure is described for determining total organics, carbon dioxide, carbon monoxide, and methane emitted from web offset printing presses. Data are reported on a number of controlled and uncontrolled sources and emission levels are related to process variables such as press speed, ink coverage and dryer type. For controlled sources employing either catalytic or thermal incineration units, conversion efficiencies are reported as a function of temperature. Operational curves are presented for each control system studied indicating the dependency of carbon dioxide, NO_xt and organic output to incineration temperatures.     

An Evaluation of Emissions and Control Technologies for the Metal Decorating Process

Data are reported on a number of controlled and uncontrolled sources from various metal decorating operations. Emission levels are related to process variables such as ink coverage, coater speed, sheet size, and applied coating film weight. Results are presented depicting variation of organic emission levels from a coating process line with elapsed process time. For controlled sources employing either catalytic or thermal incineration, conversion efficiencies are reported as a function of temperature. Operational curves are presented for each control system studied indicating the dependence of carbon dioxide, NO_x, and organic output on incineration temperatures.     

The Impact of Particulate Emissions Control On the Control of Other MWC Air Emissions

On December 20, 1989, the Environmental Protection Agency (EPA) proposed revised new source performance standards for new municipal waste combustion (MWC) units and guidelines for existing sources. The proposed national regulations require tighter particulate matter control and address pre-combustion, combustion, and post-combustion controls, the latter two depending on capacity and age of the facility.

The air pollutants of concern when municipal solid waste (MSW) is burned will be discussed. Generally, particulate control is an inherent part of the systems used to limit the emissions of these air pollutants. The relationships between MWC air emissions (acid gases, trace organics, and trace heavy metals) control and particulate control will be discussed. Test results to quantify air pollutant emissions from MWC units and their control will be presented and compared with the proposed regulations.     

Evaluation of Canisters for Measuring Emissions of Volatile Organic Air Pollutants from Hazardous Waste Incineration

Regulation to control air emissions of toxic organic compounds require the collection and analysis of effluent gas from low level sources such as hazardous waste incinerators. The standard SW- 846 Method specifies the use of Tenax and Tenax/charcoal adsorbent traps for collection of volatile organics from incinerators. This study evaluates passivated stainless steel canisters as an alternative to adsorbent traps to eliminate some of the problems associated with adsorbent sampling. Initially the stability of 18 nonpolar, volatile organic compounds was determined in Summa-treated stainless steel canisters with greater than 100 ppmv HCI and saturated with water vapor. All 18 components were stable for a twoweek period; however, an Interference caused a 10-fold increase In the FID response of trlchloroethylene, toluene, and chlorobenzene. No Interference of the ECD response was found for any of the 11 compounds detected with the ECD including trlchloroethylene. A pilot scale incinerator was sampled using canisters, and the destruction efficiency of 1,1,1-trichloroethane was determined at a concentration of less than 0.5 ppbv while determining 1,1-dichloroethylene, the major product of Incomplete combustion, at a concentration of 8000 ppbv from the same sample.     

An Evaluation of Techniques for the Determination of the Photochemical Reactivity of Organic Emissions

The concept that control of organic substances in emissions should be based on the relative ability to cause the effects associated with photochemical air pollution (reactivity) rather than on gross emission levels has gained wide acceptance. Two general types of reactivity response scales have been proposed. One of these is based on rates of hydrocarbon reaction or nitrogen dioxide formation. This scale covers a wide range because of the very high rates associated with olefins having internal double-bonds. The other scale is based on product yields combined with biological effect measurements. This type of scale is considered superior to one based on rates. This latter scale covers a narrow response range because olefins with internal double bonds have only slightly higher product yields and biological effects than do other reactive olefins and alkylbenzenes. Use of a response scale based on product yields and biological effects also permits use of less detailed instrumental procedures. A simple subtractive column technique combined with a flame ionization analyzer should be sufficient to estimate hydrocarbon emissions. Gas chromatographic analyses of hydrocarbon emissions are of value when used with either type of reactivity response scale. However, detailed gas chromatographic analyses are essential for a response scale based on rates. The response scale based on product yields and biological effects indicates much less improvement in reactivity from fuel composition changes than would be predicted from a response scale based on rates. The most desirable approach is to use a variety of control and engine modification techniques to reduce all reactive organics to the lowest level possible.     

Recommendations on a Preferred Procedure for the Determination of Particulate in Gaseous Emissions

Studies were made over a 3 year period to evaluate the EPA Method 5 manual particulate sampling procedure in the forest products industry through laboratory and field studies. Results of the study showed that several modifications could be made to improve the performance and suitability of the method for routine source particulate measurements. Physical system changes included the use of a Teflon-lined umbilical cord to the collection system. Procedure changes included changing the isokinetic sampling rate variations to ±20% for emission sources where the particles were smaller than three micrometers in aerodynamic diameter, purging the impinger solutions with an inert gas immediately following collection, and separate evaporation of impinger organics and inorganics at 25 °C and 105°C, respectively. Calculation changes included inclusion of impinger-caught particulate and separate consideration of inorganic and organic particulates.