Particulate Matter Generation Research Articles

Particulate Generation Mechanisms during Bulk Filling and Mitigation via New Glass Vial.

Contamination with foreign particulate matter continues to be a leading cause of parenteral drug recalls, despite extensive control and inspection during manufacturing. Glass is a significant source of particulate matter contamination; however, the mechanism, source, and quantification have not been extensively analyzed. Quantification of particulate matter generation with lab simulations suggests that glass-to-glass contact on the filling line produces large quantities of glass particles of various sizes. A new strengthened glass vial with a low coefficient of friction surface is proposed to address this root cause of glass particle generation. Lab simulations and two line trials using this new vial demonstrated a substantial reduction of glass particulate generation, of resulting product contamination, as well as of the frequency of required filling line interventions. These results suggest that substantial reductions in particulate matter contamination of all types, glass and non-glass, can be achieved through the use of a new glass vial designed to effectively eliminate a root cause of glass particle generation.LAY ABSTRACT: Contamination with foreign particulate contamination continues to be a leading cause of injectable drug recalls, despite extensive control and inspection during manufacturing. Glass particles are one of the most common types of particulate identified; however, the generation mechanism has not been extensively studied. Lab simulations suggest that routine glass-to-glass contact of vials during the filling process results in large quantities of glass particulate. A new, strengthened glass vial with a low coefficient of friction surface is proposed to address this mechanism. Lab simulations and multiple filling line trials demonstrated a substantial reduction of glass particulate matter generation and product contamination with use of the new vial. These results suggest that this new vial reduces contamination risk by eliminating a root cause of glass particulate generation.

Performance and emission reduction potential of micro-gasifier improved through better design

Biomass gasification is getting popular for household cooking application in most developing countries including Ethiopia. The preference for biomass gasification is due to the generation of less CO (Carbon Monoxide) and PM (Particulate Matter) in comparison with other biomass cookstoves. Our study showed the improvement in thermal efficiency and emission reduction potential of micro-gasifier. A prototype micro-gasifier was built and tested using the water boiling test protocol. The test results gave a thermal efficiency of 39.6% and a specific fuel consumption of 57 g of fuel/ liter of water. With regard to indoor air pollution, the maximum CO & PM registered were 12.5 ppm and 1.85 mg/m3, respectively. Using clean development mechanism (CDM) methodology, the estimated emission reduction potential of the micro-gasifier is 1.30 tCO2 per micro-gasifier per year. Generally, the micro-gasifier has better performance compared to the previous designs proposed by other researchers. Thus, disseminating our micro-gasifier at a larger scale in developing countries such as Ethiopia will be beneficial in reducing deforestation and emission that will be brought about by using open-fire stoves and thus, helps to obtain carbon credit.

Performance of Ni/dolomite pellet catalyst on gas distribution from cassava rhizome gasification with a modular fixed-bed gasifier

ABSTRACTThermal conversion of cassava rhizome was performed using a modular downdraft gasifier with the addition of Ni-based catalysts as promising tar eliminating and produced gas upgrading techniques. The activities of a synthesized 5% Ni/dolomite pellet catalyst prepared by impregnation method were investigated in a secondary reactor downstream of the gasifier. High reforming activity of the Ni/dolomite pellet catalyst on tar reduction was achieved. The conversion to H2 and CO was improved via steam reforming of methane and char reaction with CO2. Moreover, the formation of CH4 and CxHy was diminished through the tar or condensable hydrocarbon reformed on the catalyst surface. The carbon and hydrogen conversions of cassava rhizome with prepared catalyst were 83.79% and 61.78%, respectively, at an air flow rate of 1.98 m3/hr. At this condition, tar formation was low, while the lower heating value was 4.39 MJ/m3 and H2 to CO molar ratio was 1.22. Generally, the addition of a catalyst not only enhanced gas production, but also reduced tar and particulate matter generation; thus, its implementation should help lessen the pollution control requirement and cost of operation, while allowing higher quality fuel gas production.

Observer design for exhaust gas recirculation rate estimation in a variable-geometry turbocharger diesel engine using a model reference identification scheme

Exhaust gas recirculation systems are used in diesel engines to reduce nitrogen oxide emissions. Since excessive recirculation in the cylinders may lead to an increase in generation of particulate matter and to unstable combustion, the exhaust gas recirculation rate should be measured correctly and should be controlled precisely. Unfortunately, the harsh conditions of the exhaust gas recirculation path make it difficult to measure the exhaust gas recirculation mass flow rate directly by using the relevant sensors. Therefore, precise control of the exhaust gas recirculation system depends on accurate estimation of the exhaust gas recirculation rate. To estimate accurately the exhaust gas recirculation rate in a turbocharged diesel engine, we propose an observer based on a model reference identification scheme. A linear parameter-varying model of the intake manifold pressure was derived to serve as the observer’s reference model. An update rule of the observer was designed with the model reference identification scheme. The intake and exhaust temperature models were developed through an empirical approach. Convergence of the proposed observer was proven in terms of the Lyapunov stability criterion. The proposed observer was implemented on a real-time embedded system and validated successfully through experiments on the engine.

Effect of H2O and SO2 on the distribution characteristics of trace elements in particulate matter at high temperature under oxy-fuel combustion

The purpose of this work is to clarify the effects of high concentrations of H2O and SO2 on the generation of particulate matter (PM) and the distribution characteristics of trace elements in PM under oxy-fuel coal combustion. The experiments were carried out in a high temperature drop tube furnace which was set as 1500°C, and the Dekati Gravimetric Impactor (DGI) sampling system was applied to collect the PM at the outlet of the furnace (sampling temperature, 135°C). The results indicate that, compared to air combustion, oxy-fuel combustion significantly decreases the amount of PM and the total mass of trace elements in PM, but enhances the concentrations of trace elements in PM, except Mn. Under oxy-fuel combustion, similar conclusions about the formation of PM and migration of trace elements can be drawn, with the decreasing oxygen concentration. There is no significant difference in the amount of PM with the SO2 addition, but the total mass of trace elements or the concentrations of trace elements in PM decreases. Steam enhances the amount of PM and the total mass of trace elements in PM to a great extent but decreases the concentrations of trace elements in PM.

Efficient control of air pollution through plants, a cost-effective alternative: studies on Dalbergia sissoo Roxb

Plants can be used as both passive biomonitors and biomitigators in urban and industrial environments to indicate the environmental quality and to ameliorate pollution level in a locality. Many studies reveal that plants are negatively affected by the ambient levels of air pollutants. The present study was conducted to evaluate the impact of air pollution on comparative basis with reference to changes in photosynthetic pigments, plant height, leaves, as well as, biochemical parameters of plants of different sites around Udaipur city receiving varying levels of pollution load. The investigated tree species Dalbergia sissoo Roxb. (Family: Fabaceae) exhibited a reduction in various physiological and biochemical growth parameters that correspond with air pollution levels at different sites. The tree species growing in polluted and control areas were compared with respect to foliar dust load, leaf area, and chlorophyll and total carbohydrate and total protein concentration in the leaves. Our studies suggest that D. sissoo Roxb. can successfully be grown in an area for monitoring air pollution, where it is mild and droughts are common. It will prove as an ideal tree species to control pollution effectively beside acting as a shade tree and being a source of food for birds and animals. By plantation of D. sissoo Roxb., mitigative measure at the polluted sites to control generation of particulate matter and the air quality required can be ensured. Our results also confirm that industrial and vehicular air pollution level in Udaipur city is shifting beyond limits.

Particulate matter concentrations and emissions in rabbit farms

The extent of the potential health hazards of particulate matter (PM) inside rabbit farms and the magnitude of emission levels to the outside environment are still unknown, as data on PM concentrations and emissions in and from such buildings is scarce. The purpose of this study was to quantify airborne PM10 and PM2.5 concentrations and emissions on two rabbit farms in Mediterranean conditions and identify the main factors related with farm activities influencing PM generation. Concentrations of PM10 and PM2.5 were determined continuously using a tapered element oscillating microbalance (TEOM) in one farm with fattening rabbits and one reproductive doe farm in autumn. At the same time as PM sampling, the time and type of human farm activity being performed was recorded. Additionally, temperature, relative humidity and ventilation rate were recorded continuously. Emissions were calculated using a mass balance on each farm. Results showed PM concentrations in rabbit farms are low compared with poultry and pig farms. Average PM10 concentrations were 0.082±0.059 mg/m 3 (fattening rabbits), and 0.048 ±0.058 mg/m 3 (reproductive does). Average PM2.5 concentrations were 0.012±0.016 mg/m 3 (fattening rabbits), and 0.012±0.035 mg/m 3 (reproductive does). Particulate matter concentrations were significantly influenced by the type of human farm activity carried out in the building rather than by animal activity. The main PM-generating activity on the fattening rabbit farm was sweeping, and the major PM-generating activity in reproductive does was sweeping and burning hair from the cages. Average PM10 emissions were 5.987±6.144 mg/place/day (fattening rabbits), and 14.9±31.5 mg/place/day (reproductive does). Average PM2.5 emissions were 0.20±1.26 mg/place/day (fattening rabbits), and 2.83±19.54 mg/place/day (reproductive does). Emission results indicate that rabbit farms can be considered relevant point sources of PM emissions, comparable to other livestock species. Our results improve the knowledge on factors affecting concentration and emissions of PM in rabbit farms and can contribute to the design of suitable PM reduction measures to control not only PM inside rabbit houses, but also its emission into the atmosphere.

Combustion particles emitted during church services: Implications for human respiratory health

Burning candles and incense generate particulate matter (PM) that produces poor indoor air quality and may cause human pulmonary problems. This study physically characterised combustion particles collected in a church during services. In addition, the emissions from five types of candles and two types of incense were investigated using a combustion chamber. The plasmid scission assay was used to determine the oxidative capacities of these church particles. The corresponding risk factor (CRf) was derived from the emission factor (Ef) and the oxidative DNA damage, and used to evaluate the relative respiratory exposure risks. Real-time PM measurements in the church during candle–incense burning services showed that the levels (91.6μg/m3 for PM10; 38.9μg/m3 for PM2.5) exceeded the European Union (EU) air quality guidelines. The combustion chamber testing, using the same environmental conditions, showed that the incense Ef for both PM10 (490.6–587.9mg/g) and PM2.5 (290.1–417.2mg/g) exceeded that of candles; particularly the PM2.5 emissions. These CRf results suggested that the exposure to significant amounts of incense PM could result in a higher risk of oxidative DNA adducts (27.4–32.8 times) than tobacco PM. The generation and subsequent inhalation of PM during church activities may therefore pose significant risks in terms of respiratory health effects.

A study of emissions from a Euro 4 light duty diesel vehicle with the European particulate measurement programme

The California Air Resources Board, CARB, has participated in a program to quantify particulate matter (PM) emissions with a European methodology, which is known as the Particulate Measurement Programme (PMP). The essence of the PMP methodology is that the diesel PM from a Euro 4 vehicle equipped with a Diesel Particulate Filter (DPF) consists primarily of solid particles with a size range greater than 23 nm. The PMP testing and the enhanced testing performed by CARB have enabled an increased understanding of both the progress that has been made in PM reduction, and the future remaining challenges for new and improved DPF-equipped diesel vehicles. A comparison of measured regulated emissions and solid particle number emissions with the results obtained by the PMP participating international laboratories was a success, and CARB’s measurements and standard deviations compared well with the other laboratories. Enhanced measurements of the influence of vehicle conditioning prior to testing on PM mass and solid particle number results were performed, and some significant influences were discovered. For example, the influence of vehicle preconditioning on particle number results was significant for both the European and USA test driving cycles. However, the trends for the cycles were opposite with one cycle showing an increase and the other cycle showing a decrease in particle number emissions. If solid particle size distribution and total particle numbers are to be used as proposed in PMP, then a greater understanding of the quality and errors associated with measurement technologies is advisable. In general, particle counting instruments gave results with similar trends, but cycle-to-cycle testing variation was observed. Continuous measurements of particle number concentrations during test cycles have given detailed insight into PM generation. At the present time there is significant variation in the capabilities of the particle counting instruments in terms of particle size and concentration. Current measurements show the existence of a large number of volatile and semi-volatile particles of yet-to-be-resolved chemical composition in diesel exhaust, especially during DPF regeneration, and these particles are not included in the PMP methodology because they are smaller than 20 nm. It will be very challenging to improve our understanding of this class of diesel particulate matter.

Performance evaluation of six different aerosol samplers in a particulate matter generation chamber

The present study was carried out with the aim of evaluating the performance of six different aerosol samplers in terms of mass concentration, particle size distribution, and mass fraction for the international size-sampling conventions. The international size-sampling criteria were defined as inhalable, thoracic, and respirable mass fractions with 50% cutoff at an aerodynamic equivalent diameter of 100 μm, 10 μm, and 4 μm, respectively. Two Andersen, four total suspended particulate (TSP), two RespiCon, four PM 10, two DustTrak, and two SidePak samplers were selected and tested to quantitatively estimate human exposure in a carefully controlled particulate matter (PM) test chamber. The overall results indicate that (1) Andersen samplers underestimate total suspended PM and overestimate thoracic and respirable PM due to particle bounce and carryover between stages, (2) TSP samplers provide total suspended PM as reference samplers, (3) TSP samplers quantified by a coulter counter multisizer provide no information below an equivalent spherical diameter of 2 μm and therefore underestimate respirable PM, (4) RespiCon samplers are free from particle bounce as inhalable samplers but underestimate total suspended PM, (5) PM 10 samplers overestimate thoracic PM, and (6) DustTrak and SidePak samplers provide relative PM concentrations instead of absolute PM concentrations.

PM and $\hbox{NO}_{\rm x}$ Removal for Diesel Engine Emission Using Ozonizer and Chemical Hybrid Reactor

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Over the years, we have investigated particulate matter (PM) and <formula formulatype="inline"><tex Notation="TeX">$ \hbox{NO}_{\rm x}$</tex></formula> reduction using nonthermal plasma-chemical hybrid processes without using catalysts. Among nonthermal plasma hybrid processes, the ozonizer combined with the chemical hybrid reactor was investigated using a 479 cc (5.5 kW) power generation diesel engine. The PM deposited on the diesel particulate filter can be incinerated by ozone and <formula formulatype="inline"><tex Notation="TeX">$\hbox{NO}_{2}$</tex></formula> in a wide range of flue gas temperature. The NO was oxidized to form <formula formulatype="inline"><tex Notation="TeX">$\hbox{NO}_{2}$</tex> </formula> by ozone, and <formula formulatype="inline"><tex Notation="TeX">$\hbox{NO}_{2}$</tex></formula> was reduced by the 3% <formula formulatype="inline"><tex Notation="TeX">$\hbox{Na}_{2}\hbox{SO}_{3}$</tex></formula> chemical reactor. As the results, PM deposited on both metal and ceramic filters were successfully removed even at ambient temperature. The rate of PM incineration depends on the amount of ozone injected and was significantly higher than the rate of PM generation. Using 2.4% ozone concentration with a flow rate of 10 L/min, 82% of NO having 720 L/min was oxidized to <formula formulatype="inline"><tex Notation="TeX">$\hbox{NO}_{2}$</tex></formula>, and 78% of <formula formulatype="inline"><tex Notation="TeX">$ \hbox{NO}_{\rm x}$</tex></formula> was removed as a chemical scrubber. However, <formula formulatype="inline"><tex Notation="TeX">$ \hbox{NO}_{\rm x}$</tex></formula> removal was deteriorated about 10% after 1-h operation. This was attributed to <formula formulatype="inline"><tex Notation="TeX">$\hbox{Na}_{2}\hbox{SO}_{3}$</tex></formula> oxidation by air, which was evidenced by the reduction of pH in the chemical reactor. </para>

Bioethanol and diesel/bioethanol blends emissions abatement

Oxygenated diesel fuel blends have a potential to reduce the emission of particulate matter (PM) and to be an alternative to diesel fuel. This paper shows that pre-sulfated 1%Pt/γ-Al 2O 3 and pre-sulfated 1%Pt–2%Sn/γ-Al 2O 3 are very active at PM emissions abatement when, bioethanol or diesel/bioethanol are used as fuels. Results obtained showed that the addition of bioethanol to the diesel fuel may be necessary to decrease diesel PM generation during combustion and to enhance the rate of the oxidation of this diesel PM on pre-sulfated 1%Pt/γ-Al 2O 3 and pre-sulfated 1%Pt–2%Sn/γ-Al 2O 3.

Generation of particulate matter during handling of needle and syringe packaging

Generation of airborne particulate matter during the handling and opening of various syringe and needle packages in a laminar-airflow workbench (LAFW) and in a biological safety cabinet (BSC) was measured to compare the effects on air cleanliness conditions (International Organization for Standardization [ISO] class 5 within the LAFW or BSC and ISO class 7 in buffer areas). Twenty-five to 50 packages of each of 12 needle or syringe products were opened. Probes were configured to count airborne particles during the separation of strip packages and the opening of packages by peeling back the top web or pushing the device through the packaging (for soft packages) or by twisting apart hard packages. The numbers of particles were not significantly different between the LAFW and BSC. The separation of strip packages generated visible particles and raised airborne particle counts. Peeling open plastic film packages and opening hard plastic packages generated fewer airborne particulates than did pushing devices through the packaging. For all methods of package opening, average counts downstream from the direct compounding area exceeded ISO class 5 conditions. Counts in the LAFW buffer area did not exceed ISO class 7. All methods of separating and opening the packaging of needles and syringes generated particles. The peel-and-present technique generated the lowest particulate volume. The LAFW and BSC were equally effective in maintaining low particle counts.

Limestone selection criteria for EDR water remineralization

Water scarcity in Mediterranean regions has led to projects that increase water resources by desalination. In this context, it is planned to expand and improve the drinking water treatment plant of the Llobregat River near Barcelona (Catalonia, NE Spain), building the largest electrodialysis reversal (EDR) plant in the world. Llobregat River water shows high salinity due to the occurrence and exploitation of several geological formations upstream with minerals having high contents of Na, K, Cl, and Br. EDR desalinated water is highly reactive and shows a low degree of mineralization. In consequence, remineralization is necessary to equilibrate the water in order to avoid aggressiveness and corrosion in pipelines and to re-introduce some essential ions for human health. Running outlet water through limestone (CaCO 3) is a simple and cheap process for remineralization. Five commercially available limestones were characterized (mineralogical and chemical composition, BET surface area, SEM analysis) and compared experimentally at both laboratory and pilot-plant scales during the EDR remineralization process. The main criteria in selecting a limestone for EDR water remineralization are its compositional purity in terms of both mineralogy and chemistry, and its textural characteristics. Texture mainly influences the suspended particulate matter (PM) generation, i.e., consumption and system performance. To minimize the negative effects of these features, an assessment, using SEM analysis and batch tests contacting limestones and desalinated water, of the capacity of PM generation is recommended.

Kinetic Analysis of Competition between Aerosol Particle Removal and Generation by Ionization Air Purifiers

Ionization air purifiers are increasingly used to remove aerosol particles from indoor air. However, certain ionization air purifiers also emit ozone. Reactions between the emitted ozone and unsaturated volatile organic compounds (VOC) commonly found in indoor air produce additional respirable aerosol particles in the ultrafine (<0.1 microm) and fine (<2.5 microm) size domains. A simple kinetic model is used to analyze the competition between the removal and generation of particulate matter by ionization air purifiers under conditions of a typical residential building. This model predicts that certain widely used ionization air purifiers may actually increase the mass concentration of fine and ultrafine particulates in the presence of common unsaturated VOC, such as limonene contained in many household cleaning products. This prediction is supported by an explicit observation of ultrafine particle nucleation events caused by the addition of D-limonene to a ventilated office room equipped with a common ionization air purifier.

Climatic conditions linked to high PM10 concentration in a bi-national airshed: Nogales (Arizona, USA, and Sonora, Mexico)

Traditional particulate matter (PM) studies focus on atmospheric transport and source identification. Focusing on a problematic airshed in southwestern North America, we analyzed atmospheric characteristics and hydroclimatic conditions leading to high concentrations of PM most representative of dust (PM10). The bi-national airshed of Nogales (Arizona, USA and Sonora, Mexico), has been historically characterized by high PM10 concentrations, which tend to be much higher on the Sonora side. Concentrations in greater Nogales tend to be highest in fall and winter and lowest in summer, despite climatologically moister soil conditions in fall and winter. Within the fall, winter, and spring seasons, days of high and low PM10 concentration were primarily distinguished by the condi- tion of the atmosphere, with less emphasis on soil moisture. However, when PM10 concentrations were high, soil moisture was most important in discerning days of very high concentrations on the Arizona side of the border during the most problematic seasons of fall and winter. This was not the case on the Sonora side. Furthermore, drier soil conditions were linked to anomalies in PM10 on the Arizona side of Nogales that were higher than the corresponding anomaly on the Sonora side. The generation of PM on the Sonora side is less reliant on dry soil than it is on the Arizona side, indicating a higher level of anthropogenic dust production on the Sonora side.

Application of a Microscale Emission Factor Model for Particulate Matter to Calculate Vehicle–Generated Contributions to Fine Particulate Emissions

This paper discusses the evaluation and application of a new generation of particulate matter (PM) emission factor model (MicroFacPM). MicroFacPM that was evaluated in Tuscarora Mountain Tunnel, Pennsylvania Turnpike, PA shows good agreement between measured and modeled emissions. MicroFacPM application is presented to the vehicle traffic on the main approach road to the Ambassador Bridge, which is one of the most important international border entry points in North America, connecting Detroit, MI, with Windsor, Ontario, Canada. An increase in border security has forced heavy–duty diesel vehicles to line up for several kilometers through the city of Windsor causing concern about elevated concentrations of ambient PM. MicroFacPM has been developed to model vehicle–generated PM (fine [PM2.5] and coarse ≤10 μm [PM10]) from the on–road vehicle fleet, which in this case includes traffic at very low speeds (10 km/h). The Windsor case study gives vehicle generated PM2.5 sources and their breakdown by vehicle age and class. It shows that the primary sources of vehicle–generated PM2.5 emissions are the late–model heavy–duty diesel vehicles. We also applied CALINE4 and AERMOD in conjunction with MicroFacPM, using Canadian traffic and climate conditions, to describe the vehicle–generated PM2.5 dispersion near this roadway during the month of May in 2003.

Particle size distribution of PM-10 and heavy metal emission with different temperature and HCl concentrations from incinerators

Emission characteristics of particulate matter and heavy metals from 12 small waste incinerators, whose capacity ranged from 25 to 200 kg/h of waste, were investigated to determine the factors affecting the particulate matter generation and growth mechanisms. The ratio of fine particles to coarse particles increased with the flue gas temperature. Particulate matter showed bimodal forms in particle size distributions. The finer particle mode in particle size distribution shifted toward the coarser particle mode with a decrease in flue gas temperature. Experimental results were in agreement with coagulation theory: It is thought that the coarser particles were mechanically generated and the finer particles were generated by gas-to-particle conversion mechanisms such as nucleation, condensation, and coagulation. Heavy metal enrichment in finer particulate matter was also observed and related to particle formation and growth from vaporized metals. Emission of all heavy metals except zinc was affected by hydrogen chloride concentrations, while some metal emissions such as manganese, chromium, and copper were not varied with flue gas temperature.

"Optimally spaced" excimer laser coronary catheters: performance analysis.

Excimer laser angioplasty is a percutaneous treatment modality for management of selected patients with severe obstructive coronary artery disease. This technology entails application of multifiber catheters that vaporize intra-arterial plaque and thrombus with the 308-nm wavelength light. A coronary laser catheter ("OS") with increased space between its optic fibers (90 microns) at the tip was recently developed. The previous design used a closely packed fiber bundle ("CP") with a smaller space between the fibers (77 microns). We sought to determine the ablation characteristics of the new, OS design. Experiments testing the new catheter and comparing it to the existing catheter included: (1) measurement of the laser output beam sizes and divergences; (2) evaluation of particulate matter generation during ablation of atherosclerotic tissue; (3) measurement of ablation hole sizes and tissue penetration rates; (4) histopathologic examination of laser-induced in vivo vessel wall injury. The new OS catheters produce a wider beam with higher divergence than the traditional CP catheters (6.7 degrees vs. 4.7 degrees, respectively). Testing two different levels of energy revealed the generation of a reduced number of particulate matter and shallower penetration depth with the OS catheter compared with traditional CP catheters. The OS catheters created a larger diameter of ablated hole than the CP catheters (for 2.0-mm catheters: 2.7 mm2 vs. 1.5 mm2, respectively, p = 0.01). Lasing with the OS catheters with slow advancement rates (0.2-0.5 mm/sec) resulted in creation of significantly larger-diameter holes than those produced at higher speeds (1-3 mm/sec). The in vivo vessel wall injury scores were similar among the two types of catheters tested. A new design of spaced optical fibers for coronary laser catheters provides increased tissue ablation in comparison to the traditional closely packed fibers catheter. Slow advancement rates during lasing with the new OS catheter are crucial for achievement of adequate plaque debulking.

Leaf-shredding Insects as a Source of Dissolved Organic Carbon in Headwater Streams

This study investigated the importance of leaf-shredding insects as generators of dissolved organic carbon (DOC) in a headwater stream. Three common southern Appalachian shredder species (Peltoperla maria, Pteronarcys scotti and Tipula spp.) were allowed to feed on naturally conditioned leaves, and the rates at which DOC was generated were measured. DOC generation rates of actively feeding shredders ranged from 0. 2-160 ,ug C mg shredder AFDWI day-', and 62 % of this variation could be explained by organism weight. Weight-specific rates increased as body size decreased, presumably in response to an increase in weight-specific metabolic rate. DOC generation rate per individual increased as animal size increased. DOC generation increased as generation of particulate matter increased, with a mean of 60 Ag DOC produced per mg AFDW particles generated. Less than 10% of DOC generated was produced by mechanical breaking up of the leaves. The DOC generated by shredders was predominantly in the high (> 10,000 daltons) molecular weight fraction. The rates presented are underestimates of actual rates; experiments with sterilized leaves demonstrated that microbial activity during experiments with natural leaves reduced the amount of DOC accumulating in the chambers. DOC released by actively feeding shredders is a potentially significant source of DOC in a small headwater southern Appalachian stream during low flow conditions. Shredder feeding is potentially as important a source of DOC in small streams as leaching of leaf litter. INTRODUCTION Dissolved organic carbon (DOC) is an important source of organic carbon in forested headwater streams; e.g., in Bear Brook, New Hampshire, 47 % of total organic carbon inputs was in the dissolved fraction (Fisher and Likens, 1973). DOC is taken up by microbial and chemical processes in the benthos (Cummins et al., 1972; Wetzel and Manny, 1972; Lush and Hynes, 1978; Dahm, 1981), and some is exported from the system as respired CO2 (McDowell and Fisher, 1976). Previous studies of DOC in streams have dealt primarily with sources and fates of allochthonous DOC (Fisher and Likens, 1973; McDowell and Fisher, 1976; Dahm, 1981). In this study we evaluate the potential importance of DOC released by the feeding activities of leaf-shredding aquatic insects. In headwater forested streams, where leaf litter inputs are high, leaf-shredding insects are one of the dominant functional groups in the benthos (Vannote et al., 1980). In southern Appalachian streams, shredder feeding accelerates leaf decomposition, and insect feces are an important source of seston (Wallace et al., 1982a). Our goal in this study was to determine if insect feeding could also contribute significant quantities of DOC in a stream. Release of DOC by invertebrates has been documented in a number of marine Uohannes and Satomi, 1967; Johannes and Webb, 1970) and freshwater groups Uohannes and Webb, 1970; Hargrave, 1971). Rates of release vary as a function of animal size and feeding habits: Hyallela azteca released only 5% of ingested calories (Hargrave, 1971) while Palaemonetes pugio released 33% of ingested organic carbon