Passive aerosol sampler for particle concentrations and size distributions

This research evaluated the UNC passive aerosol sampler as a tool to measure particle mass concentrations and size distributions. The exposure scenario represented high concentrations and exposure periods of a few hours. Mass concentrations measured with the passive sampler were compared to concentrations measured using both a dichotomous sampler and an aerodynamic particle sizer (APS). In addition, the size distributions measured with the passive sampler were compared to those measured using the APS. Mass concentrations measured using the dichotomous sampler and the APS agreed well. The passive sampler tracked, but tended to overestimate, mass concentrations measured by the other two instruments. Size distributions measured with the passive sampler followed the general pattern of those measured using the APS. Overall, the passive sampler demonstrated both its utility and its limitations in these tests. The concentration measurements and size distributions found using passive samplers were more variable than those of the other instruments, but generally followed the data taken using the other methods. The advantages of low cost and ease of use offset the limitations in data quality with the passive sampler; these advantages are particularly welcome for sampling situations where aerosol properties vary over space or time.     

Bioindicators of enhanced nitrogen deposition

Increased deposition of atmospheric N largely from intensive agriculture is affecting biodiversity and the composition of natural and semi-natural vegetation in Europe. The value of species based bioindicators such as the Ellenberg N index and measurements of total tissue N and free amino acids in key plant species, is described with reference to a mixed woodland downwind of a livestock farm in the Scottish Borders, operated for over 20 years with a measured spatial gradient of ammonia concentration (29-1.5 microg m(-3)). All the indicators examined showed a relationship with N deposition and provided some indication of vegetation change. Total tissue N and arginine concentrations were most closely linked with ammonia concentrations and N deposition, with r(2) values of >0.97 and >0.78 respectively.     

Dust Deposit Profiles in a High Velocity Pulse-Jet Fabric Filter

Dust deposit profiles in a pilot-scale pulse-jet fabric filter were measured using a beta gauge. Fly ash was collected on polyester needled felt bags, and the dust profiles were measured after the test system was operated to equilibrium at superficial filtration velocities of 50, 75,100,125, and 150 mm/s. The profiles measured show that a large mass of dust is retained on the fabric of a pulse-jet filter when operated at high filtration velocities. This dust mass retention can be caused by two mechanisms: the failure to remove dust from the fabric during a cleaning pulse, and the redeposition of suspended dust onto the fabric after a cleaning pulse. The dust deposit measured at the highest test velocity was found to be much different from the deposits measured at all other velocities. The deposit found at 150 mm/s had almost twice the average areal density and was more evenly distributed than the deposits found at lower velocities.     

Early Effects of Atmospheric Ammonia Deposition on Calluna Vulgaris (L.) Hull Growing on an Ombrotrophic Peat Bog

This paper reports data from a field study investigating the impacts of elevated ammonia (NH₃) deposition on Calluna vulgaris growing on an ombrotrophic peat bog in S.E. Scotland. Shoot extension, foliar N concentrations, chlorophyll concentration and chlorophyll fluorescence were measured during the second growing season of exposure to a gradient of ammonia concentrations. Results indicate that NH₃ increases growth between 150–200 kg N ha^–1y^–1 cumulative deposition. Foliar N content increased significantly in response to NH₃ cumulative deposition up to 400 kg N ha^–1 y^–1 whereas chlorophyll a content significantly decreased. Measurements of Fv/Fm suggest that although NH₃ exposure altered the growth and reduced chlorophyll a, the efficiency of photosystem II was insensitive to NH₃-N deposition at this stage.     

Quantifying dry NH3 deposition to an ombrotrophic bog from an automated NH3 field release system

Providing an accurate estimate of the dry component of N deposition to low N background, semi-natural habitats, such as bogs and upland moors dominated by Calluna vulgaris is difficult, but essential to relate nitrogen deposition to effects in these communities. To quantify the effects of NH₃ inputs to moorland vegetation growing on a bog at a field scale, a field release NH₃ fumigation system was established at Whim Moss (Scottish Borders) in 2002. Gaseous NH₃ from a line source was released along of a 60 m transect, when meteorological conditions (wind speed >2.5 m s^–1 and wind direction in the sector 180–215°) were met, thereby providing a profile of decreasing NH₃ concentration with distance from the source. In a complementary study, using a NH₃ flux chamber system, the relationships between NH₃ concentrations and cuticular resistances were quantified for a range of NH₃ concentrations and micrometeorological conditions for moorland vegetation. Cuticular resistances increased with NH₃ concentration from 11 s m^–1 at 3.0 g m^–3 to 30 s m^–1 at 30 g m^–3. The NH₃ concentration data and the concentration-dependent canopy resistance are used to calculate NH₃ deposition taking into account leaf surface wetness. The implications of using an NH₃ concentration-dependent cuticular resistance and the importance for refining critical loads are discussed.     

An Automated Wet Deposition System to Compare the Effects of Reduced and Oxidised N on Ombrotrophic Bog Species: Practical Considerations

Critical N loads for ombrotrophic bogs, which often contain rare and N-sensitive plants (especially those in lower plant groups: lichens, mosses and liverworts), are based on very few experimental data from measured, low background N deposition areas. Additionally the relative effects of reduced versus oxidised N are largely unknown. This paper describes an automated field exposure system (30 km S. of Edinburgh, Scotland) for treating ombrotrophic bog vegetation with fine droplets of oxidised N (NaNO₃) and reduced N (NH₄Cl). Whim Moss exists in an area of low ambient N deposition (ca. 8 kg N ha^–1 y^–1), the sources and quantification of which are described. The wet N treatment system is run continuously, and is controlled/activated by wind speed and rainfall to provide a unique simulation of real world treatment patterns (no rain=no treatment). Simulated precipitation is supplied at ionic concentrations below4mMin rainwater collected on site. Treatments provide a replicated dose response to 16, 32 and 64 kg N ha^–1 y^–1 adjusted for ambient deposition (8 kg N ha^–1 y^–1). The 16 and 64 kg N ha^–1 y^–1 are duplicated with a P+K supplement. Baseline soil chemistry and foliar nutrient status was established for all 44 plots for Calluna vulgaris, Sphagnum capillifolium, Hypnum jutlandicum and Cladonia portentosa.     

Performance of a Pulse-Jet Filter at High Filtration Velocity I. Particle Collection

The fly ash collection characteristics of a pulse-jet fabric filter have been studied. Fly ash penetration was found to decrease as the dust deposit increased from 0 to 60 micrometers in thickness, to increase as face velocity through the bags increased from 5 to 15 cm/s, and to remain relatively constant for particles from 0.3 to 4.0 µm in diameter. Experiments employing chemically tagged fly ash were performed to investigate three dust penetration mechanisms. On resumption of filtering after cleaning, penetration by straight through dust loss declined rapidly from its maximum, reached a minimum, and then increased. Seepage of dust through the fabric was found to be constant throughout the filtration cycle. Dust lost as pinhole plugs increased after cleaning, passed through a maximum, and then declined. The pinholes appeared to open the way for further penetration by the straight through mechanism.     

Impaction and Particle Bounce at High Stokes Numbers

The information in this paper is directed to those concerned with controlling SO₂ emissions from power plants, and particularly with retrofitting controls onto existing plants. The paper describes an FGD system based on the dolomitic lime process and the scrubber design that have proved successful at the Colstrip plant in eastern Montana. A single scrubber vessel sized to treat all the gas from a 350-MWe coal-fired unit combines the functions of prequenching, absorption, washing, mist elimination, and recycle storage. Downflow Injection of gas along the vessel centerline and regulation of gas flow by the wash tray make the gas velocity uniform and permit scaling up to this large size. A high concentration of dissolved alkalinity in the scrubbing slurry provides rapid absorption and permits low L/G—40 gal/1000 acf—when coal with 2.5% sulfur is burned. Complete oxidation of sulfite makes gypsum of wallboard quality and the process can discharge clarified liquor low in COD if necessary to control chlorides. Since only the single scrubber vessel and the recycle pumps must be located close to the back end of the boiler, the system is particularly well suited for retrofit applications.     

Effect of Dust Size Distribution on the Collection Efficiency of Pulse-Jet Fabric Filters

Recent advances in vehicle emission control technology have reduced the effectiveness of the conventional tailpipe test used In inspection and maintenance programs. A different approach Is being followed in Harris County, Texas (Houston area), based on identification and correction of misfuellng and tampering. Misfueling Is being identified by using a lead-sensitive test paper to detect lead deposits in the tailpipe that result from using leaded gasoline. Field tests of this procedure demonstrated that it Is reliable and accurate for the Intended purpose. The data also indicated the need to observe certain precautions to avoid contamination and other potential sources of error. This procedure and other emission-related checks have been added to the annual safety inspections. These tests are conducted on vehicles of 1980 model year and later, by approximately 1150 Inspection stations throughout the county that conduct annual safety Inspections. Experience with the first few months of this program has been excellent.