Performance of the Annular Denuder System with Different Arrangements for HNO3 and HNO2 Measurements in Taiwan

ABSTRACT

Experiments on different annular denuder system (ADS)arrangements for sampling nitrous acid (HNO₂) and ni-tric acid (HNO₃) gases were conducted in this study toevaluate their sampling artifacts. The evaluation basis isthe one that employed one sodium chloride denuder forsampling HNO₃ gas and two sodium carbonate (Na₂CO₃)denuders for sampling HNO₂ gas, which is a commonlyemployed ADS arrangement in many field applicationsin the United States. A field study was conducted inHsinchu, Taiwan, and the results indicated that this ADSarrangement may yield over 80% relative errors for HNO₃gas. It also showed that the relative errors for HNO₂ gascan be less than 10% as sampled with only one Na₂CO₃denuder. This is attributed to the fact that the ambientHNO₃ concentration measured in this study was relativelylow while the HNO₂ concentration was high, as comparedto typical concentrations of these two gases measured inthe United States.

The sampling error of HNO₃ gas may be due to highconcentrations of N-containing interfering speciespresent in Taiwan’s atmosphere. Because the relative sam-pling errors of HNO₃ and HNO₂ gases depend mainly ontheir concentrations in the atmosphere as well as con-centrations caused by interfering species, the risk for higherror while measuring low HNO₂ concentrations by onlyone Na₂CO₃ denuder is also possible. As a result, it is sug-gested that pretests are necessary to evaluate possiblesources and degrees of sampling errors before fieldsampling of HNO₂ and HNO₃ gases. The sampling errorsof these two gases can, therefore, be minimized with abetter arrangement of the ADS.     

Dry Deposition of Ammonia at Environmental Concentrations on Selected Plant Species

The deposition velocity of NH₃ on six plant species at environmental concentrations has been studied in a dynamic plant gas exchange reactor. The total resistance to the transport of NH₃ was studied. The aerodynamic resistance was determined directly by NH₃ gas absorption in aqueous solutions at environmental concentrations in a two-phase gradientless reactor modeling the transfer processes through the stomata in a leaf. The concentration of NH₃ in the gas phase ranged from 50 to 1000 ppb and the temperature varied from 25 to 30°C. The results for the deposition velocity for NH₃, during the day, varied from 0.3 to 1.3 cm/s. The deposition velocities at night were about one order of magnitude smaller. These results are compared with estimates from the Frdssling equation which consistently yields higher values of the same order of magnitude. To determine accurate atmospheric transport models or global budget models, a variable deposition velocity should be used to account for the diurnal and seasonal variations in the surface resistance.     

Spotting of Automotive Finishes from the Interactions Between Dry Deposition of Crustal Material and Wet Deposition of Sulfate

During the summer of 1988, General Motors Research Laboratories operated a mobile atmospheric research laboratory in Jacksonville, Florida to determine the cause of environmentally- related damage that occurs on automotive finishes In many parts of the U.S. The damage occurs as circular, elliptical, or irregular spots that appear as deposits or precipitates. The results of the present study show that a wetting event (rain or dew) is a prerequisite for damage to occur. Sulfuric acid contained in the rain or dew reacts on surfaces with drydeposited calcium which Is a common constituent of soli. As the droplets evaporate, a calcium sulfate precipitate forms on horizontal surfaces around the perimeter of the droplet. Subsequent washing of the surface may remove the precipitate, but on clearcoats, where the calcium sulfate was present, scars remain.     

Economic Comparison of Selected Scenarios for Electrostatic Precipitators and Fabric Filters

Compliance with particulate standards for utility boilers burning low sulfur western coal has resulted in the installation and proposed installation of several fabric filter collectors where cold or hot electrostatic precipitators would have traditionally been applied. Recently, SO3 conditioning has been used to improve cold precipitator performance resulting in considerable reduction in specific collection area (SCA). All this suggests that trade-offs exist indicating ranges of SCA, A/C ratio, and power plant size (Mw) where fabric filters become competitive with electrostatic precipitators. Conceptual cost models are presented which indicate total capital investment and annual costs for the control devices. Precipitator costs are correlated with collecting area, gas flow rate, and power input and are presented as functions of SCA and Mw. Fabric filter costs are keyed to gross filter area, pressure drop, and gas flow rate. Fabric filters become competitive when a cold precipitator requires SCAs in excess of 600 to 800 and competitive when a hot precipitator requires equivalent cold precipitator SCAs in excess of 600 to 1000 depending on A/C ratio, Mw, and hot precipitator SCA credit allowance. The S0₃ conditioned precipitator scenario is shown to be economically competitive with fabric filters.     

Effects of Land Use Data on Dry Deposition in a Regional Photochemical Model for Eastern Texas

ABSTRACT

Land use data are among the inputs used to determine dry deposition velocities for photochemical grid models such as the Comprehensive Air Quality Model with extensions (CAMx) that is currently used for attainment demonstrations and air quality planning by the state of Texas. The sensitivity of dry deposition and O₃ mixing ratios to land use classification was investigated by comparing predictions based on default U.S. Geological Survey (USGS) land use data to predictions based on recently compiled land use data that were collected to improve biogenic emissions estimates. Dry deposition of O₃ decreased throughout much of eastern Texas, especially in urban areas, with the new land use data. Predicted 1-hr averaged O₃ mixing ratios with the new land use data were as much as 11 ppbv greater and 6 ppbv less than predictions based on USGS land use data during the late afternoon. In addition, the area with peak O₃ mixing ratios in excess of 100 ppbv increased significantly in urban areas when deposition velocities were calculated based on the new land use data. Finally, more detailed data on land use within urban areas resulted in peak changes in O₃ mixing ratios of ~2 ppbv. These results indicate the importance of establishing accurate, internally consistent land use data for photochemical modeling in urban areas in Texas. They also indicate the need for field validation of deposition rates in areas experiencing changing land use patterns, such as during urban reforestation programs or residential and commercial development.     

Feasibility of Applying a Stable Isotopic Tracer for Direct Determination of Dry Particulate Deposition to Soybean Plants

ABSTRACT

A stable rare-earth isotopic tracer was used to measure the deposition of KNO₃ particles on soybean leaves by direct measurement of the tracer on the plant surfaces by thermal-ionization mass spectrometry. Submicrometer particles, made from a solution containing 3 |mg mL^-1 neodymium isotope (¹⁴⁸Nd, 87.9%) and 1,000 mg mL^-1 KNO₃, were dispersed with a two-fluid nozzle and released upwind of a soybean field. Total suspended- and size-fractionated-aerosol particles were collected on an open-face filter and in a micro-orifice impactor, respectively, at a distance of 40 m from the release point. Soybean leaves exposed to the plume were collected at distances ranging from 25 to 100 m. As little as 5.5 pg of the tracer (i.e., excess ¹⁴⁸Nd) was detected in soybean leaves at signal-to-noise ratios ranging from 7,500 to 240,000, in the presence of 200 to 2,700 pg of naturally occurring Nd. The dry-particle deposition velocity, determined from the ratio of the aerial concentration and directly deposited aerosol (geometric mass mean diameter, 0.20 mm) flux, and its corresponding analytical uncertainty were 0.30 cm sec^-1 and 2.5%, respectively.     

Preparation of Calcium Silicate Reagent from Fly Ash and Lime in a Flow Reactor

Abstract

The batch reaction between fly ash and hydrated lime in water to produce high surface area calcium silicates for flue gas desulfurization has been examined extensively. This paper examines the reaction in a flow reactor using two low-calcium fly ashes and introducing gypsum, calcium sulf ite hemihydrate, and calcium chloride as additives to the reaction. The flow system is compared to the batch reaction at similar operating conditions and a segregated flow model is used to approximate flow reactor behavior.

Experiments with calcium chloride and gypsum additives were modeled fairly well by the segregated flow approximation at residence times less than 12 hours. The flow reactor produced low surface area material at longer residence times when gypsum was present. Because the changing solution chemistry affected the batch reaction rate the fly ash and hydrated lime system without gypsum or calcium chloride could not be approximated using batch reaction data. In this case, the flow reactor produced higher surface area product than the batch reactor for a given residence time due to the increased calcium hydroxide availability.     

Laboratory and Field Evaluation of the Controlled Condensation System for S03 Measurements in Flue Gas Streams

The study reported by this paper involves the use of the Controlled Condensation System (Goksoyr/Ross Coil) for flue gas S0₃ measurements in both the laboratory and the field, under low and high mass loadings. The Controlled Condensation System cools the flue gas to below the dewpoint of H₂S0₄ but above the H₂0 dewpoint. The resulting aerosol is collected either on the coil walls or on the back-up glass frit. The laboratory recovery of the H₂S0₄ in streams of varying S0₂, H₂0, and H₂S0₄ content was found to be 95 ± 6%. A new quartz filter holder was designed to meet the filtration problems encountered in collecting S0₃ from particle laden flue gas streams. This quartz system, when heated to above 250°C, quantitatively passed the H₂S0₄ into the condensation coil. Later studies with this filter system preloaded with fly ash equivalent to a mass loading of 1.3 g/m³ yielded a 80-85% recovery of H₂S0₄. The laboratory system was simultaneously tested at a 150 megawatt, pulverized coal-fired power plant prior to and after a wet limestone FGD. The inlet grain loading to the FGD ranged from 0.06 g/m³ to 11.4 g/m³ with S0₂ concentrations as high as 4000 ppm. The average inlet H₂S0₄ value was 8.3 ppm and the outlet from the FGD was 3.1 ppm. The source fluctuation value was determined to be ±65%.     

A Constant-Volume Rapid Exhaust Dilution System for Motor Vehicle Particulate Matter Number and Mass Measurements

Abstract

An improved version of the constant volume sampling (CVS) methodology that overcomes a number of obstacles that exist with the current CVS dilution tunnel system used in most diesel and gasoline vehicle emissions test facilities is presented. The key feature of the new sampling system is the introduction of dilution air immediately at the vehicle tailpipe. In the present implementation, this is done concentrically through a cylindrical air filter. Elimination of the transfer hose conventionally used to connect the tailpipe to the dilution tunnel significantly reduces the hydrocarbon and particulate matter (PM) storage release artifacts that can lead to wildly incorrect particle number counts and to erroneous filter-collected PM mass. It provides accurate representations of particle size distributions for diesel vehicles by avoiding the particle coagulation that occurs in the transfer hose. Furthermore, it removes the variable delay time that otherwise exists between the time that emissions exit the tailpipe and when they are detected in the dilution tunnel. The performance of the improved CVS system is examined with respect to diesel, gasoline, and compressed natural gas vehicles.     

Air Quality Measurements for the Aerosol Research and Inhalation Epidemiology Study

Abstract

Measurements of pollutant gases, airborne particulate matter mass and composition, and meteorology have been made at a core site near downtown Atlanta, GA, since August 1998 in support of the Aerosol Research and Inhalation Epidemiology Study (ARIES). This site is one of eight in the Southeastern Aerosol Research and Characterization network. The measurement objective is to provide a long-term, multivariate dataset suitable for investigating statistical associations of respiratory and cardiovascular disease with airborne particulate matter composition, meteorology, and copollutant gases through epidemiologic modeling. Measurements are expected to continue through 2010. Ancillary multiyear measurements at additional sites in the Atlanta metropolitan area and in short-term exposure assessments have been used to estimate the exposure/measurement error associated with using data from a central site to approximate human exposures for the entire area. To date, 13-, 25-, and 53-month air quality datasets have been used in epidemiologic analyses.     

Information Required for the Selection and Application of Electrostatic Precipitators for the Collection of Dry Particulate Material

This report is a continuation of two prior papers on the selection and application of electrostatic precipitators. The first papers submitted by the TA-5 committee of APCA were primarily concerned with the collection of fly ash from boiler gases. Three other major applications of industrial precipitators include the ferrous, pulp and paper, and cement fields. Other industries utilizing the precipitator but to a lesser degree are: chemical, petroleum, and non-ferrous metals. New application areas in the United States include municipal incinerators and high temperature-high pressure gas cleaning.

While a similarity of theory and equipment is common to all of the above applications, there are sufficient differences both in the processes and types of material collected to make the selection of the Individual precipitator subject to a comprehensive evaluation. In order properly to make this evaluation, it is necessary that a suitable means of communication be established between user and supplier. It is the purpose of this report to recommend ’? terminology, emphasize design factors, and list the information needed by the supplier to make a proper application of his equipment.     

Assessment of the Ozone-Nitrogen Oxide-Volatile Organic Compound Sensitivity of Mexico City through an Indicator-Based Approach: Measurements and Numerical Simulations Comparison

Abstract

The ozone (O₃) sensitivity to nitrogen oxides (NO_x, or nitric oxide [NO] + nitrogen dioxide [NO₂]) versus volatile organic compounds (VOCs) in the Mexico City metropolitan area (MCMA) is a current issue of scientific controversy. To shed light on this issue, we compared measurements of the indicator species O₃/NO_y (where NO_y represents the sum of NO + NO₂ + nitric acid [HNO₃] + peroxyacetyl nitrate [PAN] + others), NO_y, and the semiempirically derived O₃/NO_{z surrogate} (where NO_{z surrogate} is the derived surrogate NO_z, and NO_z represents NO_x reaction products, or NO_y – NO_x) with results of numerical predictions reproducing the transition regimes between NO_x and VOC sensitivities. Ambient air concentrations of O₃, NO_x, and NO_y were measured from April 14 to 25, 2004 in one downwind receptor site of photo-chemically aged air masses within Mexico City. MCMA-derived transition values for an episode day occurring during the same monitoring period were obtained through a series of photochemical simulations using the Multiscale Climate and Chemistry Model (MCCM). The comparison between the measured indicator species and the simulated spatial distribution of the indicators O₃/NO_y, O₃/NO_{z surrogate}, and NO_y in MCMA suggest that O₃ in this megacity is likely VOC-sensitive. This is in opposition to past studies that, on the basis of the observed morning VOC/NO_x ratios, have concluded that O₃ in Mexico City is NO_x-sensitive. Simulated MCMA-derived sensitive transition values for O₃/NO_y, hydrogen peroxide (H₂O₂)/HNO₃, and NO_y were found to be in agreement with threshold criteria proposed for other regions in North America and Europe, although the transition crossover for O₃/NO_z and O₃/HNO₃ was not consistent with values reported elsewhere. An additional empirical evaluation of weekend/weekday differences in average maximum O₃ concentrations and 6:00- to 9:00-a.m. NO_x and NO levels registered at the same site in April 2004 indirectly confirmed the above results. A preliminary conclusion is that additional reductions in NO_x emissions in MCMA might cause an increase in presently high O₃ levels.     

Dry and wet removal of sulphur from the atmosphere

Dry deposition and removal in precipitation of SO₂ and of paniculate sulphate are considered in turn. Many assessments of the dry deposition of SO₂ to various surfaces give deposition velocities of about 0.8cm s⁻¹, although variations with season and weather conditions are important. The deposition velocity of the sulphate aerosol is probably about 0.l cm s⁻¹. Removal of SO₂ in rain is also a rather inefficient process and theoretical and experimental results suggest that the sulphur in precipitation results chiefly from the rainout of cloud condensation nuclei. The removal time constants for SO₂ and sulphate by moderate rain are probably of order 10⁻⁵ and 10⁻⁴s⁻¹ respectively. A much simplified model suggests that about a half of the SO₂ emitted to the atmosphere is removed by dry deposition, the remainder is oxidised to sulphate and removed in precipitation and the atmospheric residence time is about 5 days for sulphur. The method and climatological statistics for a more realistic treatment do not yet appear to be available.     

The 1999 Fresno Particulate Matter Exposure Studies: Comparison of Community,Outdoor, and Residential PM Mass Measurements

ABSTRACT

Two collaborative studies have been conducted by the U.S. Environmental Protection Agency (EPA) National Exposure Research Laboratory (NERL) and National Health and Environmental Effects Research Laboratory to determine personal exposures and physiological responses to par-ticulate matter (PM) of elderly persons living in a retirement facility in Fresno, CA. Measurements of PM and other criteria air pollutants were made inside selected individual residences within the retirement facility and at a central outdoor site on the premises. In addition, personal PM exposure monitoring was conducted for a subset of the participants, and ambient PM monitoring data were available for comparison from the NERL PM research monitoring platform in central Fresno. Both a winter (February 1-28, 1999) and a spring (April 19-May 16, 1999) study were completed so that seasonal effects could be     

Toxicity of Selected Pharmaceuticals to the Anostracan Crustacean Thamnocephalus platyurus - Comparison of Sublethal and Lethal Effect Levels with the 1h Rapidtoxkit and the 24h Thamnotoxkit Microbiotests

- DOI: http://dx.doi.org/10.1065/espr2006.01.005 Background, Aims and Scope In view of the limited amount of information on the potential hazard of the ever increasing amounts of drugs in surface waters to aquatic biota, a study was undertaken to determine the effect levels of 28 selected pharmaceuticals to the crustacean test species Thamnocephalus platyurus. The drugs belong to 5 different groups: non steroidal anti-inflammatory agents, biocides, cardiovascular compounds, nervous system drugs and purine alkaloids. Methods Toxicity tests were carried out with the 1h Rapidtoxkit and the 24h Thamnotoxkit microbiotests in order to make a comparison of sublethal effects (visible as stress through absence of feeding) measured after a very short time of exposure (1h) and lethal effects after prolonged exposure (24h). Dilution series starting at 200 mg l–1 were prepared and applied, and median effects levels were calculated and transformed into Toxic Units (TU) for easy data comparison. Results and Discussion The toxic effects found have been ranked into 4 arbitrary toxicity classes: not toxic (TU<0.2), low toxicity (0.2<TU<1.0), toxic (1.0<TU<10) and very toxic (TU>10). The toxicity levels noted ranged from virtually no effects for a few of the pharmaceuticals, at the highest concentration tested out, to LC50's below 1 mg l–1 (>100 TU) for 3 nervous system drugs (Amitryptiline, Thioridazine and Chlorpromazine). According to the toxicity classification, 17 of the 28 compounds (i.e. 67%), belong to the same class for the lethal and the sublethal tests. More pronounced differences in effect levels between the two assays were observed mainly for the pharmaceuticals which were either not toxic or only slightly toxic at the 200 mg l–1 level. For 90% of the toxic drugs the ratio between the toxicity values for both tests is below 5. Conclusion An overall correlation coefficient of 0.96 was found between the 2 microbiotests, confirming the good predictive potential of the 1h stress-based Rapidtoxkit in revealing important biological effects (mortality) after more prolonged exposure of the crustacean test species to chemical compounds. Recommendation and Outlook The present study clearly shows that new microbiotests such as the 1h Rapidtoxkit and the 24h Thamnotoxkit are attractive tools for rapid cost-effective screening of 'new' pollutants such as drugs which may threaten the biological communities of the aquatic environment.     

Measurements of the scavenging of sulfate and nitrate in clouds

Measurements are presented on the scavenging of sulfate and nitrate by cumulus, stratus and strato-cumulus clouds. Assuming that all of the particulate sulfate was in the size range 0.1–1.0 μm radius and that sulfate was scavenged with the same efficiency as sub-micrometer particles in general, the nucleation scavenging coefficient of sulfate in these clouds was deduced to be 0.7 ±0.2 and evidence for sulfate production (1.0±0.3 μgm⁻³) within cloud water was also obtained. Evidence for nitrate scavenging, by nitrates serving as cloud condensation nuclei or by the absorption of HNO₃ by cloud droplets, is also presented. The data suggest that either gaseous nitrogen compounds in the air other than HNO₃ can dissolve and contribute to the nitrate concentration in cloud water or that nitrate can be produced within cloud droplets.     

Measurements and simulations of the visual effects of particulate plumes

In this paper we present field measurements of the visual effects of particulate plumes from two power plants and a copper smelter. The measurements were conducted at downwind distances ranging from 7 to 34 km and for sun-observer angles ranging from 40 to 160°. The visual effects of the power plant plumes were relatively small due to atmospheric dispersion (Kincaid power plant plume in February 1981) or hazy background (Labadie power plant plume in August 1981). The plume from the San Manuel smelter was more visible because of the clean environment. The measurements of plume contrasts range from − 0.15 to + 0.15. Further development of the EPA plume visibility model to improve the treatment of multiple scattering of light and incorporate light absorption by carbonaceous aerosols is described. Teleradiometer measurements and model simulations are in reasonable agreement for cases in which experimental uncertainties are small. The model appears to underpredict forward scattering of light by plume particles.