Kinetic Sequential Sampling (KSS) System: An Automated Sampling System for Measuring Vertical Concentration Profiles of Airborne Particles

ABSTRACT

An electronically controlled lift system carrying a realtime particle monitor has been developed for sampling air sequentially, at different heights within the breathing zone. Data are automatically logged at the different receptor levels, for the determination of average vertical concentration profiles of airborne particulate matter. The system is easy to operate, portable, and easily extended to different heights or modified for use with other types of monitors (e.g., a portable CO analyzer). For measuring airborne particle concentrations, a Grimm Dust Monitor 1.104/5 was used. The results of trial runs, which were carried out indoors and in a relatively open semi-rural area, are presented, and applications of the kinetic sequential sampling (KSS) system are discussed.     

A Wind Tunnel Study to Design Large,Open-top Chambers for Whole-tree Pollutant Exposure Experiments

A wind tunnel study was conducted to determine the optimal design features of a large, open-top chamber, as needed for pollution exposure studies on mature trees. An optimally-designed, open-top chamber must minimize the incursion of ambient air through its opening and maintain a uniform treatment concentration throughout the chamber. The design features of interest are the diameter and height of the chamber and the deflection angle and opening size of any frustum that may be mounted on top of a model chamber.

Design specifications depend on the turbulence regime about the chamber, which is influenced by the nature of the surrounding vegetation. Consequently, our investigation was performed on scale-model, open-top chambers in a wind tunnel populated with a model coniferous forest. Turbulence measurements demonstrated the similarity between the turbulence regime of the model and a natural forest. A hydrocarbon tracer was injected into the wind tunnel flow to characterize chamber performance.

The main design features of open-top chambers are the velocity of air exiting through the top and the relationship between the length scale of the turbulence and the diameter of the chamber opening. As exit velocities increase, the proportion of eddies with sufficient force to penetrate into the chamber decrease. Therefore, for equal volumetric air flows, smaller opening sizes increase the exit velocities and reduce the number and extent of ambient air incursions. Almost total exclusion of ambient air is achieved as the exit velocity of the air exceeds the magnitude of one standard deviation of the vertical wind velocity measured at the chamber top. The incursion of ambient air is also reduced when the diameter of the chamber opening is smaller than the characteristic length scale of the turbulence, a measure of mean eddy size.

Frusta deflect air flow over the chamber. Three prototypes, with 30?, 45? and 60-degree angles were tested. A 30-degree frustum slightly improves the performance of the chamber and is more effective in preventing ambient air from entraining into the chamber opening than frusta with either a 45? or 60-degree angle. A flatter frustum allows for a smoother transition in the wind velocity streamline and is less apt to cause wake turbulence, as is the case with steeper frusta.

Knowledge of the turbulence characteristics of plant canopies are readily available in the literature and can aid scientists and engineers in designing the optimal chamber and frusta dimensions for their particular application. Therefore, the empirical approach to chamber design can be avoided, and substantial savings can be realized.     

Design of A Large Scale Exposure and Sampling Facility for Street Level Auto Exhaust Emissions

A unique air handling facility was designed to introduce up to 12,000 cfm of street level air into laminar flow animal exposure chambers in an unaltered state except for the heating and cooling necessary in extreme weather to provide the animals with an habitable climate. The facility was built to determine the possible effect of street level exhaust emissions on the health of the general population. Another objective was to determine, by means of direct reading and recording instruments, the concentration of contaminants such as carbon monoxide, carbon dioxide, aerosols, nitrogen oxides, total oxidant, and unburned hydrocarbons.     

Frank A. Chambers

Abstract

This work assessed the usefulness of a current air quality model (American Meteorological Society/Environmental Protection Agency Regulatory Model [AERMOD]) for predicting air concentrations and deposition of perfluorooctanoate (PFO) near a manufacturing facility. Air quality models play an important role in providing information for verifying permitting conditions and for exposure assessment purposes. It is important to ensure traditional modeling approaches are applicable to perfluorinated compounds, which are known to have unusual properties. Measured field data were compared with modeling predictions to show that AERMOD adequately located the maximum air concentration in the study area, provided representative or conservative air concentration estimates, and demonstrated bias and scatter not significantly different than that reported for other compounds. Surface soil/grass concentrations resulting from modeled deposition flux also showed acceptable bias and scatter compared with measured concentrations of PFO in soil/grass samples. Errors in predictions of air concentrations or deposition may be best explained by meteorological input uncertainty and conservatism in the PRIME algorithm used to account for building downwash. In general, AERMOD was found to be a useful screening tool for modeling the dispersion and deposition of PFO in air near a manufacturing facility.     

A Comparative Study of Particulate Loadings in Plumes Using Multiple Sampling Devices

Particle size distributions, particulate concentrations, and particle identities must be known to relate effluents to reduction in visibility and soiling. Similar types of emissions were measured with cascade impactor, membrane filter, and rotorod samplers. The different particle size distributions, concentrations, and identifications are reported. Discussion of and recommendations for utilization of these three methods of sampling are made.     

A Low-Level Air Sampling and Meteorological Sounding System

A captive-balloon borne radio transmitting device measuring temperature and humidity at desired levels in the lower thousand feet of the atmosphere over a city is described. A companion device which captures a sample of air at a desired altitude and a method of later determining trace gas concentrations in the sample is presented. Temperature, humidity, and methane concentrations in air samples taken above Cincinnati were-determined and are presented as examples of the system’s capabilities.     

A Technique for Respirable Sampling

The purpose of this paper is to describe instrumentation to aerodynamically size suspended particulates found in ambient air and to summarize results of field testing utilizing the new technique.

A four-stage, multiorifice high-volume fractionating impactor with backup filter, which can be operated as a component of the standard high-volume sampler, collects particulate matter in five separate aerodynamic size ranges: 7 micrometer (μm) or larger, 3.3 to 7 μm, 2.0 to 3.3 μm, 1.1 to 2.0 μm, and 0.01 to 1.1 μm.

Comparative field tests utilizing duplicate sampling techniques were conducted to determine the feasibility of using the size fractionator on a routine basis in field operations. Verification of the actual particle size separation was not undertaken; however, earlier tests utilizing laboratory-generated aerosols have been performed with satisfactory results.

The results of field tests indicate that the fractionator can be used to determine the aerodynamic size distribution of particulate matter. A glass fiber surface with a pH of 11.0 was found to adsorb atmospheric acid gases during sampling and thus gave erroneous mass concentration results when compared to the standard high-volume sampler. Glass fiber filters with a pH of 6.5 eliminated the acid gas adsorption.     

High Volume Sampling: Errors Incurred during Passive Sample Exposure Periods

The current Federal EPA reference method for the determination of total suspended particulate matter (TSP) in the atmosphere is the high volume method (hi-vol).¹ The hi-vol sampler is normally operated for a 24 hr period by drawing air through an 8 X 10 in. glass fiber filter at an air sampling flow rate of between 40-60 cfm. TSP samples are presently collected in this manner every 6th day (61 samples/year). Results are used to determine compliance with existing National Primary Ambient Air Quality Standards for TSP (i.e., 260 µg/m³, maximum 24 hr average, not to be exceeded more than once a year; 75 µg/m³, annual geometric mean). However, when the sampling frequency is diminished to only 61 out of a possible 365 measurements each year, the degree of certainty associated with meeting these air quality standards is also decreased.^2,3 This partial sampling schedule also introduces other sampling errors. One such error caused by the exposure of the collection filter both prior and subsequent to the desired sampling day is the subject of the following discussion.     

A Tethered Balloon Air Sampling System for Determining the Vertical Distribution of Atmospheric Tracers

Abstract

A lightweight, constant–flow air sampling pump has been adapted for attaching to a balloon tether line for the vertical sampling of atmospheric perfluorocarbon tracers. Constant flow was maintained up to an altitude of 6,250 m. The pump design, construction, and sampling technique are described. Typical vertical concentration results obtained during a perfluorocarbon tracer release experiment are presented.     

A Fabric Denuder for Sampling Semi-Volatile Species

ABSTRACT

A new style of diffusion denuder has been evaluated specifically for sampling HNO₃. A coated fabric is used as the denuder substrate, which can be loaded directly into a standard filter holder. This approach allows direct denuder sampling with no additional capital costs over filter sampling and simplifies the coating and extraction process.

Potential denuder materials and coatings were evaluated in the laboratory to test the removal efficiency. NaCl coatings were used to assess more than 20 materials for HNO₃ collection efficiency. Particle retention, which would cause a denuder to have a positive bias for gas concentration measurements, was evaluated by ambient air sampling using particulate sulfate as the reference aerosol. Particle retention varied from 0 to 15%, depending on the denuder material tested. The best performing material showed an average particle retention of less than 3%.

Denuder efficiency of four fabric materials was tested under ambient conditions to determine removal efficiency. The fabric denuder method was compared with a long path-length Fourier transform infrared (FTIR) spectrometer, a tunable diode laser absorption spectrometer (TDLAS), and a denuder difference sampler to independently measure HNO₃. HNO₃ collection efficiency was typically 90% for the denuders, whether coated with NaCl or not. For 10-L/min sampling rates with the fabric denuder, the square of the correlation coefficient with the FTIR spectrometer was 0.73, compared to 0.24 with the TDLAS.     

A Cyclone for Size-Selective Sampling of Ambient Air

A cyclone with a 47 mm after-filter has been developed for ambient air size-selective monitoring. It has been extensively evaluated with laboratory-generated aerosol. Variation of the pressure drop and 50% cut point with flow rate show that the cyclone operates in a single flow regime with a vortex in the outlet flow. The particle size cutoff curve is comparable in sharpness to a cascade impactor and is the same for solid or liquid particles. At 21.7 L/min, D ₅₀ is 2.5μm and at 15.4 L/min, D ₅₀ is 3.5 μm. Collection efficiency data for flow rates from 8 to 27 L/min fit a universal curve when plotted vs. the normalized particle diameter, (D-D ₅₀)/D ₅₀ Reentrainment of previously deposited particles is less than 1 % of the loading per day. In field tests the cyclone has proved to be a very satisfactory size-selective sampler.     

Passive Sampling for Ozone

The Brigham Young University (BYU) organic sampling system (BOSS) and the high flow rate multi-system BYU organic sampling system (BIG BOSS), which use multichannel diffusion denuder sampling techniques, were both used to collect samples of atmospheric fine particulate organic material. Both systems were used at the Meadview sampling site located at the western boundary of the Grand Canyon National Park in northwestern Arizona for the Project MOHAVE summer intensive sampling program in August 1992. The concentrations of total fine particulate carbonaceous material determined by temperature programmed volatilization for BOSS collocated replicate samples were in agreement with an uncertainty of ±14%. A comparable agreement was seen between the BOSS and BIG BOSS samples. Carbonaceous material collected by the second of two sequential quartz filters was shown to have originated from organic material lost from particles during sampling. About one-half of the fine particulate organic material was lost from particles during sample collection. These semi-volatile organic compounds lost from particles during sampling were characterized by GC/MS analysis. The concentrations of n-alkanes, n-fatty acids, n-fatty methyl esters, and phthalic acid as a function of fine particulate size were obtained for compounds both retained by and lost from particles during sampling. The possible sources of fine particulate semi-volatile organic material collected at Meadview, and the particle size distribution of fine particulate organic material, n-alkanes, n-fatty acids, and n-fatty esters are discussed.     

A Method for Checking Instrument Performance at Remote Sampling Sites

This paper describes a quality control technique used by the central headquarters operation of the Continuous Air Monitoring Program in an ejjort to insure valid data production from instruments located at remote sampling stations.

The procedure consists of preparation of 0.10 to 2.00 ppm mixtures of SO₂ or NO₂ in duplicate Mylar bags, each encased in a corrugated paper box.

These mixtures are analyzed during make-up to insure duplication. One box is shipped to the field station where it is analyzed on-site. The control mixture is analyzed in the central lab at the same time. Correlation between measurements indicates the usefulness of this dynamic calibration check.

The techniques used are described and results of the program are presented.     

Proportional Sampling System for the Collection of an Integrated Auto Exhaust Gas Sample

Carbon baking process involves evolution of fumes containing hydrocarbons and soot particles which cannot be discharged directly into the atmosphere. An incinerator can be used to clean these fumes. However, length of the baking cycle, nature of the fumes and variations in fume volume and temperature may result in excessive auxiliary fuel usage and inefficient incineration, if the incinerator is not designed properly. This paper describes the application of fundamental knowledge of aerodynamics, reaction kinetics and combustion, together with clear understanding of the process, in design of a highly efficient, fully automated incinerator. The design incorporates a unique but simple control system which results in reduction of auxiliary fuel usage without endangering the safety and efficiency of the incineration process. Operations and economics of the incinerator are described by illustrating a typical baking cycle and comparing actual fuel usage with the thermal ratings of the incinerator. Operating experience from a number of installations in the U. S. and Canada is also noted.     

A Movable Laboratory for Controlled Clinical Studies of Air Pollution Exposure

The cause of the Yokkaichi asthma episode (1960-1969) has been analyzed. It Is concluded that the respiratory diseases were due not to sulfur dioxide but to concentrated sulfuric acid mists emitted from stacks of calciners of a titanium oxide manufacturing plant located windward of the residential area.     

Wind Tunnel Testing of Open Top Field Chambers for Plant Effects Assessment

ABSTRACT

This study reports the first field measurements of airborne exavalent chromium (Cr(vi)) in southwestern Ontario. Hexavalent chromium was identified as an inhalation carcinogen and an air toxic of concern during the 1991-93 Windsor Air Quality Study. The results of that study indicated that approximately 20% of the routinely monitored ambient airborne chromium (Cr) was in the hexavalent form. In addition, the range of carcinogenic health risks attributable to airborne Cr(vi) was determined to be between 1.4 x IO⁶ and 3.0 x 10^-4 for people living in the Windsor area. During the summer of 1993, analyses of concurrent indoor and outdoor 24-hour air quality samples taken at 33 residences in Hamilton resulted in geometric mean Cr(vi) concentrations of 0.20 r|g/m³ and 0.55 r|g/m³, respectively, and little or no relationship between the indoor and outdoor sample sets. During the summer of 1994, an airborne Cr(vi) size-fractionation study was conducted in Hamilton, the results of which suggested that the majority of the Cr(vi) was in the inhalable fraction.