Isokinetic Sampler for Continuous Airborne Aerosol Measurements

For aerosol measurements, especially those concerned with the aerosol particle size distribution, it is important to sample in isokinetic conditions. Most available instrumentation for aerosol measurements is intended for use on the ground under light wind conditions; intake air speeds rarely exceed a few meters per second. If the same instrumentation is used onboard an aircraft, the air must be decelerated 60 or more m/sec before It is sampled by individual instruments.

On The Pennsylvania State University Meteorology research aircraft, the air for all aerosol instruments is decelerated in a single isokinetic sampler located above the roof of the cabin outside the aircraft boundary layer. The air enters the sampler through a carefully designed circular intake. Its velocity is reduced as the cross section increases along a 7° conical diffuser. The expansion cone terminates in a cylindrical chamber in which the air velocity is 1/16 the aircraft speed. Behind the sampling chamber the air is accelerated in a second conical section to an end exhaust port. Exhaust porf "pumping" is used to compensate internal losses and, thus, helps preserve the isokinetic nature of the sampler.

Tubes leading to individual instruments are located in the sampling chamber and may be individually adapted to match the air sampling velocity with the local air speed inside the sampling chamber. The level of turbulence (u_rms/û) in the sampling section is =^0.05.

The sampler has been thoroughly wind tunnel and flight tested and successfully used in August and November, 1974, for field programs in the St. Louis and Tucson metropolitan areas, respectively.     

Aerosol Aerodynamic Size Conventions For Inertia! Sampler Calibration

The body of information presented in this paper is directed to investigators using inertial samplers for precise and accurate studies of respirable aerosols. The conventions commonly used for aerodynamic size for aerosol particles are discussed including the definition popularized by the "Task Group on Lung Dynamics" of the ICRP, and the "Lovelace" definition. To emphasize the distinction, the Task Group definition (unit density sphere equivalent) is called the aerodynamic equivalent diameter, D_ae, and the Lovelace definition (characteristic expression based upon viscous resistance) is called the aerodynamic resistance diameter, D_ar. The implications and efficacy of these conventions are related to procedures for calibration of cascade impactors, cyclones, and spiral centrifuges. The calibration of a spiral centrifuge at different altitudes is used as an example of the potential problems associated with the use of the different conventions for describing aerodynamic size. The aerodynamic resistance diameter is recommended for calibration of inertial samplers to be used to collect aerosols in the respirable size range.     

An Aerosol Sampler for Determination of Particle Concentration as a Function of Size and Time

A high flow rate four-stage impacfor was developed for the determination of aerosol concentration as a function of both particle size and time. The unit is very useful for long-term sampling intervals (24 hr) and for sampling very dusty atmospheres. Gas-borne particulate matter is collected out on four rotating drums, each with a collection surface area of about 10 sq in.; this allows a large quantity of materials to be collected without danger of particle build-up and blow-off. A particle size-collection efficiency calibration for the unit is presented together with experimental data on wall losses, surface coatings, and other important operational considerations.     

Development and Testing of a Portable Wind Sensitive Directional Air Sampler

Abstract

This paper reports on the performance of the Kimoto 180 sampler and the Wedding ambient PM10 beta gauge sampler. Monodisperse ammonium fluorescein test particles were generated in the laboratory and used to determine the penetration curve of the Kimoto 180 cyclonic inlet. It was found that the actual DpaSOof the Kimoto 180 inlet, 3.5 (xm, is much lower than the designated standard value, 10 um. In the field test, the two beta gauge samplers were collocated with an Andersen SA1200 high-volume sampler to compare their measured daily average PM10 concentrations.

The low Dpa50 of the Kimoto 180 inlet serves to explain why its daily average PM10 concentrations were much lower than the actual PM10 concentrations found in the field study. In addition, the PM10 concentrations of the Kimoto 180 beta gauge sampler were found to be seriously affected by the water vapor content of the ambient air. In contrast, the daily average PM10 concentrations of the Wedding beta gauge sampler were found to be more accurate, and influences by ambient conditions were insignificant     

Comparison of the Particle Size Distribution of Heavy-Duty Diesel Exhaust Using a Dilution Tailpipe Sampler and an In-Plume Sampler during On-Road Operation

ABSTRACT

Originally constructed to develop gaseous emission factors for heavy-duty diesel trucks, the U.S. Environmental Protection Agency's (EPA) On-Road Diesel Emissions Characterization Facility has been modified to incorporate particle measurement instrumentation. An electrical low-pressure impactor designed to continuously measure and record size distribution data was used to monitor the particle size distribution of heavy-duty diesel truck exhaust. For this study, which involved a high-mileage (900,000 mi) truck running at full load, samples were collected by two different methods. One sample was obtained directly from the exhaust stack using an adaptation of the University of Minnesota's air-ejector-based mini-dilution sampler. The second sample was pulled from the plume just above the enclosed trailer, at a point ~11 m from the exhaust discharge. Typical dilution ratios of about 300:1 were obtained for both the dilution and plume sampling systems. Hundreds of particle size distributions were obtained at each sampling location. These were compared both selectively and cumulatively to evaluate the performance of the dilution system in simulating real-world exhaust plumes. The data show that, in its current residence-time configuration, the dilution system imposes a statistically significant bias toward smaller particles, with substantially more nanoparticles being collected than from the plume sample.     

The Aerosol Research and Inhalation Epidemiology Study (ARIES): PM25 Mass and Aerosol Component Concentrations and Sampler Intercomparisons

ABSTRACT

The Aerosol Research and Inhalation Epidemiology Study (ARIES) was designed to provide high-quality measurements of PM₂₅, its components, and co-varying pollutants for an air pollution epidemiology study in Atlanta, GA.

Air pollution epidemiology studies have typically relied on available data on particle mass often collected using filter-based methods. Filter-based PM_2.5 sampling is susceptible to both positive and negative errors in the measurement of aerosol mass and particle-phase component concentrations in the undisturbed atmosphere. These biases are introduced by collection of gas-phase aerosol components on the filter media or by volatilization of particle phase components from collected particles. As part of the ARIES, we collected daily 24-hr PM_2.5 mass and speciation samples and continuous PM_2.5 data at a mixed residential-light industrial site in Atlanta. These data facilitate analysis of the effects of a wide variety of factors on sampler performance. We assess the relative importance of PM_2.5 components and consider associations and potential mechanistic linkages of PM_2.5 mass concentrations with several PM_2.5 components.

For the 12 months of validated data collected to date (August 1, 1998-July 31, 1999), the monthly average Federal Reference Method (FRM) PM_{2 5} mass always exceeded the proposed annual average standard (12-month average = 20.3 ± 9.5 ug/m³). The particulate SO₄ ^2- fraction (as (NH₄)₂SO₄) was largest in the summer and exceeded 50% of the FRM mass. The contribution of (NH₄)₂SO₄ to FRM PM_2.5 mass dropped to less than 30% in winter. Particu-late NO₃ ^- collected on a denuded nylon filter averaged 1.1 ± 0.9 ug/m³. Particle-phase organic compounds (as organic carbon × 1.4) measured on a denuded quartz filter sampler averaged 6.4 ± 3.1 ug/m³ (32% of FRM PM_{2 5} mass) with less seasonal variability than SO₄ ^2-.     

Atmospheric Aerosol Composition and Concentration as a Function of Particle Size and of Time

As a step toward better understanding the reactive Los Angeles air basin atmosphere, a study was undertaken at the University of California—Riverside Campus, to determine the composition and concentration of atmospheric particulate matter as a function of particle size and time. The study involved developing a method for obtaining size-classified, time-fractionated aerosol samples amenable to chemical and physical (including microscopic) analysis. During a 15-day period, samples were obtained over 4-hr periods and subsequently analyzed for nitrate, sulfate, iron, and lead. Concentration of six gaseous pollutantsj total aerosol light-scattering, and several meteorological measurements were simultaneously recorded and averaged over the 4-hr intervals. This data was presented graphically to show the diurnal variation in and relationship between gaseous, particulate, and meteorological measurements. A strong relationship between gaseous peroxyacetyl nitrate, particulate nitrate, and aerosol light-scattering was found. High concentrations of ammonium nitrate particles, mainly in the 0.5-2μ, diameter size range, were found in the atmospheric particulate samples collected on days of very high smog (very limited visibility).     

Electrical Measurement of the Mass Concentration of a Self-Preserving Aerosol Size Distribution

Recently fifty-eight measurements of urban aerosol size distributions by Clark have shown that these distributions agree quite well with the self preserving form proposed by Friedlander within the size range of 0.05 to 5 microns radius. This paper shows that for an aerosol obeying the self preserving distribution model, the volume concentration (and, hence, the mass concentration for constant density) is directly proportional to the electric current collected when the aerosol is unipolarly charged, passed through a weak electric field to remove particles smaller than 0.05 micron and then collected by a current collector. It is shown that the linear relation between the mass concentration and collected current is independent of the unipolar charging method used. A test of this theory using Clark’s electric counter data was encouraging and suggests that the electric measurement of urban aerosol mass concentrations by properly designed instruments may be feasible.     

Optical Measurements of Aerosol Size Distributions in Great Smoky Mountains National Park: Dry Aerosol Characterization

ABSTRACT

Aerosol size distributions were measured during the summertime 1995 Southeastern Aerosol and Visibility Study (SEAVS) in Great Smoky Mountains National Park using an Active Scattering Aerosol Spectrometer (ASASP-X) optical particle counter. We present an overview of the experimental method, our data inversion technique, timelines of the size distribution parameters, and calculations of dry accumulation mode aerosol density and refractive index. Aerosol size distributions were recorded during daylight hours for aerosol in the size range 0.1 < Dp < 2.5 u,m. The particle refractive index used for the data inversion was calculated with the partial molar refractive index approach using 12-hr measured aerosol chemical composition. Aerosol accumulation mode volume concentrations ranging from 1 to 26 u,m³ cm^-3 were observed, with an average of 7 ± 5 u,m³ cm^-3. The study average dry accumulation mode geometric volume median diameter was 0.27 ± 0.03 u,m, and the mean geometric standard deviation was 1.45 ± 0.06. Using an internally mixed aerosol model, and assuming chemical homogeneity across the measured particle distribution, an average accumulation mode dry sulfate ion mass scattering efficiency of 3.8 ± 0.6 m² g^-1 was calculated.     

A High-Volume Sampler for the Determination of Particle Size Distributions in Ambient Air

A size selective particle sampler has been developed for continuous sampling of the urban aerosol over periods ranging from hours to weeks, providing relatively large sample weights. The system, which is now operating in New York City, uses a parallel array of two-stage samplers. The cyclones used as the first stage collectors have 50% particle retention at 3.5,2.5,1.5 and 0.5 µm aerodynamic diameter, respectively. Undersize particles which pass through the cyclones are captured on glass fiber filters. Equal intake velocities are assured by using flow equalizers on the inlets to the cyclones. Accurate control of the flow through the cyclones is obtained by the use of an integrated circuit pressure transducer in conjunction with a specially designed feedback control circuit. The collection efficiencies of the cyclone were calibrated using monodisperse ferric oxide test aerosols tagged with Tc-99m. Mass balances of the par-ticulates collected on the cyclones and filters are obtained for the five sampling stages. Preliminary results show the distributions of the total suspended particulates in New York City to be bimodal. The distributions of lead, copper, and manganese with particle size are also discussed.     

Design and Operating Parameters for a Large Ambient Aerosol Chamber

Recent investigations of ambient aerosol behavior over urban areas have pointed out the need for controlled experimental data to link together field investigation results and computer simulation studies. This paper describes the design considerations, construction details and operating parameters of a large (8000 ft³) outside reaction chamber constructed in rural North Carolina. The chamber is triangular in cross-section, 20 ft wide, 20 ft high and 40 ft long, and is covered with clear 5 ml Teflon film. The outdoor location of the chamber permits the reaction volume to be exposed to the natural conditions of temperature and solar radiation. A recirculating air system allows the air in the chamber to be passed through an “absolute” fiberglas filter for adjustment of condensation nuclei concentration and also through driers for humidity adjustment. Internal fans are provided for mixing of the chamber contents without use of the recirculating system so that various degrees of turbulence can be approximated. A sampling line from the chamber passes directly to an instrument room, located directly under the chamber, where direct analyses for particle composition, concentration, and size, and gas composition and concentration are carried out. Parameters which can be varied in this system include number, size, distribution, and chemical composition of pre-existing nuclei, as well as humidity, solar radiation, temperature, and trace gas concentration and composition.     

Size Distribution and Sources of Aerosol in Launceston,Australia, during Winter 1997

ABSTRACT

As part of a pilot study into the chemical and physical properties of Australian fine particles, a suite of aerosol samples was collected at Ti Tree Bend in Launceston, Tasmania, during June and July 1997. This period represents midwinter in the Southern Hemisphere, a period when aerosol sources in Launceston are dominated by smoke from domestic wood burning. This paper describes the results from this measurement campaign, with the aim of assessing the effect of wood smoke on the chemical and physical characteristics of ambient aerosol. A micro orifice uniform deposit impactor (MOUDI) was used to measure the size distributions of the aerosol from 0.05 to 20 n m aerodynamic diameter. Continuous measurements of fine particle mass were made using a PM_2.5 tapered element oscillating microbalance (TEOM) and light scattering coefficients at 530 nm were measured with nephelometers.

Mass size distributions tended to be bimodal, with the diameter of the dominant mode tending to smaller sizes with increases in total mass. Non-sea salt potassium and polycyclic aromatic hydrocarbons (PAHs) were used as chemical tracers for wood smoke. Wood smoke was found to increase absolute particle mass (enough to regularly exceed air quality standards), and to concentrate mass in a single mode below 1 μm aerodynamic diameter. The acid-base equilibrium of the aerosol was altered by the wood smoke source, with free acidity hydrogen ion, non-sea salt sulfate, and ammonium concentrations being higher and the concentration of all species, including nitrate (to differing extents), focused in the fine particle size ranges. The wood smoke source also heavily influenced the aerosol scattering efficiency, adding to a strong diurnal cycle in both mass concentration and light scattering.     

Testing Re-entrained Aerosol Kinetic Emissions from Roads : a new approach to infer silt loading on roadways

PM₁₀ and PM_2.5 emissions from roadways are currently estimated using the silt loading on the road surface as a surrogate for the emissions potential of road dust. While the United States Environmental Protection Agency prescribes this method in AP-42, there is considerable cost associated with silt loading measurements; it is feasible to sample only a small portion of a roadway network. A new approach for measuring the concentration of suspendable PM₁₀ above road surfaces has been developed to obtain a more spatially representative estimate of a road's potential to emit dust. The Testing Re-entrained Aerosols Kinetic Emissions from Roads (TRAKER) system uses real-time aerosol sensors mounted on a vehicle to measure the concentration of dust suspended from the road while the vehicle is in motion. When coupled with a Global Positioning System (GPS) instrument, TRAKER can be used to efficiently survey the changes in suspendable particles due to varying road conditions over a large spatial domain.In a recent study on paved roads in Las Vegas, the TRAKER system was compared with collocated silt loading measurements. The TRAKER system was also used to survey the relative amounts of suspendable road dust on approximately 300 miles of paved roads. The system provides a unique perspective on road dust sources and their spatial distribution.Results of this study indicated that the difference of the PM₁₀ concentrations measured behind the tire and on the hood is exponentially related to vehicle speed. This was an interesting finding because current AP-42 road dust emissions estimation methods do not include vehicle speed as a factor in the emissions calculations. The experiment also demonstrated that the distribution of suspendable material on roadways is highly variable and that a large number of samples are needed to represent road dust emissions potential on an urban scale for a variety of road and activity conditions.     

Development and Evaluation of an Impactor for a PM2.5 Speciation Sampler

ABSTRACT

A conventional impactor for a particle speciation sampler was developed and validated through laboratory and field tests. The speciation sampler consists of the following components: a PM_2.5 conventional impactor that removes particles larger than 2.5 μm, an all-glass, coated honeycomb diffusion denuder, and a 47-mm filter pack. The speciation sampler can operate at two different sampling rates: 10 and 16.7 L/min. An experimental characterization of the impactor’s performance was conducted. The impactor’s collection efficiency was examined as a function of critical design parameters such as Reynolds number, the distance from the nozzle exit to the impac-tion plate, and the impaction substrate coating method. The bounce of particles larger than the cut point was successfully minimized by using a greased surface as the im-paction substrate. Additionally, a series of field intercomparison experiments were conducted at both 10 and 16.7 L/min airflow. PM_2.5 mass and SO₄ ^2- concentrations were measured and compared with the Federal Reference Method (FRM) and found to be in good agreement. Results of the laboratory chamber tests also indicated that the impactor’s performance was in good agreement with the FRM.     

新型膜法SBR系列间歇充氧式生活污水净化装置

采用“水解沉淀 生物过滤 SBR生物接触氧化 沉淀过滤”这一独特的工艺路线处理生活污水。该装置利用污水提升过程中的动能和势能进行射流曝气，通过液位计代替PLC程控装置等技改措施实现自动控制，从而使装置的一次性投资、运行费用和操作维护的劳动强度大为降低。因此可作为城市污水处理场的补充，具有广泛的推广应用价值。     

Analysis of Ambient Concentrations of Organic Vapors with a Passive Sampler

Volatile organic compounds can contribute to the failure of electronic equipment in both switching offices and data centers. They can also be useful indicators of ventilation needs. Only within the past decade have ambient concentrations of volatile organics been measured routinely. In standard sampling approach, a pump is used to pull a known volume of air through an adsorbent. This study examines a sampling procedure that does not use a pump, but instead depends on molecular diffusion for eventual contact between the vapor phase compounds and the charcoal sorbent (passive sampling). The technique is both simpler and less expensive than active sampling with a pump. This method has been validated for low-level sampling over extended time intervals. This study demonstrates that collected amounts vary linearly with airborne concentrations for sampling intervals in excess of four weeks: even after eight weeks of sampling at typical ambient concentrations, the amount of material collected does not approach the capacity of the sorbent. The method is applicable for concentrations spanning six orders of magnitude; reproducibility averages 13 percent of the mean value; and the sensitivity is excellent (0.06 μg/m³ or roughly 0.015 ppbv for a compound with a molecular weight of 100). The procedure has already been used successfully to monitor indoor air quality at almost a dozen telephone office and data center sites.     

A Field Intercomparison and Fundamental Characterization of Various Dust Samplers with a Reference Sampler

The European Economic Community Council Directive 80/779/EEC¹ describes air quality limit values and guide values for sulfur dioxide and suspended particulates. However, article 10, paragraph 1 does not define well enough the reference method required, amongst others, for the gravimetric measurement of suspended particulates. It is explicity stated in article 10, paragraph 5 of the directive, that “the commission shall, in selected locations in the member states and in cooperation with the latter, carry out studies on the sampling…of suspended particulates. These studies shall be designed in particular to promote the harmonization of methods of sampling and analysis of these pollutants.” Therefore, in a joint research program the Umweltbundesamt (grant #104 02263), the commission of European Communities (grant #84-B-6642-11-017-11-N) and the U.S. EPA (grant #2-43211-3580) funded the development of a reference dust sampler by the Fraunhofer-lnstitute of Toxicology and Aerosol Research (FhITA, in Hannover, Federal Republic of Germany) in order: ? to study the particle size distribution of ambient air aerosol at a number of selected sites;

? to compare the results obtained with the reference dust sampler with those of particle samplers operated in Europe and the United States;

? to verify the applicability of wind tunnel results to sampling behaviour in the free atmosphere.

     

The Validation of a Passive Sampler for Indoor and Outdoor Concentrations of Volatile Organic Compounds

Abstract

Volatile organlcs compounds (VOCs) are ubiquitous in the air we breathe. The use of passive samplers to measure these concentrations can be an effective technique. When exposed for long durations, a passive sampler may be a good tool for investigating chronic exposures to chemicals in the environment. A passive sampler that was designed for occupational exposures can be used as such a tool. Laboratory validation under as many conditions as possible needs to be accomplished so as to characterize the sampler with known parameters. This paper describes the methods and results of an investigation into the validity of using a passive monitor to sample VOCs for a three-week period. Two concentration levels, two relative humidities, and five VOCs were studied. Results indicate that the samplers work best under conditions of high concentration with low relative humidity and low concentration with high relative humidity. For the passive sampler, excluding chloroform, percent deviations from the predicted values varied between ?41 and +22 percent; while the values between the passive and the active samplers varied between ?27 and +24 percent. Benzene, heptane, and perchloroethylene were sampled with equal precision and accuracy.