Atmospheric Research Chamber Projects
Calspan
Prepared by
Thomas Albrechcinski
(716) 631-6764
Table of Contents
PHYSICAL CONTROLS:
(1) Physical characteristics; (2) Chamber Surface; (3) Air Purification; (4) Air Humidity Control; (5) Liquid Flushing System; (6) Photo-irradiation SourcesINSTRUMENTATION:
(7) Aerosol Monitoring Instrumentation; (8) Gas Analysis Instrumentation (Ambient); (9) Other Gas Analysis Instrumentation; (10) Engine Exhaust Instrumentation; (11) Filter Sampling Support Equipment; (12) Other chamber Support InstrumentationOPERATIONAL CAPABILITIES OF THE ENVIRONMENTAL CHAMBER: (1) Cloud Nucleation and Fog Formation Studies; (2) Haze, Aerosol Formation and Growth Studies; (3) Photolysis Reaction Studies; (4) Exhaust Emission Studies; (5) Military Smoke Screen Studies
Calspan's Ashford test chamber was originally designed as a part of an ordnance test facility. Extensive modifications have been made over the past few years, converting it to a unique facility for atmospheric simulation, air pollution, cloud physics, and aerosol research studies. Relevant facility characteristics are described below:
The heart of the test facility is a cylindrical chamber of 9 m diameter and 9 m height. The total volume is 600 m3 (20,000 ft3), making it one of the largest available test chambers in the United States, especially valuable in minimizing wall effects and closely simulating actual atmospheric conditions. The chamber wall is constructed of 0.5 inch plate steel designed for pressure differentials up to 9 psig.
Figure 1 presents a cut-away view of the facility. Figure 2 (floor plan) shows the chamber location relative to the auxiliary facilities housed in the same laboratory complex. An interior view of the chamber is shown in Figure 3.The inner chamber surface is covered with a special coating developed at the United States Naval Research Laboratory (
Figure 4). This coating material is a highly fluorinated epoxy-polyurethane copolymer. The in situ curing of the polyurethane base enables good adhesion to the chamber surface. The very high fluorine content provides, in analogy to fluorocarbon polymers, both high chemical stability and low surface energy. Such favorable physical and chemical characteristics add further to the capability of the chamber in minimizing possible wall effects during photochemical aerosol studies.A schematic diagram of the chamber air ventilation system is shown in
Figure 5. Absolute filters are incorporated to permit virtually total removal of particulates (<200 Aitken nuclei/cm3). Impregnated charcoal filter panels (not shown in Figure 2) are installed to enable the removal of gaseous contaminants. Some of the most difficult to remove contaminants, such as CO and CH4, are present only at minimum concentrations in the unpurified ambient air due to the rural location of the test facility (about 35 miles south of Buffalo, New York). The air purification system is thus capable of preconditioning the chamber for studies of pollutant effects even at minute concentrations.Humidistatically controlled cooling coils installed in the ductwork in series with the absolute filters serve to dehumidify the chamber air. Humidity increases are achieved by nebulizing distilled water from a nozzle installed in the chamber ceiling (
Figure 6).The chamber is equipped with a water flush system as shown schematically in
Figure 7. Prepurified water with or without addition of a detergent can be introduced into the chamber through a rotating jet sprayer. This flush system reaches all areas of the chamber wall, provides for a very effective surface cleaning, and may also be utilized on some occasions for gross adjustment of humidity.Photolysis lamps simulating the near UV portion of the earth's ground level solar radiation spectrum are located around the chamber wall to permit near uniform intensity distribution within the chamber (
Figure 8). Twenty-four individual light fixtures, each containing two special Sylvania high intensity blacklight lamps, two 215W fluorescent GE sunlamps, and eight GE-F72T12/HO/BL blacklight lamps, are arranged in three horizontal rows and eight vertical columns radially spaced equally along the chamber wall. Each of the light source combinations is encased in a gas-tight enclosure equiped with a 15" x 96" Pyrex glass front panel. Forced air cooling (separated from the chamber air) is used to minimize possible temperature rises at these light source fixtures. The resulting light intensity (in the near UV range pertinent to photochemistry) corresponds to approximately 50% of the average mid-day solar radiation at sea level in mid-latitudes. Some of the light fixtures may be seen in Figure 4 which shows an inside view of the chamber. Gentle stirring at low rpm by the fan in the foreground prevents the formation of inhomogeneities that would be caused by unavoidable light intensity and temperature gradients in stagnant air.(7) Aerosol Monitoring Instrumentation
Equipment available for monitoring aerosol particulate size distributions, concentrations and related parameters is listed below:
a) Size Distribution and Particle Concentrations
b) Mass Loading
(8) Gas Analysis Instrumentation (Ambient)
Highly sensitive instrumentation for analysis of prevalent gaseous pollutants is incorporated as a part of the test facility capabilities (
Figure 9). The instruments described below aspirate samples through a Teflon tube protruding 2 meters into the chamber.(a) Bendix Model 8002 Ozone Analyzer - An instrument based on the principle of photometric detection of chemiluminescence resulting from the reaction of ozone with ethylene.
Minimum detection limit =.001 ppm; 7 ranges:.01, .02, .05, .l, .2, .5, 1.0 ppm
(b) Bendix Model 8101-B Nitrogen Oxides Analyzer- Photometric detection based on chemiluminescent reaction between NO and ozone. N02 is detectable through a prior conversion to NO.
NO
NO2 0-0.5 ppm, 0-1.0 ppm, 0-5 ppm
NOx
(c) Meloy Model 5A260 Flame Photometric Total Sulfur Gas Analyzer - The detection principle is based on sulfur atom excitation in a hydrogen-rich flame.
(d) Bendix Model 820 Reactive Hydrocarbon Analyzer - This instrument uses flame ionization detection to provide quantitative analysis of methane (CH4), total hydrocarbons (THC), and reactive (non-methane) hydrocarbons (NMHC).
THC: 0-1 ppm, 0-20 ppm, 0-50 ppm
CH4: 0-2.0 ppm, 0-5 ppm, 0-10 ppm
(8A) Gas Chromatography/Mass Spectrometry
(a) Hewlett Packard Model 5890 Series II GC with Flame Ionization Detection (FID) and Teledyne Discovery II Ion Mass Spectrometer are used to determine hydrocarbon concentrations in the chamber (
(9) Other Gas Analysis Instrumentation
(a) Welsback Model T-408 Ozone Generator - 1 ppm per hour - chamber concentration.
(10) Engine Exhaust Instrumentation
Instrumentation for analysis of raw exhaust gaseous and particulate emissions are also incorporated as part of the test facility capabilities. These instruments provide measurements of vehicle performance and stability.
(a) Thermo-electron Model 10A Chemiluminescent Analyzer; Raw Exhaust NO measurements
Range: 0-2.5 ppm, 0-10 ppm, 0-25 ppm, 0-100 ppm, 0-1000 ppm, 0-2500 ppm, 0-10,000 ppm
(b) Beckman Model 402 Heated Flame Ionization Detector; Raw Exhaust Total Hydrocarbon measurements
Range: X1, X5, X1 0, X50, X1 00, X500, X5000
(c) Bosch Smokemeter
(11) Filter Sampling Support Equipment
A variety of sampling systems are available and are used to obtain aerosol filter samples directly from the chamber for chemical and biological analyses and for the determination of aerosol mass loading.
The primary sampling systems are listed below.
(a) Low-volume sampling system.
Positive displacement pump driven
Capacity: 2 filters (90 mm diameter)
Sampling rate: ~8 cfm (Nominal)
(b) Standard 47 mm filter holders.
Capacity: 1 filter (47 mm diameter)
Sampling Rate: 1 cfm (Nominal)
(12) Other chamber Support Instrumentation
Pressure, temperature and dew point measurement and visibility instruments are available for continuous monitoring of chamber and outdoor air ambient conditions:
(a) Dewall Temperature and Humidity Sensor
(b) Standard Laboratory Mercury Barometers
(c) Infrared transmissometer for measuring liquid water content in clouds/fog
OPERATIONAL CAPABILITIES OF THE ENVIRONMENTAL CHAMBER
The Environmental Chamber is used extensively for a variety of aerosol/fog related investigations requiring accurate simulation of atmospheric conditions. Fog and haze formation, fog modification, aerosol formation and growth, aerosol interactions, exhaust emission and photochemical reaction studies have been conducted within the facility.
(1) Cloud Nucleation and Fog Formation Studies -- The experimental procedure normally consists of fog production and characterization, nuclei introduction, and aerosol detection steps. First, the chamber wall is wetted thoroughly with water from the rotating spray nozzle. The chamber air is over pressurized to about 30 mb, and the air is circulated to establish the desired equilibrium conditions. Fog formation is induced by venting the chamber air at a controlled average rate of about 3 mb/min. After reaching ambient pressure, fog persistence is achieved by continued slow expansion of the chamber air to a pressure about 30 mb below ambient. In this way, fogs and clouds closely approximating those found in nature can be produced. Seeding concepts designed to study aerosol-droplet interaction or to improve visibility in fog can be tested by injecting artificial nuclei into the fog with a jet mill located near the chamber ceiling.
(2) Haze, Aerosol Formation and Growth Studies -- By carefully controlling humidity and the aerosol population, a variety of haze and aerosol grow studies can be conducted in the Chamber. Prescribed aerosol populations can be readily produced from solution through use of a Collison nebulizer. Dehumidifiers and a fine-control humidification system are an integral part of the Chamber's support capabilities. Effects of relative humidity, particulate type and concentration, and various gaseous contaminants on aerosol growth rates can be repeatably studied. Fogs can be formed on resultant aerosol to study effects of pollutants on fog formation processes.
(3) Photolysis Reaction Studies -- Recent chamber modifications providing high intensity illumination sources (i.e., simulating ~50% of noontime sun's UV intensity as received at the surface), air purification systems, and an inert chamber surface coating are designed for conducting chemical reaction studies. Photochemical reactions are known to play important roles in gas to particle conversion. The interrelationship between aerosol size distributions, gaseous constituents, and photochemical processes are a subject of major interest in current research programs utilizing the Calspan chamber facilities. The catalytic oxidation of reactants such as S02 in high humidity or fog conditions has been effectively studied in Chamber experiments. Recently, the photolysis of dimethylsulfide to methane sulfonic acid, S02 and H2SO4 has been successfully simulated in the chamber.
(4) Exhaust Emission Studies -- Ongoing programs to develop methodologies for determining the effects of fuel and fuel additive combustion products on atmospheric visibility and exhaust emission characteristics were performed in the Ashford Chamber site. Test vehicles were individually operated on a chassis dynamometer in an attached room while a portion of the auto exhaust was introduced into the smog chamber. The auto exhaust mixture was then irradiated with artificial sunlight while visibility and aerosol characterization measurements and aerosol collections (for chemical analysis) were made. The effects of additives, as well as high and low sulfur fuels on test results, have been investigated. Experiments involving both gasoline and diesel-fueled vehicles have been conducted.
(5) Military Smoke Screen Studies -- Tests involving a variety of military smoke screen materials have been conducted in the chamber. These tests have included both powders and pyrotechnically generated aerosols at relative humidities in the range 20-97%. Control of RH permits the effective study of the impact of changing RH on the aerosol size spectra, mass-loading and extinction (visible to far IR wavelengths) characteristics of smoke screens. The chamber has also been used in dosage/exposure tests of certain detectors to certain aerosol/smoke contaminants.
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