Analyzer Checks Upper Atmosphere Ozone Armour Research Foundation device measures ozone for Air Force weather studies

would be to separate and evolve the gas while keeping down volatilization of the metal. Dr. Fassel applies a bit of chemistry here. He uses a carbon electrode as the anode. The arc dis­charge melts the sample in an argon atmosphere.

The molten metal readily dissolves some of the carbon electrode. Then the dissolved carbon reacts with oxide, nitride, and hydride in the sample, re­duces them to carbon monoxide, nitro­gen, and hydrogen. These gases evolve rapidly into the argon atmos­phere, where the arc dissociates and excites them. As the gases evolve, the dissolved carbon reduces volatility of the metal itself.

Oxygen, nitrogen, and hydrogen evolve quantitatively, Dr. Fassel says. However, the rate and degree of evolu­tion do depend critically on conditions in the carbon electrode. One of the important factors: The anode spot of the discharge must rest directly on the molten globule of sample so that its temperature equals the boiling point of the globule material, Dr. Fassel points out. The rest of the globule has a precipitous temperature gradient to about 1500° C. at the electrode-melt interface. Both the localized temper­ature and the efficient convection stir­ring induced by the large temperature gradient contribute to high reaction rates and rapid gas evolution.

Simple arcing of such metals as zirconium, titanium, and thorium in graphite electrodes does not cause sufficiently reproducible evolution of the sample's oxygen content. Dr. Fas­sel gets around this difficulty by using an electrode assembly which gives a molten platinum bath after the arc is initiated. Thus, the platinum bath provides a medium in which the gas evolution reactions can proceed rapidly and reproducibly. For most metal sys­tems Dr. Fassel has studied, a com­plete alloy of the sample and platinum is needed before any of the metal sam­ple reacts with the graphite electrode.

Save Time. Two operators, one for the excitation and another for plate measurements and calculations, can analyze spectrometrically up to 50 samples per day. By measuring in­tensity electronically and readying out-gassed electrodes in advance, opera­tors can complete an analysis in five minutes. This time saving, Dr. Mor­rison and Dr. Fassel feel, provides their incentive to apply emission spec­troscopy to new materials and to ex­tend its sensitivity range.

A new continuous ozone analyzer will soon join the Air Force's arsenal of in­struments for studying weather condi­tions in the upper atmosphere. The unit, developed by Armour Research Foundation for the Air Force Research Division at Cambridge, Mass., is based on ozone's heat of decomposition. It adds further versatility to the lineup of current ozone analysis techniques, can easily be adapted to monitor ozone in high-flying aircraft or to measure ozone content in on-the-ground air pollution, Armour says.

The Air Force plans to use the in­strument to study the ozone layer ex­isting between 40,000 and 150,000 ft. and its effect on circulations in the mésosphère. Most absorption of the sun's energy at these altitudes is due to the ozone layer, which converts the energy to heat. This in turn causes thermal currents. The Air Force wants to know how all this ties in with weather conditions.

Thermistors Used. The analyzer, developed by ARF's Dr. Roland Mc-

Cully, Dr. E. S. Gordon, and Dr. J. N. Van Scoyoc, consists of a detection cell, amplifier, and recorder. Inlet and outlet probes extending through the aircraft's skin into the atmosphere pro­vide a constant air flow through the detection cell. Two thermistors in the cell—part of a simple Wheatstone bridge—pick up ozone's heat of decom­position and send a signal via the am­plifier to the recorder.

Heart of the detection cell is a ro­tor, cast from epoxy resin. It consists of two concentric hollow cylinders, 1 / 2 in. and 3 / 4 in. in diameter. These are bisected, except in the annulus at the top, by a plane that also binds the cylinders to a concentric shaft. One half of the rotor surfaces, says Dr. McCully, is painted with a water sus­pension of catalyst—Mine Safety Ap­pliances' Hopcalite, a mixture of copper and manganese oxides. The water evaporates, leaving a solid coat­ing of catalyst on the rotor.

In operation, the rotor splits air flowing through the cell into two

STRATOSPHERE STUDIES. Armour Research's Dr. Roland McCully checks recorded data from the ozone analyzer that the AF will use to measure ozone content between 40,000 and 150,000 ft. and to study its effect on thermal currents in the mésosphère

J U L Y 4, 1960 C & E N 55

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streams, one passing over the catalyst, the other over the uncoated half, Dr. McCully explains. In addition, a mo­tor turns the rotor at 4 r.p.m.. Thus, thermistors are alternately exposed to air warmed from catalytic ozone de­composition, then to air that has not been contacted by catalyst. This compensates for any lack of symmetry between thermistors.

About 42% of the ozone coming into the cell decomposes—almost all of that on the catalyst side, hardly any on the other. For 1 p.p.m. of ozone in air, Dr. McCully points out, the maximum theoretical temperature rise is 0.003° C , corresponding to 88 mi­crovolts from the thermistor. But, thermal and electrical losses eat up about half of this, thus limiting instru­ment sensitivity.

The Armour device has a range up to about -50 p.p.m., with/a sensitivity of 0.1 p.p.m. Dr. McCully notes that the concentration which might be ex­pected at 80,000 ft. would be around 10 p.p.m. At 20,000 to 30,000 ft.: about 0.1 p.p.m.

Advantages. While both coulo-metric and spectrophotometric ozone analysis methods are well suited to their special uses, they are limited in many applications. For example, the coulometric analyzer, which depends on a potassium iodide titration, has an ambient pressure limit because of so­lution vapor pressures. And the spec­trophotometric method, used in bal­loon ascents, is based on differences in absorption of the sun's rays. Thus, it's not well suited to horizontal flights.

The new instrument, says Dr. Mc­Cully, can be adapted to ground measurements, such as air pollution studies, by adding a dry ice trap and a pump for circulating the air. The dry ice trap is needed to get rid of mois­ture in the air.

Ozone in dry air decomposes to oxygen. But in wet air, it decomposes through an intermediate which is probably hydrogen peroxide, accord­ing to Dr. McCully. This introduces an error into the measurement, he says.

ARF also feels the analyzer could serve as a monitor for high-flying air­craft. More knowledge of ozone's toxicity may show such a device is needed. Earlier studies by ARF showed that, in sensitive persons, con­centrations as low as 2 p.p.m. can cause severe lung irritation in less than an hour.

Colorimetric Air Tester Checks HCHO Pollution

Scientists at the Ontario Department of Health have developed a technique to measure formaldehyde concentra­tions in air as low as δ p.p.b. and to detect this air contaminant at levels as low as 1 p.p.b. This means, say Arthur C. Rayner and Dr. Clarence M. Jephcott, that their method—a colorimetric one—measures the very small amounts of formaldehyde usu­ally present in outdoor air.

Formaldehyde makes up nearly half of the total amount of aldehydes and ketones present in the atmos­phere, Mr. Rayner told the Chemical Institute of Canada, meeting in Ot­tawa. Formaldehyde content in air is one index of pollution from incomplete combustion of gasoline, fuels, and ref­use. No limits have yet been legis­lated for emission of this compound into the atmosphere, but a recent Soviet report suggests a maximum of 0.035 mg. per cubic meter in ambient air, Mr. Rayner says.

Colorimetric Method. The scien­tists draw air through an impinger, containing 60 to 75 ml. of 0.005N hy­drochloric acid, at 1 cu. ft. per min. Collection efficiency of this solution runs around 72%. When air being sampled contains less than 0.05 p.p.m. of formaldehyde, they draw a 60-cu.-ft. sample. This gives them one anal­ysis per hour.

By using SchifFs reagent (decolor­ized fuchsin), the ODH research workers compare the aliquot samples they collect with standard formalde­hyde solutions. They read optical densities of the test solutions against a reagent blank in a spectrophotometer.

Testing the air at street level in mid-town Toronto (College and Bay Streets), Mr. Rayner and Dr. Jephcott set up automatic impingers which gave hourly samples continuously over several days. These preliminary 24-hour-a-day analyses show that the formaldehyde content varies through­out the day in what they consider typical urban air. The location se­lected has moderate to high densities of both buildings and traffic. Regu­lar highs for formaldehyde concentra­tion seem to occur there between 8 A.M. and 10 A.M. and from 4 P .M. to 6 P .M. Concentrations ranged from below 1 p.p.b. to highs of 40 to 50 p.p.b.

56 C & E N J U L Y 4, 1960

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Palladium alloy for use in diffusion systems for hydrogen purification is being produced by J. Bishop & Co., Malvern, Pa. The alloy doesn't de­form during heating or cooling in a hydrogen atmosphere, is more per­meable to hydrogen and costs less than pure palladium, and is easy to fabri­cate, the company says. Ε 4

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