Continuous measurement of atmospheric ozone by an automatic photoelectric method

Abstract

An au tomatic photoelectric instrument and method for t he continuous meas urement of t he ozone in the earth's atmosphere at low altitudes are described. The method is physical rather t han chemical in character and is based upon t he optical absorption characteristics of ozone in the Hartley and Huggins ul t raviolet bands. Th e ins trument makes use of a lowpressure mercury are, which is situated at a di stance of 1,450 feet from the reco rding s tation t hat emp loys a 1P28 photo mult iplier as a d etector . The lig ht beam is modulated, at 510 cycles per se cond, so that the output of t he photomultiplier is fed into a t uned alternatingcurrent ampllfier and amphfied to the recorder level. By means of a Geneva m ec han is m which changes t he glass filters, the radiant energy from t he lamp is separated into band~ primarily at wavelengths 253 .7, 365.5, a nd 405 .0 millimi cro ns. From the ratios of the de1kctions for t he different spectral regions it is possible to d etermine ozone concentration in t he range from a few te nths of 1 part to many p ar ts per 100 million.

Standard of spectral radiance for the region of 0.25 to 2.6 microns

“…Leiss double quartz prism monochromators with relative aperture ranges of F /6.4 to F /7.2 were employed as shown in figures 2 and 3 . The detector used at the exit slit of the monochromator for the wavelengths from 0.7 to 2.6 μ was an uncooled lead sulfide cell, while for the wavelength range of 0.25 to 0.75 μ a photomultiplier, type 1P28 was employed [ 9 ]. In all cases care was taken (through the use of filters to reduce the light intensity when required, and by other means) in using the photomultiplier to make certain that the detector was not exposed to excessive radiation which might produce a change or nonlinear character in the photoelectric response.…”

Natural Sources of Gaseous Pollutants in the Atmosphere

“…In most locations near the earth's surface the ozone drops down to 2 or 3 parts per hundred million by volume. This value of 2 or 3 pphm by volume has been confirmed by infrared YATES, 1956, 1957;BIRKELAND, ET AL., 1957), ultraviolet (BAUM andDUNKEL-MAN, 1955;STAIR, ET AL., 1954), and chemical measurements ( HAAGEN-SMIT, 1955) in locations distant from industrialized urban centers.…”

“…Significant changes in ozone concentration with the movement of weather fronts have been reported (STAIR, ET AL., 1954;DOBSON, 1950). Such variations have been observed in ground level measurements of ozone on the North American continent (STAIR, ET AL., 1954) and in total atmospheric ozone over the continent of Europe.…”

Air Pollution

“…a number of nieasurements on a more precise basis. Stair and con-orkers (411) made continuous estimations of ozone in Kashington with a 1450foot path instrument using the Hartley band a t 250 to 260 mp. Automatic insertion of filters passing bands ccntered a t 253.7, 365.jj and 405 nip provided for correction of effect of other attenuants.…”