A N A L Y T I C A L CHEMISTRY
996 solution usually used with silver-silver chloride electrodes. Not only are the results uniformly good, but the amount of drift and fluctuation of voltage values is negligible compared to the technique described previously. .4s a result of this stabilization of the instrument, an analysis can be completed in 30 minutes. The data show that the limit of the accuracy of the method is 0.1 t o 0.2 mg. of chloride as potassium chloride. ACKNOWLEDGMENT
The authors gratefully acknowledge their indebtedness to G. R.
Leader for making available the fractional freezing apparatua shown in Figure 1 which he designed and constructed. LITERATURE CITED
(1) Leader, G. R., J . Am. Chem. Soc., 73,856 (1951). (2) Magill, P.L., I d . Eng. Chem.,26, 611 (1934). (3) Rao, S., J. Indian Chem. SOC.,18, 337 (1941). (4) Smith, G. F., J . Chem. Soc., 53, 3257 (1931). ( 5 ) Verhoek, F., J . Am. Chem. Soc., 58, 2577 (19361. RECEIVED for review August 13, 1951. Accepted March 27,
1952.
Evaluation of Particulate Concentrations with Collecting Apparatus Examination of Air Pollution Levels in Los Angeles County STANLEY R. HALL The Albert L. Chaney Chemical Laboratory, Glendale 6, Calif. Air pollution control programs require some method of assessing the effectiveness of the corrective procedures. Human observations are subject to many limitations and their accuracy w i l l be seriously questioned as time passes. Long-period weather cycles, shift in population centers, industrial growth, and changes in chemical processes all produce subtle changes that cannot readily be detected by direct visual observations. Measurements based on a reproducible procedure offer a logical and acceptable means for evaluating pollution levels. Particulates are collected on flat filter disks and measured by means of a wyell-known apparatus. Limitations and advantages of a proposed scaleof valuesfor particulate
I
N AIR pollution research or in the administration of an air pollution control program, it is essential to determine the air
contamination levels over extended periods of time for comparison with previous years or corresponding times in other meas. Gradual increases or decreases in air pollution levels over a n extended period of time are not easily detectable and are always debatable when general observations are used for such purposes. Varying meteorological conditions make the problem doubly difficult and render general observance almost worthless. Some reliable and integrated measuring procedure is required. The first indication of common city air pollution is the haze and decrease in visibility. Because visibility is affected by the relative humidity, light levels, clouds, fog or water droplets, and particulates, it cannot be used alone as an index of air pollution. It is further subject to the limitation of darkness. The use of particulate mass would seem to provide a much better approach t o evaluation of air pollution levels. If the particulates are collected from measured volumes of air, and their mace and general composition determined, a pollution level for the particulates is established. The composition identifies the general sources and any change in these sources will be reflected in future measurements. From the best information now available, It s e e m that most nonparticulate centaminants also rise and fall with the particulate level ( I , l a ) . For evaluation of air pollution levels, these mass measurements should be taken continuously over extended periods of time. Each
levels are discussed. Procedures for calibrating the scale of particulates in terms of carbon or other materials are given. An automatic collecting apparatus is briefly described. For research studies a curve of particulate level variation is extremely useful in analyzing other related data. iiir pollution control officials can use the procedures for obtaining accurate comparable data to evaluate the effectiveness of control measures. Particulate levels and their variations with time are obtained with a minimum of labor. Personnel may be more effectively used, as data may be collected continuously and stored. Later, the most important periods may be studied as time and importance permit.
sample should be for a relatively short period and then all the samples should be integrated and correlated against meteorological data. Collecting and analyzing so many samples could be extremely time-consuming and expensive. Any scale of mass values could be used. Such a scale of values should be easy to obtain, proportional to m s per unit of volume, and for convenience, be in terms of small numbers. If values are in mass per unit of volume, the data for one area may be readily correlated and compared with those from another area. They should in themselves be a reference value t o which the various pollution constituents may be related. The mechanism of determining their mass values should be adaptable to automatic recording devices. METHOD
The samples are collected by drawing the air through filter paper in much the same way as was done by Shaw and Owens (IO)and others (4, 8). A 25-cubic-foot volume of air is drawn a t a uniform rate through a 1-square-inch area of filter paper during 1 hour. (Only a uniformly white paper of high quality should be used. Selected lots of Whatman No. 52 and the equivalent acidextracted Type 540, 5.5-em. diameter, are satisfactory.) This leaves a dark deposit on the paper. This darkening of the paper is measured and used aa an indication of the mass collected. The darkening is measured by the light reflected from the de osit when compared to that reflected from the clean filter paper ~y! a reflectance attachment of the Beckman DU spectrophotometer a t a wave length of 400 mp. The readings are recorded in terms of
V O L U M E 24, N O . 6, J U N E 1 9 5 2
997 for patent applications by the A. L. Chaney Chemical Laboratory,
Table I.
Relationshio of R. DE. and IC,
._"
"....
a.oo
0.022 0.046 0.071
95
90 85
80 ,* 70 65
4.19 6.46
8.83
0-09: "..*"
11
0.155
14.11
55
50
30
.I.YY
0.187 0.222 0.260 0.301
60
attention until a i filter blanks are used, at which ti& i t will shut down unless reloaded. The machine is normally checked once every 24 hours, but can be attended less often if required.
"0
0 O M
1""
Glendale. Calif.)
17.02 20.20 23.66 27.30
The sampler is equipped to take parallel samples; one on filter paper at the hourly rate, and the other in a prepared Gooch CNCiLie on a 24hour basis. The Gooch crucible may be seen in Figure 1 just under the weather cap beside the air inlet. On the left is the magmine for the unused portion of the filter belt or strip; t,he.~~~ rinht-hnnd m x e n h e haR hem removed to show the filter belt. I n the bottom of the upper case is the control box and panel, on which are mounted clock, running time meter, fuse holders, switches, n e w s a n , controls, and timer adjustments. Should there he a current failure, the clock will record the time, while the length of the shutdown may be determined from the running time meter. In the stand or lower case on the top shelf are meter and temerature indicators. On the bottom shelf is a vacuum ump with gbricator and gage. The upper and lower cases m a y i e quickly disassembled for convenience in transporting. Magazines and upper case have dust- and rain-tight covers for all-weather opera~
the optical density scale of the instrument, log 10 100/R, where R is the per cent reflectance.
For compssisou with similar samples of other volumes and areas, these readings are converted into a scale designated as K, values: t h e m equivalents of the deposit Per cubic meter. A unit value may be defined as that deposit which produces an optical density of 0.1 when the deposit area is 1 sq. om. and the volume of air sampled is 1 cubic meter. For a sample volume of 25 cubic feet and a filter area of 1 square inch:
K,
= 91 DE
where DB is the optical density equivalent for R. If V O ~ U ~and ~ S areas are kept uniform and if much work is to he done, a dire& reading K, scale may he installed on the measuring instrument. Normally the K, runs from.2 t o 20 for the Los Angeles ares, but occasionally will be lower, and a maximum value of nearly 30 has been recorded. Table I shows the relationship among R, DB, and K, in the useful range for a sample volume of 25 ouhic feet and a sample area of 1 square inch Inasmuch aa carbon and tany materials represent a proportionately large portion of the particulate constituents (1, 12) which contribute to the black color of the depoait, i t has been possible t o estimate the carbon content of the individual samples.
~
~
~~
tion. All parta are corrosion-protected or of corrosion-resistant materials. Partsthat contact the filter papers me of stainless steel or other noncontaminating materials. The air inlet has a standard glass joint taper, so that the equipment may he fitted with an extended sampling tube.
Simultmmus with every set oi 21 hourly filter paper samples, B p,mllcl a m p l e oi approximately 170 ru& fret of air is dr.t\m tbroueh x Cooch wucible with 3 6wciallv nwnxred nsbe3tos I ) H ~ . The
