Nmmmber
Iltmorpheric Pollutlon
Iese
The results of a 2-year study on air contaminants and techniques for microsampling are reported by the Los Angeles Air Pollution Control District C. McCube
bg Lo&
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HE h r d annual report of the Los Angelcs County Air Ax €'ollutioo Contml District (Z) "88 r e l e d esrly in October. The two previous reports dealt with the meteorological henome m and with some of the sasilv easily reoomieed reoognieed B O U T C ~ S of &mor pheric contamination. The current cur&nt oncia one ia devoted, for the moet mod oart. f 2 years vesm of part, to B 6um-w summary o of of chemical ohemicol research into the littlr understood &d&tood e%m&&f a u m of e irritation, ccrop ikitation, m p damage, and reduced visibility and. inoidentag, to the techniques developed for microsampling. The rewrt samDline report is B valuable addition hv hy the district snd its &ili&d sffiliated researih research sgenaiee to previous work work.(l, (I, 3.5,8 ) on an Auman task.
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This is further confirmed by moithly analysis of duqtfall jars. A m a r c h project, sponsored by the district a t the Univemity of California at Los Anwlea. has exolored the rneehenism of the pes.
heavy contamination snd the weigh* of isopropyl and csrbon tetrachloride fractions. Infrend spectrographic anslysis of u!vcrel samples gnvo the first clue to the presence of oxygenated hydrooarbons and hydmaarhoits oontsiniirg carbon-nitrogen bonds. A rneehnnienl filteringsystem was developed for collecting large sanlples of aolids snd nonvolatile liquid particles from the air stream. Filtering NBS &wornplisbed hy mem8 of two lmm Whatman No. 4 filter papers (Figure 0 which were connectPd to a ~nmtive pressure pump operating at 120 cubic feet er minute (4). Ethcrextractionsofthr collected mntcriill BIP sirnikr to those o d Ieoted bv the electrical omdoitstor. The pmsenca of aldehydes, organic acids, or nip peroxides, snd acid anh drides are being canfirmed by &&tographic techniques. 6enensc'elouds of oil aerosols were formed in the laboratory by combining the vapors of unsaturated hydroesrbons with omone. The material collected on the filters, as well as that synthesized in the laboratory by the sction of ozone on u m t u rated h.ydrccerbon8, produoes dnmngp t.o leafy vegetables similar to t,hrtt encountwed in t,he field. of
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Figure 1. Holder for Filter Paper Disks M d C u . Meter-__ Dsy of
intense pollution
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on DSY
of I"fen%e
Poliuiion. 9
Clear (lay
Infrared Analysis of A l d r u l and Carbun Tetraohbride Extraction~. ~
Ab-
wave
mrp.
iewth,
tion.
3.52
"70 io
i.80
15
mDrOn8
Inter,,rera',on
bund. by. drmarhon c-0 C-c. *Ido. hydtl. ketanr
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8.4
7.36
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add CH. or CH' scraishf cham hydroearbon OiYnniC
Atniospheric contaminants present in the air as p e e s and vapors wem eollcctcd by n freoae-out method which consiste of series of traps (Figure 2) which nze immersed in pro colder freezing mixtures. The traps may be preoeded%%?. lowed by a mechnasnioal filter. The dry iceneetana traps are at -80' C. followed by the trap imorsed in liquid nitmgsn at -184" C. The atmaaphere containing the mntaminents ia d r a w through these traps and the ghws and vapors oandenae on the cold surfsoee. The trap are kept at these low tempemtures until ready for aaslysia. Lsrgeaiaed articles impinge on tho aurisoe of the t r a p and small particlea &Ilow the stresmline flow of the a*. and may escspe oolleetion. Collection efficiency o m be increased by psoking the inside of tho traps with BIB"Fin@, glasa wool, or stainless steol washers or by reducing the rate of eampling. Sample8 collected by the freeeedut teohni "ea on d s B of in teme air pollution during the 1949-185Operio%gave the Esulte:
wing
.
A. Infrmd absorption Thiophene 2. Carbowohloride bond 3. Oxygenated hydrocarbons ( i n f m d absorption = 5.85 rmGrnna) (c~nrinuedon iie A ) 1.
Cllr. stvaiy1,t. chain hudruoar. bon
115 A
Atmospheric Pollution B. Mass spectrometer The results indicate the presence of paraffins and C,H2, materials which could be eithei cyclics or olefins. Mass peaks of 31 and 45 indicate the presence of oxygenated brganic compounds.
C. Chemical analysis
1. Acidity, pH 2. Aldehydes Total, mg. Formaldehyde, mg. Acrolein Formaldehyde, %
Dry Ice
Liquid Nitrogen
Total
3.8
2.9
...
0.38
0.515 0 356
0 09 0 00 23 7
0 00 69 2
0.895
0 446 0.00 49 8
The work done for the district a t U.C.L.A. showed that in the presence of sunlight a small ercentage of sulfur dioxide is converted to sulfuric acid. It ago indicated that some compounds similar to aldehydes would be oxidized in the same manner.
+ sunlight +an activated SO,; SOz(activated) + Op+SO, + 0 Aldehydes + sunlight +an activated aldehyde; RCNO(activated) + 02 ---+ acid + 0
SO2
Data collected on the day of low visibilities shows the strongest infrared absorption band a t 5.9 microns, a wave length indicative of oxygenated organic material. Analyses of the drops found in various air samples taken by both the cascade microimpactor and the electrical precipitator indicate the presence of oxygenated organic compounds.
Figure 2.
Freeze-out E q u i p m e n t for Atmospheric Samp1es
The measurements of the oxidizing effect of Los Angeles air has shown that hi h concentrations of an unknown oxidizing agent are present. %his again is an indication that an oxygenated material may exist in the atmosphere. No source of this material has been found, thus leading to the belief that the oxidation takes place in the atmosphere. Research work is continuing on this phase of the problem. An appraisal of the work done to measure ozone indicates that no more than normal concentrations of this gas are resent Presumably, any ozone formed in a secondary reaction d e n SUI: fur dioxide is oxidized to sulfur trioxide reacts with the pollution. The high oxidizing effect of the air may be accounted for by photochemical reactions. Since the type organic material found in air samples msy play a part in reducing visibility, damaging crops, and producing eye irritation, research is being accelerated. As the oxides of nitrogen may give a similar reaction, they are included in the study.
Literature &ted Johnstone, H. F., I n d . Hug. Toxitol., 30, So. 6, 358 (1948). Larson, Gordon P., 3rd Ann. Report, Los Angeles County Air Pollution Control District, 5201 Santa Fe Ave., Los Angeles, Calif. (1950). McCabe, L. C., et. al., IND.ENG.CHEM., 41, 2388 (1949). Mader, P. P., Anal. Chem., 22, 1181 (1950). Magill, P. L., IND. ENG.CNEM., 41, 2476 (1949). Stanford Research Inst.. 1st (1948) and 2nd (1949) Interim Reports.
116 A
