Trace Element Composition in Atmospheric Particulates During 1973 and the Summer of 1974 at Chadron, Neb. .
hrthur V, Struempler Chadron -StateCollege, Chadron, Neb. 69337
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Air was collected continuously on filters in northwestern Nebraska during 1973 and the summer of 1974 and the particulate matter was analyzed for Ag, Al, Cd, co, Cu, Mn, Pb, T1, and Zn. Noticeable and consistent seasonal differye evident, in gerosol A1, Mn, and Pb. Those metals wrosol particulates are lslrgely soil derived if tJeir are likewise high in the soil. Conversely, aerosol metals are more likely to be associated with anthropogenic sources if their concentrations are low in the soil. Aerosol P b appears to be largely derived from the combustion of leaded gasoline, but the aerosol sources of Ag and Cd are more difficult to document. The data will serve to &for any changes in air quality as additional coal-fired p’oweipfants are-constructed at upwind locations.
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Plains states, the land is relatively flat and is used principally for grazing. Prevailing winds are from the south, west, and north, and it is estimated that surface winds blowing from the northwest and north and over the residential area of Chadron to the sampling site occurred less than 10% of the time. Therefore, most collections represent surface winds from virtually uninhabited areas. .The metals were analyzed with a Model 303 Perkin-
Table I. Metal Concentrations (Ng/M3)of Atmospheric Particulates During 1973 at Chadron, Neb. Week
beginning
Jan.
By necessity, more coal must be used in the future to meet our energy needs. Utilization of coal from Wyoming, Colorado, and Montana will certainly increase because it is economically mineable and relatively low in sulfur. Also, because of economics, more coal-fired plants will be constructed near these coal reserves and may alter the aerosol concentrations of some pollutants. Nebraska is located b tHe east and downwind from these coal reserves. Since aerosol particulates are readily transported by the wind, Chadron’s location in northwest Nebraska is ideal for establishing the concentrations of various atmospheric metals before additional coal-fired power plants are constructed in neighboring western states. To obtain this information, air was collected continuously during 1973 and the summer of 1974, and its particulate matter analyzed for aerosol Ag, Al, Cd, Co, Cu, Mn, Pb, T1, and Zn. Metal concentrations and their variability were evaluated for seasonal trends and sources. The data are of further use in monitoring air quality and assessing any change in metal concentrations.
Experimental Air was aspirated continuously through filters at the rate of 14 l./min during all of 1973 and from June through September in 1974. Filters were changed each Monday, and the various aerosol metals were analyzed after each season’s collections. The air-sampling gear was housed in a greenhouse, and consisted of a vacuum pump which collected outside air through a 37-mm diameter Millipore filter (type AA, 0.8-wm mean pore size) made of mixed esters of cellulose. The filter was located 11/4m above the earth’s surface and was protected from precipitation by a polypropylene lined box. Air collections were made on the southeast corner of the college campus, which is located a t the extreme southeast corner of Chadron, Neb., a town with a population of 6000, located in the sparsely populated Northern Plains (42O 50’N, 103’ 05’W, 1000 m above sea level). No roads were located within 1 mi of the sampling site within a compass reading of 45 through 270 degrees. A few roads exist in the region beyond 1 mi of the sampling site, within the arc of 45 through 270 degrees, but the region is virtually uninhabited for hundreds of miles. As with most Northern 1164
Environmental Science & Technology
Ag
AI
1 0.06 40 8 0.02 50 15 0.02 690 22 0.02 90 29 0.03 250 Feb. 5 0.03 200 12 0.03 260 19 0.02 310 26 0.03 740 Mar. 5 0.03 830 12 0.03 630 19 0.03 700 26 0.03 660 Apr. 2 0.03 310 9 0.04 1070 16 0.25 350 23 0.08 470 30 0.15 560 Mav 7 0.18 980 14 0.36 2230 21 0.47 640 28 1.80 400 June 4 0.12 280 11 0.11 760 18 0.16 610 25 0.46 230 July 2 0.07 870 9 0.03 810 16 0.04 790 23 0.40 1000 30 0.03 610 Aug. 6 0.29 1020 13 0.09 1000 20 0.04 740 27 0.04 540 Sept. 3 0.09 300 10 0.12 310 17 0.15 430 24 0.07 380 Oct. 1 0.23 930 8 0.21 390 15 0.22 940 22 0.05 610 29 0.17 170 Nov. 5 0.12 140 12 0.04 430 19 0.05 250 26 0.12 300’ Dec. 3 0.05 180 10 0.19 230 70 17 0.23 24 0.10 60 X 0.15 535 U 0.26 382
Cd
Co
Cu
Mn
Pb
0.65 4.3 5.0 3.2 20 0.46 2.6 4.6 2.5 14 0.44 4.7 5.0 8.8 69 0.31 4.0 4.5 4.2 56 0.48 2.8 5.5 3.7 59 0.32 4.1 4.7 3.2 67 0.33 3.7 4.6 3.9 51 0.34 3.4 4.8 4.5 42 0.32 4.3 4.3 7.9 35 0.56 4.7 3.9 9.6 34 0.58 5.0 4.1 7.1 60 0.27 4.6 4.5 6.7 38 0.31 3.9 4.3 7.7 42 0.66 2.5 3.6 4.6 34 0.89 4.1 3.9 10.3 56 0.66 3.7 4.6 3.5 20 0.44 2.9 4.4 5.7 38 0.54 3.2 5.1 5.7 77 0.91 3.6 5.4 8.2 39 0.68 4.1 6.6 15I6 36 0.59 2.8 5.7 5.4 18 0.87 2.7 5.5 5.8 20 0.93 3.0 3.6 3.5 9 0.83 3.9 5.7 6.3 19 0.55 2.8 6.0 4.1 22 0.83 1.6 5.6 3.1 24 0.84 2.6 5.0 7.1 20 0.99 1.6 5.3 6.3 26 0.52 2.8 5.8 5.0 28 1.32 4.7 6.7 7.0 38 0.74 3.4 5.5 4.3 26 0.46 5.1 5.7 7.6 35 0.48 3.1 5.9 11.7 24 0.54 3.1 5.9 12.7 36 0.37 4.1 5.5 6.2 35 0.61 3.0 5.7 6.3 50 0.27 3.0 5.3 5.7 40 0.48 2.9 4.8 6.5 44 0.32 3.5 4.8 3.1 73 0.67 1.6 7.3 8.2 89 0.67 3.7 5.5 3.7 87 1.07 3.1 6.7 7.3 68 0.53 2.6 6.3 5.8 69 0.36 1.9 5.0 2.4 57 0.31 3.1 5.5 2.1 73 0.26 2.8 5.1 3.5 39 0.29 2.2 5.1 4.1 62 0.42 2.1 5.1 3.3 52 0.46 2.8 6.7 2.5 46 0.34 3.2 6.8 3.7 69 0.77 2.7 6.7 1.7 85 0.72 3.0 6.6 3.0 70 0.57 3.3 5.3 5.7 45 0.24 0.9 0.9 2.8 21 ~
TI
Zn
16 11 21 19 16 14 11 8 12 18 25 21 16 23 19 26 18 27 0.22 21 0127 22 0.25 26 0.48 12 0.20 6 0.26 16 0.20 21 0.15 14 0.16 15 0.14 12 0.32 13 0.42 16 0.25 9 0.28 12 0.20 9 0.21 26 0.19 14 0.19 15 0.16 40 0.22 21 0.19 11 0.07 21 0.23 25 0.26 21 0.15 25 0.13 9 0.14 18 0.11 3 0.12 4 0.18 4 0.12 21 0.14 13 0.12 4 0.13 10 0.22 16 0.08 7 0.42 0.30 0.32 0.25 0.14 0.21 0.22 0.20 0.31 0.23 0.26 0.35 0.22 0.15 0.30 0.22 0.18 0.18
Elmer atomic absorption spectrometer, equipped with a HGA-2000 heated graphite atomizer and a deuterium background corrector. The statistics were calculated with a Hewlett-Packard 9810A programming calculator. Container cleaning methods and laboratory procedures have been described previously by Struempler (I).Only new 1-02 Nalgene linear polyethylene containers were used for storage or analysis. Any containers with blank solutions with a detectable background of Zn (the most contaminatable metal under study) after the acid soaking and cleaning process were discarded. Extreme care was exercised to minimize metal loss or contamination effects. Only ultrapure acids were used in all instances except in the container washing process. Aerosol particulates were removed from the filter by ultrasonic treatment for 1 hr in 10 ml of ion-free water acidified to 0.2% with HN03. Completeness of metal dissolution from the filters was compared by quartering test filters and: Dry ashing in Pt crucibles a t 3OOOC for 30 min followed by continued ashing a t 500°C for 1 hr and reconstituting the metals in an aqueous solvent containing 1%H N 0 3 Dry ashing similar to above, but metals were reconstituted in minimum H F and H N 0 3 (1 3), followed by evaporation to dryness and appropriately diluting Wet ashing in minimum H N 0 3 with warming until the filter dissolved. Metals were then reconstituted in an aqueous solution In all cases, blanks were carried through. Both dry and
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Table I I. Metal Concentrations (Ng/M3) of Atmospheric Particulates During the 1974 Summer Season at Chadron, Neb. Week beginning
wet ashing procedures proved erratic for some metals and could not be used as the principal technique for metal analysis. Neither could strong acid concentrations be used for dissolution purposes, as this enhanced interference effects. Hence, the ultrasonic treatment method was used for dissolution of metals from the filters. The deuterium background corrector was used for all analyses.
Results and Discussion Table I shows the concentration of nine metals in aerosol particulate matter during 1973. The means and standard deviations are also shown at the bottom of the table. As elsewhere in this report, the concentrations of the tested eIements are reported in ng metal/m3, and m e w s are rapre* , , sented as the arithmetic mean. Seasonal differences are evident in the data. Silver was found in highest concentrations during the AprilJuly period. Aluminum was noticeably low during December and January. Aerosol P b increased during the autumn season. The test for standard deviation is based on a normal diet+ " '. bution. Silver exhibited a larger standard deviation thw the mean; hence, this test was invalid for Ag. T&elarge Agv *r concentrations during the summer season account for &is ,* ' deviation. However, if the large Ag value'of May 28 de-.' leted, the mean then becomes 0.12 with a sigma sf 0.12, The large aerosol Ag concentrations during the summer months were of particular interest, as no cloud seeding operations with AgI were believed to have occurred within several hundred miles of Chadron during the May-June 1 period. * Mainly to determine if the large aerosol Ag concentra_. tion was seasonal, air was again sampled and analyzed for ' all nine elements during the June-September tiqe pejiqg, . k ' of 1974. Climatic conditions were different during the 1974 season as western Nebraska experienced a drought during the summer of 1974 when only 11.5 cm of rain fell in Chadron during the 17-week 1974 summer seasqn as compared to 21.8 cm during this same time period in 1973 (2, 3). The results of the 1974 collection are shown in Table I1 and E) comparison of the means and standard deviations between ,t. ' the two seasons are shown in Table 111. Three and one-half times less Ag was detected during the 17-week 1974 sum4 mer season as compared to the 1973 summer season. Approximately a 50% decrease in Cd, Co, T1, apd Zn was like: ' wise noted. Little difference in the aerosol concentrations of the other metals was observed between the two summer seasons. An interesting aspect of the data is the consistent and greater abundance of A1 and Mn during both of the 17, week 1973 and 1974 summer seasons as compared to their abundance during the entire 52-week period. Trace ele* I. ments arising from airborne dust would be in greater can;, , centrations during the drier summer months, and their associated convective storms, than during a snow-covered
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1
Ag
June
3 0.04 16 0.03 17 0.04 24 0.04 July 1 0.04 8 0.04 15 0.05 22 0.04 29 0.03 Aug. 5 0.04 12 0.04 19 0.03 26 0.03 Sept. 2 0.05 9 0.03 16 0.02 23 0.03 X 0.04 U 0.01
AI
Cd
Co
Cu
Mn
380 270 670 980 820 810 680 810 670 520 750 740 590 710 460 710 720 664 175
0.26 0.36 0.32 0.54 0.39 0.20 0.21 0.26 0.18 0.21 0.28 0.31 0.17 0.39 0.22 0.27 0.51 0.30 0.11
3.5 2.6 3.4 2.8 2.0 2.3 1.9 1.8 1.6 2.1 1.8 2.6 1.0 3.0 1.2 2.8 1.8 2.2 0.7
5.8 5.1 6.9 6.2 5.7 6.0 6.0 6.0 5.3 5.8 6.5 5.9 5.6 7.9 5.6 6.7 7.2 6.1 0.7
3.3 2.7 7.6 1.0.6 9.3 10.9 7.0 10.4 7.6 5.0 5.8 6.2 6.9 7.7 5.6 7.0 8.2 7.2 2.3
Pb
TI
34 0.16 19 0.09 19 0.13 19 0.19 22 0.14 17 0.19 19 0.14 23 0.16 25 0.14 16 0.17 20 0.10 2 1 0.13 2 1 0.11 35 0.23 48 0.10 43 0.18 4 1 0.11 26 0.15 10 0.04
Zn
3
1
7 17 3 9 6 3 3 4 11 6 1 3 3 9 11 6 4
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Table Ill. Means and Standard Deviations of Aerosol Metals in Atmospheric Particulates for 1973 and 1974
1973 (52 weeks)
X X U
1974 (June-SeDtember)
AI
Cd
co
cu
Mn
Pb
0.15 0.26
53 5 382
0.57 0.24
3.3 0.9
5.3 0.9
5.7 2.8
45 21
0.22 . 0.08
0.14 0.13
6 28 271
0.65 0.28
3.2 0.9
5.5 0.7
6.3 2.6
32 15
0.22 0.07
16 8
0.04 0.01
664 175
0.30 0.1 1
2.2 0.7
6.1 0.7
7.2 2.3
26 10
0.15 0.04
4
TI
ZCl
,
-
U
1973 (June-September)
Ag
'
16 7
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X U
Volume 9, Number 13, December 1975
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1165 '.C
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Table I V . Aerosol Metal Concentrations at Various Locations (Ng/M3) Location and year(s) sampled
Ag
AI
Many U.S. u r b a n stations
(1964-65)(4) N.W. Indiana, 25 stations
