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Regional and local determinations of particulate matter and visibility in the southwestern United States during June and July, 1979
ooo4-6981/81/102011~‘~02.00/0 C 1981 Pcrgamon Pnss
Ltd.
REGIONAL AND LOCAL DETERMINATIONS OF PARTICULATE MATTER AND VISIBILITY IN THE SOUTHWESTERN UNITED STATES DURING JUNE AND JULY, 1979* T. A. CAHILL, B. H. KUSKO, L. L. ASHBAUGH,J. B. BARONE,R. A. ELDRED Air Quality Group, Cracker Nuclear Laboratory and Department of Physics, University of California, Davis, CA 95616, U.S.A. and F. G. WALTHER Visibility Research Center of the John Muir Institute, Department of Physics, University of Nevada, Las Vegas, Nevada 89154, U.S.A. (First receioed 15 Sepreniber 1980 and in~~u~~orrn 29 January 1981) Abstract-Data on ambient particulate concentrations by size and elemental composition taken in Arizona and Utah are compared to simultaneous telephotometer measurements of standard visual range. Particulate samples were collected during the VIS’ITA program from 26 June to 11 July 1979,at Zilnez Mesa, Arizona, and compared to similar 24 h m~sure~n~ made as part of a long term research program at Zion and Canyonlands National Parks in Utah. Samples were collected with rotating drum Multiday impactors which provide three aerodynamic size ranges; 15pm-3.5pm; 3.5 pm-0.5pm, and less than 0.5pm. Elemental composition of samples was measured using the particle induced X-ray emission (PIXE) system at the Cracker Nuclear Laboratory. Measurements of visibility were made at Canyonlands National Park and Zilnez Mesa using both multiwavelength telephotometers and nephelometers. Results indicate that the particulate matter in each size range behaves to a large degree independently of the other size ranges, but that correlations are often observed between sites. On 29 June, an episode of elevated sulfur concentrations, z 1 pg m _ 3 of S, was observed at ail three sites. Decreased visibiiities were recorded for the episode period at both Canyonlands and Ziinez Mesa. Sulfur episodes on 22-24 June and 20-21 July measured at Zion and Canyonlands also correlated well with reduced visibility at Canyonlands. Episodes of reduced visibilities also occurred during periods of stable sulfur v&es. The strongest of these, on 17-18 June, as well as a weaker one, 4-7 June, correlated well with fine soils in the 0.5-3.5 pm size range. The conclusion is that reduced visibility is associated with regional episodes of both increased sulfur and increased fine soils, with best correlations occurring in both cases for sizes somewhat greater than 0.5pm dia.
INTRODUCTION
Establishment of causal factors associated with periods of reduced visibility in the arid regions of the western U.S.A. requires extensive information on the sources and nature of fine particulate matter. However, the enormous area under consideration, roughly 3 x 106 km2, the strong seasonal, synoptic, and diurnal meteorological variations, and the contributions of both natural and anthropogenic particulate sources to the low ambient mass concentrations make generation of such info~ation dificult. The existence of a short term, intensivestudy such as VISTTA (Visibility Impact by Sulfur Transformations and Transport in the Atmosphere) in a region possessing numerous long term fine particle and visibility monitoring stations associated with the Western Fine Particle Network (WFPN) and JM/EPA Visibility program presents a rare opportunity to * Paper presented at the Symposium on Plumes and Visibility: Measurements and Model Components. Grand Canyon, Arizona, U.S.A. 10-14 November 1980.
develop such information. The detailed information generated at the Zilnez Mesa site by VISTTA participants provides the in-depth analyses logistically impossible for continuously operating research studies covering large areas, while the results of the WFPN stations can put the local data into statistical and regional perspective by establishing how typical is the period and site used for the intensive program. In order to strengthen these connections, fine particle monitoring units similar to the WFPN stations at Zion, Bryce (Henrieville), Canyonlands, and Yellowstone National Parks were operated at Zilnez Mesa in the VISTTA program (Fig. 1,).
E~FERIMENTAL TECHNIQUES Particulate monitoring was performed at ground level (1.5 m) on Ziinez Mesa in the period from 26 June to 11 July 1979, using muitiday sizing impactorsand stacked filter units. The former are rotating drum impactors of the Lundgren design extensively used in stud& of fine particles and visibility (Flocchini Edal., 1976; Barone et al., 1978)due to the ability to operate automatically for 7 days at a time while
2011
2012
T. A. CAHILL et al.
Fig. 1. Map of sampling sites used in this progmm. The Henrieville site is close to Bryce Canyon National Park.
delivering size cuts close to both the minimum of the bimodal distribution at 3.5 pm dia., and the wavelength of light at 0.5 ,um. These units have been operated at Zion, Bryce, and Canyonlands National Parks (Utah), and Yellowstone National Park (Wyoming) since 1978 on a daily basis (Flocchini eb al., 198Ob;Pitchford et al., 1980). The stacked filter units (SFUs) were of the early manual design (Spumy et al., 1969; Cahitl et J., 1977) but operationally equivalent to the forty used in the WFPN effort (Flccchini et nl., 198Oc). The unit delivers a dichotomous cut at 2.5 m dia. through the capture characteristics of an Apiezon L grease coated (Cahill et ai., 1979; John et al., 1980) 8pm Nuciepore tracketched filters operated at lScms_’ face velocity. Both units participated successfully in the EPA-DOE sponsored Charleston intercomparison of particulate monitoring instruments (Camp ef uf., I980), although since coated filters were not used in the SFUs in that test, a few per cent ofcoarse soif like particulate mass penetrated to the tine filter. Both laboratory and field tests confirm that the coatings used in the VISTTA and WFPN samplers sharply reduce this effect, to the point that it is negligible in field conditions (Cahill et al., 1979; Lyons et al., 1979) while the effective 50% cut point, even in extreme laboratory conditions with dry potassium biphthalate particles becomes about 2.7~ {John et al., 1980). Samples were analyzed by particle induced X-ray emission (PIXE) (Cahill er oL, 1976), accurate to & 5 %, and by weighing (Engelbr~ht el al., 1980). The a~eement between the multidays and SFUs on a daily basis was good (the ratio SFU/MD for sulfur was 0.97 +O.il), as was agreement with SFUs run for 48 h (SFIJ/MD, sulfur, 1.04 + 0.06) and 72 h integration periods (SFU/MD, sulfur, 0.97 + 0.14). Comparisons of typically coarse mode particles were made more difficult due to intake and cut-point factors (ratio SFU/MD for Si was 0.93 kO.16; while for Fe it was 0.80 kO.18). Agreement between the various sampling instruments and analytic& methods for fine particulate species such as sulfur ranged from good to excellent, with typical differences between groups less than 10 y/, (McMurry et al., 1980). Measurements of standard visual range were made using four wavelength telephotometers in three observations per
day. Mean daily visual ranges were then calculated for comparison with particulate values.
FINE PARTICLE VALUES
Particulate concentrations at Zion, Btyce, and Canyonlands National Parks are dominated by short term (average, ~4 days) episodes in which levels rise by a factor of three to twelve times median values (Flocchini, 1980b). For example, sulfur levels reached 1 $gm-3 behavior
six times during 19’78 at Zion, and similar was exhibited at all sites in 1979 (Figs 2 and
3). The values for silicon, a soil tracer generally associated with aluminum, potassium, calcium, titanium, manganese, and iron, tend to show a seasonal trend as well as episodes of high dust levels. Very fine particles, < 0.5 pm, do not correlate well with coarse soil mass, but appear to be soil derived (Pitchford et al., 1980). Soil values usually anticorrelate with sulfur values, both day to day and by season, as suIfur values show a weak seasonal minima in the spring at times of high soil loadings and elevated wind velocities. Sulfur particies in the three size modes have largely independent behavior in time, showing a larger size variation from day to day than any other major element. The thrusts of these studies are to understand the sources of the elevated episodes, and to investigate the degree of association of such periods with degraded visibility. One sulfur episode occurred during VJSTTA, on 29 June. The regional character of this episode is shown in Fig. 4, which compares sulfur values measured at Zion, Canyonlands, and Zilnez Mesa during the
2013
Particulate matter and visibility 24 hour meon
Conyonlonds
P 600
Stoge
2
P -
600
0 Stoge
6
Feb
Mor
Apr
May February
Jun 1979
Jul
I
Aw
to December
Sep
act
NW
OW
1979
Fig. 2. Silicon particulate matter at Canyonlands National Park, Island in the Sky, for 1979. Stage 1, 3.5-15pm; Stage 2, 0.5-3.5pm; Stage 3, < 0.5 pm dia. particles.
VISITA period. Sulfur values on 28 June and in the period 6 July through 10 July were typical of the cleaner or baseline values below which summer values rarely go. The period of the 29 June-30 June episode also corresponded to the peak values of other fine pollutants; zinc (11 ng m- ‘); lead (47 ng m- 3); and bromine (22ngme3). Significantly, fine copper did not peak in this episode. Since elevated sulfur values associated with smelter operations have elevated fine copper values, and since the Zn, Pb and Br values have ratios similar to urban conditions, one can infer an urban source. Trajectory analyses confirm this hypothesis and indicate a southern California source. The Br/Pb ratio, 0.47 + 0.10, is close to current automotive values. This is worthy of comment, since Br/Pb ratios in the southern California area are severely depressed in summer in the fine size ranges, typically 0.17 (Flocchini et al., 1976; Eldred et al., 1978). This could indicate that the lead seen at VISTTA is due to a local automotive source, or it could support the hypothesis that Br loss in southern California samples is due to aerosol acidity on the collection surface. Thus, PbBrCl transported as an aerosol from Los Angeles and not collected until the
aerosol is dilute and, possibly, neutralized would retain its automotive source signature (Feeney et al., 1975). The Pb/S ratio for particles at 28 southern California sites on 26 June 1979, was 0.30 (Calif. Air Quality Data, 1979), while typical values previously published are similar, 0.38 f0.13, (Flocchini et al., 1976). The difference can be partially explained by the much greater use of unleaded gasoline in California since 1973, the date of the earlier work. The Zn/S ratio from that study was 0.034 f 0.017. Thus, the PbjS and Zn/S ratios seen at Zilnez Mesa, 0.043 and 0.010 respectively, are depressed by factors of 7 and 3.4 from those of the presumed source, even if one subtracts from the S value the median S value seen at the site as a “background” correction. Since the particle sizes are roughly equivalent, removal processes should be similar. Thus, one can invoke either additional sources of particulate and gaseous sulfur between southern California and Zilnez Mesa, or invoke gas to particle conversion as a means to replenish the sulfur concentration. Early results from the WFPN indicate that urban transport is not the source of all (or even most) of the sulfur episodes at the Utah parks, as elevated sulfur levels with associated copper particles
2014
T. A. CAHILL
Feb
Mar
Apr
May
Februwy
et a/.
Jm
..tui
I979
to lhramber
rwv
oec
1979
Fig,3. Sulfur particulate matter at Canyoonfands, National Park, Istand in
the Sky, for 1979. Stage 1, 3.5-f5@~ Stage 2, D.S-3.5~~ < 0.5 pm dia. particles.
oftenexist during summer months its the ArizonaNew Mexico region, presumably due to smelter operations (Flocchini et al., 198Oa), and the pattern often extends into Utah. Other particles of interest include a strong enhance,
I
I
/
,
Stage 3,
ment of fine potassium during the fire period, 160ng M - 3excessover soils, giving a predicted carbon mass of about 2.7 pg m- j if one uses the potassium ta fine carbon ratio seen in studies of Oregon field burning (Lyons et a/., 1979).
I
1
I’,
,
/
,
,
Sulfur particles CJ Conywttands N P , multiday Zion N P. I muitiday D Zrhez Mew, multidoy
a l
27
28 June
29
30
I
2
3
4
2llne.z Meso, stocked fitter
5
6
7
9
IO
II
I2
J'J&, 1979
Fig. 4. Sulfur values measured at Zion, Canyonlands, and Zilnez Mesa sites during the VISTfA period.
2015
Particulate matter and visibility CORRELATIONS
WITH VISIBILITY
Extracting local from regional influences in visibility studies can be di5cult without accurate spatial profiles of pollutant values. Comparisons between telephotometer measurements taken at Canyonlands as part of the EPA/JM visibility investigation and visibility readings at Zilnez Mesa, confirm that the reduction in visual range seen at Zilnez Mesa in the 29-30 June period was regional, while the strong local influence of the fires did not strongly extend into the site paths of the Canyonlands telephotometer, despite the use of Navajo Mountain as one of the targets (Fig. 5). Figure 5 shows the excellent correlation between elements in the soil derived particles typical of coarse (Multiday Stage 1, 3.5-15pm) and intermediate (Multiday Stage 2,0.5-3.5 m) particles. The elements normally included are Al, Si, K, Ca, Ti, Mn, Fe and, when sensitivities allow, Sr and Zr. The finest particles (Multiday Stage 3, < 0.5pm) show systematically weaker correlations. Also in Fig. 5, the eight periods in June and July 1979. in which standard visual range at Canyonlands Ccmymlandr
Multidoystage2
decreased below 100 miles (160 km) are listed in order (a-h). Baseline values are approximately 260 km during this period. The period of regional sulfur impact from southern California on 29-30 June (episode a) corresponded with the poorest visibilities seen ( z 90 km) and the highest values for intermediate sulfur particles (Multiday Stage 2, 0.5 to 3.5pm) of 550ngme3, and total sulfur, 15OOr1gm-~. This latter value is presumably equivalent to about 5.4 pg m - 3 of ammonium sulfate. Episodes b, e and h also correlate with enhanced sulfur values, especially with enhancement in the intermediate size range. Episode c may represent some smoke incursion from forest fires. Episode d correlates well with enhanced soil mass which, in the < 3.5 pm size mode, sums to about 4.5 pg m- 3 of total mass, including typical oxides. This episode corresponded to the passage of a frontal system, with increased winds from the northwest. Episode g likewise correlates well with soils but not with sulfur, while Episode f has support from both soil and sulfur mass. Of particular interest is the lack of correlation between sulfur and visibility on l-3 June. This episode was characterized by very fine sulfur size profiles, finer by a factor of 5 24 hour mean 0.5 to 3.5 microns
0.1 to 0.5 microns
I
I June I979
Fig. 5. Comparison of particulate matter and standard visual range at Canyonlands for June-July 1979. The spisode of 29,30 June was regional in nature, while the smoke impacts of early July at Zilnez Mesa were not.
T. A. CAHILL et al.
2016
than those seen 30 June according to the Stage 2-Stage 3 ratios. Without more detailed size information, the actual mass median diameter of the l-3 June sulfur cannot be determined, but it may be well below the wavelength of light. The sulfur size dist~bution strongly influences visibility in California (Barone er at., 1978; Cahill er af., 1980). Other matches to periods of reduced visibility can be qualitatively associated with particulate matter. leading to the appreciation that, at Canyonlands and Zilnez Mesa, at least three particulate sources influence visibility; fine soils, forest fires, and some, but not all, sulfur-rich transported plumes from anthro~genic sources, urban, smelter and, ~tent~lIy, power plants. Statistical methods can allow a more quantitative estimate of the strengths of the factors associated with reduced visibility. The method of multiple linear regressions was applied to the Canyonlands data set, with the inclusion of some climatic data from Grand Junction, Colorado, on relative humidity. One problem encountered involved the rather weak correlation between the Canyonlands nephelometer and telephotometer. Although they usually tracked quite well, there were limited periods during which they disagreed badly, and these reduced the associations. The particulate data plus relative humidity explain much less of the variance in visual range at Canyonlands than they do at polluted urban sites in California (Barone er at., 1978), although they do isolate sulfur and soils as two primary factors, and illustrate an influence of the sulfur size distribution on extinction. These calculations are conlinuing with the addition of more representative meteorological data from sites with less important terrain effects than the Grand Junction meteorological site. CONCLUSlONS
The data generated at the Utah National Park since 1978 show that particulate matter and visibility both show episodic behavior on synoptic meteorological time scales of a few days duration. The VISTTA program sampled two episodes of elevated particulate matter and reduced visibility, associated with a southern California urban plume and relatively local forest fire activity, along clean periods of high visual range. Two other types of episodes were not sampled-high fine particulate dust loadings and southern Arizona smelter effluents. Analysis of visual range over June and July 1979, showed that all periods of reduced visibility correlated with increased levels of fine particulate matter. Acknowledgements-The authors wish to thank other members of the Air Quality Group at Davis, the John Muir Institute-EPA visibility program, and EMSL-EPA laboratory at Las Vegas. We especially thank the personnel of the National Park Service.who made the geld program a success. REFERENCES
Barone J. B., Cahill T. A., Eldred R. A., Flocchini R. G., Shadoan D. J., Dietz T. M., (1978) A multivariate statistical analysis of visibility degradation at four California cities. Atmospheric Environment 12, 2213-2221.
Cahill T. A., Flocchini R. G., Eldred R. A., Feeney P. J., Lange S., Shadoan D. J. and Wolfe G., (1976) Monitoring of smog aerosols with elemental analysis by accelerator beams. In Accuracy in Trace Analysis; Sampling, Sample Handling, Analysis, National Bureau of Standards, 442, 1119-l 136.
Cahill T. A., Ashhaugh L. L., Barone J. B., Eidred R. A., Feeney P. J., Flocchini R. G., Goodart C., Shadoan D. J. and Wolfe G. W. (1977) Analysis of respirable fractions in atmospheric particulates via sequential filtration, J. Air Pollut. Control Ass. 27, 675677.
Cahill T. A., Eldred R. A., Barone J. B. and Ashbaugh L. L. (1979) Ambient aerosol sampling with stacked filter units, Fed. Hiehwav Adm. Renort FHWARD-78-178 l-73. Cahill T. i., B&one J. B:, Eldred R. A., Flocchini R. G., Shadoan D. J. and Dietz R. M. (1980) Influence of sulfur size distribution on optical extinction, Envir. nnd Cfimatic Impact ofCoal Uri~~~uf~on (Edited by J, Singh, A. Deepak), Academic Press, New York, pp. 215-224. California Air Quality Data, April, May, June, 1979, Vol. XI, No. 2. Camp D., Van Lenh A. L. and Loo B. W. (1978) Intercomparison of samplers used in the determination of aerosolcomposition, EPA Report No. 600/7-78-l 18. Eldred R. A.. Cahill T. A. and Flocchini R. G. (1978) Bromine loss from automotive particulates at California sites, Proc. 71st Annual meeting, APCA 7869.6. Engelbrecht D. R., Cahill T. A., Feeney P. J., (1980) Electrostatic effects on gravimetric analysis of membrane filters, J. Air Poflut. Controf Ass. 30, 391-394.
Feeney P. J., Cahill T. A., Flocchini R. G., Eldred R. A., Shadoan D. J., and Dunn T. (1975) Effect of roadbed configuration on traffic derived aerosols, J. Air Poflut. Control Ass. 25, 1145-l 147. Flocchini R. G., Cahill T. A., Shadoan D. J., Lange S., Eldred R. A., Feeney P. J. and Shadoan, D. J. (1980 a) Regional scale synoptic air monitoring for visibility evaluation based on PIXE analysis, in press Nucl. Instrum. Meth. 181, 403-410. FIocchini R. G., Cahill T. A., Ashbaugh L. L.. Eldred R. A. and Pitchford M., (1980 b) Seasonal behavior of particulate matter at three rural Utah sites Atmospheric Environment 15, 315-320. Flocchini R. G., Cahill T. A., Pitchford M. L., Eldred R. A., Feeney P. J. and Ashbaugh L. L. (1980 c) Characterization of particles in the arid west. Atmospheric Environment (in press). John W., Reischi G., Goren S. and Plotkin D., (1977) Anomalous filtration of solid particles by Nuclenore filters. Atmospheric Environment 12; 1555-lSj7.
_
John W.. Herina S.. Reischl G. and Wesolowski J. J.. (1980) Investigation
Ltd.
REGIONAL AND LOCAL DETERMINATIONS OF PARTICULATE MATTER AND VISIBILITY IN THE SOUTHWESTERN UNITED STATES DURING JUNE AND JULY, 1979* T. A. CAHILL, B. H. KUSKO, L. L. ASHBAUGH,J. B. BARONE,R. A. ELDRED Air Quality Group, Cracker Nuclear Laboratory and Department of Physics, University of California, Davis, CA 95616, U.S.A. and F. G. WALTHER Visibility Research Center of the John Muir Institute, Department of Physics, University of Nevada, Las Vegas, Nevada 89154, U.S.A. (First receioed 15 Sepreniber 1980 and in~~u~~orrn 29 January 1981) Abstract-Data on ambient particulate concentrations by size and elemental composition taken in Arizona and Utah are compared to simultaneous telephotometer measurements of standard visual range. Particulate samples were collected during the VIS’ITA program from 26 June to 11 July 1979,at Zilnez Mesa, Arizona, and compared to similar 24 h m~sure~n~ made as part of a long term research program at Zion and Canyonlands National Parks in Utah. Samples were collected with rotating drum Multiday impactors which provide three aerodynamic size ranges; 15pm-3.5pm; 3.5 pm-0.5pm, and less than 0.5pm. Elemental composition of samples was measured using the particle induced X-ray emission (PIXE) system at the Cracker Nuclear Laboratory. Measurements of visibility were made at Canyonlands National Park and Zilnez Mesa using both multiwavelength telephotometers and nephelometers. Results indicate that the particulate matter in each size range behaves to a large degree independently of the other size ranges, but that correlations are often observed between sites. On 29 June, an episode of elevated sulfur concentrations, z 1 pg m _ 3 of S, was observed at ail three sites. Decreased visibiiities were recorded for the episode period at both Canyonlands and Ziinez Mesa. Sulfur episodes on 22-24 June and 20-21 July measured at Zion and Canyonlands also correlated well with reduced visibility at Canyonlands. Episodes of reduced visibilities also occurred during periods of stable sulfur v&es. The strongest of these, on 17-18 June, as well as a weaker one, 4-7 June, correlated well with fine soils in the 0.5-3.5 pm size range. The conclusion is that reduced visibility is associated with regional episodes of both increased sulfur and increased fine soils, with best correlations occurring in both cases for sizes somewhat greater than 0.5pm dia.
INTRODUCTION
Establishment of causal factors associated with periods of reduced visibility in the arid regions of the western U.S.A. requires extensive information on the sources and nature of fine particulate matter. However, the enormous area under consideration, roughly 3 x 106 km2, the strong seasonal, synoptic, and diurnal meteorological variations, and the contributions of both natural and anthropogenic particulate sources to the low ambient mass concentrations make generation of such info~ation dificult. The existence of a short term, intensivestudy such as VISTTA (Visibility Impact by Sulfur Transformations and Transport in the Atmosphere) in a region possessing numerous long term fine particle and visibility monitoring stations associated with the Western Fine Particle Network (WFPN) and JM/EPA Visibility program presents a rare opportunity to * Paper presented at the Symposium on Plumes and Visibility: Measurements and Model Components. Grand Canyon, Arizona, U.S.A. 10-14 November 1980.
develop such information. The detailed information generated at the Zilnez Mesa site by VISTTA participants provides the in-depth analyses logistically impossible for continuously operating research studies covering large areas, while the results of the WFPN stations can put the local data into statistical and regional perspective by establishing how typical is the period and site used for the intensive program. In order to strengthen these connections, fine particle monitoring units similar to the WFPN stations at Zion, Bryce (Henrieville), Canyonlands, and Yellowstone National Parks were operated at Zilnez Mesa in the VISTTA program (Fig. 1,).
E~FERIMENTAL TECHNIQUES Particulate monitoring was performed at ground level (1.5 m) on Ziinez Mesa in the period from 26 June to 11 July 1979, using muitiday sizing impactorsand stacked filter units. The former are rotating drum impactors of the Lundgren design extensively used in stud& of fine particles and visibility (Flocchini Edal., 1976; Barone et al., 1978)due to the ability to operate automatically for 7 days at a time while
2011
2012
T. A. CAHILL et al.
Fig. 1. Map of sampling sites used in this progmm. The Henrieville site is close to Bryce Canyon National Park.
delivering size cuts close to both the minimum of the bimodal distribution at 3.5 pm dia., and the wavelength of light at 0.5 ,um. These units have been operated at Zion, Bryce, and Canyonlands National Parks (Utah), and Yellowstone National Park (Wyoming) since 1978 on a daily basis (Flocchini eb al., 198Ob;Pitchford et al., 1980). The stacked filter units (SFUs) were of the early manual design (Spumy et al., 1969; Cahitl et J., 1977) but operationally equivalent to the forty used in the WFPN effort (Flccchini et nl., 198Oc). The unit delivers a dichotomous cut at 2.5 m dia. through the capture characteristics of an Apiezon L grease coated (Cahill et ai., 1979; John et al., 1980) 8pm Nuciepore tracketched filters operated at lScms_’ face velocity. Both units participated successfully in the EPA-DOE sponsored Charleston intercomparison of particulate monitoring instruments (Camp ef uf., I980), although since coated filters were not used in the SFUs in that test, a few per cent ofcoarse soif like particulate mass penetrated to the tine filter. Both laboratory and field tests confirm that the coatings used in the VISTTA and WFPN samplers sharply reduce this effect, to the point that it is negligible in field conditions (Cahill et al., 1979; Lyons et al., 1979) while the effective 50% cut point, even in extreme laboratory conditions with dry potassium biphthalate particles becomes about 2.7~ {John et al., 1980). Samples were analyzed by particle induced X-ray emission (PIXE) (Cahill er oL, 1976), accurate to & 5 %, and by weighing (Engelbr~ht el al., 1980). The a~eement between the multidays and SFUs on a daily basis was good (the ratio SFU/MD for sulfur was 0.97 +O.il), as was agreement with SFUs run for 48 h (SFIJ/MD, sulfur, 1.04 + 0.06) and 72 h integration periods (SFU/MD, sulfur, 0.97 + 0.14). Comparisons of typically coarse mode particles were made more difficult due to intake and cut-point factors (ratio SFU/MD for Si was 0.93 kO.16; while for Fe it was 0.80 kO.18). Agreement between the various sampling instruments and analytic& methods for fine particulate species such as sulfur ranged from good to excellent, with typical differences between groups less than 10 y/, (McMurry et al., 1980). Measurements of standard visual range were made using four wavelength telephotometers in three observations per
day. Mean daily visual ranges were then calculated for comparison with particulate values.
FINE PARTICLE VALUES
Particulate concentrations at Zion, Btyce, and Canyonlands National Parks are dominated by short term (average, ~4 days) episodes in which levels rise by a factor of three to twelve times median values (Flocchini, 1980b). For example, sulfur levels reached 1 $gm-3 behavior
six times during 19’78 at Zion, and similar was exhibited at all sites in 1979 (Figs 2 and
3). The values for silicon, a soil tracer generally associated with aluminum, potassium, calcium, titanium, manganese, and iron, tend to show a seasonal trend as well as episodes of high dust levels. Very fine particles, < 0.5 pm, do not correlate well with coarse soil mass, but appear to be soil derived (Pitchford et al., 1980). Soil values usually anticorrelate with sulfur values, both day to day and by season, as suIfur values show a weak seasonal minima in the spring at times of high soil loadings and elevated wind velocities. Sulfur particies in the three size modes have largely independent behavior in time, showing a larger size variation from day to day than any other major element. The thrusts of these studies are to understand the sources of the elevated episodes, and to investigate the degree of association of such periods with degraded visibility. One sulfur episode occurred during VJSTTA, on 29 June. The regional character of this episode is shown in Fig. 4, which compares sulfur values measured at Zion, Canyonlands, and Zilnez Mesa during the
2013
Particulate matter and visibility 24 hour meon
Conyonlonds
P 600
Stoge
2
P -
600
0 Stoge
6
Feb
Mor
Apr
May February
Jun 1979
Jul
I
Aw
to December
Sep
act
NW
OW
1979
Fig. 2. Silicon particulate matter at Canyonlands National Park, Island in the Sky, for 1979. Stage 1, 3.5-15pm; Stage 2, 0.5-3.5pm; Stage 3, < 0.5 pm dia. particles.
VISITA period. Sulfur values on 28 June and in the period 6 July through 10 July were typical of the cleaner or baseline values below which summer values rarely go. The period of the 29 June-30 June episode also corresponded to the peak values of other fine pollutants; zinc (11 ng m- ‘); lead (47 ng m- 3); and bromine (22ngme3). Significantly, fine copper did not peak in this episode. Since elevated sulfur values associated with smelter operations have elevated fine copper values, and since the Zn, Pb and Br values have ratios similar to urban conditions, one can infer an urban source. Trajectory analyses confirm this hypothesis and indicate a southern California source. The Br/Pb ratio, 0.47 + 0.10, is close to current automotive values. This is worthy of comment, since Br/Pb ratios in the southern California area are severely depressed in summer in the fine size ranges, typically 0.17 (Flocchini et al., 1976; Eldred et al., 1978). This could indicate that the lead seen at VISTTA is due to a local automotive source, or it could support the hypothesis that Br loss in southern California samples is due to aerosol acidity on the collection surface. Thus, PbBrCl transported as an aerosol from Los Angeles and not collected until the
aerosol is dilute and, possibly, neutralized would retain its automotive source signature (Feeney et al., 1975). The Pb/S ratio for particles at 28 southern California sites on 26 June 1979, was 0.30 (Calif. Air Quality Data, 1979), while typical values previously published are similar, 0.38 f0.13, (Flocchini et al., 1976). The difference can be partially explained by the much greater use of unleaded gasoline in California since 1973, the date of the earlier work. The Zn/S ratio from that study was 0.034 f 0.017. Thus, the PbjS and Zn/S ratios seen at Zilnez Mesa, 0.043 and 0.010 respectively, are depressed by factors of 7 and 3.4 from those of the presumed source, even if one subtracts from the S value the median S value seen at the site as a “background” correction. Since the particle sizes are roughly equivalent, removal processes should be similar. Thus, one can invoke either additional sources of particulate and gaseous sulfur between southern California and Zilnez Mesa, or invoke gas to particle conversion as a means to replenish the sulfur concentration. Early results from the WFPN indicate that urban transport is not the source of all (or even most) of the sulfur episodes at the Utah parks, as elevated sulfur levels with associated copper particles
2014
T. A. CAHILL
Feb
Mar
Apr
May
Februwy
et a/.
Jm
..tui
I979
to lhramber
rwv
oec
1979
Fig,3. Sulfur particulate matter at Canyoonfands, National Park, Istand in
the Sky, for 1979. Stage 1, 3.5-f5@~ Stage 2, D.S-3.5~~ < 0.5 pm dia. particles.
oftenexist during summer months its the ArizonaNew Mexico region, presumably due to smelter operations (Flocchini et al., 198Oa), and the pattern often extends into Utah. Other particles of interest include a strong enhance,
I
I
/
,
Stage 3,
ment of fine potassium during the fire period, 160ng M - 3excessover soils, giving a predicted carbon mass of about 2.7 pg m- j if one uses the potassium ta fine carbon ratio seen in studies of Oregon field burning (Lyons et a/., 1979).
I
1
I’,
,
/
,
,
Sulfur particles CJ Conywttands N P , multiday Zion N P. I muitiday D Zrhez Mew, multidoy
a l
27
28 June
29
30
I
2
3
4
2llne.z Meso, stocked fitter
5
6
7
9
IO
II
I2
J'J&, 1979
Fig. 4. Sulfur values measured at Zion, Canyonlands, and Zilnez Mesa sites during the VISTfA period.
2015
Particulate matter and visibility CORRELATIONS
WITH VISIBILITY
Extracting local from regional influences in visibility studies can be di5cult without accurate spatial profiles of pollutant values. Comparisons between telephotometer measurements taken at Canyonlands as part of the EPA/JM visibility investigation and visibility readings at Zilnez Mesa, confirm that the reduction in visual range seen at Zilnez Mesa in the 29-30 June period was regional, while the strong local influence of the fires did not strongly extend into the site paths of the Canyonlands telephotometer, despite the use of Navajo Mountain as one of the targets (Fig. 5). Figure 5 shows the excellent correlation between elements in the soil derived particles typical of coarse (Multiday Stage 1, 3.5-15pm) and intermediate (Multiday Stage 2,0.5-3.5 m) particles. The elements normally included are Al, Si, K, Ca, Ti, Mn, Fe and, when sensitivities allow, Sr and Zr. The finest particles (Multiday Stage 3, < 0.5pm) show systematically weaker correlations. Also in Fig. 5, the eight periods in June and July 1979. in which standard visual range at Canyonlands Ccmymlandr
Multidoystage2
decreased below 100 miles (160 km) are listed in order (a-h). Baseline values are approximately 260 km during this period. The period of regional sulfur impact from southern California on 29-30 June (episode a) corresponded with the poorest visibilities seen ( z 90 km) and the highest values for intermediate sulfur particles (Multiday Stage 2, 0.5 to 3.5pm) of 550ngme3, and total sulfur, 15OOr1gm-~. This latter value is presumably equivalent to about 5.4 pg m - 3 of ammonium sulfate. Episodes b, e and h also correlate with enhanced sulfur values, especially with enhancement in the intermediate size range. Episode c may represent some smoke incursion from forest fires. Episode d correlates well with enhanced soil mass which, in the < 3.5 pm size mode, sums to about 4.5 pg m- 3 of total mass, including typical oxides. This episode corresponded to the passage of a frontal system, with increased winds from the northwest. Episode g likewise correlates well with soils but not with sulfur, while Episode f has support from both soil and sulfur mass. Of particular interest is the lack of correlation between sulfur and visibility on l-3 June. This episode was characterized by very fine sulfur size profiles, finer by a factor of 5 24 hour mean 0.5 to 3.5 microns
0.1 to 0.5 microns
I
I June I979
Fig. 5. Comparison of particulate matter and standard visual range at Canyonlands for June-July 1979. The spisode of 29,30 June was regional in nature, while the smoke impacts of early July at Zilnez Mesa were not.
T. A. CAHILL et al.
2016
than those seen 30 June according to the Stage 2-Stage 3 ratios. Without more detailed size information, the actual mass median diameter of the l-3 June sulfur cannot be determined, but it may be well below the wavelength of light. The sulfur size dist~bution strongly influences visibility in California (Barone er at., 1978; Cahill er af., 1980). Other matches to periods of reduced visibility can be qualitatively associated with particulate matter. leading to the appreciation that, at Canyonlands and Zilnez Mesa, at least three particulate sources influence visibility; fine soils, forest fires, and some, but not all, sulfur-rich transported plumes from anthro~genic sources, urban, smelter and, ~tent~lIy, power plants. Statistical methods can allow a more quantitative estimate of the strengths of the factors associated with reduced visibility. The method of multiple linear regressions was applied to the Canyonlands data set, with the inclusion of some climatic data from Grand Junction, Colorado, on relative humidity. One problem encountered involved the rather weak correlation between the Canyonlands nephelometer and telephotometer. Although they usually tracked quite well, there were limited periods during which they disagreed badly, and these reduced the associations. The particulate data plus relative humidity explain much less of the variance in visual range at Canyonlands than they do at polluted urban sites in California (Barone er at., 1978), although they do isolate sulfur and soils as two primary factors, and illustrate an influence of the sulfur size distribution on extinction. These calculations are conlinuing with the addition of more representative meteorological data from sites with less important terrain effects than the Grand Junction meteorological site. CONCLUSlONS
The data generated at the Utah National Park since 1978 show that particulate matter and visibility both show episodic behavior on synoptic meteorological time scales of a few days duration. The VISTTA program sampled two episodes of elevated particulate matter and reduced visibility, associated with a southern California urban plume and relatively local forest fire activity, along clean periods of high visual range. Two other types of episodes were not sampled-high fine particulate dust loadings and southern Arizona smelter effluents. Analysis of visual range over June and July 1979, showed that all periods of reduced visibility correlated with increased levels of fine particulate matter. Acknowledgements-The authors wish to thank other members of the Air Quality Group at Davis, the John Muir Institute-EPA visibility program, and EMSL-EPA laboratory at Las Vegas. We especially thank the personnel of the National Park Service.who made the geld program a success. REFERENCES
Barone J. B., Cahill T. A., Eldred R. A., Flocchini R. G., Shadoan D. J., Dietz T. M., (1978) A multivariate statistical analysis of visibility degradation at four California cities. Atmospheric Environment 12, 2213-2221.
Cahill T. A., Flocchini R. G., Eldred R. A., Feeney P. J., Lange S., Shadoan D. J. and Wolfe G., (1976) Monitoring of smog aerosols with elemental analysis by accelerator beams. In Accuracy in Trace Analysis; Sampling, Sample Handling, Analysis, National Bureau of Standards, 442, 1119-l 136.
Cahill T. A., Ashhaugh L. L., Barone J. B., Eidred R. A., Feeney P. J., Flocchini R. G., Goodart C., Shadoan D. J. and Wolfe G. W. (1977) Analysis of respirable fractions in atmospheric particulates via sequential filtration, J. Air Pollut. Control Ass. 27, 675677.
Cahill T. A., Eldred R. A., Barone J. B. and Ashbaugh L. L. (1979) Ambient aerosol sampling with stacked filter units, Fed. Hiehwav Adm. Renort FHWARD-78-178 l-73. Cahill T. i., B&one J. B:, Eldred R. A., Flocchini R. G., Shadoan D. J. and Dietz R. M. (1980) Influence of sulfur size distribution on optical extinction, Envir. nnd Cfimatic Impact ofCoal Uri~~~uf~on (Edited by J, Singh, A. Deepak), Academic Press, New York, pp. 215-224. California Air Quality Data, April, May, June, 1979, Vol. XI, No. 2. Camp D., Van Lenh A. L. and Loo B. W. (1978) Intercomparison of samplers used in the determination of aerosolcomposition, EPA Report No. 600/7-78-l 18. Eldred R. A.. Cahill T. A. and Flocchini R. G. (1978) Bromine loss from automotive particulates at California sites, Proc. 71st Annual meeting, APCA 7869.6. Engelbrecht D. R., Cahill T. A., Feeney P. J., (1980) Electrostatic effects on gravimetric analysis of membrane filters, J. Air Poflut. Controf Ass. 30, 391-394.
Feeney P. J., Cahill T. A., Flocchini R. G., Eldred R. A., Shadoan D. J., and Dunn T. (1975) Effect of roadbed configuration on traffic derived aerosols, J. Air Poflut. Control Ass. 25, 1145-l 147. Flocchini R. G., Cahill T. A., Shadoan D. J., Lange S., Eldred R. A., Feeney P. J. and Shadoan, D. J. (1980 a) Regional scale synoptic air monitoring for visibility evaluation based on PIXE analysis, in press Nucl. Instrum. Meth. 181, 403-410. FIocchini R. G., Cahill T. A., Ashbaugh L. L.. Eldred R. A. and Pitchford M., (1980 b) Seasonal behavior of particulate matter at three rural Utah sites Atmospheric Environment 15, 315-320. Flocchini R. G., Cahill T. A., Pitchford M. L., Eldred R. A., Feeney P. J. and Ashbaugh L. L. (1980 c) Characterization of particles in the arid west. Atmospheric Environment (in press). John W., Reischi G., Goren S. and Plotkin D., (1977) Anomalous filtration of solid particles by Nuclenore filters. Atmospheric Environment 12; 1555-lSj7.
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John W.. Herina S.. Reischl G. and Wesolowski J. J.. (1980) Investigation