Estimation of Organic and Total Mercury in Seawater around the Japanese Archipelago Masahiko Fujita” and Kiyoshi lwashima The institute of Public Health, 6-1, Shirokanedai 4-chome, Minatoku, Tokyo-108, Japan
An analytical procedure for the determination of total and organic mercury in seawater is described. Mercurials in seawater were complexed with diethyldithiocarbamate, and the complex was concentrated on XAD-2 resin. A portion of the resin was used for analysis of total mercury. After elution of the resin with solvent consisting of 3 M HCl and methanol (l:l), organic mercury was extracted with benzene and then back-extracted with cysteine solution. The extraction procedure was repeated again. Organic mercury in cysteine solution was determined by flameless atomic absorption spectrometry (FAA),and total mercury adsorbed on the resin was also analyzed by FAA. The lower limit of detection in seawater is 0.1 ng/L for organic mercury, when 80 L of seawater is treated. Application of the proposed method to the seawater around the Japanese archipelago is described, and the resulting mercurial speciation is discussed. Introduction
Fish contains considerably high concentrations of mercurial compounds, most of which are in the chemical form of methylmercury ( I ), Methylmercury is biosynthesized from inorganic mercury by microorganisms within sediments ( 2 ) , and it has been reported that methylmercury may be released from sediments to seawater, either in the dissolved form or adsorbed on particulate materials ( 3 ) . These facts strongly suggest that methylmercury may be present in seawater. Consequently some work has been done in developing analytical techniques to differentiate and determine both the inorganic and organic forms in seawater. Hosohara et al. ( 4 ) and Fitzgerald and Lyons (5)estimated the occurence of mercury associated with organic molecules. Leatherland et al. (6)also suggested that not all of the mercury in seawater was present in inorganic form. Baker (7) individually estimated total and “reactive” mercury concentrations in seawater. Fukai and Huynh-Ngoc (8) attempted to apply anodic stripping voltammetry to determine methylmercury in seawater. Davies et al. (9)indirectly estimated the methylmercury concentration in seawater by determining the methylmercury level accumulated by mussels exposed to the seawater. Egawa and Tajima (IO) detected methylmercury in seawater only from Minamata Bay, Japan, an area with a history of gross mercury pollution from industrial discharge. In spite of these works, little is known about the chemical forms of mercury present in seawater. This seems to be due to the extremely low concentrations of mercury, which are well below the sensitivities of recent analytical techniques. We have developed a method for preconcentrating mercurial compounds with an adsorptive resin, in order to achieve the necessary sensitivity for quantitative detection. The method has been applied to the determination of total and organic mercury levels in seawater, both offshore and onshore around the Japanese archipelago. E x p e r i m e n t a l Section
Apparatus. For analysis of mercury, samples were ignited a t 850 “C in an oxygen stream in a quartz furnace (Sugiyamagen MV-250). The evolved mercury was trapped on a gold trap, and immediately after complete combustion the trap was 0013-936X/81/0915-0929$01.25/0
@
1981 American Chemical Society
heated. The released mercury was measured by a flameless atomic absorption spectrometer (Shimazu UV-201). Measurement of the radioactivity of z03Hgwas carried out with a thallium-activated sodium iodide (NaI(T1))scintillation crystal detector coupled with an Aloka TDC-5 universal scaler. Reagents. Sodium diethyldithiocarbamate (DDC): Atomic absorption analysis grade was used. All other chemicals were of the purest grade available. [203Hg]CH3HgC1:The specific activity was 3.7 mCi/mg of CH3HgC1(New England Nuclear Co.),and the radiochemical purity was more than 99% as determined by TLC. [203Hg]HgC12:The specific activity was 2.65 mCi/mg of HgClz (New England Nuclear Co.). Adsorptive resin: Amberlite XAD-2 (30-60 mesh, Tokyo Organic Chemical Industries Co.) was used. The resin was washed successively with a mixture of 3 M HC1 and methanol (1:l)and with water. Cysteine acetate solution (1%): One gram of L-cysteine monohydrochloride, 0.8 g of sodium acetate, and 12.5 g of sodium sulfate were dissolved in 100 mL of water. This solution was washed 3 times with 10 mL of benzene. Sodium chloride solution (20%): Twenty grams of sodium chloride was dissolved in 100 mL of water, and the solution was washed 3 times with 10 mL of benzene. High-purity water: Deionized water was passed through a column packed with XAD-2 resin, which was previously adsorbed with DDC, and then distilled. This water was used throughout this work. Procedure
Methods of Sampling and Preserving Seawater Samples. Sample collection and handling were done with careful attention to avoid contamination ( 1 1 ) .Surface samples were collected with a polyethylene bucket, which was previously acid-washed and rinsed well with seawater a t the sampling point. Deeper samples were collected after pumping up for 30 min through a PVC tube. Determination of Organic Mercury in Seawater. In order to remove suspended particles, 80 L of the sampled seawater was filtered through a membrane filter (pore size, 0.45 ym). After 360 mg of sodium diethyldithiocarbamate and 80 mL of Amberlite XAD-2 were added to the filtered seawater, the mixture was stirred with a rotator made from Pyrex glass for -24 h to absorb and concentrate the mercurial compounds onto the resin. The resin was filtered off, and a portion of it (-100 mg) was rendered for analysis of total mercury. The residual portion of resin was shaken for 3 h in 1.6 L of 3 M hydrochloric acid and methanol solution (1:l). After filtration the solution was extracted twice with 500 mL of benzene. The combined benzene solution was washed 3 times with 100 mL of 20% sodium chloride solution, and the organic mercury was back-extracted 3 times with 10 mL of 1%’ cysteine acetate solution. The combined aqueous layer was adjusted to pH 1with 4 M HC1 and was extracted 3 times with 5 mL of benzene. The combined benzene layer was again extracted with 2 mL of cysteine solution. A portion of the cysteine solution was transferred to the quartz boat of the furnace unit, and organic mercury was determined by flameless atomic absorption. Volume 15, Number 8, August 1981
929
Table 1. Distribution Ratio of Mercuric Compounds in the Organic Solvents to Those in 3 0 % NaCl Solutiona organic solvent
CtjHs
mercurlc compds
[H'I,
3.3
5.0
M
1.7
8
x
10-1
9
x
1
10-2
x
1
107
x
10-8
CH3HgCI
3.9
4.6
8.9
9.9
CHC13
0.014 2.9
0.006 3.4
6.2 0.005 5.4
7.3
HgC1z CHSHgCI
0.007 6.1
0.007 7.0
0.016 8.8
0.024 8.0
DlBK
HgCb CH3HgCI
0.007 2.2
2.8
0.007 3.1
0.007 3.6
4.1
0.007 6.6
0.007 6.5
HG1z
0.05
0.02
0.01
0.008
0.009
0.105
0.10
i
10.2
Aqueous solution of mercuric or methylmercuric chloride was shaken for 5 min with organic solvents, and the mercury levels in each solution were measured. DlBK = diisobutyl ketone. a
Table II. Amount of Resin Necessary for Collection of Methylmercury from 500 mL of Seawater vol of resln, mL
collection mean f SD, %
0.5
98.0 f 0.0
2.0
97.0
1.o
98.3 f 2.3
5.0
98.7
voI of resin, mL
collectlon mean f SD, %
f 0.0 f 3.8 0 CH3HgCI
Determination of Total Mercury in Seawater. A portion of the resin containing the concentrated mercurials from seawater was air-dried at room temperature for 24 h. The resin was weighed into the quartz boat of the furnace unit and decomposed as described above. Total mercury was determined by flameless atomic absorption spectrometry. Determination of Total Mercury in Suspended Particles. The suspended particles on the filter paper, through which 80 L of seawater was filtered, was digested under reflux with nitric acid and 30% hydrogen peroxide, using a modified digestion apparatus as described in the AOAC method (12). After digestion mercury was reduced with stannous chloride, and evolved mercury was determined by atomic absorption spectrometer.
Results Distribution Ratio of Mercuric and Methylmercuric Chloride between Seawater and Organic Solvents. In order to extract and concentrate mercurials from seawater with organic solvents, we studied the extraction ratio of mercuric and methylmercuric chloride with benzene, chloroform, or diisobutyl ketone (DIBK) at a constant concentration of chloride ion (30%).As shown in Table I, the distribution ratio ( K D )with benzene was slightly higher than those with the other organic solvents. The value was highest at around neutral pH, and the value had a tendency to decline with pH. The K D value of methylmercury was much higher than that of inorganic mercury at any pH and for any of the three organic solvents studied. The same phenomena were observed at a low concentration of chloride ion (3%). Effect of pH on the Collection of Mercuric and Methylmercuric Chloride by the Resin. Resin retention for mercuric compounds was estimated over the pH range of 1.0-10.0 at a chloride ion concentration of 30% by adding 203HgC12or CH3203HgC1at a concentration of 0.25 ng of Hg/mL. One milliliter of the resin was shaken in the mercurial solution containing 18 pM DDC until the radioisotope equilibrated with the resin and the activity of mercury remaining in the solution was measured. The results of this experiment are presented in Figure 1,which shows that both mercuric and methylmercuric compounds were quantitatively adsorbed onto the resin above pH 5.0, while at pH lower than 4.0 the resin failed to collect mercuric compounds at all. Amount of Resin and Time of Shaking for Adsorption of Mercurials. The amount of resin necessary for complete 930
Environmental Science & Technology
! HgCI,
1
2
3
4
5PH 6
7
8
9
10
Figure 1. Adsorption of inorganic and methylmercury on XAD-2 resin as a function of pH in the presence of diethyldithiocarbamate. Mercurials were added to 20 mL of seawater containing 18 mM DDC at a concentration of 0.25 ng of Hg/mL and then shaken with 1 mL of XAD-2 resin.
collection of mercurials was determined by shaking various amounts of the resin in 500 mL of seawater containing mercuric and methylmercuric chloride. The resin corresponding to a hundredth and a thousandth volume of seawater could collect more than 98.0% of mercurials from seawater (Table 11).It was found that collection of mercurials from seawater became complete with an increase of shaking time, recovery time being 24 h (Figure 2). Desorption of Methylmercury from the Resin. Mercurial compounds adsorbed onto the resin were eluted with various concentrations of hydrochloric acid or with a mixture of hydrochloric acid and methanol. The recoveries are shown in Table 111. It was found that raising the concentration of hydrochloric acid could increase the recovery but that a concentration of 4 M could give a recovery of only 81%.The better recovery was obtained by mixing methanol into hydrochloric acid. The mixture (1:l)of 3 M hydrochloric acid and methanol achieved a 96% recovery of methylmercury. The recovery for inorganic mercury was only 31% by the same solution. Extraction of Methylmercury from the Eluate. In order to extract methylmercury which was eluted from the resin, we used benzene as the solvent for extraction. When 6 mL of eluate containing mercurials a t a concentration of l ng of Hg/mL was extracted with 6 mL of benzene, 97% of the methylmercury was extracted, while only 3% of the inorganic mercury was extracted. Back-Extraction of Methylmercury from the Benzene by Cysteine Solution. Methylmercury in 200 mL of benzene was shaken for 30 min and extracted with various volumes of cysteine solution. Methylmercury extracted in cysteine solution was measured, and the results are shown in Figure 3.
25
50
hours
Figure 2. Collection efficiency of methylmercury as a function of shaking time.
Table 111. Recovery of Mercuric Compounds from the Resin with Various Kinds of Eluents recovery, Yo methylmercury
eluents
2 M HCI 3 M HCI 4 M HCI 2 M HCI-MeOH 3 M HCI-MeOH 4 M HCI-MeOH 2 M HCI-MeOH 3 M HCI-MeOH 4 M HCI-MeOH
(2: 1)
(2:1) (2: 1) (1:l) (1:l) (1:1)
Inorganic mercury
71 f 1 77 f 1 81 f 1 83 f 2 93 f 2 87 f 2 88 f 2 95 f 2 91 f 2
31 f 1
0 30 r n i n . 5
min.
I 0.001 0.01 0.1 Volume of cysteine s o l u t i o n / v o l u m e of seawater
Figure 3. Extraction efficiency as a function of volume of cysteine solution.
Using either 2 or 20 mL as the volume of extractant gave more than 98% recovery, and even 0.5 mL gave 96.0% recovery. But when the shaking time was shorter than 5 min, methylmercury could not be extracted quantitatively with 10 mL of cysteine solution. Complete extraction was achieved by shaking for 30 min.
Discussion Benzene has been widely used to extract methylmercury from aqueous solution as reported by Westoo. As to the efficiency of the organic solvent for extracting methylmercury, benzene was compared with chloroform and diisobutyl ketone.
Of the three organic solvents, benzene was most efficient for extraction of methylmercury. The distribution ratio ( K D )of methylmercury between benzene and aqueous solution is -lo3 times that for inorganic mercury, which indicates that extraction with benzene makes possible the selective extraction of methylmercury in the presence of inorganic mercury. Over the pH range examined, the K Dof methylmercury was highest at pH -7.0 and only half at 2 M hydrochloric acid. The K Dvalue became small for the coexistence of organic compounds which have sulfhydryl functional groups. Bovine serum albumin did not effect the K D at a concentration of 1 ppm, but the K D decreased to 0.64 at 10 ppm and to 0.06 at 100 ppm of albumin. But when the hydrogen ion concentration was increased, the K Dwas improved. The K Dwas 6.8 at pH 1.1even in the presence of 10 ppm albumin. A number of organic compounds are present in seawater; therefore, it is necessary to acidify the sample solution to pH 1.1in order to extract methylmercury from seawater with benzene. Methylmercury was repeatedly extracted with benzene from seawater adjusted to pH 1.1,and the K Dwas determined. At the first extraction the K Dwas 10.3 f 0.6, and the K Dwas 9.4 f 1.3 at the second extraction. These results show that methylmercury was extracted in constant proportion by the repeated extraction procedure. On the other hand, the small K Dsuggested that it is difficult to extract methylmercury from seawater with benzene and concentrate it by a factor of ca. 10 000. Consequently preconcentration by an adsorptive resin was examined thereafter. DDC is widely used as a chelating reagent, with which trace metals are extracted into organic solvent. On the other hand, the XAD-2 resin has also been used for concentration of organic compounds in aqueous solution. It has been reported that the complex-forming coefficient of DDC-Hg(I1) is significantly larger than those of many other metals (13). Therefore, a valuable preconcentration method for the trace analysis of mercury in seawater is first used to complex mercuric compounds with DDC followed by concentration onto XAD-2 resin. As we expected, mercuric and methylmercuric compounds were quantitatively concentrated on the resin a t pH 5.0 or above (Figure 1). Organic solvents are generally used to elute the organic compounds which collect on the XAD-2 resin, and an acidic solution is used to elute the metal ions which are adsorbed on the ion-exchange resin. So we used a mixture of hydrochloric acid and methanol to elute the DDC complex of mercurials which were adsorbed on the XAD-2 resin. The higher concentration of hydrochloric acid results in an elevation in elution of methylmercury from the resin, but hydrochloric acid alone could not give quantitative elution. Addition of methanol to hydrochloric acid improved the recovery; 3 M HC1/ MeOH (1:l)gave 95% or better recovery. On the other hand, the solution gave an elution of only 3% of inorganic mercury. The result suggested that it would be possible to selectively remove the inorganic mercury, since coexistence would result in error in the data obtained by atomic absorption analysis. So it is necessary to remove inorganic mercury and concentrate methylmercury selectively before measurement. In order to reduce the amount of inorganic mercury, we examined benzene extraction and cysteine back-extraction as described by Westoo. An examination of the recoveries of inorganic and methylmercuric compounds a t the extraction step using HgClz and CHSHgC1 labeled with 203Hgindicated the values of 0.2 f 0.01 and 97 f 1%,respectively. Since inorganic mercury is presumably present at a considerably higher concentration as compared with the amount of methylmercury in seawater, it is assumed that a single extraction is insufficient to remove inorganic mercury. When the extraction procedure was repeated twice, it was assumed that the ratio of inorganic mercury mixed in the final concentration Volume 15,Number 8,August 1981
931
Table IV. Concentrations of Total Mercury and Methylmercury in Seawater around the Japanese Archipelago filtered seawatera sampling polnt
Sagami Bay Pacific Ocean
1
Japan Sea
2 1
Suruga Bay
Kagoshima Bay
a
depth,
CH3Hg
1.o 0.3
2.2
3.9
0.2
1.2
0.2 0.4
3.2 3.5
0.2
2.3 1.a
0.2
7.4
0.2 0.3 0.3
(4Oo36'N, 141'42'E)
0 0
0.2
0 0
0.1
0 0 0 0
0.2 0.5 ND
(37'44'N,
138'13'E)
suspended substances CbHg total Hg
0.2 0.2
0 6
total Hg
12.5 3.8
( 3 s 0 i 4 ' ~ ,i 3 g 0 0 a ' ~ ) (30~45'~ 1 .4 3 ~ o a ' ~ )
0.9
1.5
2 3
(40°03'N, 139'34'E)
1 2
( 3 3 0 4 2 ' ~ ,i 3 a 0 3 5 ' ~ ) (33057'~,138033'~)
3
(340 12",
4
(34°25r~,1 3 8 ~ 2 7 ' ~ )
5 1 2
(34040'~,138032'~)
0
(31°40'N, 130'40'E)
6
130'40'E)
135
3
(31'39'N, 130'46'E)
17
3.0
2.5
4
(3lo39'N, 130'46'E)
37
3.9
3.8
5
(31°39'N, 130'46'E)
128
2.9
2.8
(39'05'N,
(3 1'40".
134'35'E)
~38~30'~)
Values represent ng of Hg/L. Values represent (ng of Hg/SS)/L
Environmental Science & Technology
0.1
0.2 6.4
1.a 11.4
0.3
6.7
ND
19.6 13.9
ND is lower than 0.1 ng of Hg/L.
was 0.04% or less. Thus, when one assumes that the total mercurial concentration in the seawater in Table IV was solely derived from inorganic mercury, this would account for an additional error of 0.001-0.005 ng/L, a t the most, over the amount of organic mercury determined. This is equivalent to a maximum error of 3% per 0.15 ng/L of determined organic mercury Table IV, and therefore any impact introduced by the inorganic mercury is negligible. The organic mercury blank in the reagents used was measured by the procedure described in the Experimental Section. The methylmercury blank for the total procedure was estimated to be 0.03-0.005 ng/L. When this reagent blank is taken into account, the lower detection limit of the present analytical procedure is 0.1 ng/L. Table IV shows the results of our measurements of organic and total mercury concentration in the seawater. When the seawater was filtered through the membrane filter (pore size, 0.45 pm), the organic mercury concentration was -0.2 ng/L with certain variances depending on the area in which the seawater was sampled. On the other hand, the organic mercury concentration in the suspended substances (SS) (mostly phytoplankton) remaining on the filter showed an approximately constant value of 0.2-0.3 (ng/SS)/L. In the soluble fraction, 3-23% of the mercury in seawater is present as organic mercury. This percentage seems to be relatively small as compared with that of fish. The values for total mercury are similar to those reported by the following authors: Fitzgerald and Lyons ( 5 ) ,8 f 3 ng/L for the Northwest Atlantic; Leatherland et al. (6),3-20 ng/L for the Northeast Atlantic; Burton and Leatherland ( 1 4 ) , 11-28 ng/L for the English Channel; and Baker (15), 0.9-7.7 ng/L for the sea around the United Kingdom. The vertical distribution of total mercury at station No. 5 of Kagoshima Bay is shown in Figure 4.The total mercury concentrations ranged from 2.2 to 9.5 ng/L; the average was 4.2 ng/L. A maximum in concentration appears a t 20 m from the bottom. The amplitude of the variation coincided roughly with that of varying p H values which may be associated with solubilization of mercury. Kagoshima Bay is situated in the center of a volcanic region, where an active volcano, Sakurajima, has discharged volcanic ash since the earliest records. Although it is known that certain fish species caught a t the bay contain relatively high concentrations of mercury, we found that mercury levels are almost the same as those of samples collected around Japan. 932
m
Figure 4.
Total mercury and pH profiles for seawater of Kagoshima
Bay. According to the present analytical method, there is a possibility that organic mercury other than methylmercury is measured; however, since no other form of organic mercury than methylmercury has, as yet, been detected in the natural environment including both biosphere and geosphere (16), we believe that the probability of measuring organic mercury other than methylmercury in our study is slim. Confirmation regarding this point, needless to say, awaits identification by gas chromatography-mass spectrometry. Acknowledgment
We thank Mr. I. Fukuoka for technical assistance, Dr. H. Tsubota for measurements of pH, Dr. M. Shimizu for valuable comments, and the staff at the Laboratory of Fisheries, Tokyo University, and Tokyo Fishery College who sampled the seawater. L i t e r a t u r e Cited (1) Westoo, G. Acta Chem. Scand. 1967,21,1790. ( 2 ) Jensen, S.; Jernelov, A. Nature (London)1969,223,753.
(3) Jernelov, A. Limnol. Oceanogr. 1970,15,958. (4) Hosohara, K. J . Chem. SOC.J p n . , Pure Chem. Sect. 1961, 82, 1107. (5) Fitzgerald, W. F.; Lyons, W. B. Limnol. Oceanogr. 1970, 29, 469.
(6) Leatherland, T . M.; Burton, J. D.; Culkin, F.; McCartney, M. J.; Morris, R. J. Deep-sea Res. 1973,20,679. (7) Baker, C. W. Nature (London) 1977,270,230. (8) Fukai, R.; Huynh-Ngoc, L. Anal. Chim. Acta 1976,83,375. (9) Davies, I. M.; Graham, W. C.; Pirie, J. M. Mar. Chern. 1979, 7, 111. (10) Egawa, H.; Tajima, S. “Proceedings of the 2nd U.S.-Japan Expert Meeting,” Tokyo, Japan, Oct 1976. (11) Balley, G. E.; Gardner, D. Water Res. 1977,II, 745. (12) “Official Methods of Analysis of the Association of Analytical Chemists”; Washington, 1975; p 454.
(13) Wittenbach, A.; Bajo, S. Anal Chem. 1975,47, 1813. (14) Burton, J . D.; Leatherland, T . M. Nature (London) 1971,231, 440. (15) Baker, C. W. Nature (London) 1977,270,230. (16) Vostal, J. “Mercury in the Environment”; Friberg, L., Vostal, J., Eds.; CRC Press: Cleveland, OH, 1972; p 25.
Received for review August 26,1980 Accepted March 17,1981. This work was supported i n part by grants from the Ministry of Education, Japan.
Effect of NO, Emission Rates on Smog Formation in the California South Coast Air Basin David P. Chock,* Alan M. Dunker, Sudarshan Kumar, and Christine S. Sloane Environmental Science Department, General Motors Research Laboratories, Warren, Michigan 48090
The effect of changes in NO, emissions on downwind regions of the California South Coast Air Basin was investigated with the ELSTAR trajectory model. Smog formation was simulated in air parcels which originated near Los Angeles in the early morning, passed through the San Gabriel Valley, and arrived at or near San Bernardino in the mid to late afternoon on days of moderate to high ozone. With nonvehicular emissions held fixed at the 1973 levels, the planned reduction in motor vehicle emissions is predicted to result in reduced atmospheric concentrations of CO, NO, NO2,03, PAN, and “03 along the air parcel trajectories. However, when the hydrocarbon emissions are held fixed at a projected future level, a decrease in NO, emissions will result in a decrease in NO2 concentrations, but an increase in 0 3 and PAN concentrations at all positions along the trajectories. H
I. Introduction There is a consensus in the technical community that hydrocarbon (HC) control is required to reduce photochemical oxidants. However, there has been no such consensus as to the role of oxides of nitrogen (NO,) ( I ) . I t has been known for some time that NO, both inhibits and promotes smog formation (2). Recently, there has been a controversy concerning the effect that reducing motor vehicle NO, emissions will have on cities such as Riverside and San Bernardino, which are downwind of the Los Angeles metropolitan area. To study this problem, we have utilized a simulation approach. There are two simulation tools that can be used to predict the effect of emissions changes on air quality. These are laboratory (or smog-chamber) simulations and mathematical simulations. Both tools have been used with specific applications to determine the effects of NO, emissions changes on smog in the South Coast Air Basin of California. The smogchamber simulation has been presented by Glasson ( 3 ) .The present paper describes a mathematical simulation. While smog chambers have provided the backbone of our current understanding of air pollution photochemistry, they encounter difficulties in simulating many complex aspects of ambient smog formation. In particular, the spatial and temporal variations of primary pollutant emissions, mixing height, transport, and diffusion cannot be simulated satisfactorily in smog chambers. Indeed, mathematical simulation is an attempt to circumvent these difficulties by coupling the knowledge of photochemistry gained from laboratory studies with a detailed representation of the emissions and dispersion which occur in the real world. 0013-936X/81/0915-0933$01.25/0 @ 1981 American Chemical Society
To answer the specific question of how future motor-vehicle NO, emissions affect smog in the downwind areas of the California South Coast Air Basin, we have employed the ELSTAR (Environmental Lagrangian Simulator of Transport and Atmospheric Reactions) model ( 4 , 5 ) .ELSTAR was developed and tested by using the data base provided by the 1973 Los Angeles Reactive Pollutant Program (LARPP). In section 11, a brief description of the model will be presented. The trajectory selection, emissions inventory, and the initial conditions will be described in section 111. The availability of a 1973 emissions inventory as well as the LARPP measurements (useful in providing certain meteorological information and as a guide in determining certain initial conditions) prompted us to choose 1973 for our base-case study. The model predictions for the base case were compared with interpolated observed values before future scenarios were considered. Recently, the California Air Resources Board (CARB) estimated the lifetime average emissions for 1983 and subsequent model vehicles (6). Two sets of average emissions were estimated: the first set was based on the CARB’s proposed pollution control program for post-1982 vehicles; the second set was based on the 1983 Federal emission standards. We chose as one future scenario the vehicle lifetime average emissions projected for CARB’s proposed pollution control program. Our second scenario is the same as the first except that we chose the NO, vehicle emissions projected for the less-stringent Federal standard. Comparing the model results for these two scenarios indicates the effects of NO, emissions changes on smog formation. The results of the base-case and scenario studies are presented in section 111,which is followed by a Discussion section.
II. M o d e l Description A detailed description of the formulation, development, testing, and usage of the ELSTAR model is available elsewhere ( 4 , 5 ) .For completeness, a very brief description of the model is included here. The ELSTAR model simulates photochemical reactions of air pollutants in a column of air moving along a trajectory. A trajectory is determined by the model based on surface wind measurements. The model then calculates the vertical eddy diffusivities within the mixed layer along the trajectory, based on vertical temperature profiles, surface temperatures, and assumptions about the vertical gradients of wind and temperature. The diffusivities are further assumed to follow Volume 15, Number 8, August 1981
933
