Distribution of Airborne Polycyclic Aromatic Hydrocarbons Throughout Los Angeles Robert J. Gordon Department of Pathology, University of Southern California School of Medicine, Los Angeles, Calif. 90033
High-volume air samplers were used to collect samples of airborne particulate matter on an intermittent schedule a t 39 locations throughout Los Angeles County for a full year. Composites were extracted and analyzed for 14 polycyclic aromatic hydrocarbons (PAH). Major PAH show high seasonal correlations (negative) with median early morning atmospheric inversion heights. PAH are highest during the November-January quarter but ranges for different PAH vary by factors 4-10 during the year. Comparison of relative PAH concentration patterns for different areas suggests that PAH in the better ventilated coastal areas arise primarily from automobiles, while in the areas farthest inland additional smaller amounts of PAH arise from nonautomobile sources. Benzo(a)pyrene averaged 0.46 ng/m3, but no composite concentration was higher than 2.0 ng/m3.
In a large-volume air sampling program in Los Angeles, differences in concentrations of polycyclic aromatic hydrocarbons (PAH) were found among four locations ( 1 ) . The patterns of relative concentrations of various PAH were similar and resembled that of auto exhaust except when affected by nearby localized sources. Observations of lung cancer rate excesses in one area of the county (2) led to a further brief survey in that area to define current PAH levels (3). This was then extended to the entire County in a detailed year-long air sampling survey described here.
Experimental Conventional “high volume” samplers as described by the Intersociety Committee ( 4 ) were used. The samplers
were located a t firestations (all but two were on one or two story roofs) and were serviced as before ( 3 ) .Thirteen areas had been selected along census tract boundaries to divide the basin (2). In each area three collection sites (A, B, and C) were chosen. During one month all 13 A sites were sampled, next month the B sites, the third month the C sites, and then back to A, and so on for the full year. In one month the A series, for example, was sampled for seven days spread through the month (including each day of the week once only), then the samplers were moved to the B sites for a similar sequence. Site locations and areas are shown in Figure 1. The filters were equilibrated a t constant humidity and weighed before and after exposure. For the first quarter the seven filters for any one month and area were combined and extracted with benzene. Since no striking differences in PAH patterns were seen among the A, B, and C sites within any area, thereafter the three sites were made into quarterly composites for extraction, to reduce the amount of analytical work. There were therefore 13 composites of seven filters for each of the first three months and 13 composites of 21 filters for each of the last three quarters. Sampling went from February 1974 through January 1975. Extractions and PAH analyses by chromatography and ultraviolet spectrophotometry were done as before ( I , 3). From reports of the Los Angeles Air Pollution Control District the inversion heights for 0600 h a t Los Angeles Airport for each sampling day were obtained. Since there are numerous low-level inversions recorded as 100 ft and no heights above 9900 ft are listed, median rather than mean values were used to compare different periods. Average morning (0600-1200) wind speeds and the medians of the maximum calculated inversion heights for downtown Los Angeles during the sample periods were also derived from APCD reports.
Table I . Sample Yields, pg/m3 Area
Quarter 1 2 3
4 Gcom. mean, year
3
1
2
0.75
Mi/Da/MiZ ( 5 ) Automobile Traffic Density (ATD), 1.2 1.5 1.5 2.0 1.2 0.65 0.4 0.8 1.05 Suspended Particulate Matter (SPM), Quarterly Geometric Means
59.1 101.9 109.0 76.6 84.2
4
6
5
7
8
9
10
12
13
0.95
0.95
0.9
71.9 68.8 57.3 67.4
92.2 76.7 84.1 83.5
82.1 72.0 82.0 80.4
66.1 87.2 74.5 85.5 85.8 109.5 128.0 118.8 106.8 82.4 Benzene-soluble Particulate Matter (BSPM), Composites Except 1st Quartera
83.9
79.0
75.6 84.7 97.3 93.2
75.4 69.4 73.5 80.2
92.2 83.2 82.4 84.5
84.7 90.4 83.2 85.1
94.1 108.8 116.8 120.1
113.5 116.1 156.1 130.4
101.6 123.5 130.7 121.4
106.0 100.4 112.0 109.3
106.1 84.7 74.7 68.8
Quarter la 5.9 10.0 2 7.4 7.2 3 9.1 8.4 4 8.7 14.0 Geom. mean, year 7.7 9.6 a Geometric mean of A , B, a n d
9.0 3.9 4.3 11.8
11.0 6.7 5.9 15.1
10.0 7.5 5.3 12.6
11.1 8.6 10.0 17.0
11.5 7.4 10.9 14.6
9.0 7.5 8.8 12.0
9.4 4.4 7.1 13.0
11.6 5.0 5.9 8.4
7.9 3.7 3.0 8.6
8.4 4.2 4.4 14.1
7.0 4.2 4.0 10.0
6.5
9.0
8.4
11.3
10.8
9.2
7.9
7.3
5.3
6.8
5.9
C composites (see text).
370 Environmental Science & Technology ..
11
yearly means are found at areas 6, 7, and 8. The range among areas and by quarters is about threefold a t most. The highest levels are uniformly in the first and fourth quarters (except for area 1). (This is unlike the case for SPM, where quarterly variation is smaller and highest levels are sometimes in the third quarter.) The BSPM fraction of the SPM annual means by area is fairly uniform (7.411.0%) but by quarters the fraction ranges 6.4-13.3%, highest in winter. BSPM does not correlate with ATD. Polycyclic Aromatic Hydrocarbons (PAH). Concentrations of 14 PAH are shown as quarterly geometric means for all sites combined in Table 11. All PAH are highest in the fourth and first quarters. This is parallel to BSPM levels, but the quarterly PAH ranges are wider, up to tenfold in some areas. The PAH concentrations are listed by area in Table 111; the upper figure in each pair is the geometric mean of the observed values over the full year. The lowest observed levels are found a t the coastal areas 11 and 13, and the highest at inland areas 6 and 7. The ranges vary
Results Traffic Densities (ATD). The ATD values given in Table I are averages for the three sample sites in each area, derived as before ( I ) from data of Roberts et al. (5). Suspended Particulate Matter (SPM). Geometric means of S P M by quarters and for the year for each area are given in Table I. The highest concentrations are found at inland areas 6-9, where the levels may sometimes be more than twice those a t coastal locations. The means for the whole year vary among areas by less than twofold (areas 7 and 11) and do not relate to ATD. Variation by quarter is only 30-40% except for area 1. Benzene-Soluble Particulate Matter (BSPM). Extract yields of BSPM are also shown in Table I. Highest
Table II. PAH Concentrations, ng/m3 Quarterly geometric means of all areas Quarter PAHa
1
2
3
4
Year, geom. mean
PYR
0.58 0.38 0.30 0.70 1.30 0.77
0.23 0.15 0.06 0.26 0.42 0.17 0.24 0.06 0.07
0.25 0.24 0.10 0.44 0.62 0.26 0.33 0.12 0.15 0.06 0.14 2.71 1.oo 1.66
1.24 0.68 0.59 1.57 1.96 1.27 1.30 0.43 0.52 0.22 0.79 8.25 2.64 4.44
0.45 0.31 0.18 0.60 0.90 0.46 (0.54)b 0.17 0.20 (0.1 O)b 0.23 3.27 1.34 2.13
FLT BAA CHY BEP
BAP BBF BJ F BKF PER
ANT GEE
INP
COR
0.26 0.27 0.22 0.33 3.80 1.79 2.49
0.08 1.35 0.68 1.13
a PAH identities are given in Nomenclature section. b
Figure 1. Los Angeles County divided into 13 areas (excluding sparsely populated northern portion)
Based on incomplete data.
Dots denote air sampling sites
Table I l l . Observed PAH A n n u a l Geometric Mean Concentrations, n g / m 3 a n d Calculated Based on Patterns in Coastal Areasa Area PAH
1
2
3
4
5
6
7
8
9
10
11
12
13
PY R
0.41 0.36 0.28 0.23 0.18 0.13 0.62 0.44 0.81 0.75 0.47 0.32 0.17 0.13 0.16 0.14 0.25 0.18 2.86 2.73 1.10 1.09 1.83
0.46 0.50 0.32 0.32 0.18 0.18 0.68 0.60 1.01 1.04 0.63 0.45 0.25 0.19 0.26 0.19 0.35 0.25 3.78 3.79 1.22 1.51 2.54
0.37 0.40 0.20 0.26 0.15 0.15 0.36 0.49 0.73 0.85 0.41 0.36 0.17 0.15 0.16 0.15 0.28 0.21 3.02 3.08 1.11 1.22 2.06
0.49 0.60 0.33 0.39 0.26 0.22 0.65 0.72 1.06 1.26 0.56 0.54 0.18 0.22 0.21 0.23 0.29 0.31 4.33 4.57 1.89 1.82 3.06
0.47 0.48 0.30 0.31 0.21 0.18 0.76 0.59 1.00 1.02 0.54 0.44 0.23 0.18 0.23 0.18 0.26 0.25 3.84 3.69 1.55 1.47 2.47
0.76b 0.61 0.50 0.40 0.44 0.23 0.92 0.75 1.34 1.30 0.77 0.56 0.28 0.23 0.27 0.23 0.42 0.32 5.01 4.72 2.05 1.88 3.16
0.84 0.46 0.61 0.30 0.23 0.17 1.02 0.57 1.22 0.98 0.76 0.42 0.26 0.17 0.29 0.18 0.38 0.24 4.02 3.56 1.96 1.41 2.38
0.67 0.33 0.55 0.21 0.24 0.12 0.68 0.40 0.88 0.69 0.53 0.30 0.14 0.12 0.25 0.13 0.25 0.17 2.67 2.52 1.18 1.00 1.69
0.34 0.39 0.25 0.25 0.10 0.15 0.53 0.48 0.92 0.83 0.41 0.36 0.14 0.15 0.14 0.15 0.18 0.20 2.99 3.02 1.33 1.20 2.02
0.34 0.38 0.27 0.25 0.12 0.14 0.42 0.46 0.77 0.80 0.35 0.35 0.14 0.14 0.16 0.14 0.15 0.20 3.05 2.91 1.18 1.16 1.95
0.33 0.30 0.21 0.19 0.11 0.11 0.38 0.36 0.65 0.63 0.24 0.27 0.10 0.11 0.11 0.11 0.13 0.15 2.31 2.29 0.90 0.91 1.53
0.42 0.44 0.30 0.28 0.17 0.16 0.66 0.53 0.89 0.92 0.38 0.40 0.15 0.16 0.19 0.17 0.17 0.22 3.41 3.35 1.48 1.33 2.24
0.29 0.30 0.22 0.19 0.1 1 0.1 1 0.45 0.37 0.70 0.63 0.27 0.27 0.1 1 0.11 0.11 0.1 1 0.12 0.15 2.32 2.30 1.01 0.91 1.54
F LT
BAA
CHY BEP
BAP BJ F BKF
ANT GEE INP
COR a Upper value in each pair = observed; lower value calculated using the average PAH/COR ratio for areas 3, 11, a n d 13. Italicized observed values exceed calculated values by at least three times the coefficient of variance among 3, 11, a n d 13.
*
Volume
10, Number 4, April 1976
371
Table I V . Correlation Between Air Concentration, and Median Inversion Height, H log C = a + bH Variable
a
SPM BSPM
1.951 1.069
COR
0.600
GEE
0.857 0.104
BAP
r
b
3.9 x -1.568 x -2.776 X -3.515 x -4.567 x
0.28 -0.97 -0.96 -0.95 -0.99
c,
7
P
