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Ambient air measurements of aromatic and halogenated hydrocarbons at urban, rural and motorway locations
The Science o f the Total Environment, 39 (1984) 265--279 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
265
AMBIENT AIR MEASUREMENTS OF AROMATIC A N D HALOGENATED HYDROCARBONS AT URBAN, R U R A L A N D MOTORWAY LOCATIONS
A. I. CLARK, A. E. McINTYRE, J. N. LESTER and R. PERRY Public Health and Water Resource Engineering, Imperial College, London S W 7 2BU (United Kingdom) (Received 23rd February, 1984; accepted 10th March, 1984)
ABSTRACT
Concern over the carcinogenic properties o f certain volatile organics in air, particularly benzene, has recently been expressed. Reductions in the lead content of petrol in the United Kingdom and other European countries are predicted to change the concentrations of aromatic and halogenated hydrocarbons (1,2-dichloroethane and 1,2-dibromoethane) in ambient air. In order to provide baseline air quality data, prior to progressive reductions in the lead content of petrol, this study reports the results of a monitoring survey of ambient air concentrations o f aromatic and halogenated hydrocarbon concentrations at urban, rural and m o t o r w a y locations. A thermal desorption/gas chromatographic method analysing Tenax GC sampling tubes was utilised. Highest concentrations for benzene (9.7 ppb) and toluene (15.5 ppb) were measured at the urban site. The average benzene concentration is comparable with a proposed ambient air quality standard in the Federal Republic of Germany. Multiple regression analysis of nonmethane hydrocarbon and carbon monoxide air quality data demonstrated the importance o f meteorological variables in defining measured concentrations. The toluene/ benzene ratio (w/w) provided useful information in determining the degree of vehiclerelated air pollution and supported evidence obtained from dynamometer studies o f dealkylation o f higher aromatics to benzene in engines operating at high speed and load at the m o t o r w a y site.
INTRODUCTION
Considerable concern has recently been expressed about volatile organic compounds in the atmosphere because of their role in the formation of ozone and organic aerosols and since volatile organics may themselves have adverse health effects (Singh et al., 1982; Harkov, 1982). The potential health effects of benzene, and to a lesser extent alkylbenzenes, are of most concern because of their known carcinogenicity (Goodwin, 1980). As a result, benzene is the volatile organic compound most heavily scrutinised by regulatory decision makers. Various occupational and ambient air quality standards have been proposed for its control (Goldstein, 1983; Sartorius et al., 1983).
266
In Europe, considerable public and scientific debate over the environmental effects of lead emissions from vehicle exhausts has resulted in increasing pressure on governments to introduce legislation to limit the lead content in petrol. In the United Kingdom (U.K.) the lead content is to be reduced from 0.4g1-1 to 0.15g1-1 by the end of 1985 (Government of Great Britain, 1980), the limit currently adopted in the Federal Republic of Germany (F.R.G.) and Sweden (Associated Octel, 1982). The British government is committed to lead-free petrol by a target date of 1990 (Government of Great Britain, 1983). This initiative within the European Economic Communities (EEC) already has the support of the F.R.G., the Netherlands and Denmark, and the Commission has been requested by the Council of EEC Environment Ministers to examine ways of reducing lead in petrol, including eliminating it altogether (National Society for Clean Air, 1983). Due to changing refinery practice (increasing use of catalytic reformate) and the need to maintain octane numbers, it has been predicted that the content of aromatic hydrocarbons in petrol will increase by approximately 20% (Hall et al., 1983) in countries reducing the lead content to 0.15g1-1 in petrol. The changing situation in Europe with respect to the lead content of petrol and its associated aromatic content is presented in Table 1. The major aromatic compounds present in petrol are benzene, toluene, ortho-, metaand para-xylenes and ethylbenzene. The annual emission of benzene into the atmosphere in the F.R.G. amounts to approximately 55000--70000ty-' of which 90% is derived from motor vehicles (Sartorius et al., 1983). Similar quantities of toluene and C 8-alkylbenzene are also emitted from either motor vehicles or from their use as solvents in industry. The increasing aromatic content of petrol will also result in elevated ambient atmospheric concentrations of these compounds as a consequence of evaporative losses and vehicle exhaust emissions (Oelert et al., 1974). It is generally accepted that the aromatic content of petrol is associated with emissions of polycyclic aromatic hydrocarbons (PAH) either in the gas phase or associated with particulates, although the exact relationship has been a point of some contention (Pedersen et al., 1980; Candeli et al., 1983; Jacob, 1983; Nunnemann, 1983). Many PAH compounds have proven carcinogenic or mutagenic properties (Haroz, 1983). In addition the lead scavengers 1,2~libromoethane (EDB) and 1,2
267 TABLE 1 LEAD AND AROMATIC HYDROCARBON CONTENT OF EUROPEAN PREMIUM PETROL (after Associated Octel, 1981, 1982) Country
Italy France U.K. F.R.G.
Lead content
Aromatic content
(g1-1 )
(% v/v)
1980
1981
1980
1981
0.64 0.5 0.45 0.15
0.38 0.39 0.38 0.14
29.0 33.1 35.1 42.7
32.6 36.8 34.5 43.1
MATERIALS AND METHODS A mobile air pollution laboratory, equipped for sampling and analysis of aromatic and halogenated hydrocarbons, non-methane hydrocarbons (NMHC), carbon monoxide (CO) and the meteorological parameters, temperature, wind speed and direction, was located at each site {Clark et al., 1984a). The m e t h o d for sampling and analysis of vehicle-related aromatic and halogenated hydrocarbons has been evaluated previously (Clark et al., 1982) and a full description of the m e t h o d can be found elsewhere (Clark et al., i 9 8 4 b ) . Therefore, only a brief summary of the method is presented. Ambient air was drawn from a Teflon duct through two stainless steel sampling tubes packed with Tenax GC (0.13g, 3 5 / 6 0 m e s h , Chrompack Ltd., London, U.K.) at a flow-rate of 1 0 0 m l min -1 for 2 0 m i n in order to maintain a sampling efficiency of at least 99% at 2 0 ° C for both aromatic and halogenated hydrocarbons. The tubes were then thermally desorbed into either an electron capture (EC) or flame ionisation detector (FID) equipped Hewlett Packard 5700 A gas chromatograph (Hewlett Packard Ltd., Winnersh, U.K.). Calibration for all determinands was achieved by direct injection of standard atmospheres of various concentrations in glass flasks, established by static dilution of headspace vapour of the pure compounds. A Teflon tube (0.62 mm diameter) was connected via a glass-lined stainless steel inlet port in the duct through which sample air was drawn in order to minimise losses due to degradation or adsorption, to a Beckman model 6800 Air Quality Chromatograph (Beckman Ltd., Peterborough, U.K.). Daily measurements of total particulate and organic lead in ambient air were also carried o u t for reference purposes at the urban and m o t o r w a y sites and 48 h measurements at the rural site at a height of 4 m , utilising the m e t h o d developed b y Birch et al. (1980). The use of sites of contrasting degrees of vehicle influence, two sites influenced greatly by traffic and one rural site used as a control, permits the
268
relationship between traffic and air quality to be assessed. This dualmonitoring approach was suggested by Ott {1977) as the most suitable in assessing traffic-related pollutants. In order to assess the concentrations of aromatic and halogenated hydrocarbons in ambient air in relation to traffic density and vehicular driving mode, three contrasting sites were chosen. The monitoring period at each site was approximately 4 weeks, from 8 May 1983 to 7 August 1983, with an intensive week of sampling for aromatic and halogenated hydrocarbons at each site. The urban site (Exhibition Road, London SW7) is a dual carriageway running north--south, surrounded by buildings approximately 15 m high and at this site the mobile laboratory was located approximately 5 m from the kerb. The rural site, chosen as a control, was at Silwood Park (approximately 45 km southwest of central London) in a field adjacent to a group of small buildings. The nearest road, shielded by woodland, was approximately 1 km from the sampling site. The third site was approximately 15 m from the M1 m o t o r w a y near T o d d i n g t o n , Bedfordshire, in open undulating countryside (approximately 65 km from central London). Multiple regression analysis of NMHC and CO data (both primary trafficrelated pollutants) was undertaken in an attempt to define the relative importance of meteorological variables in determining observed pollutant concentrations. The following multiple regression equation, suggested by Keddie et al. (1979) which also accounts for persistence in emissions and meteorological variables, was adopted. lnc
= a+bl
lnu+b2
lnT+b3
lnc I
(1)
where c = the ambient pollutant concentration; c 1 = the previous hourly concentration (lagged concentration); u = t h e wind speed and T = the ambient temperature. The constants a, b l, b2 and b3 are the regression coefficients.
RESULTS A summary of hourly aromatic and halogenated hydrocarbons ambient air concentrations at the three sites is presented in Table 2. Concentrations of all aromatic hydrocarbons were most elevated at the urban site compared to the rural and m o t o r w a y sites. Highest arithmetic mean (~) and maximum hourly concentrations were found for benzene ( ~ = 9 . 7 p p b ) , maxim u m = 26.4 ppb) and toluene (~ = 15.5 ppb, maximum = 42.2 ppb). Hourly arithmetic mean concentrations of EDC were 0.30 p p b with a maximum of 0.87 ppb, whilst EDB displayed a mean concentration of 0.03 p p b with a maximum of 0.08 ppb. Measured concentrations for both aromatic and halogenated hydrocarbons at the rural site were up to one order of magnitude lower than at the urban site. Arithmetic mean hourly concentrations for benzene, toluene,
2
0.07 15.67
0.00 1.14
0.17 0.26
0.00 0.70
0.14 0.11
0.05 2.17
0.78 0.49
ethylbenzene
1 ppb benzene s 3.25 ef rns3 ; 1 ppb toluene E 3.85pg lppb EDC E 4.12pgm ; 1 ppb EDB E 7.8 l.(g me3
0.06 12.72
2.69 2.66
2.6 2.02
minimum maximum n = 184
0.20 6.40
0.40 5.00
minimum maximum n = 204 Motorway mean (X) standard deviation ((T)
1.27 0.90
0.84 42.37
0.64 26.42
1.64 0.80
15.54 8.83
toluene
(ppb)
6.96 5.41
benzene
Concentration
mean (Z) standard deviation (u)
mean (q standard deviation (u) minimum maximum n = 267 Rural
Urban
Site
m-3
; 1 ppb
0.00 6.41
1.02 0.98
0.00 4.10
0.50 0.31
0.11 6.30
2.30 1.32
ethylbenzene
m- and p-xylene
g 4.42pg
0.00 2.06
0.27 0.35
0.00 3.70
0.21 0.08
0.02 2.27
0.77 0.45
o-xylene
me3
; 1 ppb
z 4.42pg
me3
0.00 0.15
0.00 0.10 8.20
0.04 0.30
0.04
0.00
0.019 0.01
0.01 0.08
0.03 0.02
EDB
AT
0.00
0.02 0.18
0.10
1.29 1.07
0.00
0.02 0.02
0.71 0.63
4.24
0.03 0.87
0.06 8.50
0.00
0.30 0.12
3.07 1.84
EDC
MEASURED
xylenes
total xylenes
SUMMARY OF HOURLY CONCENTRATIONS OF AROMATIC AND HALOGENATED HYDROCARBONS THE URBAN, RURAL AND MOTORWAY SITES DURING INTENSIVE SAMPLING PERIODS
TABLE
;
270 TABLE 3 CONCENTRATIONS OF PARTICULATE AND ORGANIC LEAD MEASURED AT THE URBAN, RURAL AND MOTORWAY SITES Site
Exhibition Road (urban) n=7 Silwood Park (rural) n=4 Toddington (motorway)
Particulate lead
Organic lead
Total lead
(ng m -3 )
(ng m -3 )
(ng m -3 )
208
18
222
92
3.8
95.7
196
15
211
n=7
ethylbenzene, total xylenes, ECD and EDB were 1.64, 1.27, 0.71, 0.02 and 0 . 0 1 9 p p b , respectively. Maximum concentrations were also lower than at the urban site. At the m o t o r w a y site concentrations were higher than at the rural site but lower than at the urban except in the case of EDB. Arithmetic mean hourly concentrations for benzene, toluene, ethylbenzene, total xylenes, ECD and EDB were 2.6, 2.69, 0.17, 1.29, 0.02 and 0 . 0 4 p p b , respectively. The maximum hourly EDB concentration was 0.15 p p b as compared to 0.08 ppb at the urban sites. Concentrations of particulate and organic lead measured at the urban, rural and m o t o r w a y sites are presented in Table 3. Concentrations of both particulate and organic lead were similar at the urban and m o t o r w a y sites (208 and 1 9 6 n g m -3, particulate lead; 18 and 1 5 n g m -3, organic lead, respectively). At the rural site, concentrations of particulate and organic lead were lower (92 ng m -3 and 3.7 ng m -3 , respectively). Diurnal averages for aromatic and halogenated hydrocarbons are presented in Fig. la--f. The diurnal variation of aromatic hydrocarbons compared favourably with the diurnal averages for NMHC and CO at the three sites presented in Fig. 2a--f (particularly at the urban site). Correlation analysis was performed on the aromatic and halogenated hydrocarbons data from the three sites. In general, only benzene and toluene were consistently well correlated with coefficients of 0.96 (urban site), 0.86 (rural site) and 0.94 (motorway site) being determined. Reasonable correlations between EDC and EDB were found at the urban site (0.76) and the m o t o r w a y site (0.60). At the urban site, the wind direction was predominantly from the northeast (30 ° ) (approximately parallel to the road) with wind speeds generally between 3 and 4 m s -1 . The wind direction at the rural site was far more variable and generaly emanated from the 240--90 ° arc with wind speeds > 6 m s -1 frequently occurring. In contrast, low windspeeds were recorded at the m o t o r w a y site which were consistently below 4 m s -1 during the monitoring period. In addition, the wind direction occurred in the
2
2
6
14
14
(b)
10
(PI
10
6
18
18
Time
22 h
Time
22 h
of
of
day
a04 0.
9
day
0.1
L 2
-
6
_ A.,
_'
1
14 (f)
10
(c
I8
22 h
_'c
-EEC ---ED
B
Fig. 1. Diurnal average concentrations of aromatic and halogenated hydrocarbons at the three sites. (a) Exhibition Road; (b) Silwood Park; (c) Toddington; (d) Exhibition Road; (e) Silwood Park; (f) Toddington.
(d)
(a)
272
0.8 0-7
0.8 0"7
0'8 0-7
0"6
0.6
NMHC ppm
0.5
0.5
0"5
0"4
0"4
O.Z,
0.3
0-3
0.3
0.2
0.2
0.1
0-1
0
I
I
I
2
6 10
I
I
01
I
14 18 2 2 h
I
0
I
(a)
CO pprn
I
(b)
L Time
o of
+.oil+.° I
4"0
3"0
3-0
2"0
20
1"0
1"0
I
I
2
6
I
10 14
(d)
I
I
18 22 h
0
I
I
I
I
10 14 18 22h (c)
+10F
4"0
3"0
I
I
6
day
40
0 /
I
2
2-0
1"0
I
I
I
2
6
10
I
~
t
0
14 16 2 2 h
(e)
Time of dciy
i
i
2
6
[
I
i
I
10 14 18 22h
(!)
Figure 2. Diurnal average concentrations of N M H C and C O at the three sites. (a) Exhibition Road; (b) Silwood Park; (c) Toddington; (d) Exhibition Road; (e) Silwood Park; (f) Toddington.
150--180 ° arc for over 6 0 % of the time (i.e.away from the mobile laboratory towards the motorway). The individual and combined effects of the windspeed, temperature and lagged concentrations of N M H C and C O were estimated by applying Eqn. (1) and the multiple regression statisticsare presented in Table 4 (R 2 denotes the total explained variance and n is the number of hourly samples). This demonstrates that the single most important parameter evaluated was that of lagged concentrations. If not included, significantreductions in the total explained variance were calculated. However, a positive correlation was found between N M H C and temperature and, to a m u c h lesser extent, with C O and temperature at this site. Similarly, a positive correlation was determined at the rural sitefor N M H C and temperature and also wind speed. A negative correlation was calculated for C O and wind speed at this site and at the motorway site.In contrast to the other two sites, a negative correlation was found between N M H C and temperature at the motorway site.
DISCUSSION
At the three contrasting sites (urban, rural and motorway) highest mean and m a x i m u m concentrations of aromatic hydrocarbons and E D C were
273 TABLE 4 MULTIPLE REGRESSION SITES
Site
Urban Rural Motorway
Compound
NMHC CO NMHC CO NMHC CO
STATISTICS AT THE URBAN, RURAL AND MOTORWAY
n
572 562 539 518 449 356
a
-- 1.64 -- 0.21 a -- 0.85 --0.21 a -- 0.44 a -- 0.74
Wind b1
speed
0.04 a 0.01 a 0.08 --0.08 0.08 -- 0.07
Temperature
Lagged
b2
cone.
0.48 0.09 0.24 0.06 a -- 0.32 0.14 a
0.75 0.87 0.88 0.80 0.79 0.60
R2
67.7 75.7 84.7 72.0 67.3 45.3
aNot significant at the 5% level.
exhibited at the urban site (EDB concentrations were slightly higher at the m o t o r w a y site). The major sources of these c o m p o u n d s in the atmosphere are vehicle emissions (Harkov, 1982). H y d r o c a r b o n emissions have been shown to be dependent on driving mode and are most elevated during deceleration and acceleration, a driving mode typical of urban roads. In addition evaporative losses from vehicles can also contribute between 20 and 30% of the total hydrocarbon vehicle emissions (Black et al., 1980; Nelson et al., 1979). The multiple regression analysis provided information on the role of temperature in defining observed concentrations of NMHC due to evaporative losses of aromatic hydrocarbons as they account for approximately 30% (by weight) of the NMHC (Nelson and Quigley, 1982; Nutmagul et al., 1983). At the urban site this relationship was demonstrated by the significant positive correlation of 0.48. In contrast, CO showed only a weak correlation with temperature which does not imply a causative relationship. At the urban site, wind speed had no significant correlation with either CO or NMHC demonstrating that the measured concentrations are typical of those found in London as confirmed by a recent review of air pollution in this city (Schwar and Ball, 1983). The diurnal pattern of the aromatic hydrocarbons at this site was similar to that observed in Los Angeles (Altshuller and Bufalini, 1971) to that observed in a previous survey at the same site (Clark et al., 1984b). However, the diurnal variation of benzene is more pronounced than that observed in three large cities in the United States (Singh et al., 1982). The arithmetic mean aromatic hydrocarbon data compare well with other reported values compiled in Table 5 which utilised a variety of analytical techniques for the preconcentration of ambient air samples. In the F.R.G. an ambient air quality standard of 3 0 # g m -3 ( 9 . 2 p p b ) for benzene annual average has been recently recommended by the Federal Environmental Agency (Sartorius et al., 1983). As can be seen from Table 5, ambient air concentrations above this proposed standard are frequently
1975 1975 (Nov) 1976
The Hague Berlin
Johannesburg Los Angeles Sydney New Jersey Newark Elizabeth Camden London London
1968 1971 1971
Los Angeles Zurich Toronto
3.4 6.04 2.6 1.03 1.05 1.11 8.8 9.69
1981 1981 1981 1982 1983
4.65 2.89 1.82 13.5 15.5
10.3 11.72 8.9
38.4
27.4
15.1 18.1
17.9 26.1
37.0 39.0 30.0
toluene
8.9 15.1
15.0 54.0 13.0
benzene
0.33 0.26 0.17 0.88 0.78
1.9 2.25 1.3
-
-
3.1 -
6.0 8.7 9.0 -
0.99 0.75 0.49 2.8 2.30
4.5 4.61 1.3
22.6
13.6
12.4 18.1
21 -
p-xylene
0.26 0.22 0.15 1.2 0.77
1.6 1.93 1.5
-
3.1 -
8 9.3
o-xylene
Clark et al. (1984b) This work
Harkov et al. (1983)
Louw et al. (1977) Singh et al. (1982) Nelson and Quigley (1982)
Lonneman et al. (1968) Grob and Grob (1971) Pilar and Graydon (1973) Burghardt and Jeltes (1975) Seifert and Ulrich (1978)
Reference
MEASURED AT DIFFERENT LOCATIONS
23
m-xylene
CONCENTRATIONS
ethylbenzene
HYDROCARBON
Concentration (ppb)
(Nov) 1977 1979 1980
1976
(Jul)
Year
Location
COMPARISON OF AROMATIC
TABLE 5
275 found in many European and American cities. The most serious consequence of a high benzene intake is leukemia (Goodwin, 1980). In addition, the long term exposure to relatively low concentrations of benzene and other aromatic hydrocarbons is an area of increasing concern (Harkov et al., 1983). EDC concentrations were highest at the urban site (~ = 0.30 ppb) which compared well with values of 0.22 and 0.26 ppb determined at the same site in 1979 and 1982, respectively (Tsani-Bazaca et al., 1981, Clarke et al., 1984b) and to concentrations derived at sites in Iberville, LA (~ = 0.34 ppb) and Los Angeles (~-- 0.52 ppb) in the United states (Pellizzari, 1982; Singh et al., 1982). EDB concentrations {~ = 0.03 ppb) measured at the urban site were identical to concentrations measured at the same site previously (Clark et al., 1984b). Measured EDB concentrations are also in the same range ( 0 . 0 1 - - 0 . 0 4 p p b ) as determined by other workers (Johns, 1976; Leinster et al., 1978; Tsani-Bazaca et al., 1981; Singh et al., 1982) at similar locations. Concentrations of both aromatic and halogenated hydrocarbons were low at the rural site and compared well with data obtained from the same site previously (Clark et al., 1984b). The low level concentrations were primarily related to the low incidence of vehicular pollutant sources in the area. NMHC concentrations correlated positively with wind speed and temperature suggested that the majority of emissions were derived from vehicle NMHC (and consequently aromatic and halogenated hydrocarbons) concentrations can be considered typical of background concentrations. At the m o t o r w a y site, vehicle numbers passing the laboratory were high ( ~ 3500 vehicles an hour). However, the low emission rates of hydrocarbons from vehicles travelling at constant high speeds and the predominant wind pattern resulted in low concentrations of measured aromatic hydrocarbons and EDC. A comparatively strong negative correlation of NMHC with temperature suggested that the majority of emissions were derived from vehicle exhaust and that high temperatures increased atmospheric turbulence, thus reducing measured concentrations. Concentrations of both aromatic and halogenated hydrocarbons were similar to those measured at the same site previously (Clark et al., 1984b). The particulate and organic lead concentrations measured at the urban and rural sites were comparable with those measured at the same sites previously and with data from other workers at similar locations (Birch et al., 1980; De Jonghe et al., 1981; Gibson and Farmer, 1981). Measurements of particulate lead were considerably lower than valuespresented by Clark et al. (1984b) at the same site. However, the predominant wind direction pattern (along the axis of the road towards the mobile laboratory) was considerably different to that determined in this study (away from the mobile laboratory towards the motorway). The proportion of organic lead to total lead, expressed as a percentage, varied between 3.9% at the rural site to 8.1% at the urban site, which is in accord with the results of other workers and indicates the importance of evaporative
276
emissions of organic lead at the urban site (Harrison and Perry, 1977; De Jonghe et al., 1981). Lonneman et al. (1968) have suggested that the toluene/benzene ratio can be used as an indication of the extent to which m o t o r traffic emissions contribute to air pollution. Criticism of the applicability of this ratio has been expressed, because of the variation in the concentrations of these compounds in petrol (Ioffe et al., 1979). However, it has been suggested that the ratio may be used to determine the degree of vehicle-related air pollution only when the variation of the toluene/benzene ratio in petrol is low (Clark et al., 1984b). Supporting evidence for this is provided by this study and others where toluene and benzene concentrations have been found to correlate well (Tsani-Bazaca et al., 1981; Harkov et al., 1983). Samples of premium and regular grade petrol, recently surveyed in the southeast of the U.K., gave an average toluene/benzene ratio of 2.79 + 0.7 in 1983 (Associated Octel, personal communication). The ratio derived from the site was 1.59 on a weight-to-weight basis. This ratio is slightly lower (1.81) than that determined at this site previously (Clark et al., 1984b) and also those compiled in Table 5, excluding this work (2.78 + 0.89). It must be noted that many of the studies cited in Table 5 contained considerably fewer samples than this study. The ratio of 0.91 at the rural site and the low level of aromatic hydrocarbons indicated that the air mass sampled was aged, as toluene is subject to more rapid photochemical decay than benzene (Hov et al., 1978). A number of workers have demonstrated through d y n a m o m e t e r studies that dealkylation of toluene, xylenes and other alkylbenzenes can occur under conditions of high engine speed and load (Oelert et al., 1974; Perry et al., 1983). Indeed, Black et al. (1980) and Morris and Dishart (1971) have suggested that this process is the critical factor in defining vehicular benzene emissions. This is also reflected in the toluene/benzene ratio of 1.00 at the m o t o r w a y site which is considerably lower than that determined at the urban site.
CONCLUSIONS
Aromatic hydrocarbon concentrations monitored at the urban site are higher than at the rural or m o t o r w a y sites and are comparable with those measured in urban areas in other countries. Multiple regression techniques at the urban site have demonstrated the importance of ambient temperature in defining measured concentrations which are typical of those found in London. Ambient air concentrations of benzene at this site are frequently in excess of a proposed ambient air quality standard in the F.R.G. The low hydrocarbon emission rates of vehicles travelling at constant high speed and the predominant wind direction resulted in low measured concentrations of aromatic hydrocarbons at the m o t o r w a y site compared to the urban site. Multiple regression techniques suggested that the majority of emissions were
277 derived f r o m vehicle e x h a u s t and n o t evaporative losses. The low a r o m a t i c h y d r o c a r b o n s c o n c e n t r a t i o n s m e a s u r e d at the rural site can be c o n s i d e r e d representative o f b a c k g r o u n d c o n c e n t r a t i o n s . A m b i e n t c o n c e n t r a t i o n s o f EDC and EDB at all t h r e e sites were low and c o m p a r a b l e with o t h e r p u b l i s h e d data. T h e use o f the t o l u e n e / b e n z e n e ratio in d e t e r m i n i n g the degree o f vehiclerelated air p o l l u t i o n , w h e n the range in variation o f these c o m p o u n d s in p e t r o l is low, has been validated. T h e ratio derived at the u r b a n site was considerably higher t h a t at the rural and m o t o r w a y sites. In addition, the ratio d e t e r m i n e d at the m o t o r w a y site s u p p o r t s evidence o b t a i n e d f r o m d y n a m o m e t e r studies o f a d e a l k y l a t i o n process o f t o l u e n e , x y l e n e and higher alkylb e n z e n e s in vehicle engines o p e r a t i n g at high speed and load, increasing b e n z e n e emissions.
REFERENCES Altshuller, A. P. and J. F. Bufalini, 1971. Photochemical aspects of air pollution: a review. Environ. Sci. Technol., 5: 39---63. Associated Octel, 1981. Octel Group Gasoline Survey and a Review of European Quality 1980. The Associated Octel Company Limited, London, U.K. Associated Octel, 1982. Octel Group Gasoline Survey and a Review of European Quality 1981. The Associated Octel Company Limited, London, U.K. Birch, J., R. M. Harrison and D. H. Laxen, 1980. A specific method for 24--48 hour analysis of tetraalkyl lead in air. Sci. Total Environ., 14: 31--42. Black, F. M., L. E. High and J. M. Lang, 1980. Composition of automobile evaporative and tailpipe hydrocarbon emissions. J. Air Pollut. Control Assoc., 30: 1216--1221. Burghardt, E. and R. Jeltes, 1975. Gas chromatographic determination of aromatic hydrocarbons in air using semi-automatic preconcentration method. Atmos. Environ., 9: 935--940. Candeli, A., G. Morozzi and M. Shapiro, 1983. PAH content of exhaust gases from fuels with different aromatic fraction. In: D. Rondia, M. Cooke and R. K. Haroz (Eds.), Mobile Source Emissions Including Polycyclic Organic Species. Reidel, Dordrecht, The Netherlands, 29--49. Clark, A. I., A. E. McIntyre, J. N. Lester and R. Perry, 1982. Evaluation o f a Tenax GC sampling procedure for collection and analysis of vehicle-related aromatic and halogenated hydrocarbons in ambient air. J. Chromatogr., 252: 147--157. Clark, A. I., A. E. McIntyre, J. N. Lester and R. Perry, 1984a. Air quality impact assessment. Environ. Monit. Assess., 4: 204--233. Clark, A. I., A. E. McIntyre, J. N. Lester and R. Perry, 1984b. Monitoring and assessment of ambient atmospheric concentrations of aromatic and halogenated hydrocarbons at urban, rural and motorway locations. Environ. Pollut. (Ser. B), 7: 141--158. De Jonghe, W. A., D. Chakraborti and F. C. Adams, 1981. Indentification and determination of individual tetraalkyl lead species in air. Environ. Sci. Technol., 15: 1217-1222. Gibson, M. J. and F. G. Farmer, 1981. Tetraalkyl lead in the. urban atmosphere of Glasgow. Environ. Technol. Lett., 2: 521--530. Goldstein, B. D., 1983. Toxic substances in the atmospheric environment. J. Air Pollut. Control Assoc., 33: 454--465. Goodwin, D. R., 1980. Benzen fugitive emissions -- background information for proposed standards. Environmental Protection Agency, Report No. EPA-450/3-80-032a., Washington, DC, U.S.A.
278 Government of Great Britain, 1980. Lead Pollution. Hansard, Column 483, H.M.S.O., London, U.K. Government of Great Britain, 1983. Response to the Ninth Report of the Royal Commission on Environmental Pollution. Pollution Paper No. 19, Department of the Environment, Central Directorate on Environmental Pollution, H.M.S.O., London, U.K. Grob, K. and G. Grob, 1971. Gas--liquid chromatographic--mass spectrometric investigation of C6--C20 organic compounds in an urban atmosphere. An application of ultra trace analysis on capillary columns. J. Chromatogr., 62: 1--13. Hall, C. A., U.S. Willoughby and B. J. French, 1983. Effect of lead antiknock regulations on gasoline aromatics and aromatic exhaust emissions. In: D. Rondia, M. Cooke and R. K. Haroz (Eds.), Mobile Source Emissions Including Polycylic Organic Species. Reidel, Dordrecht, The Netherlands, 59--76. Harkov, R., 1982. Toxic air pollutants -- assessing their importance. Sci. Total Environ., 26: 67--85. Harkov, R., B. Kebbekus, J. W. Bozzelli and P. J. Lioy, 1983. Measurement of selected volatile organic compounds at three locations in New Jersey during the summer season. J. Air Pollut. Control Assoc., 33: 1177--1183. Haroz R., 1983. The toxicology of polycyclic organic matter from exhaust gases. In: D. Rondia, M. Cooke and R. K. Haroz (Eds.), Mobile Source Emissions Including Polycyclic Organic Species. Reidel, Dordrecht, The Netherlands, 77--87. Harrison, R. M. and R. Perry, 1977. The analysis of tetraalkyl lead compounds and their significance as urban air pollutants. Atmos. Environ., 11: 847--852. Hov, O., I. S. A. Isaksen and E. Hesstvedt, 1978. Diurnal variations of ozone and other pollutants in an urban area. Atmos. Environ., 12: 2469--2479. Ioffe, B. V., V. A. Isidorov and I. G. Zenkevich, 1979. Certain regularities in the composition of volatile organic pollutants in the urban atmosphere. Environ. Sci. Technol., 13: 864--868. Jacob, J., 1983. Carcinogenic impact from automobile exhaust condensate and the dependence of the PAH-profile on various parameters. In: D. Rondia, M. Cooke and R. K. Haroz (Eds.), Mobile Source Emissions Including Polyc:~clic Organic Species. Reidel, Dordrecht, The Netherlands, 159--165. Johns, R., 1976. Air Pollution Assessment of Ethylene Dibromide. Environmental Protection Agency, Report No. MTR-7222/PB 256736, Washington DC, U.S.A. Keddie, A. W. C., J. S. Bower, R. A. Maughan, G. H. Roberts and F. P. Williams, 1979. The measurement assessment and prediction of air pollution in the F o r t h Valley of Scotland - - final report. Warren Spring Laboratory, Report No. LR279 (AP), Stevenage, U.K. Leinster, P., R. Perry and R. J. Young, 1978. Ethylene dibromide in urban air. Atmos. Environ., 12: 2383--2387. Lonneman, W., T. Bellar and A. P. Altshuller, 1968. Aromatic hydrocarbons in the Los Angeles Basin. Environ. Sci. Technol., 2: 1017--1020. Louw, C. W., J. F. Richards and P. K. Faure, 1977. Determination of volatile organic compounds in city air by gas chromatography combined with standard addition, selective subtraction, infrared spectrometry and mass spectrometry. Atmos. Environ., 11: 703--717. Morris, W. E. and K. T. Dishart, 1971. Influence of vehicle emission control systems on the relationship between gasoline and vehicle exhaust hydrocarbon composition. In: American Society for Testing and Materials, ASTM Special Technical Publication 487, Philadelphia, PA, U.S.A., 63--101. National Society for Clean Air, 1983. Government measures announced in full. Clean Air, 13: 101--104. Nelson, P. F., S. M. Quigley and E. Y. Smith, 1979. Sources of atmospheric hydrocarbons in Sydney. Proc. Seventh Int. Clean Air Conf., Adelaide, Australia, 61--79.
279 Nelson, P. F. and S. M. Quigley, 1982. Non-methane hydrocarbons in the atmosphere of Sydney, Australia. Environ. Sci. Technol., 16: 650--655. Nunnemann, F., 1983. The influcence of fuel composition on PAH-emlssion. A methodical consideration. In: D. Rondia, M. Cooke and R. K. Haroz (Eds.), Mobile Source Emissions Including Polycyclic Organic Species. Reidel, Dordrecht, The Netherlands, 211--222. Nutmagul, W., D.R. Cronn and H.H. Hill, 1983. Photoionisation/flame ionisation detection of atmospheric hydrocarbons after capillary gas chromatography. Anal. Chem., 55: 2160--2164. Oelert, H. H., W. Mayer-Gtirr and J. Zagontz, 1974. Zur motorischen verbrennung yon Benzinkohlenwasserstoffen. Erdol Kohle, 27: 146--152. Ott, W.R., 1977. Development of criteria for siting air monitoring stations. J. Air Pollut. Control Assoc., 27: 543--547. Pedersen, P. S., J. Ingwersen, T. Nielsen and E. Larsen, 1980. Effect of fuel, lubricant, and engine parameters on the emission of polycyclic aromatic hydrocarbons. Environ. Sci. Technol., 14: 71--79. Pellizzari, E. D., 1982. Analysis of organic vapour emissions near industrial and chemical waste disposal sites. Environ. Sci. Technol., 16: 781--785. Perry, R., A. E. McIntyre, J. N. Lester and A. Clarke, 1983. Vehicle emission controls and energy - - the role of aromatics and lead compounds. In: D. Rondia, M. Cooke and R. K. Haroz (Eds.), Mobile Source Emissions Including Polycyclic Organic Species. Reidel, Dordrecht, The Netherlands, 247--259. Pilaf, S. and W. F. Graydon, 1973. Benzene and toluene distribution in Toronto atmosphere. Environ. Sci. Technol., 7: 628--631. Sartorius, R., S. Dobbertin and A. Friedrich, 1983. Umweltbelastung und Wirkung von Benzol auf die menschliche Gesundheit. Staub-Reinhalt. Luft. 43: 112--115. Schwar, M. J. R. and D. J. Ball, 1983. Thirty Years On -- A Review of Air Pollution in London. Greater London Council, U.K. Seifert, V.B. and D. Ullrich, 1978. Konzentration anorganischer und organischer Luftschadstoffe an einer Stra~enkreuzung in Berlin. Staub-Reinhalt. Luft, 38: 359-364. Singh, H. B., L. J. Salas and R. E. Stiles, 1982. Distribution of selected gaseous organic mutagens and suspect carcinogens in ambient air. Environ. Sci. Technol., 16: 872-880. Tsani-Bazaca, E., A. E. McIntyre, J. N. Lester and R. Perry, 1981. Concentrations and correlations o f 1,2-dibromoethane, 1,2-dichloroethane, benzene and toluene in vehicle exhaust and ambient air. Environ. Technol. Lett., 2: 303--316.
265
AMBIENT AIR MEASUREMENTS OF AROMATIC A N D HALOGENATED HYDROCARBONS AT URBAN, R U R A L A N D MOTORWAY LOCATIONS
A. I. CLARK, A. E. McINTYRE, J. N. LESTER and R. PERRY Public Health and Water Resource Engineering, Imperial College, London S W 7 2BU (United Kingdom) (Received 23rd February, 1984; accepted 10th March, 1984)
ABSTRACT
Concern over the carcinogenic properties o f certain volatile organics in air, particularly benzene, has recently been expressed. Reductions in the lead content of petrol in the United Kingdom and other European countries are predicted to change the concentrations of aromatic and halogenated hydrocarbons (1,2-dichloroethane and 1,2-dibromoethane) in ambient air. In order to provide baseline air quality data, prior to progressive reductions in the lead content of petrol, this study reports the results of a monitoring survey of ambient air concentrations o f aromatic and halogenated hydrocarbon concentrations at urban, rural and m o t o r w a y locations. A thermal desorption/gas chromatographic method analysing Tenax GC sampling tubes was utilised. Highest concentrations for benzene (9.7 ppb) and toluene (15.5 ppb) were measured at the urban site. The average benzene concentration is comparable with a proposed ambient air quality standard in the Federal Republic of Germany. Multiple regression analysis of nonmethane hydrocarbon and carbon monoxide air quality data demonstrated the importance o f meteorological variables in defining measured concentrations. The toluene/ benzene ratio (w/w) provided useful information in determining the degree of vehiclerelated air pollution and supported evidence obtained from dynamometer studies o f dealkylation o f higher aromatics to benzene in engines operating at high speed and load at the m o t o r w a y site.
INTRODUCTION
Considerable concern has recently been expressed about volatile organic compounds in the atmosphere because of their role in the formation of ozone and organic aerosols and since volatile organics may themselves have adverse health effects (Singh et al., 1982; Harkov, 1982). The potential health effects of benzene, and to a lesser extent alkylbenzenes, are of most concern because of their known carcinogenicity (Goodwin, 1980). As a result, benzene is the volatile organic compound most heavily scrutinised by regulatory decision makers. Various occupational and ambient air quality standards have been proposed for its control (Goldstein, 1983; Sartorius et al., 1983).
266
In Europe, considerable public and scientific debate over the environmental effects of lead emissions from vehicle exhausts has resulted in increasing pressure on governments to introduce legislation to limit the lead content in petrol. In the United Kingdom (U.K.) the lead content is to be reduced from 0.4g1-1 to 0.15g1-1 by the end of 1985 (Government of Great Britain, 1980), the limit currently adopted in the Federal Republic of Germany (F.R.G.) and Sweden (Associated Octel, 1982). The British government is committed to lead-free petrol by a target date of 1990 (Government of Great Britain, 1983). This initiative within the European Economic Communities (EEC) already has the support of the F.R.G., the Netherlands and Denmark, and the Commission has been requested by the Council of EEC Environment Ministers to examine ways of reducing lead in petrol, including eliminating it altogether (National Society for Clean Air, 1983). Due to changing refinery practice (increasing use of catalytic reformate) and the need to maintain octane numbers, it has been predicted that the content of aromatic hydrocarbons in petrol will increase by approximately 20% (Hall et al., 1983) in countries reducing the lead content to 0.15g1-1 in petrol. The changing situation in Europe with respect to the lead content of petrol and its associated aromatic content is presented in Table 1. The major aromatic compounds present in petrol are benzene, toluene, ortho-, metaand para-xylenes and ethylbenzene. The annual emission of benzene into the atmosphere in the F.R.G. amounts to approximately 55000--70000ty-' of which 90% is derived from motor vehicles (Sartorius et al., 1983). Similar quantities of toluene and C 8-alkylbenzene are also emitted from either motor vehicles or from their use as solvents in industry. The increasing aromatic content of petrol will also result in elevated ambient atmospheric concentrations of these compounds as a consequence of evaporative losses and vehicle exhaust emissions (Oelert et al., 1974). It is generally accepted that the aromatic content of petrol is associated with emissions of polycyclic aromatic hydrocarbons (PAH) either in the gas phase or associated with particulates, although the exact relationship has been a point of some contention (Pedersen et al., 1980; Candeli et al., 1983; Jacob, 1983; Nunnemann, 1983). Many PAH compounds have proven carcinogenic or mutagenic properties (Haroz, 1983). In addition the lead scavengers 1,2~libromoethane (EDB) and 1,2
267 TABLE 1 LEAD AND AROMATIC HYDROCARBON CONTENT OF EUROPEAN PREMIUM PETROL (after Associated Octel, 1981, 1982) Country
Italy France U.K. F.R.G.
Lead content
Aromatic content
(g1-1 )
(% v/v)
1980
1981
1980
1981
0.64 0.5 0.45 0.15
0.38 0.39 0.38 0.14
29.0 33.1 35.1 42.7
32.6 36.8 34.5 43.1
MATERIALS AND METHODS A mobile air pollution laboratory, equipped for sampling and analysis of aromatic and halogenated hydrocarbons, non-methane hydrocarbons (NMHC), carbon monoxide (CO) and the meteorological parameters, temperature, wind speed and direction, was located at each site {Clark et al., 1984a). The m e t h o d for sampling and analysis of vehicle-related aromatic and halogenated hydrocarbons has been evaluated previously (Clark et al., 1982) and a full description of the m e t h o d can be found elsewhere (Clark et al., i 9 8 4 b ) . Therefore, only a brief summary of the method is presented. Ambient air was drawn from a Teflon duct through two stainless steel sampling tubes packed with Tenax GC (0.13g, 3 5 / 6 0 m e s h , Chrompack Ltd., London, U.K.) at a flow-rate of 1 0 0 m l min -1 for 2 0 m i n in order to maintain a sampling efficiency of at least 99% at 2 0 ° C for both aromatic and halogenated hydrocarbons. The tubes were then thermally desorbed into either an electron capture (EC) or flame ionisation detector (FID) equipped Hewlett Packard 5700 A gas chromatograph (Hewlett Packard Ltd., Winnersh, U.K.). Calibration for all determinands was achieved by direct injection of standard atmospheres of various concentrations in glass flasks, established by static dilution of headspace vapour of the pure compounds. A Teflon tube (0.62 mm diameter) was connected via a glass-lined stainless steel inlet port in the duct through which sample air was drawn in order to minimise losses due to degradation or adsorption, to a Beckman model 6800 Air Quality Chromatograph (Beckman Ltd., Peterborough, U.K.). Daily measurements of total particulate and organic lead in ambient air were also carried o u t for reference purposes at the urban and m o t o r w a y sites and 48 h measurements at the rural site at a height of 4 m , utilising the m e t h o d developed b y Birch et al. (1980). The use of sites of contrasting degrees of vehicle influence, two sites influenced greatly by traffic and one rural site used as a control, permits the
268
relationship between traffic and air quality to be assessed. This dualmonitoring approach was suggested by Ott {1977) as the most suitable in assessing traffic-related pollutants. In order to assess the concentrations of aromatic and halogenated hydrocarbons in ambient air in relation to traffic density and vehicular driving mode, three contrasting sites were chosen. The monitoring period at each site was approximately 4 weeks, from 8 May 1983 to 7 August 1983, with an intensive week of sampling for aromatic and halogenated hydrocarbons at each site. The urban site (Exhibition Road, London SW7) is a dual carriageway running north--south, surrounded by buildings approximately 15 m high and at this site the mobile laboratory was located approximately 5 m from the kerb. The rural site, chosen as a control, was at Silwood Park (approximately 45 km southwest of central London) in a field adjacent to a group of small buildings. The nearest road, shielded by woodland, was approximately 1 km from the sampling site. The third site was approximately 15 m from the M1 m o t o r w a y near T o d d i n g t o n , Bedfordshire, in open undulating countryside (approximately 65 km from central London). Multiple regression analysis of NMHC and CO data (both primary trafficrelated pollutants) was undertaken in an attempt to define the relative importance of meteorological variables in determining observed pollutant concentrations. The following multiple regression equation, suggested by Keddie et al. (1979) which also accounts for persistence in emissions and meteorological variables, was adopted. lnc
= a+bl
lnu+b2
lnT+b3
lnc I
(1)
where c = the ambient pollutant concentration; c 1 = the previous hourly concentration (lagged concentration); u = t h e wind speed and T = the ambient temperature. The constants a, b l, b2 and b3 are the regression coefficients.
RESULTS A summary of hourly aromatic and halogenated hydrocarbons ambient air concentrations at the three sites is presented in Table 2. Concentrations of all aromatic hydrocarbons were most elevated at the urban site compared to the rural and m o t o r w a y sites. Highest arithmetic mean (~) and maximum hourly concentrations were found for benzene ( ~ = 9 . 7 p p b ) , maxim u m = 26.4 ppb) and toluene (~ = 15.5 ppb, maximum = 42.2 ppb). Hourly arithmetic mean concentrations of EDC were 0.30 p p b with a maximum of 0.87 ppb, whilst EDB displayed a mean concentration of 0.03 p p b with a maximum of 0.08 ppb. Measured concentrations for both aromatic and halogenated hydrocarbons at the rural site were up to one order of magnitude lower than at the urban site. Arithmetic mean hourly concentrations for benzene, toluene,
2
0.07 15.67
0.00 1.14
0.17 0.26
0.00 0.70
0.14 0.11
0.05 2.17
0.78 0.49
ethylbenzene
1 ppb benzene s 3.25 ef rns3 ; 1 ppb toluene E 3.85pg lppb EDC E 4.12pgm ; 1 ppb EDB E 7.8 l.(g me3
0.06 12.72
2.69 2.66
2.6 2.02
minimum maximum n = 184
0.20 6.40
0.40 5.00
minimum maximum n = 204 Motorway mean (X) standard deviation ((T)
1.27 0.90
0.84 42.37
0.64 26.42
1.64 0.80
15.54 8.83
toluene
(ppb)
6.96 5.41
benzene
Concentration
mean (Z) standard deviation (u)
mean (q standard deviation (u) minimum maximum n = 267 Rural
Urban
Site
m-3
; 1 ppb
0.00 6.41
1.02 0.98
0.00 4.10
0.50 0.31
0.11 6.30
2.30 1.32
ethylbenzene
m- and p-xylene
g 4.42pg
0.00 2.06
0.27 0.35
0.00 3.70
0.21 0.08
0.02 2.27
0.77 0.45
o-xylene
me3
; 1 ppb
z 4.42pg
me3
0.00 0.15
0.00 0.10 8.20
0.04 0.30
0.04
0.00
0.019 0.01
0.01 0.08
0.03 0.02
EDB
AT
0.00
0.02 0.18
0.10
1.29 1.07
0.00
0.02 0.02
0.71 0.63
4.24
0.03 0.87
0.06 8.50
0.00
0.30 0.12
3.07 1.84
EDC
MEASURED
xylenes
total xylenes
SUMMARY OF HOURLY CONCENTRATIONS OF AROMATIC AND HALOGENATED HYDROCARBONS THE URBAN, RURAL AND MOTORWAY SITES DURING INTENSIVE SAMPLING PERIODS
TABLE
;
270 TABLE 3 CONCENTRATIONS OF PARTICULATE AND ORGANIC LEAD MEASURED AT THE URBAN, RURAL AND MOTORWAY SITES Site
Exhibition Road (urban) n=7 Silwood Park (rural) n=4 Toddington (motorway)
Particulate lead
Organic lead
Total lead
(ng m -3 )
(ng m -3 )
(ng m -3 )
208
18
222
92
3.8
95.7
196
15
211
n=7
ethylbenzene, total xylenes, ECD and EDB were 1.64, 1.27, 0.71, 0.02 and 0 . 0 1 9 p p b , respectively. Maximum concentrations were also lower than at the urban site. At the m o t o r w a y site concentrations were higher than at the rural site but lower than at the urban except in the case of EDB. Arithmetic mean hourly concentrations for benzene, toluene, ethylbenzene, total xylenes, ECD and EDB were 2.6, 2.69, 0.17, 1.29, 0.02 and 0 . 0 4 p p b , respectively. The maximum hourly EDB concentration was 0.15 p p b as compared to 0.08 ppb at the urban sites. Concentrations of particulate and organic lead measured at the urban, rural and m o t o r w a y sites are presented in Table 3. Concentrations of both particulate and organic lead were similar at the urban and m o t o r w a y sites (208 and 1 9 6 n g m -3, particulate lead; 18 and 1 5 n g m -3, organic lead, respectively). At the rural site, concentrations of particulate and organic lead were lower (92 ng m -3 and 3.7 ng m -3 , respectively). Diurnal averages for aromatic and halogenated hydrocarbons are presented in Fig. la--f. The diurnal variation of aromatic hydrocarbons compared favourably with the diurnal averages for NMHC and CO at the three sites presented in Fig. 2a--f (particularly at the urban site). Correlation analysis was performed on the aromatic and halogenated hydrocarbons data from the three sites. In general, only benzene and toluene were consistently well correlated with coefficients of 0.96 (urban site), 0.86 (rural site) and 0.94 (motorway site) being determined. Reasonable correlations between EDC and EDB were found at the urban site (0.76) and the m o t o r w a y site (0.60). At the urban site, the wind direction was predominantly from the northeast (30 ° ) (approximately parallel to the road) with wind speeds generally between 3 and 4 m s -1 . The wind direction at the rural site was far more variable and generaly emanated from the 240--90 ° arc with wind speeds > 6 m s -1 frequently occurring. In contrast, low windspeeds were recorded at the m o t o r w a y site which were consistently below 4 m s -1 during the monitoring period. In addition, the wind direction occurred in the
2
2
6
14
14
(b)
10
(PI
10
6
18
18
Time
22 h
Time
22 h
of
of
day
a04 0.
9
day
0.1
L 2
-
6
_ A.,
_'
1
14 (f)
10
(c
I8
22 h
_'c
-EEC ---ED
B
Fig. 1. Diurnal average concentrations of aromatic and halogenated hydrocarbons at the three sites. (a) Exhibition Road; (b) Silwood Park; (c) Toddington; (d) Exhibition Road; (e) Silwood Park; (f) Toddington.
(d)
(a)
272
0.8 0-7
0.8 0"7
0'8 0-7
0"6
0.6
NMHC ppm
0.5
0.5
0"5
0"4
0"4
O.Z,
0.3
0-3
0.3
0.2
0.2
0.1
0-1
0
I
I
I
2
6 10
I
I
01
I
14 18 2 2 h
I
0
I
(a)
CO pprn
I
(b)
L Time
o of
+.oil+.° I
4"0
3"0
3-0
2"0
20
1"0
1"0
I
I
2
6
I
10 14
(d)
I
I
18 22 h
0
I
I
I
I
10 14 18 22h (c)
+10F
4"0
3"0
I
I
6
day
40
0 /
I
2
2-0
1"0
I
I
I
2
6
10
I
~
t
0
14 16 2 2 h
(e)
Time of dciy
i
i
2
6
[
I
i
I
10 14 18 22h
(!)
Figure 2. Diurnal average concentrations of N M H C and C O at the three sites. (a) Exhibition Road; (b) Silwood Park; (c) Toddington; (d) Exhibition Road; (e) Silwood Park; (f) Toddington.
150--180 ° arc for over 6 0 % of the time (i.e.away from the mobile laboratory towards the motorway). The individual and combined effects of the windspeed, temperature and lagged concentrations of N M H C and C O were estimated by applying Eqn. (1) and the multiple regression statisticsare presented in Table 4 (R 2 denotes the total explained variance and n is the number of hourly samples). This demonstrates that the single most important parameter evaluated was that of lagged concentrations. If not included, significantreductions in the total explained variance were calculated. However, a positive correlation was found between N M H C and temperature and, to a m u c h lesser extent, with C O and temperature at this site. Similarly, a positive correlation was determined at the rural sitefor N M H C and temperature and also wind speed. A negative correlation was calculated for C O and wind speed at this site and at the motorway site.In contrast to the other two sites, a negative correlation was found between N M H C and temperature at the motorway site.
DISCUSSION
At the three contrasting sites (urban, rural and motorway) highest mean and m a x i m u m concentrations of aromatic hydrocarbons and E D C were
273 TABLE 4 MULTIPLE REGRESSION SITES
Site
Urban Rural Motorway
Compound
NMHC CO NMHC CO NMHC CO
STATISTICS AT THE URBAN, RURAL AND MOTORWAY
n
572 562 539 518 449 356
a
-- 1.64 -- 0.21 a -- 0.85 --0.21 a -- 0.44 a -- 0.74
Wind b1
speed
0.04 a 0.01 a 0.08 --0.08 0.08 -- 0.07
Temperature
Lagged
b2
cone.
0.48 0.09 0.24 0.06 a -- 0.32 0.14 a
0.75 0.87 0.88 0.80 0.79 0.60
R2
67.7 75.7 84.7 72.0 67.3 45.3
aNot significant at the 5% level.
exhibited at the urban site (EDB concentrations were slightly higher at the m o t o r w a y site). The major sources of these c o m p o u n d s in the atmosphere are vehicle emissions (Harkov, 1982). H y d r o c a r b o n emissions have been shown to be dependent on driving mode and are most elevated during deceleration and acceleration, a driving mode typical of urban roads. In addition evaporative losses from vehicles can also contribute between 20 and 30% of the total hydrocarbon vehicle emissions (Black et al., 1980; Nelson et al., 1979). The multiple regression analysis provided information on the role of temperature in defining observed concentrations of NMHC due to evaporative losses of aromatic hydrocarbons as they account for approximately 30% (by weight) of the NMHC (Nelson and Quigley, 1982; Nutmagul et al., 1983). At the urban site this relationship was demonstrated by the significant positive correlation of 0.48. In contrast, CO showed only a weak correlation with temperature which does not imply a causative relationship. At the urban site, wind speed had no significant correlation with either CO or NMHC demonstrating that the measured concentrations are typical of those found in London as confirmed by a recent review of air pollution in this city (Schwar and Ball, 1983). The diurnal pattern of the aromatic hydrocarbons at this site was similar to that observed in Los Angeles (Altshuller and Bufalini, 1971) to that observed in a previous survey at the same site (Clark et al., 1984b). However, the diurnal variation of benzene is more pronounced than that observed in three large cities in the United States (Singh et al., 1982). The arithmetic mean aromatic hydrocarbon data compare well with other reported values compiled in Table 5 which utilised a variety of analytical techniques for the preconcentration of ambient air samples. In the F.R.G. an ambient air quality standard of 3 0 # g m -3 ( 9 . 2 p p b ) for benzene annual average has been recently recommended by the Federal Environmental Agency (Sartorius et al., 1983). As can be seen from Table 5, ambient air concentrations above this proposed standard are frequently
1975 1975 (Nov) 1976
The Hague Berlin
Johannesburg Los Angeles Sydney New Jersey Newark Elizabeth Camden London London
1968 1971 1971
Los Angeles Zurich Toronto
3.4 6.04 2.6 1.03 1.05 1.11 8.8 9.69
1981 1981 1981 1982 1983
4.65 2.89 1.82 13.5 15.5
10.3 11.72 8.9
38.4
27.4
15.1 18.1
17.9 26.1
37.0 39.0 30.0
toluene
8.9 15.1
15.0 54.0 13.0
benzene
0.33 0.26 0.17 0.88 0.78
1.9 2.25 1.3
-
-
3.1 -
6.0 8.7 9.0 -
0.99 0.75 0.49 2.8 2.30
4.5 4.61 1.3
22.6
13.6
12.4 18.1
21 -
p-xylene
0.26 0.22 0.15 1.2 0.77
1.6 1.93 1.5
-
3.1 -
8 9.3
o-xylene
Clark et al. (1984b) This work
Harkov et al. (1983)
Louw et al. (1977) Singh et al. (1982) Nelson and Quigley (1982)
Lonneman et al. (1968) Grob and Grob (1971) Pilar and Graydon (1973) Burghardt and Jeltes (1975) Seifert and Ulrich (1978)
Reference
MEASURED AT DIFFERENT LOCATIONS
23
m-xylene
CONCENTRATIONS
ethylbenzene
HYDROCARBON
Concentration (ppb)
(Nov) 1977 1979 1980
1976
(Jul)
Year
Location
COMPARISON OF AROMATIC
TABLE 5
275 found in many European and American cities. The most serious consequence of a high benzene intake is leukemia (Goodwin, 1980). In addition, the long term exposure to relatively low concentrations of benzene and other aromatic hydrocarbons is an area of increasing concern (Harkov et al., 1983). EDC concentrations were highest at the urban site (~ = 0.30 ppb) which compared well with values of 0.22 and 0.26 ppb determined at the same site in 1979 and 1982, respectively (Tsani-Bazaca et al., 1981, Clarke et al., 1984b) and to concentrations derived at sites in Iberville, LA (~ = 0.34 ppb) and Los Angeles (~-- 0.52 ppb) in the United states (Pellizzari, 1982; Singh et al., 1982). EDB concentrations {~ = 0.03 ppb) measured at the urban site were identical to concentrations measured at the same site previously (Clark et al., 1984b). Measured EDB concentrations are also in the same range ( 0 . 0 1 - - 0 . 0 4 p p b ) as determined by other workers (Johns, 1976; Leinster et al., 1978; Tsani-Bazaca et al., 1981; Singh et al., 1982) at similar locations. Concentrations of both aromatic and halogenated hydrocarbons were low at the rural site and compared well with data obtained from the same site previously (Clark et al., 1984b). The low level concentrations were primarily related to the low incidence of vehicular pollutant sources in the area. NMHC concentrations correlated positively with wind speed and temperature suggested that the majority of emissions were derived from vehicle NMHC (and consequently aromatic and halogenated hydrocarbons) concentrations can be considered typical of background concentrations. At the m o t o r w a y site, vehicle numbers passing the laboratory were high ( ~ 3500 vehicles an hour). However, the low emission rates of hydrocarbons from vehicles travelling at constant high speeds and the predominant wind pattern resulted in low concentrations of measured aromatic hydrocarbons and EDC. A comparatively strong negative correlation of NMHC with temperature suggested that the majority of emissions were derived from vehicle exhaust and that high temperatures increased atmospheric turbulence, thus reducing measured concentrations. Concentrations of both aromatic and halogenated hydrocarbons were similar to those measured at the same site previously (Clark et al., 1984b). The particulate and organic lead concentrations measured at the urban and rural sites were comparable with those measured at the same sites previously and with data from other workers at similar locations (Birch et al., 1980; De Jonghe et al., 1981; Gibson and Farmer, 1981). Measurements of particulate lead were considerably lower than valuespresented by Clark et al. (1984b) at the same site. However, the predominant wind direction pattern (along the axis of the road towards the mobile laboratory) was considerably different to that determined in this study (away from the mobile laboratory towards the motorway). The proportion of organic lead to total lead, expressed as a percentage, varied between 3.9% at the rural site to 8.1% at the urban site, which is in accord with the results of other workers and indicates the importance of evaporative
276
emissions of organic lead at the urban site (Harrison and Perry, 1977; De Jonghe et al., 1981). Lonneman et al. (1968) have suggested that the toluene/benzene ratio can be used as an indication of the extent to which m o t o r traffic emissions contribute to air pollution. Criticism of the applicability of this ratio has been expressed, because of the variation in the concentrations of these compounds in petrol (Ioffe et al., 1979). However, it has been suggested that the ratio may be used to determine the degree of vehicle-related air pollution only when the variation of the toluene/benzene ratio in petrol is low (Clark et al., 1984b). Supporting evidence for this is provided by this study and others where toluene and benzene concentrations have been found to correlate well (Tsani-Bazaca et al., 1981; Harkov et al., 1983). Samples of premium and regular grade petrol, recently surveyed in the southeast of the U.K., gave an average toluene/benzene ratio of 2.79 + 0.7 in 1983 (Associated Octel, personal communication). The ratio derived from the site was 1.59 on a weight-to-weight basis. This ratio is slightly lower (1.81) than that determined at this site previously (Clark et al., 1984b) and also those compiled in Table 5, excluding this work (2.78 + 0.89). It must be noted that many of the studies cited in Table 5 contained considerably fewer samples than this study. The ratio of 0.91 at the rural site and the low level of aromatic hydrocarbons indicated that the air mass sampled was aged, as toluene is subject to more rapid photochemical decay than benzene (Hov et al., 1978). A number of workers have demonstrated through d y n a m o m e t e r studies that dealkylation of toluene, xylenes and other alkylbenzenes can occur under conditions of high engine speed and load (Oelert et al., 1974; Perry et al., 1983). Indeed, Black et al. (1980) and Morris and Dishart (1971) have suggested that this process is the critical factor in defining vehicular benzene emissions. This is also reflected in the toluene/benzene ratio of 1.00 at the m o t o r w a y site which is considerably lower than that determined at the urban site.
CONCLUSIONS
Aromatic hydrocarbon concentrations monitored at the urban site are higher than at the rural or m o t o r w a y sites and are comparable with those measured in urban areas in other countries. Multiple regression techniques at the urban site have demonstrated the importance of ambient temperature in defining measured concentrations which are typical of those found in London. Ambient air concentrations of benzene at this site are frequently in excess of a proposed ambient air quality standard in the F.R.G. The low hydrocarbon emission rates of vehicles travelling at constant high speed and the predominant wind direction resulted in low measured concentrations of aromatic hydrocarbons at the m o t o r w a y site compared to the urban site. Multiple regression techniques suggested that the majority of emissions were
277 derived f r o m vehicle e x h a u s t and n o t evaporative losses. The low a r o m a t i c h y d r o c a r b o n s c o n c e n t r a t i o n s m e a s u r e d at the rural site can be c o n s i d e r e d representative o f b a c k g r o u n d c o n c e n t r a t i o n s . A m b i e n t c o n c e n t r a t i o n s o f EDC and EDB at all t h r e e sites were low and c o m p a r a b l e with o t h e r p u b l i s h e d data. T h e use o f the t o l u e n e / b e n z e n e ratio in d e t e r m i n i n g the degree o f vehiclerelated air p o l l u t i o n , w h e n the range in variation o f these c o m p o u n d s in p e t r o l is low, has been validated. T h e ratio derived at the u r b a n site was considerably higher t h a t at the rural and m o t o r w a y sites. In addition, the ratio d e t e r m i n e d at the m o t o r w a y site s u p p o r t s evidence o b t a i n e d f r o m d y n a m o m e t e r studies o f a d e a l k y l a t i o n process o f t o l u e n e , x y l e n e and higher alkylb e n z e n e s in vehicle engines o p e r a t i n g at high speed and load, increasing b e n z e n e emissions.
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