The decay of benzo(a )pyrene and cyclopenteno(cd)pyrene in the atmosphere

Afmosphem

Enaironmenr

Vol. 22, No

IO. pp. 2249-2254.

1988.

ooo4 6981/88 $3.W+OoO Pergamon Press plc

Prmted m Great Britain

THE DECAY OF BENZO(a)PYRENE AND CYCLOPENTENO(cd)PYRENE IN THE ATMOSPHERE TORBEN

Chemistry

Department,

Rise National

NIELSEN Laboratory,

(First receioed 5 August 1986 and

cyclopenteno(cd)pyrene,

polycyclic

INTRODUCTION The

transformation

of polycyclic

aromatic

hydrocar-

bons in the atmosphere has been extensively discussed in recent years (van Cauwenberghe and van Vaeck, 1983; Finlayson-Pitts and Pitts, 1986; Nielsen et al., 1983; Pitts, 1983) and several laboratory investigations show that PAH are probably transformed in the atmosphere to nitro derivatives, ketones, aldehydes, quinones and other derivatives (Arey et al., 1986; JSger and Hanus, 1980; Katz et al., 1979; Nielsen, 1984a; Pitts et al., 1978, 1980; Sweetmann et al., 1986). The recent findings of 2-nitropyrene, 2nitrofluoranthene, lo-nitrobenz(a)anthracene and hydroxynitropyrenes (Arey et al., 1987; Gibson et al., 1986; Nielsen et al., 1984; Nielsen and Ramdahl, 1986; Ramdahl et al., 1986; Pitts et al., 1985) in atmospheric samples confirm that derivatives of PAH are formed in the atmosphere. This paper presents evidence that PAH actually decay in the atmosphere. The samples were collected in a rural area during the winter and early spring when ambient temperatures and concentrations of NO, and photochemical oxidants (e.g. 0,) were low. Masclet et al. (1986) have also presented evidence for degradation of benzo(a)pyrene (BaP) in the atmosphere using another approach. EXPERIMENTAL

Sampling and the sampling location Thirty 24 h samples of airborne particulate matter corresponding to ca 2000m3 were collected in the period February-April using conventional Hi-V01 samples with glass-fibre filters (Whatmann G/FA). The samples were collected at Rise National Laboratory (see Fig. I). The sampling site was shielded from easterly winds by six rows of buildings. All of the samples were collected during weekdays. The meteorological conditions were recorded at 2 and I I m above ground level and at intervals of 10 min. Rise National Laboratory, having 900 employees, is situated north of Roskilde on a peninsula at the east coast of the

Roskilde,

Denmark

received for pubkation 7 April 1988)

Abstract-The dominant source for PAH air pollution at situated 6 km south of the sampling site. Far distant sources Benzo(a)pyrene and cyclopenteno(cd)pyrene were shown to dependencies of the ratios of benzo(a)pyrene to benzo(e)pyrene + triphenylene on the wind direction and on the PAH pollution Key word index: BaP, atmospheric pollution.

DK-4000

Rise, was Roskilde with 40,ooO inhabitants of PAH were estimated to be insignificant. decay in the atmosphere by means of the and of cyclopenteno(cd)-pyrene to chrysene level. The decay appears to be relatively fast.

aromatic

hydrocarbons,

atmospheric

decay,

narrow Roskilde inlet. Each day 500 vehicles pass m and out of the area. The laboratory is heated by its central heating plant situated 1 km west of the sampling site. A main road carrying about 8000 vehicles every 24 h is situated 0.5 km east of the sampling site. The ship traffic at the inlet is negligible. Rise is surrounded by agricultural areas (on the land side). Roskilde is a town with 40,000 inhabitants. It is heated by a 25 MW waste incineration plant, and by house oil-burners and stoves. The capital of Denmark, Copenhagen, 35 km east of the sampling site has 600,000 inhabitants; in addition. 200,000 people are living in its suburbs. Analysis The samples were extracted ultrasonically 3 x 30 min with 50 ml of dichloromethane (Merck, Lichrosolv) each time. The concentrated solutions were fractionated by means of high-performance liquid chromatography using a mixture of n-hexane (Merck zur Riickstandsanalys) and benzene (Merck, p.a.) in a ratio of 3: 1 as eluent. The flow rate was 3.0 ml min- ‘. The columns (12 cm x 4.6 mm, pre-column, +25 cm x 8.0 mm) were packed with Nucleosil-S-50-5. The fraction consisting of PAH was collected and concentrated to 1.0 ml. The amounts of PAH were determined by CC with flame-ionization detection. The method is described in more detail elsewhere (Nielsen, 1983).

RESULTS AND DISCUSSION

The PAH dependency of the wind direction Figure 1 shows the position of the sampling station. The concentration of PAH is expressed in Table 1 by means of the total amount of benzo(b +j + k)fluoranthene + benzo(e)pyrene + indeno( 1,2,3-cd)pyrene (BF + BeP + IP). These five PAH are chosen as indicators, as they appear to be some of the more stable PAH in the atmosphere (Nielsen et al., 1983; Nielsen, 1984a, b) and they are almost exclusively associated with particles (Thrane and Mikalsen, 1981). In addition, the benzofluoranthenes and indeno (1,2,3-cd)pyrene are evaluated to be carcinogenic (IARC, 1983). The results from 25 of the samples had been divided into three major groups and two subgroups (Table 1) in order to elucidate the contributions from Roskilde,

TORBEN NIELSEN

2250

I

0

10

I

I

I

25

50

75

100 km

Fig. 1. A map of Zealand showing the position of the sampling location at Ris@. The most populated areas on Zealand are shaded in grey. Copenhagen and far distant sources. The remaining five samples were excluded in this investigation, because the content in the samples was influenced by Roskilde as well as other sources. A general discussion of the results has been presented earlier (Nielsen et al. 1984). The three major groups include: I-Those samples originating from the south and south-east. II-Those originating from the east. III-Those originating from the north-east, north, north-west, west and south-west. The group subgroups: IIIa-Those west.

III samples originating

have

been divided

in two

from the west and south-

III&Those originating and north-west.

from the north-east,

north

The results from the two subgroups were treated together, as the results were quite similar (see Table 1). The contributions from far distant sources with winds from the south and south-east are shown to be neghgible (q.u.). The fact that the vehicle contribution of PAH must have been higher in the IIIb samples than that in the IIIa samples is considered to be unimportant. The contribution in the IIIb samples seems to have been higher than that in the IIIa samples since the benzo(ghi)perylene (BghiP) to BeP ratio was higher in the former. BghiP is an indicator of the PAH contribution from vehicles (Daisey et a[., 1986; Grimmer et al., 1980; Pedersen et al., 1980). The ratios of the five PAH to Pb were almost the same in the IIIa

2251

Atmospheric decay of benzo(a)pyrene and cyclopenteno(cd)pyrene

Table 1. Comparison between the ratios of cyclopenteno(cd)pyrene to chrysenet triphenylene and benzo(a)pyrene to benzo(e)pyrene, the levels of PAH and inorganic pollutants, and the meteorological conditions at different wind conditions t-Test comparison between I and III II and III IIIa and IIIb

Wind sector Type No. of samples (CP)/(CH + TP) (BaP)~(BeP) (BghiP)/(~P) (BF + BeP +IP) (ng ms3)* NO, (ppb) NO, (ppb) SO, (ppb) 0, (ppb) Pb (ngme3)$ SO$- (pgSmm3)$ NO; (@gNmm3) Temperature (“C) Wind speed (m s- ‘) Rain (mm) Sunshine (h)

I 12 0.20 0.90 0.96 $l(5.5) 17 10 l&7) 2.8(11) 2.0 3.1 5.7 1.1 2.2

II

III

2 0.06 0.45 0.76

IIIa

11 6 0.11 0.11 0.64 0.68 0.88 0.77 0.82(0.91) 0.79 f3 7 7 6 6.5 1 7 6 g:: 30 36 (2) 37(9) 31(6) 2.8 (2) 2.6 (9) 2.2 (6) 0.5 1.5 1.4 -0.3 3.7 3.2 4.1 3.7 5.8 0.0 0.2 0.4 1.0 3.9 2.5

t

IIIb 5 0.11 0.59 1.01 0.86(1.49) 6 6 10 15 50(3) 3.5 (3) 1.7 4.3 2.8 0.0 5.6

2.8t 3.2t 0.9 3.27 5.0t 3.6t 0.8 2.3t 3.8t 0.2 1.1 0.4 2.47 1.2 1.4

0.9 1.1 1.1 2.4t 0.0 0.0 -. 0.4 3.6t 0.1 1.6 1.2 0.2 0.4 1.1

0.1 0.7 3.9t 0.2 0.2 0.2 1.1 3.4t 1.9 0 0.6 0.4 2.3t 0.9 1.6

I-Wind from south and south-east. II-Wind from east. III-Wind from north-east, north, north-west, west and south-west. IIIa-Wind from west and south-west. III&-Wind from north-east, north and north-west. *The numbers in f I denote the concentrations on those days Pb also were determined. t Difference significant, p ~0.05. $ The numbers in ( ) denote the numbers of samples.

and IIIb samples (see Table i), but the BghiP to BeP ratio is more confident to estimate the vehicle contribution (see the Results and Discussion later). Roskilde has been the dominant source of air pollution in the area (see Table 1). The concentration of the five PAH was about 15 times higher, 12 and 0.8 ngm -j, respectively, when the wind was coming from Roskilde compared to when it was coming from the clean air region (group III). The PAH profiles (see Fig. 2) of the samples had been almost the same, as the PAH ratios are almost identical. The cyclopenteno~~~)pyrene (CP) to chrysene + t~phenyiene (CH + TP) and BaP to BeP ratios were exceptions and will be discussed in the following sections. The concentration of dibenz(a,c + a,h)anthracene (dBA) is difficult to determine exactly, as the peak of dBA in the GC chromatogram is small and lies between the two large peaks of IP and BghiP. The inaccuracy in the determinations of dBA might have been the reason for the discrepancy between the group I and III ratio of dBA to BeP; this discrepancy was not statistically significant (t = 1.7;p > 0.05). Also CH + TP was preferred as the reference compound for the four rings PAH, ~nzo(~)naphtho(2,1-~)thiophene, CP and benz(a)anthracene, since the distribution of these three and CH +TP between the vapor phase and the particleassociated part is the same (van Cauwenberghe and van Vaeck, 1983; Thrane and Mikalsen, 1981). The similarity in the PAH profiles indicate that the emission profiles of PAH in the Roskilde region and in the clean air region are almost identical. The relative contribution of vehicles to PAH poliution in the two

regions must have been of the same magnitude, as the ratio of BghiP to BeP was almost the same. On the other hand, the ratio of the five PAH to Pb was 1.6 times higher at winds from the Roskilde region compared to winds from the clean air region. The emission patterns of PAH and Pb are totally different in various driving conditions (Nielsen, 1984b; Pedersen et al., 1980), and the discrepancy in the PAH to Pb ratios should not necessarily suggest that the ratio between heating contribution and vehicle contribution was higher in Roskilde than in the clean air region. Copenhagen was another ~ont~butor to PAH pollution at Rise. The levels of the five PAH were 3 times higher with winds from the east than with winds from the clean air regions. The results for the two regions were, however, not quite comparable, as the average temperature was lower in the Copenhagen cases than in the clean air region cases, -0.3 and 3.7”C, respectively. PAH pollution in Copenhagen is described elsewhere (Nielsen et al., 1986). The main road situated OS km east of the sampling site does not seem to have been a significant source, as the ratio of BghiP to BeP was not higher in the Copenhagen cases than those from the clean air region, and the ratios of the five PAH to Pb were almost the same. It is not surprising that the contribution from the main road traffic was negligible since the PAH emissions from vehicles at motor road conditions can be at least l&100 times less than that from vehicles at city driving conditions (Grimmer and Hildebrandt, 1975; Ingwersen et af., 1978; Pedersen et al., 1980). Also the sampling site was shielded by six rows of buildings from the main road,

2252

TORBENNIELSEN

The decay of cyclopenteno(cd)pyrene The ratio of CP to CH +TP correlation with the concentration

gave a significant of CH + TP

CP/(CH+TP)=0.059(CH+TP)+0.10 (r=0.47; p
This indicates

0.5

(1) the ratio relatively small (2) this ratio concentrations

0.0

Fig. 2. The diagram shows ratios of the concentrations of various PAH with winds from the clean air region (III) and from Roskilde (I). The striped sections represent the positive and negative standard deviations. The lines between these represent the mean values. BNT: benzo(b)naphtho(2,1d)thiophene, CH: chrysene, TP: triphenylene, CP: cyclopenteno(cd)pyrene, BaA: benz(a)anthracene, BF: benzo(b +j + Qfluoranthene, BeP: benzo(e)pyrene, BaP: benzo(a)pyrene, Per: perylene, IP: indeno(l,2,3xd)pyrene, dBA: dibenz(a,c +a,h)anthracene, BghiP: benzo(ghi)perylene and ANT: anthanthrene.

The contribution of far distant sources is estimated to be negligible. Long-distance transport episodes in the Scandinavian countries occur with winds from the west, south-west, south and south-east, and coincide with contributions of SOi- (Bjiirseth et al., 1979). Their influence if any, on the concentrations of PAH at winds from the west and south-west must have been very low, as the PAH levels were of the same magnitude as when the winds were coming from the northeast, north and north-west (see Table 1). In addition, the levels of SOi- were not elevated. Furthermore, there is no reason to believe that PAH sources west and south-west of Riser would be less important than those north of Riser. It should be noted that the levels of SOi- in Table 1 are correqted for sea-spray contributions (Kemp, 1984); the corrected values were 97% of the uncorrected. The higher levels of PAH with winds from the south and south-east are estimated to originate from Roskilde and not from far distant sources as an elevation in the content of SOi- was lacking (see Table 1). The lack of influence of distant sources in winds from the south and south-west indicates that it is reasonable to conclude that far distant source effects were also negligible in winds from the south and south-east. A detailed investigation of the PAH results, weather maps, data of the wind directions at different heights from the 150 m high meteorological mast, the ratio of SOi- to SO, and the ratio of NO; to NO, did not conflict with the conclusion that Roskilde had been the main source. Furthermore, it is hard to imagine any reasonable explanation on the significant variations of the ratios of CP to CH + TP and BaP to BeP (see Table 1 and the following sections) postulating the importance of a long distance source hypothesis.

that CP degrades

in the atmosphere,

as

of an unstable PAH to a stable one is at modest PAH concentrations, and is relatively high at high atmospheric of PAH.

The PAH concentration is a rough indicator of the inverse average transport time as long as the heights of the mixing layer are similar. Therefore, at high concentrations of PAH the dominant part of the PAH usually originates from nearby sources, while at low concentrations of PAH a much larger part of the PAH originates from sources further away. It should be added that the correlation noted above is stronger than it appears, as the concentration of CH +TP is compared with a ratio where the denominator is the concentration of CH +TP. Furthermore, the ratio of CP to CH +TP is much lower in winds from the so-called clean air region than in winds from Roskilde (Table 1); the relative amount of CP is 45% lower in the former wind directions. Assuming the relative vehicle contribution was lower for winds from Roskilde than for winds from the so-called clean air region, one would expect that the CP to CH+TP ratio would be lower in southerly winds than with the other wind directions, provided that CP was stable in the atmosphere. Thus assuming the relative vehicle contribution has been lower has decreased rather than increased the difference in the ratios. CP must, therefore, decay in the atmosphere, and the decay must be relative fast since it can be possible to observe it after the air masses had been transported over distances probably < 70 km, as (1) if CP was stable in the atmosphere or decayed slowly the ratio of CP to CH+TP in winds from Roskilde should be the same as that from the so-called clean air region, since the ratios of other PAH are independent of the wind direction (see Fig. 2); (2) it seems reasonable to assume that the major sources in all wind directions had been sources on Zealand.

The decay of benzo(a)pyrene The ratio of BaP to BeP is lower with winds from the so-called clean air region than at winds from Roskilde (see Table 1). The relative amount of BaP is 29% lower in the former wind directions. The emission ratios of BaP to BeP from, respectively, vehicles, oil burners, wood stoves and waste incineration plants, are similar, at a value of about 1.0 (Daisey et al., 1986). It should not matter, therefore, whether or not

Atmospheric

decay of benzo(a)pyrene

the relative vehicle contribution was the same or perhaps lower in the Roskilde region than in the clean air region. The significant correlation between the ratio of BaP to BeP and the concentration of BeP

and cyclopenteno(ed)pyrene

organic grateful

2253

pollutants. Dr C. Anastasi, University of York, is acknowledged for his comments on the manuscript.

REFERENCES

BaP/BeP=0.19

x BeP f0.62 (r=0.52; ~~0.01)

confirms that BaP should be degraded in the atmosphere. The decay appears to be relatively fast. Benz(u)anthracene, CH+TP, BF, BeP, IP and BghiP are expected to be more stable in the atmosphere than CP and BaP (Nielsen et al., 1983; Nielsen, 1984a), and it was impossible to reveal decay of any of these compounds. 2_nitrofluoranthene, 2nitropyrene and IO-nitrobenz(a)anthracene, transformation products of fluoranthene, pyrene and benz(a)anthracene, had been identified in the atmosphere (Nielsen, 1983; Nielsen et al., 1984; Nielsen and Ramdahi, 1986). None of these compounds had been detected in stack gases from common combustion sources and exhaust gases, or in a most thorough investigation of diesel exhaust gas (Paputa-Peck et al., 1983), and they are believed to originate from atmospheric transformation of their parent PAH (Arey et ul., 1986, 1987; Nielsen ef al., 1984; Nielsen and Ramdahl, 1986; Pitts et al., 1985; Ramdahl et al., 1986; Sweetman et al., 1986). Thus, PAH other than CP and BaP seem to decay in the atmosphere, although the decay rate constants are probably slower. The investigation was carried out during the winter with low ambient temperatures, low solar intensity and low concentrations of NO, and photochemical oxidants. One would expect the decay rate constants to be higher under summer conditions.

CONCLUSION

Roskilde, a city with 40,000 inhabitants situated 6 km south of Riser, is the dominant source for PAH pollution at Riser. Copenhagen, the capital, situated 35 km east of the sampling site was another source. The contribution from far distant sources was considered to be insignificant. The ratios of benzo(a)pyrene to benzo(e)pyrene and cyciopenteno(~~)pyrene to chrysene + triphenylene were higher in winds from Roskilde than in winds from the so-called clean air region with more distant and spread sources. The differences were ascribed to evidence for atmospheric decay of the reactive BaP and cyclopenteno(cd)pyrene. The remarkable correlations between the extent of PAH pollution and the two ratios confirm the decay conclusion. The decay appears to be relatively fast. Acknowledgements-The Danish Ministry of Energy is gratefully acknowledged for financial support. Drs A. M. Hansen, K. Kemp and B. W. Pedersen, Air Pollution Laboratory, Danish Environmental Protection Agency, are also acknowledged for the d~t~~inations of the concentrations of in-

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