ENVIRONMENTAL EFFECTS O F THE
O I L FIELD FIRES
I 1530 Enwon. Sci. Technol., VoI. 25, No. 9. 1991
0013-936w91/0925-1530$02.50/0 0 1991 American Chemical Society
By Jurgen Hahn Arab sources state that up to 6 million barrels of oil are being burned each day in the Kuwaiti oil fields. Estimates of the rates of burning based on Kuwait’s annual preinvasion oil production and reservoir pressures are significantly lower, ranging from 1.5 million to 3 million barrels of oil per day, or about 0 . 2 trillion-0.4 trillion g ( T g ) [200,000-400,000 metric t o n s [tonnes)].Although as of early June firefighters had extinguished fires at about 100 of the 500-600 oil wells set ablaze by Iraqi troops, it may take up to two years to bring the last of the fires under control. It is reasonable to assume, therefore, that the oil fires will continue to burn for at least one year at the rates estimated above, and that at least 75-150 Tg (75 million-150 million tonnes) of oil will go up in smoke. About 5-10% of the oil burned is emitted as smoke, 7.5% on average ( I ) . About 70% of the smoke emitted is in the form of elemental carbon (soot). Using the average emission factor of 7 . 5 % , one can calculate a smoke emission of about 0.016-0.032 Tg (16,000-32,000 tonnes) per day, containing between 0.011 and 0.022 Tg (11,00022,000 tonnes) of elemental carbon. Theory suggests that the rates of smoke emission and heat generation and, consequently, the atmospheric injection height and residence time of the smoke are crucial in determining whether the environmental effects are of global or only regional importance. Confirming the results of model calculations (2, 31, observations have shown that, up to now, the smoke did not rise higher than to the top of the planetary boundary layer (PBL), about 3300 m (10,000 ft) at a maximum. The PBL is the layer of the atmosphere in which friction with the Earth’s surface influences winds and temperature. In the Gulf region, the daytime PBL varies from 200 to 800 m during the cold season and from 2000 to 4000 m during the hot season. Only very small amounts of the smoke possibly reached higher altitudes during rare situations of atmospheric instability, such as thunderstorms. The environmental Views are insightful commentaries on timely environmental topics, represent on author’s opinion, and do not necessarily represent a position of the society or editors. Contrasting views are invited.
effects of the oil fires therefore are significant only in the greater Gulf region. Emitted within an area of about 40 x 40 km, the individual plumes rise, spread out, and merge to form a large, more or less dense smoke cloud which, depending on wind speed and direction, fans out into predominantly northerly, easterly, and southerly directions. The “selflofting” effect by solar heating of the black smoke appears to be small, so that analogies with nuclear winter scenarios or large volcanic eruptions are inappropriate. Most of the smoke mass apparently is transported within an altitude range of 20003000 m. The boundaries of the smoke cloud are not well defined because the outer parts form strands that gradually dissipate. After aerial transport 1500-2000 km from the source area, the smoke cloud has thinned to such an extent that it becomes undetectable. On an average, the smoke cloud covers about 6 x 10” m2. Assuming a light extinction coefficient of
The environmental effects of the oil fires. ,are significant only in the greater Gulf region. about 10 mz per gram of smoke, the optical depth of the smoke cloud decreases exponentially with increasing distance from the source area from 2 to 4 above the territory of Kuwait to 0.1-0.2 in the remote parts of the cloud. An optical depth of 4 means that only 2% of the solar radiation in the visible range of the spectrum reaches the ground below the smoke cloud. This leads to a decrease in surface temperatures as great as 10 “C. Because the size distribution of the smoke particles is not known, it is difficult to estimate their mean atmospheric residence time. However, with an average wind speed of about 3 m s-’ at the altitude i n which the smoke is transported and a transport distance of 1500-2000 km, an estimate of the mean atmospheric residence time of the smoke cloud works out to 5-8 days. Outside the cloud, scattered smoke particles may remain in the air for as long as 20 days, depending on the
frequency and intensity of wet precipitation events. Assuming that 80% of the smoke emitted over one year is deposited in the eastern territories of the greater Gulf region within a semicircle whose radius is 2000 km around the source area, the average smoke deposition per unit area would be 0.51g m-* year-’. The smoke will not be equally distributed over the deposition area, of course. Results of model calculations suggest that major smoke deposition will occur over large parts of Iran, Saudi Arabia, and the other Gulf states (2). It is estimated that about 20% of the emitted smoke mass will be deposited within a 50-km radius of the burning wells. This works out to an annual smoke deposition of 100200 g m-*, which certainly will have a tremendous impact on human health, ecosystems, seawater processing plants, and buildings. Soot is a good adsorber of organic combustion products. Therefore, the soot particles probably are sticky and form an oily coating on all kinds of surfaces including those of living plants. The toxicity of the soot particles depends on their chemical composition, and especially on the content of polycyclic aromatic hydrocarbons, tetrachlorodibenzo-p-dioxin, tetrachlorodibenzofuran, phenol, and nitrated phenols. Although no information currently is available on chemical composition, the oily coating of plant surfaces is expected to be a major environmental hazard. Moreover, direct health effects could arise from particles deposited in the lungs of humans and animals. The situation is worsened by the emission of large amounts of sulfur and nitrogen compounds, mainly in the form of SO, and NO. The burning oil contains about 2.5% S and about 0.2% N including a significant amount of NO formed in the hot flames: the daily emission is about 10,500-21,000 tonnes of SO, and about 3500-7000 tonnes of NO, (calculated as NO,). The photochemistry within the smoke cloud very likely is significantly different from that of the smoke-free troposphere. Also, because there is very little precipitation in the greater Gulf region from May through October, it is difficult to predict how and where NO,, SO,, and their oxidation products HNO, and H,SO, will be deposited. Photochemical oxidation should be largely suppressed in the denser parts of the smoke cloud, so major Environ. Sci. Technol., Vol. 25, No,9, 1991 1531
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acid deposition is likely to occur at some distance from the source area, probably as far away as 2000 km. The same should be expected for the photochemical formation of ozone and other photooxidants. Serious photooxidant episodes may occur as far away as Turkey, Afehanistan. or EthioDia. A laree Dor;ion of the' hazardois gas and)&iculate c o m p o u n d s will b e drydeposited. With little water vapor available, any aqueous film forming on surfaces probably will be acidic. The occasional rain showers that do occur probably also will be acidic. Results of model calculations suggest that the effect of the smoke emission in Kuwait on the Asian summer monsoon is small. The changes in precipitation predicted for Southeast Asia (5-30 "N; 70105 'E) exceed twice the standard deviation of the normal year-to-year variations over only 10% of the area; such precipitation changes would be increases (3). In summary, One expect severe environmental consequences of the Kuwaiti oil field fires for the territory of Kuwait and for parts Of Iraq. Jordan,and Saudi Arabia Serious effects also may be felt in Iran 1532 Environ. Sci. Technol.. Vol. 25, No. 9. 1991
and the other Gulf states, and perhaps even as far away as Turkey and Afghanistan. The surface waters of the Gulf also may he severely affected by smoke deposition. Significant environmental effects on a global or even hemispheric scale, however, are not likely to occur. References (11 Small, R.D.Nature 1991,350.11. I21 Bakan, S . et al. Nature 1991,351,367. 13) Browning, K. A. et al. Nature 1991,
351,363.
Iurgen Hohn is the head of the chemistry division of the Fmunhofer Institute for Atmospheric Environmental Reseorch in GormischPortenkirchen, G e r m a n y . From 1970 to 1986, he worked os o scientist ondgroup leader at the air chemistry division of the Max Plonck Institute for Chemistry in Mainz, Germany. During thot time. he was involved in winter studies, His current interestS are in lone. term twnds of otmosphenr rrare go& and chemic01 trunsformotrons in cloud ssstpmc
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