Air Pollution

Until recently, the Arctic environment was treated as a pristine place unspoiled by man. If we take diaries or logbooks of polar explorers from the I9'h and early 20lh centuries, we will find a large number of phrases underlying the Arctic's cleanliness, its crystal air, and sparkling ice. Opinions about the lack of pollution in the Arctic continued to be held to the beginning of the 1970s, although the first documented report of arctic air pollution (coining the term 'Arctic haze') was published in 1956 (Mitchell 1956). The renewed interest in the nature and origin of the 'Arctic haze' was caused by the growing evidence found during this time that air pollution is not only confined to small areas around urban or industrial sources, but can be transported long distances before being removed to the Earth's surface. This discovery allows us to conclude that the Arctic atmosphere can be polluted, even though it does not have local sources of pollution. Some scientists returned to the observation of 'Arctic haze' made by Mitchcll in the early 1950s and the 'ice crystal haze' by Greenaway (a Canadian flight lieutanant) in the late 1940s and pointed out that they were not only just an indication of ice crystals or of wind blown dust, but rather of air pollution originating from the mid-latitudes. From this time, there has been a decline in the view that the Arctic is a place where the original state of the globe exists and can be used as reference to measure the human influence on planet Earth.

The growing awareness that human activity can also destroy the environment of the most remote areas of the world has motivated scientists to begin more detailed studies of this problem. In the last 30 years, the efforts undertaken mainly by scientists of different disciplines from Canada, Denmark, Norway, and the USA, including glaciologists, meteorologists, and atmospheric chemists, led to a significant increase in our knowledge concerning air pollution in the Arctic. During this period hundreds of works were published. In spite of this great scientific interest, particularly in the problem of 'Arctic haze', there are still many questions unsolved (for details see Karlqvist and Heintzenberg 1992). At present, there exist several good reviews of the current state of knowledge, where the reader can find more details than will be given here (e.g., AG ASP 1984; Barrie 1986a; Stonehouse 1986; Heintzenberg 1989; Jaworowski 1989; Sturges 1991; Barrie 1992; Shaw 1995).

Jaworowski (1989) has distinguished four types of pollutant sources in the Arctic environment: (1) local natural, (2) local anthropogenic, (3) remote natural, and (4) remote anthropogenic. Most scientists assume that the currently observed levels of pollutants, which are significantly higher than they were before the industrial age, is caused by the fourth type of source and there is some evidence to support this. However, not all scientists share this opinion (sec .laworowski 1989). From a climatological point of view, the most important pollutants in the Arctic are long-lived greenhouse gases (e.g., carbon dioxide, methane, and freons) on the one hand, and short-lived gases building up the 'Arctic haze' on the other. As we know, the greenhouse gases exhibit a much more even geographical distribution and their concentration in the Arctic is at the same level as in the other regions. For this reason, every publication analysing the variation of concentration of these gases (in daily, seasonal, and longer time scales), their sources and sinks, etc. can be taken to characterise greenhouse gases in the Arctic. Here, one should only mention that systematic measurements of carbon dioxide concentration in the near surface Arctic air were started in 1961 near Barrow, Alaska. Such measurements of other radiatively active gases began significantly later (in 1970s or in 1980s). Another important fact is that the increase in the concentration of greenhouse gases will cause significantly greater warming in the Arctic than in the lower latitudes. Such a prediction for CO,- doubling is given in most of the climatic models (see Chapter 11).

Figwe 8.1. The major chemical components in Arctic haze particles < I ^ni radius. Their average total mass is 8 ng trr\ 30%m were not determined in the chemical analyses; 29% are not specified in this graph (after Heintzenberg 1989).

The present chapter, on the other hand, will focus on the problem of the 'Arctic haze' as a well-defined case of air pollution in the Arctic, which influences climate through changes in the radiation balance of the atmos

Haze Components

Figwe 8.1. The major chemical components in Arctic haze particles < I ^ni radius. Their average total mass is 8 ng trr\ 30%m were not determined in the chemical analyses; 29% are not specified in this graph (after Heintzenberg 1989).

phere. The chemical composition of the 'Arctic haze' was first analysed by Rahn et al. (1977) based on measurements carried out at Barrow between 12 April and 5 May 1976. Its average composition is presented in Figure 8.1. The major components are sulphates (31%), nitrates (6%) and elemental carbon (2%). Still, about 60% of the particles of the 'Arctic haze' are unidentified but arc believed to have an organic origin. A considerable fraction of the undetermined part may be water. The size of haze particles oscillates from 0.05 to 1 Jim and is a result of the combined effects of sourccs, transformations, and sink processes (Hcintzenberg 1989). During the transport from a distant source (5-10 days) most of the smallest (< 0.05 pm) and largest (> 1 (im) particles are eliminated by coagulation and sedimentation, respectively.

8Cf- S in ng-irr3

8Cf- S in ng-irr3

Figure 8.2. Seasonal variations of Arctic haze in terms of sulphate concentrations measured at Ny Alesund, Spitsbergen during the years 1978-1984. Data from Ottar el al. (1986). The concentrations are given as SO/ - S in |ig m 3. The measurement values fall wilhin the shaded area (after Hcintzenberg 1989).

Figure 8.2. Seasonal variations of Arctic haze in terms of sulphate concentrations measured at Ny Alesund, Spitsbergen during the years 1978-1984. Data from Ottar el al. (1986). The concentrations are given as SO/ - S in |ig m 3. The measurement values fall wilhin the shaded area (after Hcintzenberg 1989).

The strong seasonal variation of haze pollution was first observed at Barrow in the late 1970s. Later on, the measurements carried out in other parts of the Arctic showed that this trend exists in the entire Arctic. The longest chemical time series (1978-1984) of Arctic air pollution comes from Ny Alesund, Spitsbergen (Ottar et al. 1986). Figure 8.2 presents seasonal variation of sulphate concentration, which is the main component of the 'Arctic haze'. The maximum sulphate concentration was measured at Ny Alesund in March and the minimum from June to September. Winter concentrations are

10 to 20 times greater than those in summer. In addition, it was recognised that during winter the 'Arctic haze' particles were mostly of man-made origin, while in summer they mainly came from natural sources. To explain the reason for this seasonal difference, an analysis of pollution sources and their transport pathways must be taken into account, along with some meteorological criteria. According to Raatz (1991), industrial source regions covering large areas of the mid-latitudes appear to be the major contributors to arctic air pollution (northeastern USA/southeastern Canada, western and eastern Europe, western USSR, Ukraine, southern Urals, western Siberia, Korea, and Japan). To this list eastern China should also be added, according to some other sources (e.g., Rahn and Shaw 1982, Barrie 1992). The annual emission of SO, (the main component of the 'Arctic haze') is highest in these regions (Figure 8.3). From distinct natural sources of'Arctic haze', Raatz (1991) gives the deserts of northern and western China and those of the southern USSR, as well as the Sahara desert of Africa.

Figure SJ Annual emissions of SO, (10* tonnes) in regions of the Northern Hemisphere that influence the Arctic (after Barrie 1986b).

The importance of each of the above sources in contributing to Arctic air pollution depends on its strength, proximity to the Arctic region (or Arctic masses), and the frequency of synoptic situations favouring a poleward flow. The magnitude of the poleward transport of pollution from mid-latitudes depends significantly on the seasonal variation of the polar front (Rahn and McCaffrey 1980). In winter the polar front is shifted to the south (40-50"N) and the most industrial regions lie to the north of them. In such a situation, the polluted air masses can easily reach the Arctic. The main pathways for the transport of pollution aerosols between the mid-latitudes and the Arctic are shown in Figure 8,4.

Dimensions Tree Life Diagram
Figure H.4. Major sources and pathways for transport of pollutants between midlatitudes and the Arctic (after Rahn and Shaw 1982).

Moreover, the strong surface-based temperature inversions frequently occurring in this time (see Chapter 4) cause the atmosphere to stabilise, which, in turn, inhibits the turbulent transfer between the atmospheric layers. As a result of this, and also of the occurrence of only light precipitation, the removal of gases and aerosols from the Arctic atmosphere is greatly weakened. In summer, the polar front is situated to the north of the most important industrial centres and the transport of polluted air is significantly smaller. In addition, the pollution which reaches the Arctic during this time will be washed out rapidly because the region has much more rain and snow in summer than in winter. For details of the climate and meteorology of the arctic air pollution see Raatz (1991).

The question still remains as to whether the haze comes mainly from one region or from a combination of regions. In the early 1980s, atmospheric scientists proposed the following scenario, which is cited here afler Barrie (1992): "Eastern North American and South-East sources share similar features that make them less likely to contribute much haze pollution to the northern region. They are at lower latitudes (25°-50°N) than Eurasian sources (40n-65°N) and on the eastern side of continents immediately upwind of stormy oceans (Atlantic and Pacific). Their industrial waste blows mostly to the east, where it is washed out by rain over the oceans. In contrast, Eurasian pollution blows to the north-east over land which in winter is a cold, snow-covered polar desert. It encounters little rain or snow to wash it from the atmosphere. In summer, movement of Eurasian pollution to the Arctic is weaker, because winds blow less frequently to the north and because there is more rain to remove it on its pathway northwards." Barrie et al (1989), working on the chemical transport model, found that most of the pollution in a year (96%) entered the Arctic from Eurasia; the reminder (4%) came from North America (Figure 8.5). The haze pollution coming from Eurasia was approximately evenly split between western Europe, eastern Europe, and the USSR.

Arctic Haze Pollution

LONGITUDE

Figure 8.5. The amount of sulphur entering (he Arctic circle on the wind during one year (July 1979 - June 1980) according to latitude. Results are given for all pollution and then for each of the major source regions that, combined, contribute 96 per cent of the total sulphur entering the Arctic (after Barrie 1992).

LONGITUDE

Figure 8.5. The amount of sulphur entering (he Arctic circle on the wind during one year (July 1979 - June 1980) according to latitude. Results are given for all pollution and then for each of the major source regions that, combined, contribute 96 per cent of the total sulphur entering the Arctic (after Barrie 1992).

One should mention here that not all scientists share these views on the above scenario (see Jaworowski 1989; Khali! and Rasmussen 1993). Jaworowski (1989) writes that "...the current studies do not provide any evidence which unequivocally identifies the respective contributions from anthropogenic and natural emission sources, to the long-range transport of impurities into the arctic atmosphere". One of the most important arguments for the anthropogenic origin of the 'Arctic haze' is the enrichment of vanadium. Rahn and Shaw (1982) stated that the enrichment factor for vanadium (over 1.5 times) provides an extremely sensitive test of anthropogenic pollution against the natural character of aerosol, Jaworowski (1989) criticises this assumption because it is not in agreement with the results of studies indicating that many heavy metals, including vanadium, are enriched by up to several orders of magnitude in the airborne dust, both over industrialised areas and in remote ones such as the South Pole, central Greenland, and tnid-oceanic localities. This means rather that this enrichment is due to natural processes (Ducef / al. 1975; Jaworowski etal. 1981). Jaworowski (1989) further writes that "...also the ratios of concentrations of particular elements in aerosol samples and their distribution in variously sized fractions of particles, have only a hypothetical character and are of uncertain value for detailed identification of emission sources of arctic pollutants". Seasonal variations of air pollution in the Arctic also cannot be used as an indicator of the anthropogenic influence because such variations occur in the lower latitudes too. In addition, Jaworowski (1989) adds that the precipitation patterns in the Arctic may also contribute to the spring maximum of pollutants in the air. The surface-based temperature inversions and anticyclonic situations, both of which occur very frequently in spring, also have a similar influence on pollution. The general conclusion of the Jaworowski (1989) critique is that a quantitative estimate of the relative contributions of human and natural sources to arctic pollution with heavy metals, mineral, acids, etc. will not be possible until the long-term observations of the temporal trends of contaminants in the arctic air become available.

From the list of unresolved issues concerning the 'Arctic haze' (e.g., very incomplete knowledge about horizontal and vertical distribution and even about the components of the 'Arctic haze') by Heintzcnberg (1989), one can understand the point of the Jaworowski's (1989) critique. Thus Jaworowski's view, to a certain degree, has been confirmed by the measurements and analyses of 30 gases in 'Arctic haze' and in clean Arctic air made during the Arctic Gas and Aerosol Sampling Program (AGASP) during the spring of 1983, 1986, and 1989 (Khalil and Rasmussen 1993). To look for the possible origins of the haze Khalil and Rasmussen (1993) used cluster analysis to derive regional signatures of trace gases at ground-based sites in the middle and high northern latitudes. Based on this analysis, they have argued that trace gases in the 'Arctic haze' do not come from North America and China and are unlikely to come from western Europe. Further they concluded that Arctic pollution must originate from eastern European and Russian industrial regions. For the present discussion, the most important point to note is their finding that the haze originates not at distant locations in Russia, but from within the Arctic Circle. Khali! and Rasmussen (1993) argued that industrial activity in the Kola Peninsula (with the large city of Murmansk), involving power plants, mining operations, and military-industrial products, can emit large amounts of haze-producing pollutants into the Arctic atmosphere and may thus cause the 'Arctic haze'. More recently Harris and Kahl (1994) also found that the Ni-Cu smelting complex at Norilsk may be one of the major contributors to the haze. Based on the above factors, the existing opinion, expressed recently by Raatz (1991), that local sources within the inner Arctic are usually point sources which arc only of local importance and contribute little to the arctic-wide phenomenon called the 'Arctic haze', must be revised.

The climatological importance of the 'Arctic haze' results from its influence on the radiation balance of the atmosphere, in both its short-wave and long-wave components. In the solar range (0.3 - 3.0|iim), haze particles both reflect part of the incoming radiation back to space and absorb it, mainly by the black element carbon (soot). In the terrestrial infrared spectrum (> 3|tm) haze panicles can increase the radiative cooling efficiency of the atmosphere at high relative humidities (Blanchet and List 1987, Blanchet 1991). In moist air the 'Arctic haze' forms small droplets or ice crystals that have a volume up to two orders of magnitude larger than dry aerosol particles. As a result, a substantial increase of aerosol optical depth occurs that is particularly effective in the 8-l2^im window region. Because of the surface temperature inversion, the top of the haze layer can be I0-20"C warmer than the surface temperature. Since haze layers act as grey bodies to thermal radiation, they can increase the outgoing long-wave radiation by I 2 W/nr (Blanchet and List 1987). Most authors (e.g., Blanchet 1991; Shaw 1995) estimate that the net effect of the 'Arctic haze' on the radiation balance of the atmosphere is positive. However, Karlqvist and Heintzenberg (1992) have concluded that "...at present it is not possible to predict with any certainty whether the effects of 'Arctic haze' are positive or negative; in other words whether this form of pollution adds to the greenhouse effect or contributes to a cooling of the atmosphere." For more details about relations between 'Arctic haze' and climate see, e.g., Blanchet and List (1987), Valero et al (1988), or Blanchet (1991).

Pollutants may also get into the Arctic via river runoff and oceanic circulation. According to Gobeil et al. (2001) these pathways, especially the ocean, may, over a longer period of time, be more important then the atmosphere pathway. For more details see the cited paper.

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