Smoke from wood fires in Tutbury Castle in Nottingham was considered
unendurable by Eleanor of Aquitaine, wife of Henry II, causing her to move
out in 1157. A proclamation by Edward I prohibited use of coal in London
(1306), and Elizabeth I banned coal burning in London when Parliament was
in session. The repeated necessity for such royal action suggests pollution
continued to be a problem. Industrial pollution was locally important during
early and medieval times: metal smelting, ceramics, leather tanning. Pollution
problems increased with the advent of the Industrial Revolution, as coal
became a more important fuel source, and new industrial processes were
introduced. In 19th C, the main problems were associated with smoke and
ash from boiler furnaces, power plants, locomotives, ships, and domestic
fires; and acid deposition due to smelting of sulphide ores. Although public
health effects were known and many recommendations made to control emissions,
the problem increased throughout the 19th C. Patterns of pollution changed
in early 20th C with the introduction of electricity as industrial power
source shifted locus of pollution from factory to power station, though
domestic heat continued to be provided by coal. The introduction and spread
of the motor car has brought major shifts in character of pollution. the
mid-20th C saw major air pollution episodes in many urban areas, due to
a combination of high output of pollutants (especially sulphur compounds
from coal fires or smelters) and stagnant weather conditions. The type
of pollutants differs from place to place and through time, though the
importance of stagnant weather conditions in triggering air pollution
episodes remains constant.
They were very prevailent in European and North American cities during first part of 20th Century. London smogs (colloquially known as "pea-soupers" because they were thick and greenish) were infamous in the 19th and early 20th centuries, and formed every autumn and winter due to sulphur emissions from coal burning industries and domestic fires. The most severe London smog was on 4-10th December 1952, when cold, high-pressure conditions trapped coal smoke in foggy air. The output of smoke was increased by the cold weather, due to the large numbers of domestic fires. Sooty smoke produced peak daily concentrations of black smoke of 5000 microgrammes/m3 (cf. WHO 24 hr max limit of 100-150), and daily average SO2 levels of 3000-4000 microgrammes/m3 (cf. WHO 24 hr max limit of100-150). Sulphuric acid droplets resulted in pH estimated as 1.4 to 1.9: as acidic as car battery acid. Visibilty was reduced to 5m at times, and London buses had to be guided trough the street by men with lanterns during daylight hours. The smog lasted for 5 days, eventually extending over a 50km radius. Approx. 4,000 excess deaths occurred as a result of inhaling pollution, mainly old and sick and those with chest problems. According to some researchers, this figure is too low, and only refers to deaths during the smog. It does not include excess deaths after the pollution event, but perhaps triggered by it. The true figure may be as high as 10,000. Whatever the exact figure, a disaster of this scale had to provoke a reaction, and it ultimately led to the introduction of the Clean Air Acts.
Graph showing the death toll and pollution levels during the 1952 London Smog. Note that elevated death tolls continue for at least 5 days after the end of the pollution episode. (From Turco: Earth Under Seige)
However, it is important to remember that the 1952 smog was not an isolated incident: smogs were an annual occurrence in industrial and urban areas. In London, killer pollution events also occurred in 1873 (1150 excess deaths), 1880, 1882 and 1891. Nor were such events restricted to the capital. In Glasgow, one episode in 1909 killed 1063 residents. The most notorious episoide in the USA was at Donora, October 1948. At that time, Donora was an industrial town of 14,000 people, with a zinc smelter, steel mill, and sulphuric acid plant, all of which introduced sulphuric acid into the atmosphere. In October 1948, anticyclonic conditions trapped emissions near the surface, and concentrations rose as pollutants continued to be produced. The air became highly acidic, with a sickening smell of sulphur. Over a five day period, over half of the population suffered ill effects, and 22 excess deaths occurred, and 43% of the population became ill. This prompted the first effective air quality legislation in US. The Clean Air acts encouraged the transition to 'smokeless' fuels and electricity for domestic heating and cooking. Smoke (i.e.suspended particulate matter) was greatly reduced in European & North American cities, although other forms of pollution continued to increase (especially car exhausts).
Measurements from the UK's large scale smoke and sulphur dioxide sampler network extend right back to the early 1960's. The Figure shows the overall annual average from the National Survey sites up to 1981 and the overall average from the Basic Urban Network sites from 1982 to 1993. The picture that the data from this network gives is very encouraging. Levels of sulphur dioxide have fallen substantially over the last 30 years. This is because much less coal is used for heating houses, smoke control legislation has been introduced and because cleaner fuels and technologies are now being used in industry.
Sulphurous smogs are still common in other parts of the world. E.g.: Beijing, China, where high SO2 and suspended particulate levels occur every winter due to cold, clear, high pressure air (summer is the wet season). Pollution is related to coal burning, which provides 70% of all energy used in the city. Virtually all electricty generation is coal-fired, and coal is the major source of industrial power and domestic heating and cooking (highest in winter). Additionally, sulphur compounds are produced by metal smelting. However, on average 40% of the particulates in the Beijing atmosphere are due to natural sources (wind-blown dust or loess), but the remainder is mostly ash from coal burning. This is thus a situation where antural and anthropogenic pollutants combine to create very high atmospheric loads. Some control measures have been instigated (e.g. fuel switching to gas and LPG, and installation of scrubbers), but the huge capital cost required means that emissions are likely to increase in foreseeable future.
The atmospheric conditions in the LA basin commonly consist of:
The sea-breeze brings in low level, hazy air (the Marine Layer), which is trapped in the LA basin by the surrounding San Gabriel and San Bernardino Mountains. These conditions are optimum for forming and trapping photochemical smogs. Indeed, the basin was known as a pollution "hot spot" long before industrialisation. In the 16th Century, Spanish explorers found the basin draped in smog from Native camfires, and the harbour was named "Bay of Smoke".
The topographic and atmospheric situation was exarcerbated by widespread vehicle use in the 20th Century. Now, 9 million motor vehicles combined with frequent clear sky conditions and inversions combine to create serious smog problems. 70% of surface of the city is devoted to motor vehicles: roads, driveways, parking & petrol stations. Annual weather cycles mean that smogs are most serious in the autumn, when there is the most frequent occurrence of clear skies and low winds. In addition, there are characteristic diurnal cycles of pollution, with peaks in the late afternoon, reflecting patterns of emissions and photic levels (levels of sunlight). Spatial patterns of pollution reflect the frequent onshore winds, which cause smogs to drift eastwards. Thus the highest pollution levels occur in the eastern parts of the conurbation (such as Riverside), not necessarily where traffic volume is greatest. Photochemical smogs may have acute effects, including stinging eyes, burning throats and lungs. In addition, there are serious long-term effects, such as children growing up in the city showing 10-15% impairment of lung function.
UK: London 13-15 Dec 1991. Anticyclonic weather and chilling at ground level created stable air conditions, trapping exhaust products. Sunny conditions provided energy for reactions. Levels of nitrogen dioxide at street level reached 809 micrograms per cubic metre, well above WHO max. values (400). Estimated to have been responsible for 160 excess deaths. 24-28 June 1994: summer heatwave weather with high pressure conditions, combined with traffic caused photochemical smogs in many British cities, with very high ozone levels. This brought about a severe outbreak of athsma: at least 1,210 people admitted to 30 hospitals in England. Poor air quality and high pollen counts in the preceding weeks may have sensitised victims' lungs, making them more prone to attacks during the pollution event.
Developing World: Many Developing World cities suffer severe air pollution due to high traffic volumes, poor-quality fuels, and climatic factors. Examples include Delhi (India), Cairo (Egypt), and Sao Paulo (Brazil). Mexico City is perhaps the most polluted city on Earth. This is due to high output of pollutants (c. 3 million vehicles), plus a subtropical climate (i.e. frequent clear skies and high levels of sunlight), it's topographic situation (a broad basin ringed by mountains) and altitude (>7,000 feet, where combustion is less efficient). Motor vehicles are the main transport main source, and the vehicle stock old and in poor repair, running on a very rich fuel mixture due to the altitude. As a result, large volumes of hydrocarbons pass through unburnt. This results in exceptionally high levels of ozone, particulates, CO, lead, and sulphur dioxide. For example, there were unacceptable levels of CO, particulates, and ozone on 358 days in 1992. November 1992: ozone levels reached 1200 micrograms per cubic metre (cf WHO hourly limit of 150-200). It has been claimed 2,000,000 people suffer illness caused or aggravated by air pollution.
Benzene pollution reaches critical proportions in Delhi VIDYA DESHPANDE DECEMBER 18: When pollution levels touched an all time high, Delhi's sleeping bureaucracy woke up and banned the use of leaded petrol in the city. All pumps in the city began dispensing only unleaded petrol and low sulphur diesel. But what it did not reckon was by how many times the benzene content in the air would increase thanks to this move. So, when a multinational laboratory, SGS India Ltd, was commissioned by the Delhi Pollution Control Committee to check the ambient air quality, the results were shocking: The benzene content in ambient air monitored in 180 locations showed more than 100 times the permissible levels by world standards. The international levels for benzene in the air is about 30 mg per cubic metre. The SGS study showed levels that were between 1,000 and 4,000 mg per cubic metre. The study, which was conducted between March and June 1999, showed benzene levels of 1,762 around Hindu Rao Hospital in west Delhi and almost 4,100 in the posh, upper class residential colony of Greater Kailash in south Delhi. But officials are yet unwilling to accept the findings of the laboratory. A senior official in the Central Pollution Control Board (CPCB), who has been monitoring benzene levels, says that the readings as per his labs were high, but only in the hundreds and not in the thousands, as this report has shown. The CPCB has prepared a report on benzene levels in the Capital and will present it to the environment ministry early next week. However, Bhure Lal, chairman of the Environment Pollution Control Authority (EPCA), accepted that the benzene levels in the city were high. ``In highly congested areas like the ITO crossing, where the traffic movement is so dense, the levels of benzene are high,'' he says. The CPCB has been monitoring benzene levels from the start, says Lal, but had to evolve the correct methodology to study the ambient benzene levels. ``The percentage of benzene in unleaded petrol in India is 5 per cent, while it is 1 per cent in the UK,'' says the CPCB official. He says that CPCB had tested benzene levels in the air and found them to be in the hundreds, but refused to say whether the study conducted by the private lab could be inaccurate. In fact, the levels of benzene were monitored only after some non-government organisations like the Centre for Science and Environment raised the issue with the Environment Protection Control Authority (EPCA). ``It is time the CPCB made public their readings on benzene and let us know the real situation,'' says Anumita Roy Chowdhary, head of CSE's air pollution monitoring team. The EPCA has requested the petroleum ministry to work out a way by which the benzene levels in the petrol produced in the Indian refineries be brought down to 1 per cent or lower. ``We have already held talks with the petroleum ministry officials and have asked them to make the required changes in the production technology to reduce benzene levels,'' says Lal. This step would cost the petroleum ministry more than Rs 1,300 million, and this is the major hurdle in the plan. ``However, we are also working out ways of procuring low benzene petrol from other refineries abroad and should be able to come out with a solution soon,'' says Lal. Benzene is a known carcinogenic and is absorbed in the body through the skin in both the liquid and vapour phases. The presence of benzene in the ambient air of Delhi has added another harmful product to its air, in addition to the suspended particulate matter (SPM), carbon monoxide and sulphur, all of which are much higher here than the prescribed international standards.
Pollution from powerThe only way to eliminate emissions is to discontinue smelting and fossil fuel burning, but significant improvements in emission levels can be achieved through cleaner power stations. Treatment can be before, during or after combustion. Fuel switching: replacement or blending of high sulphur coal with low-sulphur coal, or switching to oil or gas or renewable sources. Shifts from domestic fossil fuel to fossil-fuel electricity generation may simply relocate the problem. Economic constraints due to availability of fuel or type of power station: blending is the most common strategy. Fuel desulphurization: removal of some sulphur before combustion. Crushing and washing can reduce SO2 by 8-15%: a reduction of 1.5 to 2 m. tonnes yr-1 has been made in the US alone. More effective & complex chemical cleaning can be done but is expensive. Reduction during combustion: basically by burning coal in the presence of lime, which fixes sulphur. Not widely applied so far, but new technologies are promising: Lime Injection Multi-Stage Burning (LIMB) is the injection of fine lime into combustion chamber, fixing sulphur, reducing emissions by 35-50%; Fluidized Bed Combustion (FBC): air under pressure is injected into fine mixture of coal, lime and sand, until whole mass behaves like a boiling fluid. Very efficient combustion, reducing sulphur emissions by 90%. Also reduces NOx because combustion temps. are relatively low. Flue Gas Desulphurization (scrubbers) removes sulphur from emissions after combustion, either by passing them through a powdered lime filter (dry scrubbers) or an alkaline liquid (wet scrubbers). Many systems achieve reduction by 80-95%. Can easily be fitted to existing stations (retro-fitting): one of main methods adopted in US, Japan and Europe. Most cost-effective overall are FBCs, but require building of new plants, rather than adaptation of existing ones. Mobile Sources Dealing with pollution from vehicles is in many ways much more problematic than stationary sources. Whereas power stations are large, single sources which are recognized by the public as pollution sources, cars are more difficult to deal with. Car use strongly linked to personal freedom and economic activity, and each user represents only a small portion of pollution. Technological solutions: Most pollution is associated with old, inefficient vehicles. The use of catalytic converters (which remove many pollutants, and break up NOx into N and O before they leave the car) and fuel injection systems, ensure more efficient combustion. Use of such measures in California ensure that most cars emit 10% of main pollutants (CO, NOx, Hc) compared with 1960s. Despite this, Los Angeles still failed to meet air quality guidelines of California Air Resources Board on 200 days in 1990. Emphasis is now on cleaner petrol with oxidizing agents (converting CO to CO2) and a new generation of low emission vehicles (LEVs). The first dual fuel cars (petrol and the less polluting gas) are now on the market, but are still beyond the price range of many people. Another technical possibility is the electric car: success depends on improved technology, particularly batteries. The only real solution to problem lies in reducing car numbers (with added benefits of reducing work hours lost to congestion, and accident figures). This will, however, be an unpopular transition. Significant reductions in pollution from car use will therefore ultimately depend on transport policies: including provision of convenient, cheap public transport provision. E.G. the Los Angeles metro. There is a pressing need for integrated policies in which public transport is comparably cheap and convenient. Emerging UK transport policy. For the first time, the UK Government has recognised need for integrated transport policy to address pollution and congestion problems, however, progress has been disappointing in the year since its launch. The current wave of petrol price increases are part of this policy, but they are already provoking angry reactions.
Internet resources:
http://www.aeat.co.uk/netcen/airqual/welcome.html
Excellent database on air quality in the UK, with up-to-date tables and maps for several key pollutants.
http://www.aeat.co.uk/netcen/airqual/reports/brochure/head.html
air quality in Edinburgh: