• No results found

Atmospheric Pollution


Academic year: 2023

Share "Atmospheric Pollution"


Loading.... (view fulltext now)

Full text

It is a subject that has served well enough with books in the past, but has become increasingly important in these early years of the 21st century. I also dare to hope that it will be of use to those involved in. discussion of such matters in the media.

Sample calculations

The parts per million (p.p.m.) concept

Nitrogen accompanying oxygen in combustion processes

Concluding comments

Sulphur pollutants

  • Origin of sulphur pollutants
  • Sulphur in fuels
  • Form of sulphur in fuels and the fate of the sulphur on combustion
  • Desulphurisation of fuels
  • Sulphur credits
  • Methods of sulphur dioxide detection
  • Sulphur pollution levels in various countries
  • Sulphur dioxide emissions from shipping
  • Acid rain
  • Acid rain in the age of greenhouse gas reductions
  • Concluding remarks
  • References

Sulfur dioxide from transport fuels is actually very low, less than 1% of the UK total. Furthermore, in none of the countries is electricity production the only source of sulfur dioxide.

Table 2.3 below gives details of the various methods for measuring amounts of sulphur dioxide
Table 2.3 below gives details of the various methods for measuring amounts of sulphur dioxide

Oxides of nitrogen

  • Introduction
  • Denitrogenation of fuels
  • NO x mitigation during burning: the ‘low NO x burner’
  • Removal of NO x from flue gas by selective catalytic reduction
  • NO x from vehicles
  • NO x from shipping
  • NO x credits
  • Means of measuring NO x
  • Concluding numerical exercise
  • References

Such lowering of the NOx levels was necessary at the time (1996) to meet local emission standards. In 'hydrocarbon selective catalytic reduction' (HC-SCR), the NOx is reduced to elemental nitrogen by unburnt hydrocarbon in the exhaust.


  • General introduction
  • Smaller particles than PM 2.5
  • Concluding comments
  • References

Annual vehicle miles traveled in Great Britain are estimated at around 250 thousand million. Total UK PM10 emissions in 2006 were 152 kilotons, 32 kilotons of which were from road transport. Diesel cars emit about 100 mg of PM10 per km traveled with a cold start up to about 30 in the same units when cruising on the highway.

The numbers are reviewed and processed in semi-quantitative calculations in the shaded area below. Solid fuels and heavy fuel oil, when used to generate electricity, cause emissions of PM10 particles of the size indicated in the calculation. From a calculation similar to the one in the shaded area above, this becomes about 1 mg per kWh of electricity.

The National Express Company has published [2] PM10 emissions values ​​from rail transport in the UK as | 235 tons per year. Domestic air travel in the UK is believed to lead to almost the same PM10 on a passenger km basis as rail travel. This is attributed to the use of wood as household fuel in areas of the country.

Table 4.1 Sources of PM 10
Table 4.1 Sources of PM 10

Volatile organic compounds (VOC) and ozone

  • Introduction
  • VOC from vehicles
  • VOC from refineries
  • Other sources of VOC
  • Measurement of VOC
  • VOC and ozone formation
  • Ozone

For example, Ford in the US operates to a standard of 29 g VOC per square meter of car surface painted. The concentration of hydrocarbons other than methane in the atmosphere is expected to be in the range p.p.b. It is also an agent in the formation of photochemical smog, as will be explained in the next section.

The former has its own chapter in this volume and the latter is dealt with in the first part of this chapter. Ozone absorbs in the ultraviolet, so air to the extent it contains ozone loses its transparency in this wavelength range. There is concern that the rapidly increasing use of ethanol (C2H5OH) as an automobile fuel will increase the amount of this form of PAN in the atmosphere.

PAN in the second sense, exclusively the acetyl form, is likely to be present at levels in the range of 5-10 p.p.b. This is an order of magnitude lower than in the 1970s, an improvement attributed to increasing restrictions on NOx, VOCs and therefore ozone during that period. While ozone levels in the atmosphere are tens or hundreds of parts per billion, the amounts of PAN as we have seen are only a few ppm.

Table 5.3 gives measured amounts of ozone at various places. Again, values should be taken as  being representative
Table 5.3 gives measured amounts of ozone at various places. Again, values should be taken as being representative

Carbon monoxide

  • Introduction
  • Contribution from motor vehicles
  • Miscellaneous sources of carbon monoxide [1]
  • Detection and measurement of carbon monoxide
  • Harmful effects of carbon monoxide
  • Concluding remarks: trends in carbon monoxide levels in air
  • References
  • Appendix to Chapter 6

These vary from place to place, but for a passenger car of recent design, a typical standard is 0.3% carbon monoxide in the exhaust at idle. Think of all the world's passenger cars as a single gas emission with a concentration of 0.3% carbon monoxide. At the end of the previous section, it was mentioned that power generation is a major source of carbon monoxide.

Being a heteronuclear diatomic molecule, carbon monoxide is active in the infrared and this can form the basis for instrumental measurements of the compound's amounts. This book is more concerned with the health effects of background levels of carbon monoxide in the atmosphere. Figures on carbon monoxide levels in the atmosphere are not available from the 1950s.

The lifetime of a carbon monoxide molecule in the atmosphere is about two months before its oxidation to carbon dioxide occurs. The decline in carbon monoxide, which began in the 1980s, is due to a number of factors. Such radiation causes photolytic reactions at levels of the atmosphere closer to the Earth's surface that produce OH radicals, reducing the lifetime of a carbon monoxide molecule.

Metals in the atmosphere

  • Lead
  • Mercury
  • Cadmium
  • Nickel
  • Arsenic 13
  • Analysis of air for metallic elements
  • References

Background levels of typically 0.5 ng m-3 (| 0.1 parts per trillion molar basis) of cadmium occur in the atmosphere. Furthermore, a surprising proportion of oesophageal cancer deaths in the Norwich area had been from non-smokers (see below). If we assume that half of it is the number on the bottom line it becomes 200.

In the limit where all nickel in the atmosphere is assumed to be from petroleum products, the residence time of a particle of nickel in the atmosphere is longer. Second, for the rationale underlying the calculations, it is not necessary to assume that nickel exists in the atmosphere as elemental nickel. The arsenic in the air is partly from natural sources, especially volcanic activity, and partly from

Levels in the atmosphere are on the order of 1 ng m-3 ({0.4 parts per trillion molar basis). It has been estimated [5] that an upper limit of cancer risk due to arsenic in the atmosphere is 3 u 10-3 per μg m-3 of arsenic in the air. Applications to three of the elements discussed in this chapter will be described in the concluding paragraph below.

Chlorinated pollutants

  • Hydrogen chloride
  • Chlorofluorocarbons (CFCs)
  • Elemental chlorine
  • Dioxins
  • References

Note that in all examples in the table, the alkane structure, whether methane or ethane, is completely substituted with halogen atoms, completely excluding hydrogen. There is some leakage to the atmosphere and this is a concern because of the effects on the ozone layer. Important to understanding the potential of the chlorine atom in ozone depletion is that it is regenerated through the mechanism shown above.

The reader can see for himself from online sources that it is known that the lifetime of a chlorine molecule in the atmosphere before it starts to react is a few minutes. Due to the extreme dangers of dioxins, the applicable emission and environmental standards are much lower than for any other air pollutant. From this we conclude that the total concentration of dioxin in the atmosphere is only on the order of a ton or less.

It follows that the sudden release of a quantity of the order of one kg would be a major incident. Also, when the releases of dioxins from an activity that produces them are summed up on a national scale, they are expected to be in the order of grams or at most tens of grams per year. A reader of the previous section may wonder how dioxins can be measured in picogram quantities.

Table 8.1 below gives details of CFCs which, it will be appreciated, are very simple compounds
Table 8.1 below gives details of CFCs which, it will be appreciated, are very simple compounds

Greenhouse gases Part I: Background

  • Introduction to the greenhouse gas chapters
  • Gas radiation
  • Why ‘greenhouse’?
  • A simplified model for the emissivity of the troposphere
  • Levels of carbon dioxide in the atmosphere
  • The distinction between fossil fuel and non-fossil fuel carbon dioxide
  • Carbon dioxide emissions from natural gas and petroleum fuels
  • Methane as a greenhouse gas
  • Sources of carbon dioxide other than fossil fuel combustion
  • References

In 2005, the amount of carbon dioxide released into the atmosphere by combustion processes was 28,192.74 million tons [6]. Carbon dioxide in the atmosphere is absorbed by plants and converted into glucose and from there into cellulose. When the cellulose is burned, the carbon dioxide is simply returned to where it came from and there is no net increase in the carbon dioxide level in the atmosphere, and the fuels are said to be carbon neutral.

In contrast, when fossil fuels are burned, carbon dioxide that has not previously existed in the atmosphere on any time scale of interest is placed. Combustion of such fuels therefore increases the carbon dioxide content of the atmosphere, and these fuels are not carbon neutral. This means that when the wood is burned, carbon dioxide is simply put back where it came from, as discussed in the previous section.

For methane, the ratio of carbon dioxide to water in the products is 1:2. Carbon dioxide from such fields can be used for enhanced oil recovery, a topic discussed in more detail in the next chapter. We have already seen that there were significant levels of carbon dioxide in the atmosphere long before industrialization.

Greenhouse gases Part II

  • Introduction
  • Reduction of carbon dioxide emissions from power generation
  • Carbon credits
  • Carbon dioxide from vehicles
  • Carbon dioxide from aircraft
  • Carbon dioxide from shipping
  • Miscellaneous sources of carbon dioxide
  • Uptake of carbon dioxide by vegetation
  • Carbon dioxide sequestration
  • Concluding remarks
  • References

We calculate in the shaded area below the carbon dioxide emissions per TJ (1012J) of energy from the cycle in each case. This choice for the reference value of the energy will be justified in a subsequent calculation.). When biodiesel is used to power a diesel engine, the cetane number index must have the correct value (about 50). In fact, it is common knowledge that only about 2% of total CO2 emissions come from commercial aircraft.

Carbon dioxide emissions from jet aircraft are around 100g per passenger kilometre, which is comparable to the figure from a one-person motor car. Carbon credits to be purchased by BA based on the figures in the previous paragraph = 0.7 million. There are estimated to be about 70,000 vessels in the world's oceans, using 200 million tons of hydrocarbon fuel per year.

In the rainforests of the world, an estimated 1050 million trees are cut down for timber per year. The loss of this to the planet's carbon sequestration capacity can easily be calculated to be 26 million tonnes per year. It is clear that the world's forests have a vital role to play in protecting against the effects of carbon dioxide.

Radioactivity in the atmosphere

  • Radon
  • Uranium
  • Thorium
  • Polonium
  • Cosmic rays
  • Carbon-14
  • Iodine
  • Caesium
  • Some nuclear incidents
  • References

This figure has largely been adopted in a comparative health physics study of the effects of the two [1]. Of the natural isotopes of uranium, the one with the shortest decay half-life is uranium-234. For the calculation, which is about times of the order of one day, we attribute this exclusively to the isotope with the shortest half-life.

They are not actually 'rays', that is, they are not a component of the electromagnetic spectrum. However, the half-life in another sense (used previously in this volume), the time it takes for half the amount of carbon-14 to be transferred from the air to other parts of the biosphere, is only about 6 years . Chemical explosion at a nuclear waste processing facility that resulted in the release of the nuclear material to the extent of 20 megacuries (MCi).

In the first half of the twentieth century there was much activity and progress in cleaning up the air and reversing the damage done previously. Now there is the added dimension of carbon dioxide emissions, which, as has already been said more than once in this volume, is a matter of the greatest possible importance in the regulation of world affairs. A person in middle age or older is likely to feel that there was a discontinuity, a "wrong line of history," in the late twentieth and early twenty-first centuries.


Table 2.3 below gives details of the various methods for measuring amounts of sulphur dioxide
Table 2.4 below gives details of case studies where acid rain is known to have had a harmful  effect on vegetation on a large scale
Table 4.1 Sources of PM 10
Table 5.3 gives measured amounts of ozone at various places. Again, values should be taken as  being representative


Related documents

He is a famous writer of prestigious and award-winning books and is a keen observer of Indian society, what happens and why it happens in society concerns him, and so he writes, in his