Climate in cities

Basics

Causes of anthropogenic air pollution

Most of the anthropogenic air pollution enters atmosphere due to combustion of fossil fuels in power plants, industry and transportation. However, in the cities of the developed countries, transportation emissions are the main air pollutants.

Sources of anthropogenic air pollution

The basic process during which anthropogenic air pollution is emitted is the combustion of fossil fuels in power plants, both organised and individual heating systems and vehicular traffic. The air pollution is emitted also by industry and by agriculture.

At the beginning of human civilisation, only the smokes from fire-places were the anthropogenic sources of air pollution. However, the importance of the problem gradually increased. Already in 1273, the king of England Edward I forbade to use coal in London as it caused enormous air pollution.

In the 20th century, the dynamic development of industry and services caused high concentration of various institutions and factories in urban and industrialised areas. It was accompanied with the significant increase of the number of habitants, cars and buildings which also concentrated there. Vehicular traffic is of special importance in the cities where the density of streets and roads is much higher than in the non-urban areas. In many cities of the developed countries traffic nowadays is the most important source of air pollution. All the mentioned factors worsen the living conditions in towns and cities. Moreover, the urban air pollution contributes to the problem of intensified greenhouse effect and global warming.

Emission and imission

In the urban areas, there are many sources (= emittors) of air pollution, but the emission of air pollutants takes place also elsewhere. The harmful gases and aerosols can be taken by the wind and transported to places located far away from the emittor. Therefore, when we measure the quality of urban air, i.e. the concentration of a certain substance in the air, we need to remember that it is the result of the imission, which means that the substance found in a certain place may have come from different sources and areas.

Units

While emissions are usually given in large amounts (e.g. thousands tonnes per year) and divided into sources and areas of origin, the immisions, or the concentrations in the air are usually given in much smaller units like µg/m³ of the air, and we talk about concentrations for the whole Earth, like in case of carbon dioxide (CO₂), or for a given place and time, e.g. sulphur dioxide (SO₂) in London in December 1952. Global content in the air (mixing ratio) is usually expressed in ppm (parts per million) or ppb (parts per billion). More about mixing ratio in the part "Higher atmosphere" (Basics, Undestanding the stratosphere, Composition).

Anthropogenic emissions

As explained in the part "What is air pollution?", some emissions have global impact on climate, while others only a local impact. Main areas with high air pollution due to human activity are: east coasts of USA and Canada, Europe, south and south-east Asia, and south-east Australia. They are also known for high air pollution emission. The emissions of sulphur dioxide (SO₂) and nitrogen oxides (NO_x) are discussed in the part about acid rain. Other pollutants emitted in large quantities which are significant for climate system functioning are carbon dioxide (CO₂) and Volatile Organic Compounds (VOCs); CO₂ and some of the VOCs (e.g. methane and CFCs) are greenhouse gases. The emissions of VOCs are presented in the part concerning impact of industry on air pollution. The table and the charts (Fig. 5) show air pollution emissions in chosen countries. The emissions vary a lot, due to many reasons, explained below for CO₂ as an example.

                        Values in the table are expressed in thousands of tonnes.

Click on the icons below to see the data from the table in the charts!

Emission of air                                       Emission of CO₂                                     Emission of air
pollution in 1997                                           in 1997                              pollution in USA in 1997

5. Air pollution emissions in chosen countries
Please click icon to see enlarged chart! (15-30 K)
Authors: Anita Bokwa, Pawel Jezioro
Source of data: Carbon Dioxide Information Analysis Center, United Nations Framework Convention on Climate Change
http://webdab.emep.int

Example:
Emissions of global impact: Carbon dioxide (CO₂)

Emissions of CO₂ have global impact on our climate as discussed in the part "Greenhouse gases". Let us see who in the world emits the largest amounts of CO₂. According to the Energy Information Administration, the global emission of CO₂ in 2001 amounted to 6567.82 million tonnes of carbon equivalent. "Carbon equivalent units" are defined as carbon dioxide equivalents multiplied by the carbon content of carbon dioxide (i.e., 12/44).

Emissions by continents

By continents and regions, Asia with Australia and Oceania emit one third of world's CO₂, and North America's emissions make further 28%, so those two regions produce almost 60% of global CO₂ emissions. However, even though both regions emit almost the same amount of CO₂ per year, the causes are quite different. About 3 882 million people live in Asia, Australia and Oceania, which is 61% of world's population, but only 5% of the population (about 400 million people, data for the year 2000) live in North America (meaning here USA, Canada and Mexico). While in Asia, Oceania and Australia the reason of high emission is large amount of people living there, in North America the reason is a very high consumption of energy in various forms.

A closer look at the emissions by continents

Figure 7 presents which country in every continent or region emits most CO₂. For example, 46% for USA means that USA emits 46% of the whole North America's emission. Totally, 33% of world's population live in those 7 countries, but they emit as much as 51% of world's CO₂ emissions (3352 million tonnes of carbon equivalent). However the emissions per capita are very differentiated (see Figure 9).

Emission by countries

Figure 8 shows countries which emit the largest amounts of CO₂ in the world, for example 23.2% for USA means that this one country emits 23.2% of the whole world's emission. As we can see, some coutries from figure 7 appear again, but some do not. United States, China and Russia emit together over 42% of CO₂ global emission, although only 27% of world's population live there. Among the 7 largest world's emittors there are no countries from Southern Hemisphere; three of them are in Europe, three in Asia and one in North America (note that Russia is both in Europe and Asia, but is usually included to European countries).

Emission per capita 

Figure 9 shows how much CO₂ is emitted in chosen countries per person, for example it is 19.7 tonnes per one citizen of USA, while in India it is only 1.1tonnes. Such huge differences are the result of various levels of economic development. The more comfortable life (e.g. usage of cars, air conditioning, various electric home appliances etc.) , the more energy it takes, and the larger CO₂ emission due to higher energy production. 

Anthropogenic emissions by sectors

Anthropogenic air pollution comes from many sources. Usually one source emits many kinds of pollutants. But we can also see that some human activities, e.g. transportation, are decisive for certain pollutants, i.e. they are mainly responsible for a certain pollutant emission. The data from UNECE/EMEP (United Nations Economic Commission for Europe/Co-operative programme for monitoring and evaluation of long range transmission of air pollutants in Europe) show which sectors of economy (i.e. what kinds of human activity) were mainly responsible for emissions of carbon monoxide (CO), nitrogen oxides (NO_x) and sulphur oxides (SO₂) in Europe, in 2001. The emissions are expressed in an SI unit Gg; 1 Gg = 1000 tonnes. 

Carbon monoxide (CO)

In Europe, in 2001, 30 679 Gg of CO was emitted. The main source of anthropogenic CO in the air was transportation (60%), and the industry contributed to 36% of the total emission. Waste management and agriculture were of marginal importance. More about CO emissions in the part "Lower atmosphere" (Basics, Greenhouse, Fire).

Nitrogen oxides (NO_x)

Transportation was also the main source of NO_x as it delivered 63% of the total emission which amounted 10 056 Gg in 2001. Industry contributed to 35% of the total emission. Again, emissions from waste management and agriculture were of marginal importance.

Sulphur oxides (SOx)

Unlike in the case of CO and NO_x, the main source of SO_x emissions was industry. It delivered 93% of the total emission of SO_x in 2001, and the total emission amounted to 5 949 Gg. All other sectors delivered the remaining 7%.
Read more about SO₂ and NO_x emissions in the section about acid rains!

Emissions in cities

For every city, both main emission sources and main air pollutants may be a bit different. It depends on such things as: what kind of industry is located there, how intensive the traffic is, what kinds of heating systems are used etc. Air pollution in cities is delivered to the atmosphere by low emission sources (e.g. individual heating systems in houses), high emission sources (e.g. high factory chimneys) and mobile sources (cars, buses). For example: Cracow is a medium-size city in southern Poland (800 000 habitants), with developed heavy industry (a steel-work, a huge power plant) and intensive traffic. Industry delivers almost whole amount of sulphur dioxide (SO₂), and as much of carbon monoxide (CO) as transportation, but much more nitrogen oxides (NO_x) and dust. Other sources of air pollution are of marginal importance. However, in many cities of West Europe, transportation is the main source of such air pollutants as CO or NO_x, because heavy industry was moved away or replaced with new, clean technologies.

14. Emission of carbon monoxide (CO), nitrogen oxides (NOx) and dust by sectors in Cracow, Poland, in 2001.
Source: Inspectorate of Environmental Protection in Cracow

Related pages:

The air pollution is emitted also by industry and by agriculture. Read more about it in:
Climate in cities - More - Unit 1 - Industry
Learn more about greenhouse effect and global warming in:
Lower Atmosphere - Basics - Unit 2 - Greenhouse gases
Read more about concentrations SO2 in London in December 1952:
Climate in cities - Basics - Unit 1 - Negative effects
Some emissions have global impact on climate, while others only a local impact. Learn more about it in:
Climate in cities - Basics - Unit 1 - What is it?
The emissions of SO2 and NOx are discussed in:
Climate in cities - Basics - Unit 3 - What is it?
You will learn more about greenhouse gases in:
Lower Atmosphere - Basics - Unit 2 - Greenhouse gases
You will find more information about emissions of VOCs in:
Climate in cities - More - Unit 1 - Industry
Emissions of CO2 have global impact on our climate. Read more about it in:
Lower Atmosphere - Basics - Unit 2 - Greenhouse gases
Further information in the parts:
Climate in cities - Basics - Unit 1 - Negative effects
Climate in cities - More - Unit 1
 

About this page:

Authors: Pawel Jezioro, Anita Bokwa - Jagiellonian University - Cracow / Poland
Supporter: Grzegorz Wawrejko
1. Scientific reviewer: Prof. Barbara Obrebska-Starkel - Jagiellonian University - Cracow / Poland - 2003-06-20
2. Scientific reviewer: Dr. Marek Nowosad - Maria Curie-Sklodowska University - Lublin / Poland - 2003-06-16
3. Scientific reviewer: Prof. Wilhelm Kuttler - University of Essen / Germany - 2003-09-12
4. Scientific reviewer: Dr. Ulrich Reuter - Stuttgart / Germany - 2003-09-03
educational reviewing: Michael Seesing - University of Duisburg - Duisburg / Germany
last update: 2004-12-17