Have you ever experienced being in an urban environment where you can taste the air or where the air is so polluted it restricts visibility, makes you cough or causes your eyes to sting? This is a common problem in many densely populated areas around the world.
Figure 1. People wearing face mask to provide some protection against air pollutants in Nizhny, Novgorod.
The increasing use of fossil fuels has lead to an increase in urban air pollution and incidents of photochemical smog. Contributing factors to this include:
In this subtopic we will be looking at:
Air pollution is linked to health problems which can result in premature death (death that occurs at an earlier age than expected and is often preventable). With reference to Figure 2, suggest reasons why there are more deaths from air pollution projected for BRIICS countries (Brazil, Russia, India, Indonesia, China and South Africa) and the rest of the world rather than for OECD (Organization for Economic Cooperation) countries?
Figure 2. Premature deaths due to particulate matter (smoke and soot) and ozone pollution (main component of photochemical smog).
To reduce air pollution, nations often set emission standards and monitor levels of pollution in the atmosphere. Below in Table 1 are the World Health Organization (WHO), EU and USA standards for some of the main air pollutants. Consider why air pollution standards are sometimes not as stringent as recommended by the WHO?
International-mindedness
The WHO provides guidelines for air pollution standards. However, air pollution standards vary from one country to another and are often not as stringent as recommended by the WHO.
Figure 1. A main source of air pollution is vehicle exhaust fumes.
The combustion of fossil fuels can lead to emissions containing carbon dioxide, water vapour, sulphur dioxide, nitrogen oxides and particulates such as smoke and soot. If combustion is incomplete there may also be emissions of carbon monoxide and hydrocarbons. These air pollutants which are directly emitted from their source are referred to as primary pollutants. Whereas, pollutants formed when primary pollutants react in the atmosphere are referred to as secondary pollutants. These include:
Nitrogen dioxide can be either a primary pollutant or secondary pollutant:
Figure 2. Primary and secondary air pollutants.
The impacts of the main primary pollutants emitted into the atmosphere from the combustion of fossil fuels are discussed below.
Both carbon dioxide and water vapour are greenhouse gases resulting in an increase in the average global temperature and contributing to climate change.
Coal and oil contain sulphur, hence when these fossil fuels are combusted they produce sulphur dioxide gas. Sulphur dioxide is toxic and can act as:
Sulphur dioxide is also linked to an increase risk of cardiac disease and death.
Figure 3. Sulphur dioxide levels in the USA are concentrated around urban areas.
Source: Environmental Protection Agency
Nitrogen oxides comprises of nitrogen oxide and nitrogen dioxide. They are formed during combustion of fossil fuels. Levels tend to be high where there is a large concentration of motor vehicles being used.
Nitrogen dioxide is a yellow brown gas that can reduce visibility and appears as a haze over urban areas. Nitrogen oxides are:
Figure 4. Global nitrogen dioxide levels.
Can you make any deductions from the information in Figure 4 and your knowledge of Environmental Systems and Societies? In order to address this question your could ask yourself a series of other questions e.g.:
Examiner Tip
Ensure you can apply your wider ESS knowledge and understanding to different scenarios. Your should be able to interpret information presented in many different ways e.g maps and graphs.
Particulates are produced during combustion of fossil fuel and emitted into the atmosphere. Suspended particulates such as smoke and soot are often categorized according to size. Of particular concern are:
The World Health Organization (WHO) estimated that in 2012 outdoor air pollution resulted in 3.7 million premature deaths.
(Based on data from WHO)
Photochemical smog is a major problem around the world. In this section we look at the formation of photochemical smog and the impacts of tropospheric ozone.
Photochemical smog occurs when sunlight activates reactions between nitrogen oxides (NOx) and volatile organic compounds (VOCs) resulting in the formation of ozone and peroxyacyl nitrates (PAN). VOCs are carbon based compounds with a low boiling point such as propane, butane and formaldehydes.
The main sources of NOx are emissions from industry, power stations and vehicles.
The main sources of volatile organic compounds (VOCs) include industry, vehicles and solvents (e.g. used in paints and adhesives).
Forest fires either accidental or intentional (e.g. slash and burn) also increase levels of VOCs and particulate matter (e.g. PM10). In addition forest fires leads to deforestation and loss of habitats.
Figure 1. Main sources of NOX and VOC.
The formation of photochemical smog involves a series of complex reactions. The mixture of over 100 different chemicals formed is dominated by ozone but also include other oxidants such as peroxyacyl nitrates (PAN) and aldehydes.
Figure 2. Photochemical smog.
Photochemical smog is mostly likely to be formed under the following conditions:
Lots of large cities around the world experience photochemical smog. However, it tends to be more common where the city is located in a valley, the weather is sunny, dry with little wind movement and where there are high emissions from cars or industry such as in Los Angeles, Rio de Janerio and Mexico City.
Important
Ensure you understand that formation of smog is affected by climate, topography, population density and amount of industry and vehicles.
Ozone formed at ground level:
Figure 4. Ozone damage.
Attribution: David B. Langston, University of Georgia, Bugwood.org
The impacts of ozone on health, reduced crop production and material degradation also contribute to a significant economic loss.
Air pollution can be blown downwind from its source. This can result in movement of pollution from urban to rural areas. Hence air pollution can impact wide areas.
Figure 5. Brown haze above Los Angeles due to presence of nitrogen dioxide associated with smog.
A yellow-brown haze associated with smog is frequently prevalent over Los Angeles, USA. Photochemical smog was first identified in Los Angeles, during the 1940s. Meteorological conditions allows for the development of a thermal inversion within the valley. The large residential population contribute to high pollution emissions from industry and vehicles. Sunlight allows the primary pollutants to react to form ozone. Low winds prevent the pollution from being dispersed.
Examiner Tip
Ensure you do not confuse the effects of ozone in the tropopshere with ozone in the stratosphere.
Policies on air pollution are used to define the specific course of action being taken to reduce primary pollutants that contribute to air pollution and the formation of photochemical smog.
Policies can occur at international level down to local level. For example the European Union (EU) has adopted policies on air pollution that involve action at national governmental level down though to local regional governmental level to be effective. Pollution reduction policies can employ the following approaches:
Figure 1. Labels used on appliances help to inform the public about the energy efficiency levels - here 'A' indicates high energy efficiency.
International-mindedness
There are many different factors that influence the approach a country takes to cut urban air pollution. Hence approaches to a common problem can vary significantly between nations.
Changing human behaviour and practices can be very difficult. Educational campaigns are often used to inform the public about:
This can involve adopting practices at an individual level that reduce energy use such as:
Figure 2. Typical areas of heat loss from a house.
Figure 3. Charging station for electric and hybrid cars.
In addition to reducing the amount of energy consumed, renewable energy sources such as solar and wind can be used to generate electricity at a domestic level.
A variety of different economic tools can be used that include:
Figure 4. Road toll payment stations.
Economic instruments also require enforcement to be effective.
A wide variety of different technologies can be used to reduce pollution production.
Catalytic converters could be used on all motor vehicles. Catalytic converters reduce the amount of potential pollutants emitted by:
Figure 5. Catalytic converter used to reduce pollution emissions from vehicles.
Increase efficiency of processes that utilize energy e.g. more energy efficient industrial processes, more efficient cars and home appliances.
There are a range of technologies available that harness renewable energy sources (e.g. solar panels and wind turbine) that could reduce air emissions.
Research is on-coming to:
Technological changes often require time and financial investment to be developed. It may also require economic support to be competitive in the market place.
Theory of Knowledge
Urban air pollution is damaging to human health and the environment - is it a moral responsibility for individuals to take action to reduce emissions?
In the previous section we considered how human activity can be altered to reduce the production of urban air pollutants. Here we consider:
A variety of legislation can be employed to reduce atmospheric pollution. However, for legislation to be effective it requires appropriate enforcement and policing.
International agreement set goals that are adopted into national policies (e.g. 1999 Gothenburg Protocol to abate acidification, eutrophication and ground level ozone sets minimum emission standards for sulphur dioxide, nitrogen oxides, volatile organic compounds and ammonia).
Legislation can be used to set more stringent emission standards for industry, power generation and vehicles. This can encourage use of low sulphur fuel e.g. gas or adoption of renewable energy sources such as solar or wind in order to meet the more stringent standards.
The following video ‘Vehicle emission regulations in LA are making a difference’ by GeoBeats News discusses the impact of controlling emissions from vehicles in Los Angeles:
Building regulations can set stringent standards that require improvements in the energy efficiency of new and existing buildings. E.g. improved insulation of house to reduce loss of heat and adoption of more efficient appliances such as boilers.
Planning regulations can be used to locate industry and power stations outside of urban areas and in places where conditions are least likely to allow air pollutants to accumulate (e.g. outside a valley). Planning regulations can also promote alternatives to private car use e.g.:
Figure 1. Cycle lane next to cycle rental stop.
Devices called ‘scrubbers’ can be used by industry and power stations to filter emissions prior to discharge to remove primary pollutants such as particulate matter and sulphur dioxide. However, once the photochemical smog is formed, ozone and PAN are highly reactive and are removed by reactions with other chemicals, hence are not long lasting. In polluted areas levels of ozone tend to fall overnight as it reacts with the nitrogen oxide to form oxygen and nitrogen dioxide.
Restoration may involve reforestation and replanting of areas affected by the smog.
Beijing has topographical and meteorological conditions that are favourable for the formation of photochemical smog. A large population contributes to high air emissions from vehicle use and industry. Visibility in the city is often poor.
Prior to the Olympic games in 2008, a concerted effort was made to reduce air pollution. The strategy involved:
The government has also made it very difficult to buy cars. In Beijing the number of new cars available each year is limited. Only Beijing natives can buy a car and then they have to wait a very long time for the right to buy.
The following video ‘Heavy smog in China: What’s the solution’ by CCTV America considers what action can be taken to reduce smog:
Theory of Knowledge
Is state control of the number of cars available for purchase justified by the benefits it contributes to the environment and society?
Prior to large car ownership and when coal was heavily used, industrial smog was more common. Industrial smog differs from photochemical smog and is caused by smoke and sulphur dioxide emissions mixing with fog. Historically many industrial cities suffered from industrial smog.
In December 1952, London experienced industrial smog over a four day period which contributed to about 4,000 deaths. There was a significant increase in the number of deaths from bronchitis and other respiratory illnesses. Perhaps surprisingly there was a rise in deaths from drowning. The lack of visibility caused by the smog resulted in some people accidentally falling into the River Thames.
Figure 2. As a result of poor visibility during the day guides with torches were used to lead buses and ambulances.
This smog incident led to UK legislation focused on cutting air pollution emissions by reducing sulphur dioxide and smoke emissions. It allowed regional governments to designate clean air areas in which smokeless fuel replaced traditional coal used in homes. The levels of both smoke and sulphur dioxide emission has fallen since The Clean Act of 1956.
With increase in vehicle use and nitrogen oxide emissions, London is now more likely to experience photochemical smog.
The following video clip ‘Weather History: The Great Smog of 1952’ provides an overview of this event: