UHI's (Urban Heat Islands) Air Quality

Specification: Air Quality: particulate pollution, photochemical smog and pollution reduction policies.

The air quality of urban areas is often more polluted than that of rural areas. This relationship can too develop in reference to scales of development. For example, within developed countries, governments are more likely to pass pollution-managing legislation that in developed countries.

In order to understand why air quality is an issue, one must first learn the main contributors toward urban pollution and why they cause issues in terms of economics, society and within the environment.

The main contributors behind urban pollution are the infamous...

• Suspended particulate matter - These are particulates exhausted from industrial units, power stations and vehicle exhausts. These guys are responsible for fog (acting as condensation nuclei), respiratory problems and the soiling of buildings. SPM's can sometimes be referred to as PM10's due to their relative diameter.

The soiling of buildings creates a thick dirt layer on buildings

• Sulphur dioxide - These pollutants produce haze, acid rain, respiratory problems, corrode buildings and damage the environment.
• Oxides of nitrogen - These pollutants product haze, acid rain, respiratory problems, corrode buildings and damage the environment. (Identical to Sulphur dioxide)
• Carbon monoxide - Will cause heart problems, headaches and fatigue.
• Photochemical oxidants - Pollutants which associate with smog and cause headaches, eye irritation and chest pain.

Air quality will vary seasonally and with changes to the weather: Pollution domes are most prevalent within static, high pressure temperature inversions in which a stable climate traps pollutants over an urban area. If conditions worsen, the mixture of fog and smoke can create smog which was known in the UK as the 'pea souper (killer fog)' which killed up to 4,000 people. For these reasons, legislation was introduced by the government to manage the levels of pollution and smog. 

Smog of the past, photochemical smog of the present: 

Where smog in developed countries is relatively a thing of the past, there has now been cited an increase to photochemical smog which is essentially low-level ozone. As with other pollutants, photochemical smog is problematic when it remains static under high pressure anticyclonic weather conditions as the pollutants remain stationary owing to the absence of wind. As a result of this, pollution domes containing photochemical smog can remain for a long duration (a few weeks) during summers (the time where pollutant trapping is most prevalent). Urban areas located within river basins where high relief creates a pollutant trapping temperature inversion are where the effects of photochemical smog are most founded. Athens is often quoted as the worst affected city due to its surrounding topography, dense populations (leading to vast exhaust emissions) and frequent sunshine which means pollutants can be trapped over the area for weeks.

In response... Pollution reduction policies: 

Pollutants cause major damage to both the human and physical environments of urban areas. For example, damage to infrastructure, human health (through respiratory problems), economies (through building damage and to an extent agricultural damage where pollution develops an urban plume downwind) and toward the environment through the loss of ecology have justified government legislation to reduce pollution in urban areas.

These policies...

• Clean Air Acts - In the 1950s and as a response to the incidence of the 'pea souper' smog, the Uk government decided to prevent smoke entering the atmosphere by introducing smoke-free zones which slowly began to clean up the air. This was enhanced in later years the Air Quality Management Areas. These are essentially areas ran by local councils in areas where pollution levels are likely to exceed their allowance.
• Vehicle Control in Inner Urban Areas - Many urban areas have controlled the output of pollution into the atmosphere by restricting or banning the movement of vehicles within the urban city centres. For example, Athens uses a driving restriction in which 2.5km² of the city centre is traffic free. The UK has too acted on pollutants by using park and ride schemes which essentially pedestrianise the CBDs. Within London, a congestion charge has been used to deter vehicle entry from the city centre by exercising a road toll to force cars entering to pay a high price to enter. In Mexico, a driving restriction scheme has been used which bans all vehicles from driving one day per week (license plate decides which day). This has helped to clear up the pollutants within the atmosphere however in times where the city is particularly endangered by pollutants such as photochemical smog, this driving restriction can be extended to two weekdays and one weekend day. 
• Increased public transport networks - Councils have launched mass propaganda campaigns to persuade the public to use public transport instead of cars. For example, London's extensive public transport network uses bus only lanes and is continuing to develop routes across the city where areas are restricted for car usage by congestion charges.
• Zoning of industry - Where possible, industry has been located downwind in cities so pollutants do not integrate into urban canopies (thus inducing a variety of socio-economical problems). In addition to this, legislation has now forced industrial chimneys to locate above an inversion layer sot hat pollutants are not trapped within the urban areas.
• Vehicle emissions technology and legislation - Motor vehicles have been fit with technologies such as the catalytic converter which removes dangerous gas such as carbon monoxide however increases the output of carbon dioxide. The promotion of lead-free petrol has too been used to reduce pollution in the UK.

Next time on the season finale of 'Urban Heat Islands'... Does the Wind have an important role in influencing the micro-climates of urban areas? Will the Venturi effect increase wind speeds along your street? 

Stay tuned, Leonard.