Air is polluted when substances, energy or effects with the potential to harm are released into what you breathe. Air pollutants cause you harm such as loss of health, comfort, stability and amenity - and may poison you due to their toxicity. They can harm species growth and damage food chains/webs in ecosystems. In the UK 29,000 a year people die prematurely because of air pollution, according to Government statistics, including hundreds of people in Bristol.
Examples of common air pollutants include: carbon dioxide; carbon monoxide; nitrogen oxide; nitrogen dioxide; ground level ozone; a range of hydrocarbons; sulphur dioxide; and particulate matter (see image above) from the microscopic through to easily visible dust.
These air pollutants originate from sources, follow certain routes, pathways, and spend extended periods in locations, sinks. Consider: carbon dioxide from Bristol homes, shops, factories and traffic building up in the atmosphere and causing climate change; radioactive substances in nuclear waste flasks from Hinkley Nuclear Power Station accumulating in Bridgewater soils; sooty particulate matter (PM10s) from vehicle exhausts penetrating deep into all our lungs. We now know more about which pollutants are where and why but still dont gather enough data and make it freely, frequently and easily available.
Rain and winds will move pollutants around and affect concentrations – and substances sometimes settle out of the air onto buildings, into soil, onto food. The mobility of a substance causing harm, or having the potential to do so, affects where it will be, when and how long it might be present. Strong sunlight can cause new pollutants to form from the cocktail pollutant mixture.
Every day too many vehicles are trying to use local roads: each weekday, half a million vehicles cross into and out of Bristol’s city centre. Bristol’s resulting traffic congestion generates serious, health damaging air pollution: in Old Market the annual mean concentration of nitrogen dioxide recorded was 63µgm3, compared to the EU limit of 40µgm3; and in St Pauls ground level ozone concentrations were 124µgm3 compared with the EU limit of 80µgm3. Traffic emissions contribute significantly to an ecological footprint 2.9 times Bristol's land area.
With respect to the pathways pollutants take we need to consider: problems of sourcing (point sources; diffuse sources); distance from source; change in pollutants during their journey; interactions between pollutants; modes of travel; modes of action and effect; and changes in environmental conditions. We need to ask questions such as: what is the pollutant like; how much is present; how long will it stay present; where will it go; where can it go; how harmful can it be?
Pollutant persistence is an important factor as substance stability determines the time it takes to break down and so reduce in harm. Pesticides you may use in the garden to kill weeds or in the home to control bugs and certain industrial wastes tend to be persistent and so hang around to cause ongoing problems. Heavy metals may be ingested and once in our bodies they bind to enzymes producing toxic effects.
Time to breakdown and mechanism of pollutant breakdown are important. Pollutants will naturally degrade but may change or break down in ways that cause harm in itself.
Toxic pollutants are those that interfere with physiological or neurological processes causing loss of health or even death. Toxins may influence enzyme function, reacting with them, stopping normal action. Pollutants may combine with cell constituents, as carbon monoxide does with haemoglobin thus affecting oxygen transport in the body. Secondary actions such as an asthma attack or heart beat irregularity may be caused.
With respect to toxicity, factors to consider are: pollutant concentration; length of exposure; frequency of exposure; age of person; activity (level of exertion); health of the exposed person, population, system; whether inhaled, ingested, or absorbed through the skin. Children are particularly vulnerable as they get a bigger dose per unit of body mass and are still developing key organs such as lungs. Those already suffering ill-health eg from asthma, bronchitis, heart problems or obesity and so on are at particular risk. Air pollution can cause coughing, chest pains and lung irritation in everyone.
Some air pollutants are carcinogens. These cause uncontrolled cell division (cancer). Examples include some pesticides, asbestos, some hydrocarbons such as are present on particulate pollution (see image at start). There is no carcinogenic air pollution level at which there is no effect. This is because cancer development results from an accumulation of irreversible cell damage. This contrasts with toxic substances, where damaging doses can be clearly established. Some carcinogens are also mutagens (chemicals or radiation that alters chromosomes) or teratogens (substances that can cause birth defects). The problem is the time lag between contact and effects.
The combined effect or two or more air pollutants is often greater than the sum of the separate effects (synergism). Smoke with sulphur dioxide and particulate matter with hydrocarbons (see image at start), are examples where the pairing causes much more harm than each individual substance. Carcinogenic hydrocarbons on microscopic particulates are delivered to the exact place they can do most harm, deep in human lungs.
Bristol allowed the building of the M32, which penetrates right into the city, between 1965 and 1975, adding to air pollution. Conventional transport planning is still very much in evidence here, with planning permission granted for the South Bristol Link (Road) and before that Cabot Circus shopping centre with its large, centrally located car park. Little wonder that air pollution problems are still very much with us. We need to tackle many different aspects: need/demand for all transport to begin with; shifting from high impact means of transport to lower impact; reducing the impact severity of high impact means of travel; harmonising planning policies and practices with sustainable transport so that one doesn't contradict the other; establishing a truly strategic, integrated Greater Bristol approach; bringing back the public service ethos of public transport; making the price of methods of travel fairly reflect their actual total costs....All this - and more - needs good democratic leadership, time, and serious money.