Air Pollution - A National Failure
An outline of the effects of air pollution and why it needs to be legislated properly.
Barry Dalgleish
O
n 16 March 2018, Glasgow City Council published its proposals on Low Emission Zones within the city. The proposal fell short of the legal requirements needed to tackle the problem of air pollution in the city. A subsequent meeting on 20 March failed to improve on the proposals.
Air pollution isn’t just a Glasgow problem, it affects the whole of the UK. This article will examine the issue of air pollution in some detail, considering the current regulatory framework and will offer a background as to why the issue needs to dealt with urgently.
S
ince the ‘Great Smog’ of London claimed over 4000 lives back in 1952, regulations on air quality have been tightened. But today’s pollution is different from the smoke induced smog’s of the past, which resulted from the burning of coal - the predominant fuel back then.
The EU has taken legal action against the UK Government. This stems from a Supreme Court ruling that the UK is in breach of the EU Air Quality Directive and “the way is open to immediate enforcement action at national or European level”.
So what are the effects of Nitrogen Dioxide (NO2) on health and what is the source of NO2 and other pollutants? The EU lists the following urban air pollutants:
Exposure times can vary for different pollutants. This is reflected in the Average period.
*Member state can apply for 5 year extension.
**Specific extension criteria available at discretion of EU Commission.
***New standard.
The Air Quality Directive (Directive 2008/50/EC) was adopted in 2008 and came into force in 2010. But as noted above states can apply for an extension. The problem with the UK is that it has failed to take steps to implement the Directive, hence the legal action.
The first two paragraphs of the Directive set the scene:
The Sixth Community Environment Action Programme adopted by Decision No 1600/2002/EC of the European Parliament and of the Council of 22 July 2002 establishes the need to reduce pollution to levels which minimise harmful effects on human health, paying particular attention to sensitive populations, and the environment as a whole, to improve the monitoring and assessment of air quality including the deposition of pollutants and to provide information to the public.
In order to protect human health and the environment as a whole, it is particularly important to combat emissions of pollutants at source and to identify and implement the most effective emission reduction measures at local, national and Community level. Therefore, emissions of harmful air pollutants should be avoided, prevented or reduced and appropriate objectives set for ambient air quality taking into account relevant World Health Organisation (WHO) standards, guidelines and programmes.
The next step in the legislative process is for member states to implement domestic legislation.
As the EU Directive has stated, the international regulatory framework is based on WHO standards and guidelines.
The key pollutants
There are two types of air pollution; Primary (emitted direct into the atmosphere) and Secondary (formed within the atmosphere). Primary air pollutants include sulphur dioxide, oxides of nitrogen, carbon monoxide, volatile organic compounds, and carbonaceous and noncarbonaceous primary particles. Secondary air pollutants arise from chemical reactions of primary pollutants in the atmosphere, often involving natural components of the environment such as oxygen and water. Secondary pollutants include ozone, oxides of nitrogen and secondary PM.
PM10,PM2.5, and ultra-fine particles (PM1 or less) are typically measured within the atmosphere and monitored. The following diagram shows the size range of airborne particles (WHO):
Oxides of nitrogen (NOx) are prevalent in high concentrations in urban areas - especially during busy periods. These are formed during high temperature combustion. From a human health perspective nitrogen dioxide (NO2) is of concern. This is formed via a reaction of nitric oxide (NO) with ozone (O3):
NO + O3 → NO2 + O2.
Carbon Monoxide (CO) is formed from the incomplete combustion of petrol.
The WHO report sums up the issues:
Emissions from road vehicles are typically thought of in terms of the exhaust, though this is only part of the story (see below). Combustion of petrol or diesel fuel leads to the production of exhaust gas containing a range of potentially harmful pollutants. In many modern vehicles this passes through a control device, such as a three-way catalytic converter, before emission to the atmosphere. Pollutants emitted from the combustion of petrol or diesel fuels typically include carbon monoxide, oxides of nitrogen, VOC and suspended particles. Some countries still use lead additives in petrol and this generates an important air pollutant emission.
Exhaust emission standards are set as limits in grams per kilometre or grams per mile of pollutant emitted over a standard driving cycle…
While exhaust emissions are often the most important emissions from a vehicle, they are far from being the only ones. Evaporative fuel emissions can also be important, especially from petrol vehicles, and these are measured and included in inventories of emissions. Far more difficult to account for, however, are the other non-exhaust emissions of PM from road vehicles that arise from sources such as the wear of brake components and tyres and the attrition of the road surface itself. Crude estimates have been made of the magnitude of these sources, which are included in many emissions inventories. However, road vehicles also cause the emission of particles by suspending particles from the road surface into the air, either through the turbulence in the wake of the vehicle or by the shear forces between the tyre and the road surface. These are far more difficult to account for and are not widely included in emissions inventories.
Emissions inventories are compiled by countries from air pollution data that has been measured and collected from relevant sources. WHO explains the general process:
In the case of road vehicles, the vehicle fleet will need to be subdivided according to the type of vehicle, the fuel it uses, and its age or any abatement technology fitted. Emission factors are developed specifically for each of these elements. In conducting calculations for an inventory, it will be necessary not only to know the type of vehicle in each category but also the annual mileage of that type of vehicle or the proportion of the total mileage that it represents on a given road link. Inventories are becoming increasingly sophisticated in disaggregating vehicles according to their age and mileage, and also in allowing for high-emission vehicles with faulty abatement devices. It is not feasible to take data directly from type approval testing and assume that a vehicle that has been operating for, say, 100 000 km produces the same emissions as a new vehicle on a dynamometer test. Test cycles, although aiming to reflect the real world, do not always do so very well.
Receptor modelling is another method of analysing air quality:
This method uses the measurements of air quality itself, often in combination with simultaneously measured meteorological data, to recognize and quantify the contributions of specific characteristic source types to air pollutant concentrations. In the case of PM, multi-component chemical analyses of consecutively collected air samples allow recognition of components that co-vary in time and therefore have the same source. Typically some 6–10 individual source types can be identified through their chemical profiles.
Exposure to air pollution
WHO defines exposure as 'the event when a person comes into contact with a pollutant of a certain concentration during a certain period of time’. This follows a distinct pollution pathway:
Source → Emissions → Concentrations → Exposure → Dose → Health effects.
Exposure also depends on location. Pollution can form in micro-environments, which may not be picked up by a stationary air monitor. So levels of exposure can vary depending on the place and time and how long the exposure lasts for. The effects of the later will depend on the pollutant and the health effect under consideration.
It should be particularly noted that exposure levels can be much higher in vehicles. For example:
in a study of taxi drivers in Paris, the average nitric oxide concentration in the taxi was more than 11 times higher than at a city background measuring site, whereas the level of nitrogen dioxide was only twice as high. Black smoke concentrations (8-hour average) in taxis were on average almost four times higher than those at a city background site. In general, cyclists and pedestrians tend to be somewhat less exposed than people in buses and cars, although this difference can be offset by longer journey times. In addition, increased breathing rates while bicycling and walking may mean that larger volumes of pollutants are inhaled.
PM exposure tends to be lower indoors because of the physical barriers to the outside.
There are several ways to determine pollution levels and exposure. Effectiveness and accuracy can vary. The following table summarises the approaches to exposure assessment:
The use of personal air monitors can offer a more representative estimate of individual exposure to pollutants.
Historical monitoring of individuals and/or sites may reveal a pattern of pollution levels and exposure and might be useful in determining disease patterns related to exposure to air pollution. It is therefore important that policy makers respond accordingly to air pollution data. The following table details possibilities for policy action in relation to indoor and outdoor sources and personal activity:
It is incumbent on policy makers to establish air quality standards that take account of potential impacts on public health and the environment. However WHO notes that:
For most air pollutants, no “safe” levels have been found whereby no health effects are observed following exposure. In fact, for many pollutants, adverse effects have been associated with low, almost background levels of exposure. Since the process of setting air quality guidelines and standards aims at defining levels that do not pose adverse effects on health, how can such levels be determined when the scientific evidence indicates that no thresholds exist?.
In other words it boils down to risk assessment and what should be regarded as an 'acceptable’ range of standards. Here in the UK that is determined by the EU.
WHO observes that:
Public opinion can be an important factor in influencing decisions, as the political capability of decision-makers is directly proportional to the interests and concerns of their constituents. Research has found that resources will often be directed to where the public perceives risks to be large, whether or not they represent the most serious hazards to society. When people understand the importance of air quality, they can demand action and be more receptive in complying with control measures. It is therefore in the interest of environmental and health authorities to ensure that the public is informed and educated about air pollution levels, sources, health impacts and possible solutions.
Maintaining an active communication strategy throughout the whole air quality management process may also help prevent crises, conciliate interests, provide advance notice for the implementation of control measures and inform stakeholders on compliance status. For these reasons, the development of communications tools that are understandable and accessible to the public is an important part of air quality management.
So the message is - if policy makers aren’t getting it then its time to put the pressure on.
How is the UK is implementing air pollution policy within the context of the WHO report and the EU Framework?
The Department for Environment Food & Rural Affairs (DEFRA) website offers guidance and links to air pollution monitoring. As part of this process, DEFRA along with the devolved administrations use air quality projections. These are models that attempt to predict future patterns of air quality. These comprise of background maps up to the year 2030. The maps consist of Excel datasets and can be referenced to any local authority in the UK.
The Community Multi-scale Air Quality (CMAQ) modeling system is used to forecast daily projections of air pollution. It was developed by the U.S. EPA Atmospheric Science Modelling Division. Other models are used, which are defined on the DEFRA website. Other useful sites include:
Air Pollution Information System (APIS). APIS provides a comprehensive source of information on air pollution and the effects on habitats and species.
National Atmospheric Emissions Inventory. The NAEI compiles estimates of emissions to the atmosphere from UK sources such as power stations, traffic, household heating, agriculture and industrial processes.
UK-AIR: Air Information Resource. Run by DEFRA. Current state of play and forecasts for air quality. There are also sites covering Scotland and Wales.
The Health Effects of Air Pollutants
The Committee on the Medical Effects of Air Pollutants (COMEAP) is an expert Committee that provides advice to government departments and agencies, via the Department of Health’s Chief Medical Officer, on all matters concerning the effects of air pollutants on health. They have produced several publications in recent years on air pollution and health.
Cardiovascular Disease and Air Pollution is an important paper published in 2006. Its worth noting that there is a lot of medical based information and data detailed within the report.
In defining cardiovascular disease (CD) the report states that it:
includes all diseases of the heart and blood vessels including stroke. It accounts for 40% of deaths in the United Kingdom and a large proportion of hospital admissions.
The most common [form] …is coronary artery disease (CAD), also known as ischaemic or atherosclerotic heart disease. Coronary artery disease is the most frequent single cause of death in the UK and is caused by atheromatous plaques occurring in the walls of the coronary arteries, the arteries which supply blood to the heart. These plaques appear first in young people and are widely distributed in the large and medium sized arteries of the body. The occurrence of plaques in the coronary arteries is particularly important as growth of these lesions can lead to progressive narrowing and eventually obstruction of the vessels in some cases. In addition, the plaques may rupture or fissure leaving an ulcer in the wall of the artery on which a thrombus (blood clot) forms. This may lead to complete blockage of the artery (coronary thrombosis or heart attack).
The report followed two research criteria:
A time-series approach, 'investigates whether air pollution is accompanied by short term changes in the incidence of cardiovascular events such as heart attacks. This method generally uses available data on daily counts of deaths or hospital admissions and relates these to ambient concentrations of air pollution on the same or previous days, measured by monitors situated in the study area – usually a city. Evidence from a large number of time-series studies show very clearly that, with few exceptions, all of the commonly measured pollutants (particles, ozone, sulphur dioxide, nitrogen dioxide and carbon monoxide) are positively associated with increased mortality and hospital admissions for cardiovascular disease.
'Compar[ing] the incidence of cardiovascular diseases between populations with different long-term exposures to pollution. These studies usually follow groups of subjects (cohorts) for a number of years and provide important information about the amount of life lost due to air pollution. Because large numbers of subjects are required and because the cohorts must be followed up for a number of years, few cohort studies have been done. The evidence from two American studies suggests that cardiovascular deaths are increased by living in areas with higher levels of particulate air pollution. This effect seems to be modified by socio-demographic and regional factors’.
The following diagram outlines the toxicological process:
The diagram considers two mechanisms that may contribute to CD. The report explains each in more detail:
Inhaled particles, especially very small particles, may set up inflammation in the lung and that this can trigger changes in the control of blood clotting. It is also suggested that changes in chemical factors in the blood can affect the stability of the fatty deposits (atheromatous plaques) found in the walls of arteries in many people – especially those in the walls of the arteries which supply blood to the muscle of the heart itself. If this is true then a link between inhalation of particles and the likelihood of, for example, heart attacks will have been established.
The inhalation of particles and perhaps some pollutant gases may trigger a reflex that leads to a subtle change in the rhythm of the heart. The triggering of a reflex begins when some stimulus is detected by a receptor, a message is sent along nerves to the spinal cord or brain and a response follows. Well known reflexes include the production of saliva on smelling appetising food and the forward kick of the leg when the tendon below the knee-cap is tapped smartly. Coughing is also a reflex: in this case the receptors are in the airways and the trigger is an irritant: perhaps a crumb of food. Air pollutants may stimulate receptors in the airways and though coughing may not be produced, reflex changes in the rhythm of the heart may occur. Such changes may lead to the heart being more susceptible to dangerous changes in rhythm: such changes can cause sudden death. Evidence for and against this theory is also presented in this chapter. Interestingly, this hypothesis links with the one above: inflammation may be involved in the early stages of both.
The above is a brief summary of the mechanisms involved in CD. There are other health effects related to air pollution including asthma and other respiratory diseases, but that would be the subject of wider research beyond the scope of this article.
First published, Mar 20th, 2018