Air pollution is the human introduction of particulate matters, chemicals or biological materials into the atmosphere which can cause harm or discomfort to humans, living organisms and the environment (Energy Environment, 2009).
The United Kingdom (UK) suffered its worst air pollution event when the Great Smog of 1952 formed over London. Within 6 days, more than 4000 people died and 100000 more were made ill due to the Smog's effects on the human respiratory tract (Fleming and Knorr, 1999; AEA Technology, 2009; UK Air Quality Archive, 2010).
This and similar events that occurred in the Meuse Valley, Belgium (1930) and Donora, Pennsylvania (1948), prompted many governments to initiate research on air pollution and eventually enact legislations aimed at improving air quality. Such regulatory efforts have done much to curb the problem in some areas, yet air pollution remains a significant concern worldwide with profound adverse effects on public health (Bell, 2004; Ezzati, 2002).
The major threat to clean air is now posed by traffic emissions; petrol and diesel-engine motor vehicles emit a wide variety of pollutants such as particulate matter (PM) which have an increasingly negative impact on urban air quality (UK Air Quality Archive, 2010).
The contribution of emissions from traffic is suspected to be considerable but the exposure of groups in different traffic microenvironments is largely unresearched.
In this study, literatures describing the measurement of particulate matter (PM) in different microenvironments; and epidemiological studies of health outcomes of exposure to this pollutant will be reviewed; an existing data set will be analysed and it will be concluded with a summary and recommendation for policies and further research.
TYPES AND SOURCES OF AIR POLLUTANTS
Three widespread air pollutants cause the most damage to the environment and human health, these are:
Sulphur dioxide (SO2): This is produced when fossil fuels high in sulphur are burned during smelting or other industrial processes. It affects lung function especially in asthmatics.
Nitrogen oxides (NOx): This is derived mainly from road transport emissions and other combustion processes. Frequent exposure to high concentrations of nitrogen oxides may cause increased incidence of acute respiratory illness especially in children.
Particulate Matter (PM): This is released from vehicles, power plants and industrial processes in equal measure.
Other pollutants include:
Carbon Monoxide (CO): This is a colourless, odourless and poisonous gas produced by incomplete or inefficient combustion of fuel especially in vehicles without catalytic converters. Carbon monoxide prevents the normal transport of oxygen by the blood which may lead to a significant reduction in oxygen supply to the heart.
Lead and Heavy Metals: Since the introduction of unleaded petrol in the United Kingdom, there has been a significant reduction in urban air lead levels. In recent years lead and metal smelting processes are the most significant contributors to the emission of these pollutants. Exposure to lead has been linked to impaired mental function and neurological damage especially in children.
Volatile Organic Compounds (VOCs): This includes hydrocarbons, alcohols, aldehydes, benzene and ethers. VOCs play a role in ozone formation and are emitted by industrial processes and combustion of petrol. Chronic health effects include: cancer, central nervous system disorders, liver damage, kidney damage, reproductive disorders and birth defects.
Ozone: This is primarily formed by a complicated series of chemical reactions initiated by sunlight. It involves the sunlight-initiated oxidation of VOCs in the presence of NOx. Ozone irritates the airways of the lungs and worsens symptoms of those suffering from lung diseases and Asthma (Kallman, 2008 and UK Air Quality Archive, 2010).
AIR QUALITY REGULATION IN THE UK
The ambient concentrations of a wide range of air pollutants are continuously measured at over 130 urban, suburban, industrial and rural locations throughout the UK. This is because of their potential impacts on human health, welfare and natural environments (AEA Technology, 2009).
The government and devolved administrations have achieved cleaner air by regulating industries and progressively tightening emission standards for vehicles.
The UK government initiatives on air quality currently include:
Cleaner Vehicles: This aims to promote the reduction of motor vehicle emissions.
Integrated Pollution Prevention and Control (IPPC): The main aim is to achieve a high level of environmental protection by preventing or reducing emissions into the air, water and land.
Air Pollution Prevention and Control (APPC): This system regulates industries in order to minimise air emissions.
The Clean Air Act: This aims to control domestic and industrial smoke emission. (Office of Public Sector Information, 2010; Department for Environment Food and Rural Affairs, 2010; UK Air Quality Archive, 2010).
TABLE 1.2.1: GUIDELINE VALUES FOR PARTICULATE MATTER
PM2.5
PM10
10 μg/m3 annual mean
25 μg/m3 24-hour mean
20 μg/m3 annual mean
50 μg/m3 24-hour mean
(WHO, 2008)
PARTICULATE MATTER
Particulate matter pollutants are air-suspended mixtures of solid and liquid particles which vary in number, size, shape, surface area, solubility and origin (Pope 2006). The association between cardiopulmonary disease and high concentrations of particulate matter (PM) is generally accepted however disagreements about what levels of PM exposure and the type of PM which affects human health exist.
1.3.1. CLASSIFICATION AND SOURCES OF PARTICULATE MATTER
Particle size influences the behaviour, atmospheric residence time, optical properties, surface area, and health effects of particles within the environment (Mayer et al., 1996; Harrison, 1996; Scherrer and Kittelson, 1981).
Based on the size of the particles in the ambient air, PM can be classified into:
Coarse Particles (PM10um): They generally arise from natural sources such as windblown soil; construction activities, pollens and sea spray. In a sample of urban air, coarse particles typically make up a small fraction of all particles but comprise a large fraction with respect to volume or mass (Charron and Harrison, 2003).
Fine Particles (PM2.5-10um): This arises mainly from motor vehicle exhausts, combustion processes and atmospheric reactions of gaseous combustion emissions. It also contains some crustal particles from finely pulverized road dust and soils (Laden et al 2000).
Ultrafine Particles (<0.1um): These are defined as particles having an aerodynamic diameter in the range of 0.005 to 0.1 microns (um). They are formed by condensation of hot vapors in tailpipe emissions, and can grow in size by coagulation (Pope 2006; Schauer and Cass 2000; Kleeman et al. 1999; Gray and Cass 1998).
Ultra fine particles (UFP) are of particular interests because; it is believed that they are more likely than larger particles to translocate from the lungs to the blood and other parts of the body, penetrate readily into indoor environments and are transported over much longer distances. Furthermore these particles may be toxic because they have sulphates, nitrates, acids, heavy metals and chemicals adsorbed onto their surfaces (Oberdorster 2005).
Minnesota Pollution Control Agency, 2010
Particle size is an important determinant of the site and efficiency of pulmonary deposition. Particulate matter enters the respiratory system through the nose and throat. The larger particulate matter (PM10um) is eliminated through coughing, sneezing and swallowing. The PM2.5um can penetrate deep into the lungs and travel all the way to the alveoli thereby delivering harmful chemicals to the blood system (EPA, 2003).
MOTOR VEHICLE EMISSION
Motor vehicles are one of the major sources of these particles and contribute to poor air quality, climate change, congestion, ill health etc. Concerns about exhaust emissions from vehicles have been increasing as a result of its Public Health effect on man which can be both substantial and costly (Health Canada, 2006).
Particles produced by diesel and spark ignition engines are of concern to engine builders because they influence engine performance, decrease visibility, and have negative impacts on environment and human health (Kittelson, 1998).
PARTICLE COMPOSITION AND STRUCTURE
Diesel exhaust particles consist mainly of highly agglomerated solid carbonaceous material, ash, volatile organic and sulphur compounds. The structure is illustrated below.
Typical particle composition for a heavy-duty diesel engine tested in a heavy-duty transient cycle.
Kittelson, 1998
Solid carbon is formed during combustion and much of it is subsequently oxidized. The residue is exhausted in the form of solid agglomerates. A tiny fraction of the fuel escapes oxidation and appears as volatile or soluble organic compounds (SOC) in the exhaust (Farrar-Khan et al., 1992; kittelson, 1998).
Most of the sulphur in the fuel is oxidized to SO2, but a small fraction is oxidized to SO3 that leads to sulphuric acid and sulphates in the exhaust particles. The composition of exhaust particles depends upon where and how they were collected. As the exhaust is diluted and cooled, nucleation, condensation and adsorption transform volatile materials to solid and liquid particulate matter (Kittelson, 1998).
HEALTH EFFECTS OF PARTICULATE MATTER
Studies using time series analyses have been conducted in a number of cities worldwide to investigate the association between daily changes in ambient air pollution and population risk of daily mortality (Hales et al., 2000; Lee et al., 1999; Stieb et al., 2002; Zmirou et al., 1996).
Particulate Matter has been linked to numerous adverse health effects including increased hospital admissions, emergency room visits, respiratory symptoms, decreased lung function and exacerbation of chronic respiratory and cardiovascular disease (EPA, 2003; Samet et al., 2000; Schwartz, 1994).
The aspect of particle size that is attracting the greatest current attention is the influence of fine and ultrafine particles on human health. Adverse health effects seem to be linked with smaller particles and this may be due to their chemical and physical characteristics (Dockery et al., 1993; Pope et al., 2002; Li et al., 1996; Brook et al., 2002; Somers et al., 2004).
Particulate matter with an aerodynamic diameter of 2.5 appears to be a risk factor for cardiopulmonary disease via pulmonary and systemic inflammation, altered cardio autonomic function and accelerated atherosclerosis (Fraser et al., 2003; Gilles and Gertler, 2000).
Ultra fine particles may provide a greater potential than PM2.5um for inducing inflammation based on their high numbers, high lung deposition efficiency and surface chemistry. They have a high cytotoxic reactive activity through which numerous inflammatory responses are induced compared to other particles (Chase et al., 2004)
Increase in human mortality and morbidity due to exposure to airborne fine particulate matter has led to the promulgation of stringent new air pollution regulations which limit the atmospheric concentration of particles with a mean aerodynamic diameter of less than 2.5 microns (National Centre for environmental assessment, 1996).
STATEMENT OF THE PROBLEM
While the health effects of particulate matter are now generally accepted, little is known about the mechanism and fraction of PM responsible for the observed effect. Some of the major current hypotheses for the responsible particle fraction are soluble transition metals, organic carbon compounds, strong aerosol acidity and ultrafine particles (United States Environmental Protection Agency 2002). Other studies suggest that particles from sources, especially traffic related particles are specifically associated with health effects (Laden et al 2000).
Though it is clear that motor vehicles significantly contribute to air pollution, the exposure of residents in different traffic microenvironment to pollutants in automobile exhausts is largely unresearched. This may be because the federal and state air quality monitoring programs are typically put in place to measure pollutants at the regional scale. It is therefore important to know about near highway exposures and the resultant effects in urban residents.
Measuring and understanding air pollution due to motor vehicle emission provides a sound scientific basis for management and control at local, national and international level.
AIM
The aim of this study is to see if people residing close to densely trafficked microenvironments show evidence of exposure to motor vehicle emissions.
1.8. OBJECTIVES
The main objective of this study is to provide a better understanding of air pollution due to motor vehicle emissions. This will be achieved by reviewing relevant scientific literatures and analyzing an existing dataset to achieve preset aims.
HYPOTHESIS
Individuals residing in densely trafficked microenvironments show evidence of increased biomarkers of exposure to vehicular emissions.
This hypothesis is worthy of careful study because if significant associations can be detected then control measures for traffic volume and/or technological improvements to fuel, engine, or catalytic converters could be implemented to protect human health.
