Air pollution in the urban atmosphere: sources and consequences

11 Air pollution in the urban atmosphere: sources and consequences K . M C D O N A L D , Concordia University College of Alberta, Canada

Abstract: The urban atmosphere is the result of the mixture of chemicals released from the complexity of emissions due to human living. Ironically, the chemicals that we release do in turn affect our health and environment. Air pollution emissions due to transportation, personal and residential choices, and industrial or commercial activities are concentrated in areas of denser population. The emissions then play a role in changing water, soil and vegetation, damaging infrastructure in the built environment, and affecting the climate and visual air quality. In the urban setting, human health effects have been linked, through epidemiological studies, to atmospheric exposure to air pollutants. In fact, individuals have a tremendous amount of control over the emissions that are generated in our metropolitan regions – about 80% of the emissions due to fuel combustion have the potential to be directly influenced by the consumer. As we recognize the damages caused by air pollution, actions to reduce emissions improve health and ecosystem outcomes. However, the developing world is eager to achieve the same wealth as developed nations through energy production and manufacturing. Opportunities for technology and knowledge transfer on a global scale can assist these countries in becoming financially sustainable while mitigating the risk of reducing global environmental safety through uncontrolled emissions. Key words: air quality, pollution sources, urban environment, urban health.

11.1

Introduction

The atmosphere is composed primarily of nitrogen (78%) and oxygen (21%); the remaining 1% is mainly argon (0.93%) and carbon dioxide (0.033%). What remains is 0.04% and it is within this small fraction of the

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Table 11.1

Atmospheric pollutant categories, chemicals, sources and impacts

Pollutant category

Dominant chemicals

Example sources

Example impacts

Acidifying chemicals

Sulfur dioxide (SO2) Nitrogen oxides (NOx) Ammonia (NH3)

Fossil fuel production and use

Ecosystem (soil, water, forest) Materials (concrete, archeological, metals) damage

Atmospheric Ozone (O3) oxidants Particulate matter (PM) Carbon monoxide (CO) Radicals (OH*, ROO*)

Primary emission and secondary formation

Respiratory and cardiac health outcomes

Atmospheric Volatile organic toxics compounds (VOCs) Hazardous air Pollutants (HAPs) Metals (Hg, Pb, Cr)

Specific chemical production and uses

Acute, chronic and cross-generational health outcomes

atmosphere that all remaining trace gases and chemical changes are found. As an example, the municipal atmosphere is a complex mixture of gases and particles released from the activities of daily living (primary pollutants) and the chemicals that result when those emissions combine (secondary pollutants). This chapter describes pollutants under categories derived from their sources and the impacts of those chemicals, including acidifying chemicals, atmospheric oxidants and atmospheric toxic substances, as described in Table 11.1. The key source sectors contributing to the urban atmosphere are compared, including those that are produced by human activity (anthropogenic including our personal emissions) and those that are from natural processes (biogenic). Environmental and human health effects of the chemicals related to specific source types are identified with an emphasis on the atmospheric contribution to those effects. Particularly, the role of atmospheric chemicals in changes to the water, soil and vegetation (acid deposition), damage to materials in the built environment (oxidation and acidification) and to climate and haze (radiation effects) are examined. This chapter identifies the role of atmospheric exposure to air sources with human health effects that are immediate (acute), long-term (chronic) or cross-generational (mutagenic). The local, regional and global challenges to the sustainability of a healthy urban atmosphere are explored. Finally, information sources and references are provided to encourage further study in the field.

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11.1 Simplified atmospheric chemistry diagram.

11.2

Categories of pollutants

Many types of pollutants are typically observed in a municipal community. While it is useful to describe the chemicals in categories with similar ecosystem and health impacts, it is important to consider that the chemistry of all these chemicals occurs simultaneously. This is the interesting challenge in the study of environmental chemistry. Referring to the simplified chemistry diagram in Fig. 11.1, the primary emissions are those gases in boxes while the transformation products are not. Note that the ozone chemistry described in Chapter 10 is connected to the acidifying chemistry through the oxidizing peroxides (HOOH) and also to the atmospheric toxics through the hydroxyl radical (*OH). For each category of pollutant, a brief history or significance of the issue, a list of contributing chemicals and their brief chemistry, and a short summary of sources of the chemical are provided.

11.2.1 Acidifying chemicals The removal of acidifying pollutants from the atmosphere to the ecosystem, or acid deposition, is the most mature and well-understood of the atmospheric issues. Acids are those chemicals that release a hydrogen ion (H+) when in water while bases release hydroxide ions (OH). The pH scale separates acids (pH less than 7) and bases (pH more than 7) at the neutral value of pH=7 where the hydrogen ion concentration is equal to the hydroxide ion concentration. While natural waters have a slightly acidic pH in the range of 5.5 to 6, acidic waters have pH values lower than 5 (NADP, 1999). As early as the 1700s, Europe was affected by rain that was more acidic than natural rainwater due to the growing industrial revolution and its

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dependence on burning coal for fuel. Conditions in the eastern USA in the mid-1800s demonstrated that the issue was not isolated to the Old World (Seinfeld and Pandis, 1998). European countries acknowledged this as a regional issue in the 1970s, introducing a framework convention to reduce the transport of acidifying emissions across borders between countries (UNECE, 2004). The USA responded to the importance of this issue in the 1980s with the Clean Air Act Amendments for acid deposition control (USEPA, 1990). In 1991, the joint Canada–United States Air Quality Agreement was enacted to manage the emissions of acidifying chemicals having transboundary effects in North America (IJC, 2010). Presently, the North American and European international agreements lead the way in emissions reduction. The emergence of the issue in developing countries aiming at increasing power production and productivity remains a global sustainability issue. The two dominant acidifying chemicals are sulfuric acid (H2SO4) and nitric acid (HNO3), created from the oxidation of the primary gaseous emissions sulfur dioxide (SO2) and nitrogen oxides (NOx) respectively. Ammonia (NH3) is also an acidifying species due to its reactions with water that release hydrogen ions into natural ecosystems. All of these chemicals have natural sources and are found in unpolluted environments at the part per billion (ppb) level in the air. In polluted ambient environments, the concentrations reach part per million (ppm) levels, one thousand times higher. The slight acidity of natural rainwater is due to the production of bicarbonate ions from the reaction of atmospheric carbon dioxide gas with water. In the presence of other inorganic acids, H2SO4 and HNO3, the pH of rainwater lowers below 5.0; this phenomenon of wet deposition is referred to as ‘acid rain’. In areas that are prone to less rainfall, acid deposition can come in the form of gases or particles. Known as dry deposition, these forms also contribute acid to the ecosystem and built environment. Depending on the local climate, wet or dry deposition processes can dominate. Figure 11.2 illustrates the relationships between these deposition processes. Locally, there is also a seasonal dependence on the relative deposition rates. As an example, the eastern and western regions of North America experience a different balance of acidic deposition. In the east, acid rain is the predominant delivery mechanism of acidity (75%), while in the arid west, dry deposition mechanisms can deliver up to 80% of the acidity (USEPA, 2005). As demonstrated in Fig. 11.3 showing the percentage source contributions of air pollutants (USEPA, 2008a), sulfur dioxide (SO2) is predominantly emitted from industrial sources (60%) and electrical utilities (20%) employing coals and other fossil fuels for energy feeds. The remaining 20% is split between transportation uses and other fuel combustion needs.

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11.2 Atmospheric deposition processes for acidifying chemicals.

11.3 Percentage contribution of primary source sectors for pollutants in the USA (USEPA, 2008a).

Nitrogen oxides (NOx) on the other hand, are emitted primarily from mobile transportation sources (60%) and the use of fuels in buildings and businesses (25%). The remaining 15% is due to industrial and electric utility emissions. Ammonia (NH3) is mainly associated with emissions from agricultural activities (85%) but, in the urban environment, ammonia is also released from humans, pets, industries and traffic.

11.2.2 Atmospheric oxidants Within a given community, oxidizing chemicals in the atmosphere will have different characteristics depending on sources, region and time of the year (Seinfeld and Pandis, 1998). Because the emissions and chemical reactivity

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tend to occur nearer to the ground, these chemicals have a greater potential for human health impacts. Typically, the term ‘smog’ is used to describe the mixture of chemicals degrading air quality in an urban setting. In the USA, smog was first recognized as a problem in California in the mid 1940s (CARB, 2011). While North America and Europe work to reduce urban air quality issues, growth in many world cities is creating air quality challenges. Notoriously poor urban air quality has been observed in Egypt, Bangladesh, Pakistan, Mexico and China (Gurjara et al., 2008; PopSci, 2008). The chemistry of urban smog was discussed in detail in Chapter 10. Generally, the primary emissions of NOx (NO + NO2), carbon monoxide (CO) and volatile organic compounds (VOCs) produce oxidizing species including ozone (O3), oxygen-containing organic chemicals (including aldehydes and organic nitrates) and particulate matter (PM). The complex interaction of these chemicals is shown Fig. 11.2. Secondary pollutants are created from the primary emissions through reactions in the atmosphere in the presence of sunlight. These processes increase the oxidizing capacity of the atmosphere, resulting in highly reactive chemistry that affects surfaces, vegetation and human health. Urban issues are largely due to numerous small and dispersed sources, most specifically automobiles. NOx emissions, which also contribute to the acidification issue, are produced during any fossil fuel burning process. Referring again to Fig. 11.3, carbon monoxide (CO) is mainly from automobile emissions (90%). Of the anthropogenic sources, 65% of VOCs are associated with fossil fuel combustion, but VOCs are also released from vegetation (75% of the total emissions), including biogenic chemicals from trees and flowers (USEPA, 2008b).

11.2.3 Toxic air pollutants Generally, chemicals in this category are less concentrated, but potentially much more hazardous than those in the other categories. Also known as hazardous air pollutants or HAPs, these chemicals are associated with damage to cells, organs and organisms (such as cancer), and include both organic and inorganic chemicals. The organic contributors include VOCs such as the BTEX (benzene, toluene, ethylbenzene and xylenes) compounds, formaldehyde and other aldehydes, phenols, organic acids, ketones and alkenes (Seinfeld and Pandis, 1998). Volatile chemicals readily evaporate into the atmosphere; these pollutants can, therefore, participate in urban chemistry and be transported long distances affecting areas far from where they are released. The main urban source of these hydrocarbons is the combustion of fossil fuels (about 50% according to Fig. 11.3), but the use of cleaning solvents (over 20%) and

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industrial processes or incineration (25%) contribute the bulk of the remaining emissions. Toxic substances in the atmosphere also include heavier chemical species such as polynuclear aromatic hydrocarbons (PAHs), organochlorines, dioxins and furans, and polychlorinated biphenyls (PCBs). While these species are generally found in particulate or aqueous phases due to their low volatility, they may enter the gas phase during combustion processes that increase the reaction temperature but are not high enough to destroy the organic species. Many of these chemicals are pesticides and herbicides that save lives and increase crop yields producing food for the human population. However, these chemicals can travel great distances over time through the atmosphere such that even pristine environments such as the arctic regions may experience chronic ecosystem and health effects (UNEP, 1997). This emphasizes the need for full life cycle accounting for the chemicals from production to environmental fate and eventual destruction. The inorganic compounds or metals are part of the natural environment through emissions from our soils, but are released into the atmosphere in polluting concentrations through incineration or when the environment is disturbed through mining. The two most common atmospheric metal contaminants are mercury and lead, although other metals used in electronics, such as cadmium, are emitted during the incineration of waste. Elemental mercury is the most volatile of metals and can be found in the atmosphere as a gas where it can travel long distances and may remain for a year after emission; hence, mercury is a global chemical (UNEP, 2008). Exposure also occurs through inhalation of the metal accumulated on particles. In the urban environment, mercury may be found in thermometers and other measurement equipment, in fluorescent light bulbs and electrical switches, and in batteries used for cameras, phones and hearing aids, for example. Therefore, the release of mercury from municipal waste incineration is a rising concern in urban centers. In the USA, efforts to reduce this municipal source reduced these emissions by over 90% between 1990 and 1999 (USEPA, 2006a) so that this source is about 10% of the total anthropogenic emissions. Mercury is also commonly concurrent with coal sources and, hence, utility and industrial boilers emit about 50% of the anthropogenic contribution of mercury to the atmosphere. As a natural compound, mercury can be found in clean air in concentrations on the order of parts per trillion, due mostly to volcanic activity. In municipal areas, concentrations can increase to part per million levels. Occupational exposure to mercury remains an issue for the working populations in dentistry applications, laboratories and the chlor-alkali industry, which uses mercury cells to produce hydrogen, caustic soda and chlorine for chemical industrial applications. Lead has been used in plumbing, surface coatings, roofing, paints,

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electronics, batteries, and gasoline additives. Release to the atmosphere was predominantly through the use of organo-lead compounds in gasoline as an anti-knock agent. The addition of tetravalent organic lead was prevalent from the 1920s until unleaded gasoline was introduced in the 1980s and was further banned in many countries in the 1990s. However, many locations have no limit on the use of leaded gasoline and the nature of the source implies that the distribution of the chemical is widespread. In the USA, mobile emissions remain the largest source sector, contributing approximately 50% of the national lead emissions (USEPA, 2008c). In urban areas, therefore, atmospheric concentrations of lead are highest near busy intersections and soils close to freeways have been demonstrated to have high concentrations of lead. Soils around homes that have been painted with exterior paints containing lead can also be a source of the metal into the home and to children playing outside (USEPA, 2000).

11.3

Sources of air pollution

The sources of urban air pollution can be generally separated into point and area sources. While a particular source may emit many different pollutants, the emission profile of a source can be quite distinct, sometimes called the source ‘fingerprint’ (Plumb, 2004). Here, anthropogenic and biogenic source sectors are discussed as a whole rather than on a chemical-by-chemical basis. Considering sources rather than chemicals is an approach that may be best associated with sustainable emission control options due to the ability to make the most cost-effective and environmentally effective decisions. That is, people are better able to understand and respond to a source of emissions (e.g. new construction materials) rather than a specific chemical (e.g. formaldehyde).

11.3.1 Anthropogenic sources Polluting emissions that are released during human activities are referred to as anthropogenic emissions. For the most part, these are related to the creation of energy to drive our transportation, industries, businesses, waste management system and homes. To provide information related to common emission sources, this section separates emissions into those that are due to transportation, to residential and personal activities, and to commercially or industrially related sources. Of course, those emissions from our businesses and industries are still driven by the demand of consumers for the products and power. Ultimately, individuals have a tremendous amount of control over the emissions that are generated in our metropolitan regions (Myers and Kent, 2003). Figure 11.4 shows that approximately 80% of the contribution to fuel combustion emissions has the potential to be directly

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11.4 Percentage contribution of fuel consumption demonstrating potential for direct consumer contribution (residential, commercial, institutional and electricity generated emissions) to criteria pollutants in the USA (USEPA, 2008a).

influenced by the consumer for each criteria contaminant in the USA (USEPA, 2008c). Transportation emissions Personal transportation in cars, trucks, boats, buses, motorcycles and other motorized vehicles is responsible for the majority of the polluting emissions found in both developed and developing cities. The combustion of diesel and gasoline products is a source of acidifying gases, particulate matter, VOCs and trace toxic chemicals (Lewtas, 2007). In cities, vehicles are a major source of nitrogen oxides, leading to acidification and ozone formation. Vehicles are the dominant source for inhalable particles (those particles that are able to penetrate deep into the lungs affecting health) typically described using PM2.5 measurements, where P.M2.5 represents particulate matter of diameter less than 2.5 μm. Diesel engines emit significantly more organic compounds and elemental carbon compared to new gasoline engines (USEPA, 2002). Toxic chemicals (including PAHs and nitro-PAHs) are also emitted due to incomplete combustion, fuel additives or other contaminants in the fuel supply. Gasoline vehicles emit relatively low amounts of particulate matter, but the potential for inhalation of gaseous and semi-volatile organic compounds is greater (Cook et al., 2007). These volatile chemical species (such as benzene, aldehydes, naphthalene and other polycyclic organic compounds) are also released from the fuel itself during use of small engines, gas-filling stations or any portable fuel containers.

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Road use, construction and maintenance all introduce particulate matter of various size fractions into the urban atmosphere. Traffic density is correlated with emissions of gases and particles, the resulting air concentrations and, hence, human exposure to the chemicals. Those who reside close to major roadways are exposed to higher concentrations of traffic emissions (Brugge et al., 2007). As these areas are often associated with neighborhoods of lower economic status, the public health implications related to poverty are interconnected. Residential and personal emissions Home construction, operation and maintenance are responsible for the emission of acidifying chemicals, particulate matter, VOCs and trace toxic compounds. New materials often emit volatile chemicals for a substantial period of time following installation. These off-gassed chemicals include formaldehyde, benzene and other potentially toxic species, especially harmful to children (Mendell, 2007). The demolition or renovation of older buildings can release substances into the atmosphere in dust that may be laden with asbestos, lead or other unknown building materials. Commercial and residential cleaning products contain a complex mixture of chemicals and add to the load of volatile emissions in the urban atmosphere (Charles et al., 2009). The indoor atmosphere, where people spend the most time and hence receive the greatest exposures, contains dust and house mites as well as the build-up of risky gases such as carbon monoxide (CO) and radon (Health Canada, 2011). Lawn care introduces pesticide and herbicide species into the urban environment around homes, businesses and green spaces where urban-living children play. Small gasoline motors such as lawnmowers and snow/leaf blowers are unregulated fossil fuel combustion source without pollution control technologies. Much of the biomass burned in urban environments is associated with personal emissions. Backyard barbeques and fires, fireplaces and woodstoves make up the main sources of emissions in the urban landscape. In the USA, 70% of primary PM2.5 and 89% of CO emissions due to biomass burning are residential (USEPA, 2008c). Fireplaces and firepits release products of wood combustion accentuated by pyrolysis (combustion without oxygen) compounds including levoglucosan from cellulose and methoxyphenols from lignin. The fine particles associated with wood smoke may be characterized by soil-sourced potassium and arsenic from wood treatment products. In Los Angeles, over 10% of total reactive organic compounds come from barbeques, garden activities and boating, depending on the day of the week and the time of the day (Coe et al., 2003). Of course, in rural communities, agricultural and forestry burning would

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contribute a much greater proportion of emissions. Vegetative burning is generally characterized by higher organic carbon and particle emissions when compared to higher efficiency fossil fuel combustion sources. However, vegetation sources emit less elemental or black carbon than fossil fuel sources in general. Biomass sources have higher soluble organic emissions and PAHs; some of these are quite specific to the source of the emission (Bostrom et al., 2002). For example, nicotine and nitrosamines are characteristic fingerprints of tobacco smoke while cholesterol and other fatty acid products are found in cooking emissions (Simoneit, 2002). Tobacco smoke impacts on human health are well documented (IARC, 2011a). Compared with other vegetative burning sources, tobacco smoke is highest in nitrogen and protein species. The presence of these species results in the formation of chemicals such as nicotine, nitrosamines and other nitrogen-containing compounds. Commercial and industrial emissions Buildings require heating, ventilation and air conditioning (HVAC) systems that have a great impact on the fuel consumption, and hence air emissions of an urban center. As many of these sources are directly related to the operation of the metropolitan system (e.g. government buildings, schools, universities and recreational facilities), there is the potential to manage fuel efficiency through municipal actions and policies. In comparison to commercial systems, home HVAC systems result in a multitude of minimally regulated emission sources (our home furnaces and air conditioners) in a variety of levels of repair. Urban HVAC fuel consumption will be based on the number of buildings, types of heating/cooling systems, fuel efficiency of available systems, and temperature variation and control due to local climate. The physical location of the metropolitan region greatly affects the mix of applications and hence fuel usage. For example, in 2003, the demand for air conditioning along the east coast of North America resulted in an energy over-demand that blacked out the entire region, affecting 50 million people (IESO, 2003). Waste incineration necessarily includes the burning of plastics, chemicals, tires and medical and other wastes, which leads to the production of hazardous air pollutants (USEPA, 2009a). Combustion conditions vary from large-scale unregulated open burning to highly regulated industrial burners. The risk is from the products of incomplete combustion of the organic compounds in the waste, including dioxins and furans, PCBs and PAHs. The incineration of medical wastes at urban hospitals may result in emissions of biologically active agents such as pathogens and viruses (Driver et al., 1990). Commercial cooking produces saturated and unsaturated fatty acid

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oxidation products and cholesterol. In urban environments, an increased number of restaurants, hotels and other eateries release high emissions of organic compounds. Cooking has been associated with emissions of a great variety of volatile organic gases including alkanes, alkanoic acids, alkenoic acids, alkanols, alkanals, ketones, dicarboxylic acids, furans, amides, steroids, PAHs and aromatic amines (Schauer et al., 1996; Straif et al., 2006). In the home, residential cooking emissions produce the greatest amount of indoor air pollutants in the home. Large industries employ a wide variety of fuel sources for power; the most common include coal, heavy petroleum products and diesel fuels. Industrial processes are classically associated with some of the first urban events that linked air pollution to morbidity and death, including the London, England event of 1952 that killed an estimated 4000 people (Whittaker et al., 2004) and the Donora, Pennsylvania event in 1948 that caused illness in half the townspeople and killed 20 (Hefland et al., 2001). Combustion of coal (which may contain up to 10% sulfur) is the main anthropogenic source of SO2 and a major source of NOx. Large point sources with tall stacks emit the gases into the atmosphere where they can undergo long-range transport. Coal combustion results in emissions of soot, fly ash, tars containing PAHs, aromatic nitrogen-containing species and other heterocyclic aromatic compounds. In the eastern USA, source apportionment studies have identified coal-fired power plants as a major source of respirable particles enhanced with sulfate and organic carbon (Polissar et al., 2001; Song et al., 2001). Diesel emissions in industrial use produce the same chemical releases as those used in transportation sources discussed earlier.

11.3.2 Biogenic sources Polluting emissions that are released from natural environments are referred to as biogenic emissions. In the urban environment, these emission sources may be restricted due to the prevalence of concrete surfaces. However, parks and green spaces, gardens and roadside trees do contribute VOCs to the atmosphere. The composition of urban biogenic organic compounds will depend on the types and dominance of emitting plant species, while the quantity will also depend on seasonal factors such as temperature and sunlight (Kesselmeier and Staudt, 1999). In many urban communities, the burden of biogenic VOC emissions can be comparable to that from anthropogenic sources. As precursor gases for the formation of ground level ozone and secondary organic particulate matter, the management of urban air quality depends on the ability to measure and model these complex chemical contributors. Models (such as the BEIS series (http://www.epa.gov/asmdnerl/biogen.html)) have been developed to account for the biogenic inventory of emissions and require

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meteorological and biological information to estimate the VOC load from urban vegetation throughout the year. The most common VOCs from plant species are isoprene and monoterpenes (terpenoids) and these are relatively well studied in terms of biosynthesis and emission factors. However, more limited information is available for the emitted alcohols and carbonyls as well as the alkanes, alkenes, acids and esters that have been isolated as biogenic VOCs. These compounds are responsible for the scents of plant species and often provide protection against pests and other stressors. In addition to VOCs from plants, urban air may be affected by natural events outside of the metropolitan area. For example, wildfire smoke or particulate matter from dust storms may travel great distances (thousands of kilometers), increasing the particle load in the air, affecting health and decreasing visibility in communities and wilderness areas (IMPROVE, 2011). Agricultural activities such as stubble burning or pesticide spraying can also affect urban areas in closer proximity. In communities near to the ocean, sea salt is another biogenic emission that enters the atmosphere. Natural weather events such as lightning storms and tropospheric folding events encourage an increase in local ozone concentrations.

11.4

Environmental and human health effects

Humans have been exposed to air pollution from the earliest cave dwellings, through the agricultural revolution and the industrial revolution. In many areas of the world, acknowledgement of these concentrations has resulted in the recognition of the need to reduce emissions to improve the quality of life and the environment on which we depend. This section is a review of current research on the links between air pollution and adverse health and environmental effects. The environmental outcomes include chemical deposition, ecosystem changes and radiation effects. The health outcomes include cardiopulmonary diseases, cancers and reproductive effects.

11.4.1 Environmental effects Ecosystem impacts The ecosystem effects of air pollution in Europe and eastern North America were first recognized in lakes and forests that were affected by acid rain in the 1970s; hence, the study of acid deposition and its impacts are mature and the developed methods have been applied to other air quality issues such as particulate matter and ground level ozone. Chemical deposition modeling is a robust tool that is used to define areas for monitoring, emission management and the impacts of new processes. Long-range transport can

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carry the acidic chemicals far downwind from the source region, affecting surrounding wilderness areas important for recreation for urban dwellers and local agricultural sources (UNECE, 2004). Acid deposition affects lakes and other surface waters that have a weak ability to neutralize the acidic species falling in the rainwater (NAPAP, 2005). The underlying soils in these sensitive areas are typically those in regions such as the Canadian and Siberian Shields that are composed of granite and have a poor ability to neutralize the acid (or low buffering capacity). As the amount of acidity increases, wide regions can be affected, as occurred in the Rhine Valley region of Europe and the eastern seaboard of North America. In regions with low buffering capacity, acid deposition will release aluminum from the surrounding soils into lakes and streams. This soluble aluminum is highly toxic to many species of aquatic wildlife. Ultimately, the way to determine if the acid deposition is sufficient to cause ecosystem damage is to make measurements on the ecosystem itself; at times, this may come too late for protection. In the urban environment, ornamental plants and trees may be affected by acidification. Plants may grow more slowly, become susceptible to damage from pests or simply die. Materials damage Particulate, acidifying and oxidizing chemicals encourage the decay of building materials. Damage can include pitted stone surfaces, paint damage or structural weakening of metals. Many of Europe’s historical buildings, cultural heritage sites and outdoor artworks are at risk due to deposition of these chemicals (Cowell and Apsimon, 1996) and the risks are increasing in all urban centers globally. Once it has occurred, the damage is permanent. For urban commuters, the damage is most evident on automobiles. As pollutants deposit on painted surfaces, the coatings are chemically damaged. This then increases the risk of corrosion of the metal body and decreases the life of the vehicle. In addition to vehicles themselves, roadways and bridges are also susceptible to the same corrosion, increasing the municipal costs to maintain transportation infrastructure (Lipfert and Daum, 1992). Visibility and radiation effects To see an object through the atmosphere, light from the sun must reflect off that object. The image that we observe is affected by the quality of light radiation reaching our eyes. The ability to see through the atmosphere therefore depends on the light scattering and absorption properties of gases and particles found between the observer and the scene. However, the sun angle with the horizon, weather phenomena (e.g. humidity), light pollution

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and the ability of the observer also play a part in determining the overall perception of visibility. Some gases and particles are able to absorb light directly. In an urban atmosphere affected by high nitrogen oxide emissions, a ‘brown cloud’ may be observed due to the absorption of light by NO2 gas. Particles that are able to directly absorb light are generally composed of black carbon from fuel combustion and forest fires, for example. Gases in the atmosphere scatter light, creating the blue sky. Particles that are about the same diameter as the wavelengths of visible light (0.4 to 0.7 μm) are the most efficient at scattering light and decreasing visibility. In most urban centers, these particles will include sulfate, nitrate and organic particles. Indeed, these are the same particles most responsible for human health implications and, therefore, visibility is a surrogate indicator for people who experience health stress due to air pollution exposure (NARSTO, 2004). Visual range, measured in distance, is used in meteorology to identify visibility concerns for aircraft safety. However, human perception of visibility depends on relative changes in air quality and the unit of the deciview (dv) has been developed to account for this relationship. A one increment or unit change in deciview is equivalent to a 10% change in light extinction and this amount has been described as a ‘just-noticeable-change’ for people and so is used as the measure to track progress on visibility improvements in the USA (IMPROVE, 2011). Emitted gases and particles influence the balance between the solar radiation that reaches the earth’s surface and the infrared radiation that is transmitted back into space. This impacts the radiation balance of the environment, changing the planet on a global scale. Processes occur both directly (direct forcing), as air pollutants scatter and absorb incoming solar and outgoing infrared radiation, and indirectly (indirect forcing), as chemicals influence cloud formation and precipitation. The balance between these can result in regional changes in temperature and climate. This process is described in greater detail in the reports of the Intergovernment Panel on Climate Change (IPCC, 2007). Changes to the energy balance of the planet are usually expressed as radiative forcing in units of watts per square meter (W/m2). Carbon dioxide and the other well-mixed greenhouse gases produce the greatest positive climate forcing of +2.64 W/m2, with a high level of scientific understanding. Changes in the amount and type of particulate air pollution, both anthropogenic and biogenic, contribute to climate change through a net cooling of the atmosphere. Therefore, increased particle concentrations are estimated to counter this forcing by anywhere from 0.4 W/m2 to as much as 2.7 W/m2. The large range emphasizes that scientific uncertainties relating to particle radiative forcings remain very large (IPCC, 2007).

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11.4.2 Human health effects The urban atmospheric environment is affected by chemical use, distribution and fate. The resulting variety and complexity of the mixture of chemicals can affect health in ways that are immediate (acute) or over long time periods (chronic). As populations in urban centers increase, general exposure to this mixture of chemicals also increases and the variety of responses to the exposure also grows. Inhalation or dermal exposure to atmospheric contaminants by individuals can result in neurotoxicity or carcinogenicity. Over generations, the transfer of genetic change to offspring can produce effects that are able to disturb the growth and development of a fetus (teratogenic) or cause chromosomal damage passing defects from mother to child (mutagenic). The result is a continuum of health effects from negligible through to reduced quality of life, then morbidity and death or transgenerational disease. The chemical complexity comes from a bewilderment of sources. This complexity challenges public health science in ways that limit the ability to effectively reduce exposure and impacts due to scientific, political and economic uncertainties. Research approaches to the study of health effects involve experiments where animals are exposed in a controlled laboratory environment and biological responses are measured (animal toxicology studies), human volunteers are exposed in a controlled setting to measure short-term reversible effects (clinical studies), individual exposure and impacts are compared (personal exposure studies) and human populations in the real world have health outcomes compared with regional ambient concentrations of chemicals of concern (epidemiology). In urban centers of large population, epidemiology is a tool that allows the investigation of a wide range of exposures and responses to chemicals. There are challenges with this approach and the method requires rigorous statistical judgment; however, epidemiology is providing valuable insight into the health effects of atmospheric pollution in communities around the globe (Krewski and Rainham, 2007; Krewski et al., 2003). Health implications of fossil fuel use As early as the mid-1700s, the products of coal combustion were known to cause scrotal cancers in chimney sweeps. Through the early 1900s, much research focused on the identification and assessment of the products that were responsible. The recognition of PAHs and benzo(a)pyrene (BaP) as carcinogenic compounds occurred as early as the 1930s (see pertinent documents listed at IARC, 2011b). These coal-burning byproducts (soot and tar) were also associated with inhalable particulate matter and associated respiratory symptoms. Nonetheless, the demand for power and

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heat derived from fuel consumption has increased air pollution due to this source in many urban centers. In the urban environment, petroleum, oil and lubricant-contaminated sites are common in locations that may have had gas stations, garages or any commercial businesses with trucking or delivery. The hydrocarbons emitted from the soils on redevelopment ore remediation are complex and varied and may also contribute to exposure and health outcomes (Nabulo et al., 2010). Recent reviews in the USA (USEPA, 2009b) and Europe (WHO-EUR, 2006) have provided evidence linking particulate air pollution to a variety of chronic health outcomes including cancer, cardiovascular disease and reproductive effects. Hundreds of chemical species have been isolated from urban particulate matter of inhalable size. However, the individual chemicals make up only a small fraction of the organic mass found in particulate form; urban organic mass can be up to 90% unknown mass. Therefore, to date, health effects have been best correlated with particulate matter as a whole rather than with individual chemicals within the mass (Hassing et al., 2009; WHO, 2011a). The human body has defense mechanisms for managing particulate matter of larger sizes including nose or throat impaction, coughing or swallowing and bronchial removal by cilia. Therefore, of greatest concern are those particles that are small enough (< 2.5 μm in diameter, PM2.5) to be able to bypass these mechanisms and enter the body system. The smallest particulate matter size fractions (ultrafine, <0.1 μm) have the highest potential for radical formation increasing reactivity of the chemicals and resulting in the production of hydroxyl radicals and increasing health implications due to DNA damage. Health outcomes from cancer to cardiovascular effects have been linked to free radicals and hydroxyl radical generation in the body. The Integrated Science Assessment for Particulate Matter (USEPA, 2009b) states that long-term exposure to particulate matter contributes a substantial fraction of total deaths. This conclusion was primarily based on three epidemiological studies involving large numbers of individuals; perhaps the most indicative was the study of Seventh Day Adventists who have very low confounding factors (e.g. non-smoking and healthy diet). This study demonstrated that an increase in the annual average PM2.5 mass by 10 μg/m3 was associated with a 13% increase in lung cancer deaths in this relatively healthy population. The overall conclusion is that exposure to particles from fuel combustion increases the risk of death from both cancer and cardiopulmonary disease. Figure 11.4 shows that, as consumers of fuel and goods, individuals in a community can greatly affect the influence of these emissions on the health of the population. The link of particulate air pollution to pregnancy difficulties, infant mortality and congenital abnormalities was identified most strongly in studies in Eastern Europe as air pollution controls were put into effect in the

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1990s (Bobak and Leon, 1999). A growing number of epidemiological studies globally have demonstrated that premature birth and low birth weights (fetal growth retardation) were associated with increased ambient air particulate matter concentrations (Ravindra and Van Grieken, 2001). In general, the fetus may be more at risk from air pollution exposure, resulting in lower immune response, decreased ability to metabolize carcinogens and lowered capacity for DNA repair. Studies of male reproductive health have not demonstrated a link between air pollution and sperm count or concentration, but there are links with sperm motility, morphology and chemistry (DeRosa et al., 2003). The use of diesel and gasoline in vehicles increases directly with population, increasing health risks to urban dwellers from exposure to the atmospheric products of the combustion of these fuels (Wang et al., 2009). Like coal burning, the byproducts include carcinogenic species such as PAHs, nitro-PAHs and BaP (Ravindra and Van Grieken, 2001). Urban environments have been shown to have three orders of magnitude greater concentrations of these carcinogenic species than rural locations. In addition, diesel characterization studies have demonstrated that mutagenic organic compounds were also prevalent, including 1-nitropyrene and 3nitrobenzeanthrone. The Health Assessment Document for Diesel Exhaust (USEPA, 2002) documents evidence from animal toxicology and human epidemiology studies from many countries and provides evidence for a causal relationship between lung cancer and diesel exposure at measured environmental concentrations. Gasoline vehicles with catalytic converters have generally lower hazardous emissions, but benzene in gasoline continues to be a carcinogenic concern (Duarte-Davidson et al., 2001). Ozone is another secondary pollutant associated with fuel consumption, which can irritate the respiratory system and reduce lung function by inflaming the cells that line the lungs (USEPA, 2006b). Ozone can aggravate chronic lung diseases such as asthma, emphysema and bronchitis and may reduce the immune system’s ability to fight off bacterial infections in the respiratory system. Repeated short-term ozone exposure to children’s developing lungs may lead to permanently reduced lung function in adulthood. In adults, ozone exposure may accelerate the natural decline in lung function that occurs as part of the normal aging process. Modern coal-fired power plants are certainly much more efficient at reducing gaseous and particulate emissions to be even lower in mass than other energy sources. The potential cancer risk of the products of these modern processes requires study, but improving technology transfer with developing nations as they increase their power production would certainly benefit health globally.

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Health implications of cooking and biomass and waste burning The burning of wood, paper or trash, the consumption of tobacco and cooking also contribute VOCs and particles to the atmosphere inside the home. Many biomarker tracers are associated with these smoke products, enabling their identification in the air for use in human health studies. Contemporary waste facilities efficiently incinerate waste, creating clean power; hence, the issue is one of technology transfer to developing nations where health issues remain a concern. Tobacco smoke is very well documented for its cancer-causing relationship (WHO, 2011b). Exposure studies are relatively reliable and quantifiable because of the distinct biomarkers associated with nicotinic species. This enhanced emission of nitrogen-containing species increases the mutagenic nature of tobacco smoke when compared with other vegetative sources. Cadmium and chromium inhaled through tobacco smoke are carcinogenic and also have gastrointestinal toxicity. There is no risk-free level of exposure to secondhand smoke. For children, exposure to smoke is a known cause of sudden infant death syndrome (SIDS), respiratory problems, ear infections and asthma attacks. In non-smoking adults, exposure increases the risk of heart disease and cancer. In addition to active tobacco smoke, other sources of fumes and airborne particles in the indoor environment, such as the burning of incense and mosquito coils, have been considered potential risk factors for lung cancer (Tang et al., 2010). Residential cooking has the highest impact on indoor air quality and hence on human exposure in urban environments (Bruce et al., 2000; Mishra et al., 2005). When cooking oils are heated to temperatures greater than 2408C, the volatile emissions have been shown to be mutagenic. The peroxidation products of polyunsaturated fatty oils are known carcinogens. The cooking of meats produces high quantities of PAHs and cyclic amine compounds and are the most likely to be associated with the cancer risk. Ambient air pollution is also affected where from 5% to 12% of the inhalable particulate mass has been associated with meat cooking in the USA (USEPA, 2006b). In developing countries, indoor unvented burning of biomass for cooking is the suspected cause of at least two million deaths a year (mainly women and children). Efforts to improve cooking facilities have improved women’s health globally (Clark et al., 2009; Qian et al., 2007; WHO-EUR, 2010). Incineration of garbage waste becomes a necessity in areas with high population densities. The burning of plastics, chemicals, tires and medical wastes results in the formation of hazardous air pollutants. Most serious for urban environments is woodstove or backyard burning and outdated municipal waste incineration processes. These processes may produce compounds, due to incomplete combustion, which are mutagenic and

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carcinogenic (Vilavert et al., 2011). Volatile organic gases and particulate matter may contain exotic chemical species of varying toxicity (Giusti, 2009). People living in the vicinity of an open composting facility or wastewater treatment plant have the potential for exposure to airborne microorganisms including bacteria and fungi (del Cimmuto et al., 2010). Health implications of indoor air pollutant exposure The indoor environment is where most people spend most of their time. Therefore, including the quality of the air inside homes, office spaces and schools is important to understanding the overall exposure of individuals to gases and particles that can affect their health and wellbeing. Referred to as indoor air quality or IAQ, this is an area of growing research into sources, exposures and health outcomes. There is increasing evidence that exposure to poor IAQ is a cause of poor quality of life, illness and even death. People working indoors often complain about eye, nose and throat irritation, headaches and fatigue (Sundell, 2004). Building and cleaning products can emit VOCs and, particularly, oxygenated compounds such as glycolic acid, glyoxal, methylglyoxal, glycolaldehyde and diacetyl, which can irritate the senses and hence encourage such complaints or lead to adverse health effects (Anderson et al., 2008). Suspended particulate matter in indoor air can similarly irritate inhalation pathways and eyes (Ghosh et al., 2001). Allergies, airway infections and sick building syndrome are associated with indoor dampness, low ventilation rates and exposure to plasticizers. Children and infants are particularly susceptible to inhaled products as their smaller body mass requires a smaller dose to result in levels that can be irritants or cause health effects. Residential studies on respiratory health have focused on allergens, moisture, mold, endotoxins, combustion products and volatile chemicals that have the potential to increase the risk of asthma, allergies and pulmonary infections (Mendell, 2007). Compounds that have been specifically isolated as risk factors include formaldehyde from particleboard, phthalates from plastic materials and organic species from paints. Renovation and cleaning activities, the purchase of new furniture and the installation of carpets or wallpaper can all emit chemicals affecting health. On the other hand, the presence of dust mites and cockroach allergens in areas of poor hygiene are also associated with respiratory distress, especially in children (Shapiro and Stout, 2002).

11.5

Future trends and sustainability challenges

As the developed world acknowledges and acts to reduce the health and ecosystem toll of uncontrolled emissions (USEPA, 2010a), the developing world eagerly embraces energy production and manufacturing to achieve

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the same wealth of the developed nations (Molina and Molina, 2004). Global fairness of enabling communities to become financially sustainable runs the risk of reducing global environmental safety. Air emissions and their related health effects are part of that concern.

11.5.1 Global trends in atmospheric pollution The United Nations estimates that, by 2050, about 60% of nine billion people globally will be living in cities (UNESA, 2004). Global emission inventories provide snapshots of past and current urban contributions to air pollution (Butler et al., 2008). However, forecasts of future air quality are confounded by economic uncertainty, technological hopes and political realities (Olewiler, 2006). Emissions of pollutants from megacities affect atmospheric concentrations from regional to global scales. Whether emissions stay near the urban population or are transported to surrounding areas (such as agricultural regions or oceans) depends strongly on regional meteorology and geography (Lawrence et al., 2007). There is a multitude of databases of air quality data available for cities around the world (Baldasano et al., 2003). Generally, sulfur control technologies have reduced the atmospheric concentration and deposition of SO2, but sulfurous fossil fuel emissions continue to increase in Central America and Asia. An increase in nitrogen emissions due to increased automobile usage is overwhelming improvements in SO2 such that NO2 levels are at the World Health Organization (WHO) guideline value around the world. The most effective way to manage acidic deposition is to consider reductions in both pollutants. Inhalable particulate matter is a major problem in almost all of Asia. Ozone is a global problem as the WHO guideline is ubiquitously exceeded. In general, there is a worldwide trend towards reduction of air pollutants because of increasing evidence of healthrelated impacts. However, in developing countries, especially those with low average incomes, concentrations of air pollutants remain high and are increasing as development proceeds, increasing the public health impacts in those regions (Baldasano et al., 2003).

11.5.2 Information needs and knowledge transfer for sustainability Monitoring and reporting are key activities for air quality management as the tendency can be to dismiss issues that are not measured. For example, to reduce uncertainties in future model estimates, there is a great need for highquality emissions data from all global cities to provide adequate information

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about urban-level activity-based emissions and comparisons (Gurjara et al., 2008). Although much information exists on the air concentrations in urban centers, there is a need to standardize the measurements and reporting methods for comparability (Baldasano et al., 2003). Data integration across disciplines is central to making sustainable decisions. The development of models that include spatial and temporal data from economic activities, policy decisions, energy and fuel use, air pollution emissions and technology adoption will help identify opportunities for residential, commercial and industrial changes that can affect fossil fuel use (Manfren et al., 2011; Zellner et al., 2008). Much focus has been given to the issue of sustainable transportation systems as they relate to air polluting emissions and resulting human exposure (Colvile et al., 2004; Wang et al., 2009). Urban regions are recognized as ‘nodes’ for international knowledge transfer and technology sharing for competitive economic purposes (Simmie, 2003). For air quality, sustainability improvements and innovation can be supported through international knowledge transfer in air pollution control technology, air quality monitoring and environmental or health impact assessment methodologies.

11.6

Sources of further information and advice

The amount of air quality information available to the public can be staggering. There is so much, giving so many opinions, that it can be difficult to determine which is trustworthy. Generally, governments are charged with public dissemination of quality information and the environmental agencies of national or municipal governments are good sources of information about communities. Baldasano et al. (2003) provide an excellent appendix of global databases available for air quality in many world cities. In the USA, the Environmental Protection Agency (http:// www.epa.gov) houses air quality science assessments, technology documents, policy decisions and partnership project reports, all available for use as public domain information. Of particular interest to this topic are the Integrated Science Assessments for atmospheric contaminants (USEPA, 2006b, 2008d, 2009b, 2010b). The International Union of Air Pollution Prevention and Environmental Protection Associations (http://www.iuappa. org) publishes the World Atlas of Atmospheric Pollution (Sokhi, 2011), which integrates global information from these reliable sources. Several textbooks have been published that integrate and review the scientific information on air quality and pollution. In particular, Seinfeld and Pandis (1998) have produced a comprehensive document on the science of air quality chemistry and physics. Vallero (2008) presents fundamental air pollution management information in an accessible format. The United

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Nations produces many rich products; of particular note is the Global Environmental Outlook series of publications (UNEP, 2007). Often, tools are available to provide personal advice on air quality related issues such as energy use or emissions production. For example, Transport Canada produces an Urban Transportation Emissions Calculator (http:// www.apps.tc.gc.ca/Prog/2/UTEC-CETU/Menu.aspx?lang=eng). Many other calculators have arisen from the focus on climate change, but this knowledge can help reduce related air emissions such as NOx as well through energy efficiency (http://www.on.ec.gc.ca/community/ecoaction/ greenhousecalcs-e.html). More overwhelming than air quality itself, the information on health outcomes due to air pollution exposure is vast and rapidly changing. Reliable sources of information are those that integrate peer-reviewed data and publications to arrive at well-considered recommendations. The World Health Organization and its regional organizations (http://www.who.int/en/) work to ensure that information is reliable and presented in a helpful manner. Similarly, government organizations have a mandate to provide to the public the results of multi-stakeholder considerations and outcomes, making them a good choice for gathering dependable information.

11.7

References

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