Literature Review

Running head: THE EFFECTS OF URBAN SPRAWL ON AIR POLLUTION

The Effects of Urban Sprawl on Air Pollution

A Literature Review

Rachel Sunday

Grand Valley State University

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Introduction

Every year, approximately 1.3 million people worldwide die prematurely from the effects

of air pollution (Schindler & Caruso, 2014, p. 13). And though these deaths can be attributed to

many different factors within the built environment and beyond, the concept of “urban sprawl” is

a major contributor to the presence of air pollution. Urban sprawl can be defined as, “a pattern of

land use in an urbanized area that exhibits low levels of some combination of eight distinct

dimensions: density, continuity, concentration, clustering, centrality, nuclearity, mixed uses, and

proximity” (Pourahmad, Baghvand, Zangenehe, & Givehchi, 2007, p. 252). Its effects on the

concentration of many pollutants are not fully known, but this paper will attempt to examine the

research that is available on this subject. Throughout this paper I will overview the history of the

urban sprawl movement, give examples on the effects of sprawl, show the effects of pollution on

the environment and our personal health related to sprawl, give some findings from recent

research studies in the field, list study limitations, and finally, state some solutions and areas for

future research.

Literature Review

History of Urban Sprawl Movement

In parts of the late 19th and early 20th centuries, the Industrial Revolution spurred a

national migration movement from rural farmlands to centralized, urban areas, creating the

framework for the modern city (Nechyba & Walsh, 2004, p. 179). Following the “Great

Migration”, the remainder of the 20th century saw the growth of suburbs within urban areas

caused by the strong demand for new housing in the 1940s (Gordon & Richardson, 2000, p. 65),

and the rise of household incomes (Nechyba & Walsh, 2004, p. 182). Since 1970, over 86%

percent of population growth has occurred in the suburbs of America (Gordon & Richardson,

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2000, p. 65-66), showing that an overwhelming majority of the population prefers to live outside

the city. However, this preference for the suburbs has proved to be one that is costly both to the

health of the environmental and our population.

The Effects of Urban Sprawl

The concept of urban sprawl is an incredibly multidimensional idea, so it may sometimes

be hard to quantify (Holcombe & Williams, 2010, p. 257). However, the actual physical effects

of urban sprawl on the population and the environment are hard to miss.

Population effects.

The effects of urban sprawl on the overall population are probably less apparent than

those on the environment, but they have the potential to be just as detrimental. For example,

spreading the population out has seemed to positively affect Americans by way of larger homes

and more land space to use (Nechyba & Walsh, 2004, p. 178). However, it can negatively affect

levels of physical activity and social connectedness that a more compact city would encourage.

Also, studies have proved that the effects of sprawl are not distributed equally throughout the

population (Frumkin, 2002, p. 202) shown by the fact that ethnic and racial minority groups are

more likely to live in the urban core where access to public goods and services may be average at

best. Nechyba and Walsh (2004) point out that greater mobility leads to greater segregation (p.

184), and that is obvious in the racial compositions of inner cities and suburbs.

Environmental effects.

Urban sprawl has a huge impact on the surrounding environment structurally, physically,

and chemically. For starters, suburbanization has continued to develop a lot of land that was

previously used for agricultural, environmental, and ecological purposes, destroying vital green

spaces outside of urban areas (Pourahmad, Baghvand, Dangenehe, & Givehchi, 2007, p. 253).

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The development of new highways and road systems have also contributed to the eradication of

open land in urban areas, potentially leading to increased future rates of car crashes and

pedestrian injuries and fatalities (Frumkin, 2002, p. 202). However, it is the mere existence of

these highways that originally encouraged sprawl. Highways, along with higher rates of vehicle

ownership, enabled people to move from city centers to much more desirable places of residence

(Nechyba & Walsh, 2004, p. 181). This in turn caused higher dependence on cars and trucks,

longer travel times to every day destinations, and most importantly, greater magnitudes of

pollution-causing vehicle emissions being released into the air (Stone, 2008, p. 689).

Air pollution is one of the biggest and most harmful effects of the urban sprawl

movement, and is a link of the causal chain between sprawl and health. According to Frumkin

(2002), the causal chain follows that “sprawl is associated with high levels of driving, driving

contributes to air pollution, and air pollution causes morbidity and mortality” (p. 203). Though

we won’t talk about the health effects of pollution on population and environmental health till

the next section, studies show that lower density developments are associated with greater

concentrations of pollution-causing vehicle emissions, increasing the potential for negative air

quality implications (Stone, 2008, p. 689). With more open space and less structural formations

to block the flow of air, decentralized development is almost crucial to the formation of ozone

(O3) (p. 691). In fact, many expansive, sprawling areas experience 62% more days with high

ozone levels than more compact cities (p. 695).

Advantages to sprawl.

Though most, if not all of the information that I’ve covered so far in this paper has been

detailing the negative qualities of urban sprawl, it wouldn’t be fair to ignore the advantages to

living in larger, open areas. In relation to air pollution, one study found that though

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concentrations of pollutants may be higher in vast, residential areas, exposure levels to these

pollutants are higher in denser, urban settings (Schweitzer & Zhou, 2010, p. 365). Another study

found that even though sprawl increases distances travelled to destinations, because there may be

less traffic on secondary roads, lower population densities can actually decrease commute times

for citizens (Holcombe & Williams, 2010, p. 262). Combining these findings with other data,

such as quality of life ratings and levels of sustainability, it looks like the idea of urban sprawl

might not be so bad after all.

The Effects of Air Pollution

Pollution is defined as, “the disturbance of mixed natural structure of air as the result of

the entrance of pollutants into air” (Pourahmad, Baghvand, Zangenehe, & Givehchi, 2007, p.

253). The effects of pollution are one of the leading health concerns among the public (Marquez

& Smith, 1999, p. 542), and for good reason. In 2009, the World Health Organization listed

exposure to outdoor air pollution as 14th among the top 15 risk factors for Global Burden of

Disease (Hankey, Marshall, & Brauer, 2012, p. 247). Below, we’ll discuss the effects of

pollution on the population and the environment.

Population effects.

At the right concentrations, pollution can have many negative effects on the human body.

These include, but are not limited to: heart disease, respiratory disease, lung cancer, asthma,

atherosclerosis, cardiopulmonary mortality, impaired lung development in children, reduced lung

function, cardiac arrhythmia, and low birth weight babies (Marshall, Brauer, & Frank, 2009, p.

1752) (Hankey, Marshall, & Brauer, 2012, p. 247). And if all of that wasn’t enough, “in polluted

U.S. cities, the mortality risk from particulate air pollution is comparable to that for obesity”

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(Marshall, Brauer, & Frank, 2009, p. 1752), proving that air pollution is a serious threat to the

health of the population.

There are certain subsets of the population that are more susceptible to the effects of air

pollution than others. Minority groups, the elderly, young children, and other similar populations

are more likely to be affected by pollutants, regardless of their levels of exposure (Frumkin,

2002, p. 202, 209). A person’s genes and family history of pollution-related diseases can also

factor into their levels of susceptibility.

Environmental effects.

Pollutants in vehicle and industrial emissions cause much of the pollution burden in the

United States. These emissions include chemicals such as: carbon monoxide (CO), carbon

dioxide (CO2), nitrogen oxides (NO), hydrocarbons, and particulate matter (PM) (Frumkin, 2002,

p. 202). However, the effects of these pollutants on the surrounding environment depend heavily

on their dilution and dispersion qualities. Without getting into a discussion on complex chemical

processes, the properties of these pollutants determine how far away, and how quickly they will

dilute and disperse themselves. This is where the geography and weather patterns of an area

come into play. For example, if we were to look at a coastal, waterfront area whose terrain was

uneven and hilly, you would likely see high levels of pollution there. This is because “greater

topographic unevenness of the terrain produces a significant increase in turbulence levels, which

leads to greater dilution of a pollutant plume and reduced concentrations downwind” (Cho &

Choi, 2014, p. 5969). Pollutants tend to pool in valleys, causing higher pollution concentrations

in cities that fit this criterion.

In less dense areas, pollution can also disrupt the workings of natural ecosystems, have

negative impacts on plant and animal life, damage agricultural and forest land, and cause overall

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deterioration of the aesthetic aspects of the environment (Marquez & Smith, 1999, p. 541).

However, research has shown that certain types of trees and other vegetation absorb pollutants

through their leaves and other foliage (Cho & Choi, 2014, p. 5970), making planting trees a

priority for contributing to the continuous decline of air pollution.

Findings Relating Urban Sprawl & Air Pollution

Throughout my research on the relationship between urban sprawl and air pollution, I

came across studies from many different disciplines that showed interesting correlations, both

positive and negative. Many of these findings have already come up in earlier sections of the

paper, but for those that haven’t, they will be discussed in the following paragraphs.

Findings concerning pollution levels.

Most studies that I came across specifically studied the effects of nitrogen oxide (NO)

and ozone (O3). For example, many studies found that compact cities tend to have higher levels

of nitrogen oxide and lower levels of ozone, while suburban areas had higher levels of ozone and

lower levels of nitrogen oxide (Marshall, Brauer, & Frank, 2009, p. 1754) (Cho & Choi, 2014, p.

5977) (Hankey, Marshall, & Brauer, 2012, p. 250) (Martins, 2012, p. 71). These findings are

linked to increases in emissions from traffic congestion in cities, and increases in vehicle miles

traveled due to low-density development (Nechyba & Walsh, 2004, p. 188). Similarly, Marshall,

Brauer, and Frank (2009) found that high-income levels are positively correlated with ozone

levels, and negatively correlated with nitrogen oxide levels (p. 1756).

As illustrated above, the area in which you live can determine the type and amount of

pollution that you’re exposed to. However, Schindler and Caruso (2014) found that even though

residents in more dense areas have higher levels of exposure to pollutants, residents in suburban,

sprawling areas have higher levels of emissions present in the air (p. 21). And what’s more, a

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similar study found that sprawling areas showed higher concentrations of all pollution types from

12 pm to 6 pm every day, showing worse levels of air quality and population exposure than

central city areas (Borrego, Martins, Tchepel, Salmim, Monteiro, & Miranda, 2006, p. 464).

Despite these findings however, it has been proven that impoverished, minority communities,

regardless of where they’re located, consistently demonstrate poorer levels of air quality

compared to other neighborhoods of predominantly white families (Schweitzer & Zhou, 2010, p.

367). These populations also tend to be more susceptible to diseases caused by air pollution

(Frumkin, 2002, p. 202), further emphasizing the presence of health inequities.

Findings concerning city/spatial development & structure.

As we’ve discussed throughout this paper, geographic location, public infrastructure

(road systems), and structural development are all important to determining an area’s levels of

air pollution. However, there are some other, more specific characteristics of the built

environment that have a big effect as well. For example, historically it has been believed that

building more roads and highway systems will help to ease the congestion and traffic on other

roads in the same area. Studies suggest otherwise. Gordon and Richardson (2000) argue that,

“increasing highway capacity attracts additional traffic equivalent to between one-third and one-

half of the new capacity” (p. 68). Though there have been some cases cited where congestion has

been significantly reduced (i.e. Houston, TX and Phoenix, AZ), typically building more roads is

not the most effective solution.

There are also areas that are better suited for either compact, or sprawling development

than others. Geographic location is a significant factor in this equation, but so is the rate of

development within each area. “The better location for infill and increased densities from a

public health perspective depends on where in the region further development occurs”

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(Schweitzer & Zhou, 2010, p. 369). It makes more sense to build up places that already have a

significant amount of development to work with, rather than to completely start from scratch.

The key to creating a compact city that is equally healthy and accessible for all populations is to

design the city around the concept of mixed land use (Martins, 2012, p. 61). Not only will this

help to break up the structural density of the city, but also will effectively reduce the presence of

air pollution.

In reality, any land development style, whether compact or spread out, has the potential

to be environmentally friendly and effective for its population (Marquez & Smith, 1999, p. 547).

With the right amount of support from constituents, and significant investments from local

government officials, anything is possible.

Other miscellaneous findings.

Along with structural and air quality related findings, there were a few other study

outcomes relating to urban sprawl and air pollution that were interesting. For example, when

researching air pollution and levels of walkability in urban areas, Marshall, Brauer, and Frank

(2009) found that the pollutant nitrogen oxide has high spatial heterogeneity. In other words,

moving even a small distance from your original location could cause a big change in NO

concentrations (p. 1755).

Advances in vehicle and emissions technologies due to government regulation and

automaker innovation have been a significant factor to lowering pollution levels as well. Though

many people still drive gas-guzzling vehicles that emit more pollutants into the air, new vehicles

that use less gas and even run on electric power have been sufficient enough to offset the

pollution produced by longer drive times and the larger number of vehicles on the road (Kahn &

Schwartz, 2008, p. 776).

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Last but not least, Holcombe and Williams (2010) present an interesting view of critics

on urban sprawl stating, “some characteristics of sprawl that critics dislike pertain to amenities

consumed as incomes rise” (p. 258). The article didn’t elaborate much further than that, however,

excessive commuting and over-consumption of environmental resources seem to be the reasons

for this.

Discussion

Throughout this paper we’ve discussed many different studies concerning urban sprawl

and air pollution. Lots of new and different ideas were examined, but many of the studies came

to similar conclusions. More compact, dense urban areas were found to be preferable over

suburban environments because of the decreased levels of emissions released into the air, the

preference for environmental preservation, shorter commute times, better neighborhood

walkability, and decreased energy consumption. However, exposure to pollutants tends to be

higher in these urban areas, negatively affecting the health of the population living there. This is

one of the reasons that the majority of Americans live in the suburbs.

There are many different types of pollutants in the environment, but the effects of

nitrogen oxide and ozone were the most commonly researched. Nitrogen oxide was found to be

more prevalent in cities, while ozone was concentrated more in the suburbs. Regardless of

location and spatial density, minority neighborhoods have consistently shown lower air quality

levels, exhibiting how pollution disproportionately affects different groups. Minorities also tend

to be more susceptible to pollution-related diseases.

Limitations

All of the studies used for this paper provided very important information on the

relationship between sprawl and air pollution. However, there were a few limitations. A few of

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the studies used self-reported information from the population in question, possibly leading to

bias. Data collection methods may not have been adequate enough in other studies, possibly

causing researchers to miss out on important findings. And finally, in some studies the complex

and diverse attributes of cities were not fully taken into account during research.

Solutions to Problems of Sprawl and Pollution

Urban sprawl and air pollution are complicated issues to solve separately, but even more

so when you attempt to solve them together. However, there are a few ideas out there that could

potentially help to fix these issues. The development of plans to implement alternative growth

patterns in cities and suburbs could help to control any further sprawl, and to encourage urban

infill (Marshall, Brauer, & Frank, 2009, p. 1756). Revitalization of urban centers and

brownfields within these urban areas will also help to attract more people who currently live in

the suburbs, back to the city. Planting more trees within and around the boundaries of cities will

not only increase valuable green space, but the vegetation will also help to absorb some of the

pollutants in the air, therefore lowering air pollution levels (Cho & Choi, 2014, p. 5970).

A commuter/congestion tax would most likely be an unpopular solution, however, it

would be effective in reducing driving distances and taking unnecessary trips (Nechyba &

Walsh, 2004, p. 194) (Schindler & Caruso, 2014, p. 19). The money raised from these taxes

could also help cities to move toward more environmentally friendly, sustainable practices in the

future (Hancock, 2000, p. 152).

Areas of Future Research

Though the research that’s available on the effects of urban sprawl on air pollution is

good, it’s not even close to being completely comprehensive, and much of it is out of date. New

studies need to be conducted in order to keep information as up-to-date as possible. Other areas

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of future research can include, but is not limited to: the relationship between urban sprawl and

transportation externalities, the effects of building configurations on the spread and/or pooling of

pollution, ways to reduce the dependence on vehicles, the difference in pollutant concentrations

on local and regional levels, individual vehicle models and their respective emission rates, and

most importantly, the influence of land use patterns on the environment as a whole.

Conclusion

Throughout this paper I have discussed the history of the urban sprawl movement, given

examples on the effects of sprawl, shown the effects of air pollution on the health of our

population and our environment, examined studies from the available research, listed study

limitations, and given some ideas for solutions and areas for future research. Air pollution is a

huge burden on populations everywhere and much of that pollution can be eliminated by finding

a solution to urban sprawl. Though there isn’t a simple solution to this problem, with more

research and the help of government officials, citizens, and other various organizations, the

issues of urban sprawl and air pollution can be a thing of the past, helping us to move one step

closer to making the world we live in a healthier place.

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