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Pollutants on the fly: Connecting the dots between pollutant sources
and us
By Brendan Doherty
Buses huff fumes and belch particles. Industrial smokestacks
spew gases. And we inhale it — at least some of it. Depending
on where you are, you may get more or less.
A novel approach to pollution research may provide a crucial link
between emissions and their effect on human health. Berkeley civil
and environmental engineer William Nazaroff is among a handful
of engineers experimenting with a newly minted analytical concept
called intake fraction, which allows researchers to quantify the
pollutants people inhale from sources.
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"Raising
new questions about which [pollutant] sources are most harmful
to public health has only just begun," says Berkeley
civil and environmental engineer William Nazaroff, one of
the few researchers investigating intake fraction.
KEN RICE PHOTO |
"Only a fraction of emissions from each source is inhaled,"
says Nazaroff, who has studied the physical and chemical processes
that control human exposure to air pollutants for more than two
decades. "We’re trying to understand what controls
that fraction, then explore how knowing it changes the way we
think about the importance of different pollution sources."
Conceived in 2002 by researchers from Berkeley, Harvard, and the
Swiss Federal Institute of Technology in Lausanne, intake
fraction — the amount of pollution a person takes in
from a specific source — unifies previous descriptions and
equations to pinpoint the emissions-to-intake relationship more
precisely than ever before.
"It’s not just how much is emitted, but where people
are located that affects exposure," says Nazaroff. "Our
goal is to understand how each emitting activity contributes to
the public’s pollutant exposures. Raising new questions
about which sources are most harmful has only just begun."
Over the past two years, Nazaroff set three graduate students
to work on this project. Their work focuses on three issues: transportation
emissions and their effect on human health, electricity and newly
emerging distributed generators, and modeling spatial relationships
between people and pollutant sources to help inform public policy.
Getting on the bus
Buses fill our city streets, carrying riders to and from work,
thereby reducing the number of cars on the road. As cities grow,
urban planners in growing numbers support the use of public transit
through a hub and corridor system. However, as Nazaroff points
out, there’s a lot to be learned about the "exposure
toll" paid by bus riders and those along the bus corridor.
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"Intake
fraction is a lens through which we can view the problem
and bring important aspects into focus that have never been
seen before," says Nazaroff (left), talking to Julian
Marshall, who is studying the "exposure toll"
paid by drivers and those who live or work along the transportation
corridors.
KEN RICE PHOTO |
Energy and Resources Group (ERG) doctoral student Julian Marshall
is using intake fraction to quantify the impact of transit choices
on public health. Looking at different modes of transportation
— automobiles and light rail — and various bus fuels
including diesel, compressed natural gas, and electricity, Marshall
hopes to determine how the potential health impact varies with
the mode of transportation.
"Causal links between motor vehicle exhaust and human health
are well established," says Marshall. "But who is exposed
and at what levels? This depends on how a city is laid out and
on which transportation options people choose."
Whether you and your neighbors hop on a train, diesel
bus, or a bike determines the type and concentrations of pollutants
emitted into the transportation corridor, typically a densely
populated area. It is often assumed that public transportation
reduces pollution, but concentrating people along efficient transportation
corridors may expose some travelers to higher concentrations of
pollutants.
"Air pollution control policy exists to protect the public
health," says Nazaroff. "What’s novel about Julian’s
work is the element of proximity. It will answer questions about
how commuting and living near a freeway could affect your health."
Local power generators
are in, but should they be?
Distributed generators, or DGs, are cheap and efficient, and they’re
catching on nationwide as the new wave of power-generating technology.
These small power generators, which can be widely distributed
near demand locales, alleviate the need for long transmission
wires, are relatively easy to deploy, and have the advantage of
offering greater control of power quality and production for the
user.
A relatively novel power source, DGs are making their way into
our lives. While they can be designed to run on diesel fuel, natural
gas, even solar and wind power, it’s those that run on natural
gas that are proliferating most quickly. While natural gas is
cleaner than most other fuels, some researchers are concerned
that even natural gas DGs may harm our health more than large
power plants because they pollute air right where we are —
at home or at work.
"They are being placed in neighborhoods all over the country
in close proximity to people, unlike more traditional, large power
plants, which were routinely located far from urban centers,"
says Garvin Heath, who is pursuing dual master’s degrees
in civil and environmental engineering (CEE) and ERG.
Power generation has been a hot button issue since the summer
of 2001, when rolling blackouts threatened Californians and the
price of electricity skyrocketed from $30 per megawatt to $330.
Traditional power plants — nuclear, coal, or natural gas-burning
plants — are tremendously expensive and time consuming to
build. Deregulated in 1996, the power industry has not built a
new major power plant in 15 years, despite growing demand.
To help alleviate that demand, industry turned to small, quick-to-build
distributed generators. The California Air Research Board estimates
that there are 11,000 distributed generators in California. There
are 40 on the Berkeley campus alone.
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In
contrast to more traditional ambient air quality monitoring,
intake fraction stresses the proximity of pollution sources
to people. Garvin Heath (left) and Abby Hoats are using intake
fraction to investigate human exposures to pollution.
KEN RICE PHOTO |
"Distributed generators are largely unregulated,"
says Heath, "and there is no clear understanding of their
impact on public health. With the intake fraction approach, we
hope to clarify key issues and gain a better understanding of
the health risks."
Using the Los Angeles air basin, Heath compared a small DG power
source to a central station plant and found a dramatic difference
in the proportion of emitted pollution that is inhaled.
"Per unit of electricity delivered, the DG unit increased
the amount of pollutants inhaled by nearby residents by an order
of magnitude," says Heath. These small generators let out
their exhaust just five meters from the ground. In contrast, large
centralized power station stacks spew their exhaust sky high.
The state of California is trying to regulate distributed generator
emissions so that they would, in theory, be equivalent to emissions
from centrally generated power on a per kilowatt-hour basis. Other
states and nations are also investigating DG policies.
"Our research puts a big exclamation point behind the word
caution," says Nazaroff. "We want to know more about
how DGs affect public health."
Public policy and
where you live
Location, location, location, say the realtors of the world. "Making
the links between pollution, location, and health is a first step
to significantly improving environmental health problems and exposure
inequities," says CEE doctoral student Abby Hoats, who is
modeling how pollutants travel from one point to another in order
to develop new tools to help shape public policy.
"Environmental justice issues are politically charged,"
says Nazaroff. "It pushes to the front burner the issues
of who benefits from specific activities and who bears the burden.
Up to now, the relationship between who benefits and who is burdened
has defied quantification. But soon, the questions cities wrestle
with about where to locate a major polluter may include an additional
component calculating the total burden of inhaled air pollutants
in the surrounding neighborhood."
While industrial emitters may know the type and amount of their
emissions, ambient air quality measurements do not always reveal
the full story of public health impacts from emissions.
"In one Southern California case, we studied the pollutant
plume around a particular fixed source," says Hoats, "We
were able to identify one demographic group there that made up
only 30 percent of the population, but may have inhaled as much
as 70 percent of the emissions simply because they lived or worked
closest to the source. We hope intake fraction will be a good
way to quantify the amount of pollution impacting different population
segments."
Demographic data, such as that managed by Geographic Information
Systems (GIS), which attaches key categories such as race and
income to location, could provide that information. "Once
we know the location of an emissions source," Hoats believes,
"quantifying it with intake fraction analysis and GIS mapping
would identify specific localities and demographic groups that
shoulder a disproportionate pollution burden."
Brendan Doherty is
a Bay Area-based science, health, and technology writer.
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