Pollutants on the fly

UC, Berkeley’s Forefront magazine has an article on Pollutants on the fly: Connecting the dots between pollutant sources and us.

William Nazaroff studies air pollution, including characterization and control of pollutants.

Intake fraction refers to the fraction of pollutant that is actually inhaled.

“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.”

Both the amount of pollutant produced, and where people are relative to that pollution, will determine how dangerous it is.

Nazaroff’s focus has been

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.

So what does concentrating people along an efficient transportation corridor do to public health? No answer provided.

A second focus was distributed generators (DGs), which are cheap and efficient and give greater control for the user. In California, about 7% of power generation is lost through the transmission and distribution. In some locations, this will be more, and DGs may make more sense there. But how does pollution compare?

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.

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.

“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.

Heath and Hoats
Heath and Hoats

An order of magnitude. This means that DGs lead to about 10 times as much pollution inhaled.

A third focus is on public policy: where you live compared to large fixed sources of pollution. Studying the flow of pollutants, and quantifying the intake fraction, will hopefully lead to better public policy so that some groups don’t suffer disproportionately.

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