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Characterization of Nanoparticles at Electric Utility Power Plants

Jeffrey HicksPrincipal ScientistExponent, Oakland, CaliforniaJhicks@exponent.com

October 7, 2008

NanoparticlesDefined as particles smaller than 0.1 μm

Are also called ultrafine particlesAre not generated by mechanical actions on solids, but are associated with condensation, combustion and nucleation formationEnvironmental nanoparticles are typically associated with combustion of fossil fuels, volcanic activity and Engineered nanoparticles are man made (e.g. carbon nanotubes)Due to their very small size, they behave differently from larger particles when they enter the body

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Nanoparticles

Nanoparticles are Implicated in being associated with a variety of adverse health effects

Some data suggests elevated exposures to nanoparticlesare related to elevated death rates (shorter life span)They are thought to adversely affect the cardiopulmonary systemThe mechanism for this is unknownThere is very limited data suggesting animals exposed to high levels of carbon nanotubes have a higher risk of developing respiratory cancers

Study Purpose and Goals

Phase 1: Measure the presence and map concentrations of nanoparticles at multiple power plants to understand potential worker exposures

Using real-time instruments to measure particle count concentrations, and surface area concentrationsThese two parameters are believed to be important measures of potential health effects

Phase 2: Collect nanoparticles from a power plant work area, and conduct physical and chemical characteristic analysis on these particles

Project Specifics

Site visits to three electric generating power plants have been completed

All are multiple units, with on-site worker populations ranging from 5 to 750One positive pressure coal fired plant in the SouthwestOne balanced draft coal fired plant in the MidwestOne gas turbine plant in the West

Mapping of nanoparticle concentrations have been completedNanoparticles have been collected at the Southwest coal fired facility, and are now being analyzed for chemical and physical characteristics at Texas A & M

Methods

Real-time measurements made at the three power plants using hand-held nanoparticle monitors

Particle surface area concentrations:• AEROTRAK™ 9000 Nanoparticle Aerosol Monitor indicates

the surface area (μm2/cm3) of nanoparticle aerosols that deposit in the lung, corresponding to the ICRP lung deposition curves for the tracheobronchial (TB) and alveolar (A) regions of the human respiratory tract.

• Two measurements for each parameter (TB and A) were collected at each sampling location (for a total of 4 measurements per specific location at each of the three plants)

MethodsReal-time measurements made at the three power plants using hand-held nanoparticle monitors

Particle counts• TSI Ptrack Ultrafine Particle Counter, provides real-time

particle counts for particles ranging from 20 nm to 1 μm (or 1000 nm)

• These measurements were taken concurrently with the Aerotrack 9000 surface concentration measurments

• ARTI Optical Particle Counter, provides real-time particle counts for particles ranging from 0.5 to 10 μm in 5 different size ranges

Methods

Nanoparticles were collected from three locations at one power plant

Samples were collected using a specially designed cascade impactorMicro-Orifice Uniform Deposit Impactor (MOUDI)Cut points are: >10,000 nm; >1,000 nm; >100 nm, and absolute filter (particles <100 nm)The final stage is what we are afterUses polycarbonate membrane filters as sampling mediaSamples collected at locations where real-time instruments showed high particle counts (near boiler and in yard area)Sampling for 6 hours = collection of 108 to 1010 nanoparticles

Coal-Fired Positive Pressure Boiler – Turbine Deck

Coal-Fired Positive Pressure Boiler (Un-enclosed)

Coal-Fired Balanced Draft Boiler (Enclosed)

Coal-Fired Balanced Draft Boiler (Enclosed) – Ash Hopper

Coal-Fired Balanced Draft Boiler (Enclosed) – Near Boiler

Gas-Fired Combustion Turbine Facility

MOUDI Cascade Impactor Near Positive Pressure Coal-Fired Boiler

MOUDI 3-stage Cascade Impactor

Preliminary ResultsHighest nanoparticle concentrations occur in the immediate vicinity of the boiler at coal fired plants

The concentrations are 100x to 1000x higher than the background concentrations found in clean ambient air upwind of the plantsThe primary source of the nanoparticles are combustion gases leaking from the boiler

Concentrations in the turbine building, auxiliary buildings, andthe yard areas of the coal fired plants are lower than around the boilers

Often the range in these areas is 1x to 100x higher than the background levels The levels inside control rooms are usually close to the background concentrations

Preliminary Results

Concentrations at gas fired combustion turbine facilities are lower than coal-fired facilities, but are higher than background

The concentrations in work areas (outside the control room) were 1x to 100x the background concentrations.These particles are most likely associated with particles released from the combustion process (e.g. combustion gases down-drafting post combustion)

How Do These Findings Compare to Other Nanoparticle Exposures?

Vehicle exhaust, especially from diesel engines, is an important nanoparticle source Nanoparticle concentrations at a freeway shoulder in Southern California are similar to the levels near a coal fired boiler

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500

1000

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Par

ticle Surfac

e Are

a (um

2/cc)

C oal F ired‐Pos itive P res s ure (Un‐enc los ed)

AT9000 Average Partic le S urfac e Area  , Alveolar(um2/c c )

Upwind

C ontrolR ooms

TurbineBuilding

F ly Ash

Welding

Near Boiler

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500

1000

1500

2000

2500

Particle Surfac

e Area

 (um

2/cc)

C oal F ired‐Pos itive P res s ure (Un‐enc los ed)AT9000 Average Partic le S urfac e Area  , Trac heobronchial 

(um2/c c )

Upwind

C ontrol Rooms

TurbineBuilding

F ly  Ash

Welding

Near Boiler

On-Going TasksLaboratory analysis is underway

Morphology (size, shape, distribution)Crystallinity/amorphicitySizing in both wet and dry statesSurface reactivityAggregation/De-aggregation potentials

Wei

ght %

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20

40

60

80

O Na Mg Al Si S K Ca Ti Fe Cu

Physical Characteristics of Filter 01; Area 1

10 μm

Scanning electron microcopyEnergy Dispersive X-ray Spectroscopy

Elemental Analyses• Particle sizes on filter # 01 range 500 nm to 5 μm

• Elemental analyses shows oxygen, sodium, aluminum, and silicon presence on a carbon background

C O Na

SSiAlMg

FeTiCaK

Chemical Characteristics of Filter 01; Area 1Elemental Mapping

• Particles on filter # 01 probably contain aluminum oxide and silicon dioxide mixture on a carbon background

• Sodium is also present

Physical Characteristics in the Wet Phase

100 1000

0

5

10

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% In

tens

ity

Aggregate Size (nm)

Filter # 01-BSB-AF Filter # 03-BCI-AF Filter # 04-AT-AF

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-20

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Sur

face

Cha

rge

(mV

)

Filter # 01-BSB-AF Filter # 03-BCI-AF Filter # 04-AT-AF

• All three particle samples collected from each filter aggregated to the same extent (davg=458.7)

• There is no significant nano-size population on any filter

• Particles collected from filter #’s 03 and 04have similar surface charge values (-36.3667 mV and -37.7667 mV, respectively).

• Particles from filter # 01 measured a slightly lower surface charge of -41.9333 mV

Surface ChargeAggregate Sizing

Samples were placed in ultrapure water from a Milli-Q water system, placed in the bath sonicator for 30 seconds, and measured at room temperature (22 °C).

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Conclusions

Real-time analysis shows that there are nanoparticles present in most work areas at power plants

Coal-fired plants have higher levels than gas fired turbine facilitiesThe highest levels were identified near the boilerThe highest concentrations are in the range of what is encountered on congested freeways

Microscopic analysis suggests that these ultrafine particles are not truly nanoparticles, but are larger than 0.2 μm