Continuous Ambient Particulate Monitors A Review of Current Technologies by Michael Corvese, Product Manager Thermo Electron Corporation Air Quality Instruments.

Continuous Ambient Particulate MonitorsA Review of Current Technologies

byMichael Corvese, Product Manager

Thermo Electron CorporationAir Quality Instruments

2

Aerosol Monitoring

Aerosol

Characteristics

Health effects

Regulatory

Background

Sampling & Analysis

Regulatory

Developments

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DEFINITION

Aerosol – small solid or liquid particles suspended in gas

• Dust from nature, wind, human activity (pollen, road dust fly ash)

• Fog from heating/cooling (clouds and fog)

• Mist from atomization and nebulizer (sulfuric acid mist)

• Spray from ultrasonics (insecticide spray)

• Smoke from combustion or flame (cigarette, soot, diesel)

• Smog from photochemicals (Urban Smog)

Aerosol Characteristics

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Aerosol Characteristics

• Physical characteristics

Size distribution

Shape

Refractive Index

Concentration (mass or number)

• Chemical characteristics

Composition (chemical or elemental)

Acidity/alkalinity

• Temporal characteristics

Chemical and physical characteristics changing with time

• Spatial characteristics

Characteristics changing with location

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SIZE, SHAPE, and REFRACTIVE INDEX

Physical Characteristics

• Size:

• Shape:

• Refractive Index:

• 0.002-100µm aerosol research; 0.1-100µm common sampling (0.1-10 m)

• Many irregular shapes; aerodynamic diameter emphasized

• Wide range; most consistent below 2.5m

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Physical Characteristics

Human Hair

(60 m diameter)

PM10

(10 m)PM2.5

(2.5 m)

Hair cross section (60 m)

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Chemical Characteristics

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Health Effects

Health effects are significant

Body of evidence is substantial

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Health Effects

• Aggravated asthma

• Chronic bronchitis

• Increase in respiratory symptoms

• Decreased lung function

• Premature death

Increased hospital admissions and emergency room visits during high PM conditions

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Health Effects

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Regulatory Background

• 1971—Promulgation of National Ambient Air Quality Standards (NAAQS) for SO2, NO2, O3, CO, and total suspended particulates (TSP)

• 1978—Promulgation of particulate Pb standard

• 1987—Promulgation of PM10 standard

• 1997—Promulgation of revised PM10 standard and

introduction of PM2.5 standard (also a revision of

the O3 standard)

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Regulatory Background

U.S. National Ambient Air Quality Standards (NAAQS)

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Common Gravimetric Ambient Aerosol Sampling Techniques

(Gross - Tare) / Air Volume = g/m3

• High volume methods: TSP, PM10, PM2.5, Air Toxics Sampler (PUF)

• Low volume methods: (PM10, PM2.5, PMCoarse)

Sampling and Analysis

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Sampling and Analysis

High Volume Methods: TSP and PM10 Samplers

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Sampling and Analysis

Low Volume Methods

PM10/PM2.5 FRM & PMc/PM2.5 Dichotomous Sampler

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Common Gravimetric Ambient Aerosol Sampling Techniques

(Gross - Tare) / Air Volume = g/m3

• Advantages: Recognized reference method, low capital cost

• Disadvantages: Limited time resolution (typically 24-hr), long turnaround times, labor intensive, and gravimetric lab maintenance/cost

Sampling and Analysis

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Common Continuous Ambient Aerosol Sampling Techniques

(m / t) / (V / t) = g/m3

• Light Scattering, Absorption, and Extinction

• Tapered Element Oscillating Microbalance

• Beta (Electron) Attenuation

• Hybrid Methods

Sampling and Analysis

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Sampling and AnalysisE

ficie

ncy

50%

100%Cut Point

Cyclone Separation

Impaction Separation

PM10 PM100PM1.0

0%

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Common Continuous Ambient Aerosol Sampling Techniques

(m / t) / (V / t) = g/m3

• Advantages: Low operational cost, better time resolution, increased statistical database, instantaneous turnaround (index reporting, increased knowledge of air shed characteristics)

• Disadvantages: 2-3x capital cost, limited reference capabilities (pending USEPA & CASAC Guidelines)

Sampling and Analysis

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Sampling and Analysis

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Continuous Methods

• Light Scattering: Excellent time resolution; limited by refractive index and aerosol distribution (particle size)

• Oscillation Frequency Measurement: Good time resolution, seasonal & regional performance issues

• Beta (Electron) Attenuation: Proven technology, minimal performance issues, versatile

Sampling and Analysis

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Sampling and Analysis

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Sampling and Analysis

AdvantagesContinuous method

Highly time resolved

High resolution

Disadvantages

Temperature dependency

Affected by vibration

Manual filter changes necessary

Seasonal and regional dependencies

Complex systems require some skill

Volatile losses

Other Technologies

Oscillation Frequency Measurement

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Heating Considerations

Actual and mean VOC loss (l and l m ) due to heated sample area at 50°C

-100%

-80%

-60%

-40%

-20%

0%

0 5 10 15 20 25 30t in days

VO

C(N

H4N

O3)

loss

l an

d l

m

l

lm

Mean NH4 NO3 -Loss lm due to heated suction tube

-50%

-40%

-30%

-20%

-10%

0%

10%

10 20 30 40 50 60 70 80 in °C

l m

= 0 * exp(E / k B T)lm = /t * (1 - exp(-t/ )) - 1

Fixed heating w/auto filter Fixed heating w/auto filter changeschanges

is an improvement over long is an improvement over long term heating on term heating on fixed spot. spot.

Series FH 62 C14Features and Benefits

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AttenuationPrinciple of Operation

• Constant flow of aerosol is metered and sampled onto a filter stain area.

• The detection of Beta Attenuation is proportional to increased mass.

• Every 1-24 hrs a new filter area is zeroed and introduced.

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SHARP MonitorPrinciple of Operation

• Combination nephelometer + beta attenuation

• High sensitivity light scattering photometer is continuously calibrated by an integral time averaged beta attenuation mass sensor

• Measured mass concentration remains independent of changes in the particle population being sampled

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Direct Attenuation

• Ambient inlet

• Sensing volume

• Source & detector Disadvantage No known

manufacturers Poor detection limit Requires very high

concentrations

Advantage Truly continuous Non-intrusive

Attenuation Technology

Sampling and Analysis

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Stepwise Attenuation

• Ambient Inlet

• Sensing Volume

• Source & detector

• Filter tape

Disadvantage Semi-continuous

Advantage Semi-continuous Sound technology Good hourly

precision

Sampling and Analysis

Attenuation Technology

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Continuous βAttenuation

• Ambient inlet

• Sensing volume

• Source & detector

• Filter tape

Advantage Continuous Sound technology Significant loading for

post-collection analysis

Sampling and Analysis

Disadvantage Potential extended

sample loss

Attenuation Technology

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Continuous SHARP Monitor

• Ambient inlet

• Sensing volume

• Source, detector, nephelometer

• Filter tape

Advantage Truly continuous Low detection limits High time resolution Intelligent moisture

control

Sampling and Analysis

Disadvantage None

Hybrid Technology

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Sensors T1..T4 P1..P3

Attenuation Principle of Operation

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Refined Mass Measurement via Dual Detector

Attenuation

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Attenuation

Refined Mass Measurement via Dual Detector • A dual (a.k.a.

proportional) detector allows the daughter nuclides of Radon gas to be measured and accounted for as a mass refining step.

• This allows the C14 BETA to be consistently stable at lower ambient concentrations.

• Important for PM2.5

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Ambient

Continuous Particulate MonitorsApplications

• NAAQS Monitoring• AQ Index Reporting• Fenceline Monitoring• Clean-up Sites

In R&D …

• Unrivaled short-term detection limits/time resolution

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Continuous Particulate MonitorsApplications

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Regulatory Developments

• 1997—promulgation of PM2.5 and revision of PM10

• 1998—PM2.5 standard challenged in court

• 1999—US Court of Appeals remanded PM2.5

standard back to EPA for revision

• 2001—US Supreme Court decision

- EPA has the right to promulgate a PM2.5 standard

- Compliance costs should not be considered

- PM Coarse should replace PM10

• 2005- Proposed revision of PM2.5 expected

• 2006-Final PM2.5 and proposed PM Coarse regulation expected

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Continuous Particulate Monitors

The End

Thank you for your time and attention