Transcript Continuous Ambient Particulate Monitors A Review of Current Technologies by

Continuous Ambient Particulate Monitors
A Review of Current Technologies
by
Michael Corvese, Product Manager
Thermo Electron Corporation
Air Quality Instruments
Aerosol Monitoring

Aerosol
Characteristics

Health effects

Regulatory
Background

Sampling & Analysis

Regulatory
Developments
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Aerosol Characteristics
DEFINITION
Aerosol – small solid or liquid particles suspended in gas
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• 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
• 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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Physical Characteristics
SIZE, SHAPE, and REFRACTIVE INDEX
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• Size:
• 0.002-100µm aerosol research;
0.1-100µm common sampling (0.1-10 mm)
• Shape:
• Many irregular shapes;
aerodynamic diameter emphasized
• Refractive Index:
• Wide range;
most consistent below 2.5mm
Physical Characteristics
Hair cross section (60 mm)
Human Hair
(60 mm diameter)
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PM10
(10 mm)
PM2.5
(2.5 mm)
Chemical Characteristics
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Health Effects
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
Health effects are significant

Body of evidence is substantial
Health Effects
Increased hospital admissions and emergency
room visits during high PM conditions
• Aggravated asthma
• Chronic bronchitis
• Increase in respiratory symptoms
• Decreased lung function
• Premature death
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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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Sampling and Analysis
Common Gravimetric Ambient Aerosol Sampling Techniques
(Gross - Tare) / Air Volume = mg/m3
• High volume methods: TSP, PM10, PM2.5, Air Toxics
Sampler (PUF)
• Low volume methods: (PM10, PM2.5, PMCoarse)
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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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Sampling and Analysis
Common Gravimetric Ambient Aerosol Sampling Techniques
(Gross - Tare) / Air Volume = mg/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
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Sampling and Analysis
Common Continuous Ambient Aerosol Sampling Techniques
(Dm / Dt) / (DV / Dt) = mg/m3
• Light Scattering, Absorption, and Extinction
• Tapered Element Oscillating Microbalance
• Beta (Electron) Attenuation
• Hybrid Methods
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Sampling and Analysis
Impaction Separation
Cyclone Separation
Cut Point
100%
50%
0%
PM1.0
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PM10
PM100
Sampling and Analysis
Common Continuous Ambient Aerosol Sampling Techniques
(Dm / Dt) / (DV / Dt) = mg/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)
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Sampling and Analysis
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Sampling and Analysis
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
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Sampling and Analysis
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Sampling and Analysis
Other Technologies
Oscillation Frequency Measurement
Advantages
Disadvantages
Continuous method
Temperature dependency
Highly time resolved
Affected by vibration
High resolution
Manual filter changes necessary
Seasonal and regional dependencies
Complex systems require some skill
Volatile losses
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Series FH 62 C14
Features and Benefits
Heating Considerations
Fixed heating w/auto filter changes
is an improvement over long term
heating on fixed spot.
Actual and mean VOC loss (l and l m ) due to
heated sample area at 50°C
Mean NH 4 NO3 -Loss lm due to heated suction tube
10%
-20%
0%
-40%
-10%
lm
VOC(NH 4NO 3) loss l and l m
0%
-60%
-30%
lm
t = t0 * exp(E / k B T)
lm = t /t * (1 - exp(-t/ t )) - 1
-40%
-80%
l
-50%
10
0
20
30
40
50
J in °C
-100%
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-20%
5
10
15
20
t in days
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30
60
70
80
b Attenuation
Principle 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 Monitor
Principle 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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Sampling and Analysis
b Attenuation Technology
Direct b Attenuation
• Ambient inlet
Advantage
 Truly continuous
 Non-intrusive
• Sensing volume
• b Source & detector
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Disadvantage
 No known
manufacturers
 Poor detection limit
 Requires very high
concentrations
Sampling and Analysis
b Attenuation Technology
Stepwise b Attenuation
• Ambient Inlet
• Sensing Volume
•  Source & detector
• Filter tape
Advantage
 Semi-continuous
 Sound technology
 Good hourly precision
Disadvantage
 Semi-continuous
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Sampling and Analysis
b Attenuation Technology
Continuous β-Attenuation
• Ambient inlet

• Sensing volume

• b Source & detector

• Filter tape
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Advantage
Continuous
Sound technology
Significant loading for
post-collection analysis
Disadvantage
 Potential extended
sample loss
Sampling and Analysis
Hybrid Technology
Continuous SHARP Monitor
Advantage
• Ambient inlet

• Sensing volume

• b Source, detector,
nephelometer

• Filter tape

Truly continuous
Low detection limits
High time resolution
Intelligent moisture
control
Disadvantage
 None
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b Attenuation
Principle of Operation
Sensors
T1..T4
P1..P3
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b Attenuation
Refined Mass Measurement via Dual Detector
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b 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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Continuous Particulate Monitors
Applications
Ambient
•
•
•
•
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 Monitors
Applications
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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
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