continuous ambient particulate monitors a review of current technologies by michael corvese, product...
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Continuous Ambient Particulate MonitorsA Review of Current Technologies
byMichael Corvese, Product Manager
Thermo Electron CorporationAir Quality Instruments
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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