"Continuous Ambient Particulate Monitors A Review of Current "
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 2 Aerosol Characteristics 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) 3 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 4 Physical Characteristics SIZE, SHAPE, and REFRACTIVE INDEX • 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 5 Physical Characteristics Hair cross section (60 mm) Human Hair PM10 PM2.5 (60 mm diameter) (10 mm) (2.5 mm) 6 Chemical Characteristics 7 Health Effects Health effects are significant Body of evidence is substantial 8 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 9 Health Effects 10 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) 11 Regulatory Background U.S. National Ambient Air Quality Standards (NAAQS) 12 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) 13 Sampling and Analysis High Volume Methods: TSP and PM10 Samplers 14 Sampling and Analysis Low Volume Methods PM10/PM2.5 FRM & PMc/PM2.5 Dichotomous Sampler 15 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 16 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 17 Sampling and Analysis Impaction Separation Cyclone Separation Cut Point 100% 50% 0% PM1.0 PM10 PM100 18 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) 19 Sampling and Analysis 20 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 21 Sampling and Analysis 22 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 23 Series FH 62 C14 Features and Benefits Heating Considerations Fixed heating w/auto filter changes is an improvement over long term Actual and mean VOC loss (l and l m ) due to heating on fixed spot. heated sample area at 50°C 0% VOC(NH 4NO 3) loss l and l m Mean NH 4 NO3 -Loss lm due to heated suction tube -20% 10% 0% -40% -10% lm -20% -60% -30% t = t0 * exp(E / k B T) lm -40% lm = t /t * (1 - exp(-t/ t)) - 1 -80% l -50% 10 20 30 40 50 60 70 80 J in °C -100% 0 5 10 15 20 25 30 t in days 24 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. 25 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 26 Sampling and Analysis b Attenuation Technology Direct b Attenuation Advantage Truly continuous • Ambient inlet Non-intrusive • Sensing volume • b Source & detector Disadvantage No known manufacturers Poor detection limit Requires very high concentrations 27 Sampling and Analysis b Attenuation Technology Stepwise b Attenuation • Ambient Inlet Advantage • Sensing Volume Semi-continuous • Source & detector Sound technology • Filter tape Good hourly precision Disadvantage Semi-continuous 28 Sampling and Analysis b Attenuation Technology Continuous β-Attenuation Advantage • Ambient inlet Continuous • Sensing volume Sound technology • b Source & detector Significant loading for post-collection analysis • Filter tape Disadvantage Potential extended sample loss 29 Sampling and Analysis Hybrid Technology Continuous SHARP Monitor Advantage • Ambient inlet Truly continuous • Sensing volume Low detection limits • b Source, detector, High time resolution nephelometer Intelligent moisture control • Filter tape Disadvantage None 30 b Attenuation Principle of Operation Sensors T1..T4 P1..P3 31 b Attenuation Refined Mass Measurement via Dual Detector 32 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 33 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 34 Continuous Particulate Monitors Applications 35 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 36 Continuous Particulate Monitors The End Thank you for your time and attention 37