DIRECT READING INSTRUMENTS FOR AEROSOLS

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1 DIRECT READING INSTRUMENTS FOR AEROSOLS Avula Sreenath, Ph.D. TSI Inc. Florida Local Section of AIHA Fall Conference 2012 Jacksonville, FL Sept 21, 2012

2 Agenda 1. Learning Objectives 2. Introduction 3. Types of Contaminants 4. Sampling strategies Why/What/Where/When/How 5. Advantages and disadvantages of real-time sampling 6. Instruments based on particle motion and optical detection 7. Instruments based on electrical techniques 8. Instruments based on super-saturation/condensation detection 9. Instruments based on particle interaction with light 10. Instruments based on mass measurement (Optical ) 11. Optical Particle Counters (OPCs) 12. Instruments based on diffusion charging 13. New trends in aerosol monitoring 14. Factors affecting the choice of an instrument

3 Learning Objectives + Understand different techniques for aerosol measurements same technique does not apply to all particle sizes + Significance of number, surface area and mass measurements + Significance of optical properties that dominate real-time particle detection + Understand the design challenges for aerosol measurements and instrument limitations

4 Introduction Measurement Methodology Particles size, shape, material, refractive index and density Environments Workplaces, clean rooms, atmospheric measurements, pharmaceutical clean rooms, research based measurements Detection techniques light scattering, light extinction, piezo piezo balance, diffusion battery, electrical mobility, condensation condensation etc. etc. Hardware Probes, inlet conditioners, area/portable/personal samplers Data Integration Facilities monitoring, perimeter monitoring, clean room standards, filter checks, wireless communications, particles losses

7 Sampling Strategies Why? + Compliance monitoring + Perimeter monitoring + Proactive sampling + Reactive monitoring + Engineering control efficacy monitoring

8 Sampling Strategies What/Where and When? + Type: Bulk, area and personal + Time: Short-term, STEL, long term, 8-hour (TWA), sequential, grab sampling, continuous + Method: Survey, real-time, regulations based + Conditions: Worse case, random, regular work shift + Number: Routine, daily, annual, cumulative

9 Sampling Strategies What/Where and When? + Weather seasonal changes, temperature and humidity effects + Heating versus cooling in the building (summer versus winter) + Doors open/closed, ventilation conditions + Outdoor traffic, indoor operations, number of people, activity level + Type of material and physical state of the material being handled

10 Sampling Strategies How? + Traditional gravimetric sampling using sampling pumps + Real-time aerosol monitoring passive and active + Gas monitoring passive, active, colorimetric, real-time + Bioaerosol monitoring

11 Advantages of Real-Time Sampling + Can look for peak exposures occurring over a short period of time + A visible indicator of hazard + STEL and TLV real-time + Very efficient use of Industrial Hygienist s time + Examine the effect of engineering controls realtime + Help develop exposure patterns and concentration maps + Significant reduction in lab analysis

12 Disadvantages of Real-Time Sampling + The instrument is as good as the calibration + Calibration gas/aerosol is different from the gas/aerosol being measured + Interference from other contaminants + Data cannot be used for compliance monitoring + Accuracy (a trade-off between accuracy and speed) + Effects of humidity and temperature on measurements

13 Real-time Monitoring Aerosols Photometers Piezobalance Beta attenuation Ultrafine aerosol monitoring CPCs, electrometers etc. Optical Particle Counters (OPCs) Aerodynamic Particle Sizer (APS) Gases FID and PID IAQ monitoring Electrochemical sensors NDIR sensors SAW sensors

14 Principle of Measurement in Most Common Aerosol Instruments Mainly optical based and hence depends on Optical properties Size Shape Wavelength of the light used to illuminate the particles Electrical mobility based Mobility sizer Electrometer Mechanical Impactors/Cyclones Quartz Crystal Microbalance Nuclear Beta Attenuation Counter

15 Instruments based on Particle Motion and Optical Detection + Detection based on accelerating particles thro a nozzle and detecting the particles one-by-one using light scattering + Particles lag the gas velocity due to inertia + The time-of-flight between 2 laser beams separated by a known distance is measured and converted to aerodynamic diameter

16 Aerodynamic Particle Sizer

17 Advantages of APS + Rapid detection of size distribution + Aerodynamic size, independent of density + High Resolution + Wide size range ( um) + UV laser can be used for biological aerosol detection

18 UVAPS Fluorescence of NADPH/Riboflavin in the nm range is detected

19 Limitations of the APS + High acceleration leads to Stokes correction (Rep > 0.1, particle velocity is no longer proportional to Dae and is now a function of shape, density and Dae) + Coincidence becomes a problem at high concentrations + Distortion of liquid particles in the flow field + Misalignment of particle flow w.r.t. laser beams

20 Instruments based on Particle Charging Techniques + Aerosols in workplaces are likely to be either positively or negatively charged due to random collisions with ions in air (~ 10 9 ions per m 3 ) + Exploit the behavior of charged particles to make measurements (mainly for nanoparticles) + Measure particle electrical mobility which is then related back to particle diameter Z q = 3πµ d

Under diffusion charging, there is a one-to-one monotonic relationship between particle size and particle charge, thus each value of electrical mobility corresponds to a unique value of particle size

21 Under diffusion charging, there is a one-to-one monotonic relationship between particle size and particle charge, thus each value of electrical mobility corresponds to a unique value of particle size Differential Mobility Analyzer (DMA) has a small slit thro which only certain particles with a narrow range of mobility can pass thro the slit a get detected by a particle sensor. By stepping the voltage gradually, size distribution can be determined

touch-screen display and intuitive graphical user interface On-board

23 NanoScan SMPS Particle size distributions from 10 to 420 nm Portable Battery operated, or use working fluid reservoir for extended use Color touch-screen display and intuitive graphical user interface On-board data storage capacity Based on industry gold standard SMPS spectrometer detection

24 Instruments Based on Super- Saturation/Condensation Downstream of the DMA/EAA, the particle detector of choice is a Condensation Nuclei Counter (CNC), or commonly also known as Condensation Particle Counter (CPC) Principle of Operation Condensation of alcohol vapor that causes the vapor to condense on particles resulting in formation of very large particles (> 1 µm) which are large enough to be detected using optical techniques

25 Schematic of a CPC

26 Counting Efficiency of CPCs

aerosols or irritants + Can also test N-95 respirators + OSHA approved + Used extensively by first

27 PortaCount + CPC based developed for reliable fit testing of any tight-fitting respirator + Eliminates guess work associated with qualitative fit testing + Uses particles in ambient air no need to generate aerosols or irritants + Can also test N-95 respirators + OSHA approved + Used extensively by first responders, health care professionals and industrial and health care workers + More relevant with H1N1 and SARS scares

28 Handheld CPC P-Trak

29 P-Trak Applications Are my filters leaking? Is my furnace exhaust stack fine? Is my building tobacco smoke free?

30 P-Trak Applications Is my office equipment generating nanoparticles? Is my kitchen properly exhausted?

31 Advantages and Disadvantages of CPCs Advantages + Very low size detection down to 2.5 nm + Live-time coincidence correction for high concentration measurement + Photometric measurement for high concentrations + With a DMA, it the most comprehensive method to determine size distribution in near real-time + Disadvantages + Very expensive + Uses Butanol which is very nasty + Sensitive to humidity newer models have a splurge pump

32 Instruments Based on Optical Properties + Some of the light incident on the particle is reflected, which another fraction is diffracted, while yet another portion is refracted + Collectively, it is referred to as scattering and the real portion of the refractive index is related to light scattering + The imaginary component of the refractive index is related to light absorption + Transparent particles have no imaginary component, while colored particles have a substantial imaginary component + Refractive index greatly depends on the wavelength of light + Glass beads = Carbon = 2 - i

33 Photometers + Size range µm + Concentration range mg/m 3 + Humidity range < 50% RH + Temperature range is 5 50 Deg.C + Zero drift mg/m 3 in 24 hours + Optics are very simple + Small collecting angle + Sheath flow not required but recommended + Calibrated using a broad size distribution like Arizona Road Dust

34 Commercially Available Photometers + PDR-1500 from Thermo + Personal DataRAM from Thermo + AM510 from TSI + DustTrak II/DRX from TSI + Haz-Dust IV from SKC Inc. + Nephelometer by Sensidyne

35 Typical Photometer Optics Main parts of an Instrument + Light source laser + Optics + Viewing volume + Photodetector + Pump + Pulse height analyzer + Data analysis + Display

DustTrak DRX + Combines photometry and single particle counting + Size segregated aerosol mass measurement + Completely GUI based + Response depends on aerosol properties

36 DustTrak DRX + Combines photometry and single particle counting + Size segregated aerosol mass measurement + Completely GUI based + Response depends on aerosol properties + Many standards still based on mass + Separate calibrations for the photometer and the single particle counting + Allows for gravimetric sampling downstream of the optics

37 Principle of Operation Aerosol Measurement Signal Acquisition and Processing Aerosol Inlet Orifice HEPA Filter Light Trap Optics Chamber Photometric DC Voltage Offset Analyzer Laser Beam Mirror Beam Shaping Optics Sheath Air Viewing Volume Photo Detector Single Particle Pulse Height Analyzer Size Segregated Mass Concentration (eg. PM 1, PM 2.5, PM 4 & PM 10 ) Laser Diode Exhaust Pump Gravimetric Filter Protection Filter Dampening Chamber Pulse Height Pulse Height Offset Photometric Signal Flowmeter No Particles (background) Low Concentration (Counting Pulses) High Concentration (Pulses + Photometry)

38 Optical Particle Counters Instrument to count individual particles Size range µm Applicable for very low concentrations No zero drift issues Complicated optics including powerful laser Large collecting angle to gather as much light from the particle as possible elliptical mirrors Sheath flow recommended Calibrated using different monodispersed PSL

39 Limitations of OPCs Response of the OPC dependent on the refractive index of the particles. Custom calibration is required Multiple values of diameter for the same scattering intensity Cannot handle high particle concentrations due to coincidence error caused by presence of more than one particle in the sensing zone Same size particle sized differently as it passes a different part of the Gaussian beam (Grazing error) Particle shape can cause errors Optical diameter is not related to aerodynamic diameter Huge error in converting number distribution to mass

40 Commercially Available OPCs Vast array of manufacturers and different market segments. Segments include: IAQ Pharma Clean rooms IH Environmental Wide range of flow rates from 1 lpm to 100 lpm or more Comes in different shapes and sizes Manufacturers PMS, Climet, Hach (MetOne), TSI and Fluke Additional Humidity and temperature probes available

41 Commercially Available OPCs

Real Time Bioaerosol Detection BioTrak + 28.

7, 1, 3, 5, 10 µm + 21501-4 compliant for total particulate + Particle collection on gelatin filter +

42 Real Time Bioaerosol Detection BioTrak lpm sample flow rate + Total and viable particulate measurement 6 size channels.5,.7, 1, 3, 5, 10 µm compliant for total particulate + Particle collection on gelatin filter + 400,000 /ft^3 concentration limit + Remote sample tube (up to 10 ft) + Fixed time or fixed volume sampling + Programmable alarm limits + Alarms + Multi lingual display + Data Storage

43 Comparison -Photometers, OPCs and CPCs Indoor Air Quality - Conventional Studies Indoor Air Quality - UF Particle Studies Industrial Workplace Monitoring Outdoor Environmental Monitoring Single channel Photometers DustTrak DRX Optical Particle Counters Portable Handheld Condensation Particle Counters Good Excellent Poor Good Excellent Fair Fair N/A N/A Excellent Excellent Excellent N/A N/A Excellent Good Excellent N/A Good Excellent Emissions Monitoring Excellent Excellent N/A N/A Good Respirator Fit Testing Good Good N/A N/A Excellent Filter Testing Good Good Good Excellent Excellent Clean Room Monitoring Poor Poor Excellent Poor Good Pharmaceutical Poor Poor Excellent Poor Good Research and Development Fair Good Good Fair Excellent Cost Comparison $ $$ $$ $ $ - $$$

Direct Mass Measurement using Beta Attenuation Provides continuous real-time mass concentration Measurement based on amount of attenuation by collected dust than is placed between the

44 Direct Mass Measurement using Beta Attenuation Provides continuous real-time mass concentration Measurement based on amount of attenuation by collected dust than is placed between the radioactive source and a sensitive detector Uses a radioactive C14 isotope (< 100 µci) Similar specifications as a photometer but is limited to a higher concentration of no more than 10 mg/m 3

45 Number, Surface area and Mass based Instruments + Number CPCs, OPCs, + Surface area EAD, LQ-1DC (Diffusion charging particle sensor), NSAM, Aeresense, NanoID + Mass Piezobalance, photometers and OPCs + Why number is becoming significant? Nanoparticles do not have mass Number is a good metric for health effects New research suggests that surface area a better metric

46 Fractional Deposition of Inhaled Particles in the Human Respiratory Tract (ICRP Model, 1994; Nose-breathing) % Regional Deposition Nasal, Pharyngeal, Laryngeal Diameter (µm) 1.0 % Regional Deposition Tracheobronchial Diameter (µm) 1.0 % Regional Deposition Alveolar Oberdörster et al, 2005; Drawing courtesy of J.Harkema Diameter (µm)

47 Instruments to measure Surface Area of Aerosols

48 New Concepts in Aerosol Monitoring

49 Video Exposure Monitoring

50 Perimeter or Fence-line Monitoring

51 Perimeter or Fence-line Monitoring

52 Factors that affect the Choice of the Instrument Cost Particle size inhalable, thoracic or respirable Measurement metric number, surface area, mass Relative or absolute concentration? Concentration range workplace versus clean rooms Workplace standards TLVs versus STELs Is calibration possible? Temperature and humidity Need exposure with respect to time? Dynamic aerosol distributions welding fumes, combustion aerosols etc. Understand the trade-offs between accuracy, cost, size and response time

53 References + Aerosol Measurement, 2 ed. (2005). Wiley Interscience, Edited by Willeke and Baron + Aerosol Science for Industrial Hygienists (1995), James H. Vincent, Pergamon Press + Prince, J. Practical Considerations For Air Monitoring With Emphasis On Direct Reading Real Time Monitors, General Motors of Canada + Collingwood, S. and Heitbrink, W.A., (2007), Field Evaluation of an Engineering Control of Respirable Crystalline Silica Exposures During Mortar Removal, Journal of Occupational and Environmental Hygiene, Vol 4(11), Questions? asreenath@tsi.com

54 Direct Mass Measurement - QCM Piezobalance consists of a piezoelectric crystal that oscillates when an alternating electric field or electric potential is applied across the crystal Resonant frequency is proportional to the mass of the crystal f = K fo m K is determined by calibration, f 0 and f is measured, m can be determined m occurs when mass is deposited on the crystal 2

55 Principle of Operation Aerosol Inlet High Voltage Outlet + Good example is the Tapered Element Oscillating Microbalance (TEOM), the only EPA approved FRM equivalence sampler + Good representation for mass for particles < 10 µm (PM10, respirable) Collected Particles Piezoelectric Crystal Electrostatic Charging and Precipitation Electronic Processing and Display

56 TEOM from Thermo Scientific Performance Specs Measurement Range: 0 to 5,000,000 μg/m³ (5 g/m³) Resolution: 0.1 μg/m³ Precision: ±1.5 μg/m³ (1-hour ave), ±0.5 μg/m³ (24-hour ave) Minimum Detectable Limit for Mass Measurement: 10 nanograms, 0.06 μg/m³ (1-hour ave) Accuracy for Mass Measurement: ±0.75%

57 Advantages of QCM + Direct mass measurement + Response independent of particle size distribution + FBAR (Film Bulk Acoustic Resonator) and SAW (surface acoustic wave) sensors are getting very cheap + Future is in this technology + Tremendous potential in biological and trace chemical detection + Lab-on-a-Chip is close to reality

58 Disadvantages of QCM + A reliable indicator of humidity. Response very sensitive to temperature and humidity + Linearity between mass deposited and change in resonant frequency lost rapidly with loading + Very erroneous for diesel exhaust and other combustion aerosols + Improper binding of particles to the crystal + Slow response time

Direct reading aerosol monitors

Health and Safety Executive Direct reading aerosol monitors 27 th June 2018 Andrew Thorpe Introduction Direct reading Aerosol Monitors (DRAMs) are often used as a complementary approach to conventional