Aerosol Short Course: Physics, Measurement, and Sampling

Transcription

1 Aerosol Short Course: Physics, Measurement, and Sampling Boeing Ed Wells Course Tom Peters The University of Iowa Department of Occupational and Environmental Health Iowa City, IA III. Sampling

2 Overview Background and Physics Measurement Sampling Aerosols at Boeing Overarching Concepts Case Study

3 Aerosol Sampling at Boeing Aircraft production and maintenance Vent contaminants away from workers Measure air cleaner efficiency Assess exposures in factories Cabin air quality Measure effectiveness of on-board aircraft systems Indicate contaminant dangers to crew Assess exposures in cabins Measure emissions from engines

4 Overarching Concepts Sampling representatively Transport Measuring air cleaner efficiency Assessing particle exposures Indicating dangerous aerosol contaminants

5 Sampling Representatively Isokinetic Sampling: velocity of airstream = velocity of probe Aerosol flow Ventilation duct Exhaust stream Collection Efficiency 100% (all size particles)

6 Sampling Situations Sub-Isokinetic Vair < Vprobe Over-sampling of large particles Isokinetic Vair = Vprobe Super-Isokinetic Vair < Vprobe Sampling Efficiency Diameter Under-sampling of large particles

7 Particle Transport Tube losses due to diffusion Tube losses due Inertia, gravity Penetration 1 0 Diameter Filter

8 Measuring Air Cleaner Efficiency Air Cleaner Particle Removal Efficiency 1 0 Filter Diameter Cyclone

9 Measuring Air Cleaner Efficiency Air Cleaner Upstream Downstream Particle Sizer Efficiency = Downstream Concentration Upstream Concentration

10 Measuring Air Cleaner Efficiency Air Cleaner Particle Sizer Concentration With Cleaner Efficiency = Concentration Without Cleaner

11 Assessing Particle Exposures Who is exposed? Workers in factories Ground crew Crew and passengers Community surrounding airports Filter Separator How do we assess? Use active samplers to collect sample Take a measurement Compare to standard Pump

12 Temporal Variability Within Worker Concentration Sampling Time LOD Frequency Frequency Concentration σ w Log (Concentration) Need large n to capture variability

13 Spatial Variability Between Worker Worker 1 Conc Worker 2 Conc Worker 3 Conc Frequency σ B Log (Average Concentration) Sampling Time Need large n to capture variability

14 New Samplers Increase Sample Size New Passive Sampler Traditional Active Personal Filter System Initial equipment investment ~ $20 per sampler ~ $1500 per sampler Analysis Light Microscopy ~ $1 per SEM ~ $25 per TEM ~ $40 per Gravimetric ~$15 per Qualitative Light, non-obtrusive, increase n in field Bulky, requires more highly trained field person

15 Indicating Danger Long term goal Low-cost, chemistry-specific sensor that provides a real-time output Intermediate goal Light scattering particle detectors for < $300 Like a smoke alarm Permanently installed

16 Indicating Danger Ventilation System Monitor Air Cleaner Sensor Fresh Air Supply Sensor Emissions Monitor Air Cleaner Sensor Exhaust

17 Example 1: Local Ventilation Controls Particle Exposures in the Workplace Connecting Ductwork Air Mover Control Equipment Hoods or Enclosures

18 Example 2: Exhaust Sampling Diesel Engine Exhaust Adapted from D.B. Kittleson AAAR presentation

19 Exhaust Particle Size Distribution

20 Dilution Leads to Nucleation Dilution ratio of 1000 after 1-2 sec Tailpipe emissions diluted by air Exhaust Solids Gas phase organics Sulfur compounds

21 Typical Double Dilution System For Particle Mass Engine Exhaust Inlet FID Air Filter Mixing Orifice Bag Sample NOx, CO, CO 2 Air Sample Filter Back-up Filter Pump

22 Dilution Ratio Strongly Influences Particle Size Particle Number Concentration PDR ~ 25 PDR ~ 40 Primary Dilution Ratio (PDR) ~ nm 100 nm 1000 nm Diameter

23 Example 3: Cabin Air Quality Hunt, Reid, Space, Tilton

24 Pratt & Whitney (PW) Turbofan Engine Fan Bypass Bleed Air Ports Diffuser and Combustor Turbine Stages Turbine Exhaust Compressor Stages

25 Bleed System Air Compressed Taxi: P = 32 psi; T = 330 ºF Takeoff: P = 430 psi; T = 1,200 ºF

26 Cabin Ventilation 12.5 air changes per hour (office building 1-2 acph) 50% Waste Cabin Bleed Air HEPA Filter Ozone Catalytic Converter P = 30 psi T = 400 ºF AC Packs Dry, sterile, dust free air 10 cfm per passenger P = 12 psi T = 60 ºF 50% Re-circulated 10 cfm per passenger

27 Discussion: Particle Contamination Sources Outdoor air Bleed air system AC packs Re-circulating air

28 Discussion: Sampling Strategy Real-time or manual methods? Sampling locations? Sampling techniques?

29 Sampling Summary Aircraft aerosols Factories, cabin, ground crew, and communities Unifying concepts Sampling and transport Measuring air cleaner efficiency Assessing particle exposures Indicating dangerous aerosol contaminants Examples