Current and Future Methods for Calibration of Black Carbon Real-Time Mass Instruments

Transcription

1 Current and Future Methods for Calibration of Black Carbon Real-Time Mass Instruments Greg Smallwood, Kevin Thomson, Fengshan Liu, Dan Clavel National Research Council Canada, Matthew Dickau, Tyler Johnson, Jason Olfert University of Alberta, Mechanical Engineering Cambridge Particle Meeting June 2014 Cambridge, UK

2 What is Black Carbon? Black Carbon is a distinct type of carbonaceous material that is formed primarily in flames, is directly emitted to the atmosphere, and has a unique combination of physical properties strongly absorbs visible light is refractory with a vaporization temperature near 4000 K exists as an aggregate of small spheres is insoluble in water and common organic solvents Bond et al., Bounding the role of black carbon in the climate system: A scientific assessment, Journal of Geophysical Research Atmospheres, 118, (2013) 2

3 Relative Effect of Aerosols on Climate Black Carbon Ramanathan Bond et al.,, J et Geophys al., Nature Res Geoscience - Atmospheres, 1 (2008) 118 (2013) Intergovernmental Panel on Climate Change (2007) 3

4 Impacts of Black Carbon BC is the most light absorbing nano-aerosol BC absorbs 680x more energy by mass than CO 2 BC is a key contributor to global warming BC effects are stronger in sensitive regions, i.e. faster ice and snow melt in the Canadian Arctic BC mitigation could rapidly slow the rate of climate change, by up to 40% within 20 years BC is implicated in numerous adverse health outcomes For BC and related combustion emissions, on a global scale the adoption of aggressive standards by 2015 would annually prevent the deaths of 200,000 people, save 13 million tons of grain and $1.5 trillion in health damages after Shindell et al, Nature Climate Change, 1 (2011) 4

5 What Attributes of PM Need to be Measured? regulated gaseous pollutants are specific CO 2, CO, SO 2, NO x, HC, etc. measurement of gaseous concentration current regulatory focus for PM is mass concentration in most jurisdictions (PM 10 and PM 2.5 ) Europe has added number concentration for on-road vehicle emissions health and environmental researchers and policymakers are asking for more specificity on PM mass concentration at smaller size fractions (PM 1.0, PM 0.5, PM 0.1?) size and size distribution composition (black carbon, organics, sulphates, nitrates, etc.) surface area and surface reactivity optical properties (absorption and scattering) 5

6 Measurement Issues (I) Traceability many instruments offer no opportunity for traceability filter-based mass can be traceable issues with sensitivity (mass of particulate vs. mass of filter) issues with filter artifacts gaseous adsorption fibre loss less than 100% removal efficiency issues with size cutoff impactors and cyclones do not cut sharply at threshold (i.e. PM 2.5 ) number concentration can be made traceable (sort of) 6

7 Measurement Issues (II) Reliability and Repeatability difficult to establish Uncertainty large uncertainties (can be order of magnitude in number, factor of 2 in mass) Reference Materials airborne particulate RMs don t exist Representativeness all ex-situ methods suffer from sampling issues how representative is the sample at the measurement location of the airborne particulates? losses, agglomeration, evaporation/condensation 7

8 Measurement Issues (III) Measuring properties with different methods most instruments are proprietary each manufacturer implements a different measurement principle difficult to intercompare results obtained with different instruments examples size mobility diameter, aerodynamic diameter, geometric diameter, radius of gyration black carbon mass directly measured, or inferred from optical absorption, extinction, or emission measurements 8

9 Measurement Issues (IV) Measuring specific properties with a myriad of interferences selectivity how does one measure properties of one component of PM when many others are present? sensitivity atmospheric concentrations are often very low (<1 µg/m 3 ) gas composition can be highly variable can influence measurement morphology spherical particles vs. fractal aggregates single particle vs. ensemble measurements variations over time, elevation, temperature, humidity, sunlight, etc. 9

10 Standard Method Balloted by SAE E-31 Committee: Mass Instrument Calibration Procedures Calibration mass instruments to be calibrated with NIOSH 5040 procedure (comparison to mass of EC collected on a filter) requires source of soot that is >80% EC optimum loading is ~200 µg EC on a 47 mm quartz filter at nominal 100 µg/m 3 concentration, requires 80 min/filter Annual Calibration requires 3 repeats each at 0, 100, 250, and 500 µg/m 3 Type Certification requires 6 repeats each at 0, 50, 100, 500, and 1000 µg/m 3

11 Standard Method Balloted by SAE E-31 Committee: Development of BC Mass Calibration at NRC Correlation to elemental carbon (EC) via thermo-optical method (NIOSH 5040)* NIOSH 5040 filter collection Dual filter in AIR 6241 holder Dump flow Pump Mass Flow Controller Production of nvpm Splitting Mass Flow Controller Pump Inverted Flame Burner Multistage dilution cyclone cyclone Mass measurement Mass Concentration Instrument to be Calibrated Mass Flow Controller Pump Mass Concentration Instrument to be Calibrated Mass Flow Controller Pump HEPA Mass Concentration Instrument to be Calibrated Mass Flow Controller Pump Make-up air Mass Concentration Instrument to be Calibrated Mass Flow Controller Pump *SAE AIR6241, Procedure for the Continuous Sampling and Measurement of Non-Volatile Particle Emissions from Aircraft Turbine Engines, (2013) Dump flow Mass Flow Controller Pump 11

12 Example SAE AIR6241 Calibration Result (Artium LII 300) 12

13 Example SAE AIR6241 Calibration Result (AVL MSS) 13

14 Future Method for Mass Instrument Calibration NIOSH 5040 mass instruments will be calibrated with NIOSH 5040 annually method is well known, but uncertainty is large (17% at 23 µg/m 3 ), it is not traceable, experiments are very time consuming CPMA-electrometer method traceable function of rotational speed, voltage, flow rate, current, and electron charge (physics-based approach) Uncertainty of ~5% 10 point calibration in less than one hour excellent method for low mass concentrations (< 100 µg/m 3 ) 14

15 Publication on CPMA-Electrometer Method in 2013 calculated combined uncertainty (k=2) for the system of 5% technique developed with silicon oil aerosol [k=2 represents a 95% confidence interval] 15

16 Experimental Setup

17 Experimental Setup Methane Fuel (1.4 slpm) Analog Inverted Flame Burner Combustion Air (17 slpm) Dilution Air (85 slpm) Production of nvpm with >99% EC a Catalytic Stripper Selection by mass/charge Uni- Polar Charge r CPMA HEPA Serial b c d Electric Precipitator DMA with maximum voltage and no sheath flow e f Keithley 6517B Electrometer Charge measurement CPC Faraday Cup Electrometer Mass Concentration Instrument to be Calibrated Uncharged particle count Analog Serial Laptop Pump Mass Flow Controller Mass Flow Controller Make-up air Mass measurement Pump 17

18 Comparison of Mass Instruments to CPMA- Electrometer System mass instruments calibrated with NIOSH 5040 EC over a few weeks (e.g. SN0340 was calibrated in different NIOSH 5040 batch) uncertainty in NIOSH 5040 is large, so compare linearity, not slopes between instruments 18

19 Measurements With and Without a Charge Neutralizer Before the Mass Instrument charge on particles appears to have minimal effect on measurements made by mass instruments 19

20 Measurements at Different CPMA Resolutions CPMA resolution setting appears to have minimal effect on measurements made by mass instruments 20

21 Sources of Uncertainty Uncertainty averaged 8.6% (k=2), as low as 5.2% (k=2) for some measurements flow rate measurement CPMA set point from voltage and rotational speed measurement CPMA resolution Largest source of uncertainty was noise and offset in current measurement Improvements to Faraday cage electrometer should reduce uncertainty to 6% or lower (k=2) 21

22 Measurement on a NIOSH 5040 EC Calibrated Mass Instrument CPMA-Electrometer method concentration range extended to 500 µg/m 3 average uncertainty reduced to 5.2% (k=2) error bars represent 95% confidence intervals (k=2) 22

23 Measurement on a NIOSH 5040 EC Calibrated Mass Instrument Repeatability CPMA-Electrometer method excellent linearity slopes within +/-5% of reported values on NIOSH 5040 EC calibrated instrument for all three repeats error bars represent 95% confidence intervals (k=2) 23

24 Summary (I) Airborne particulate matter has significant, detrimental effects on health, visibility, and climate PM 2.5 mass concentration measurements, while important, are a poor overall indicator of these effects PM metrology is required to improve reliability and repeatability of measurements, and to reduce uncertainty critically important to climate change modelling necessary to improve association between health effects and PM properties for sound policy decisions and regulations 24

25 Summary (II) Quality of measurements and intercomparability need to be improved mass concentration at smaller size fractions size and size distribution composition surface area and surface reactivity optical properties Black Carbon is one of the best PM targets due to cobenefits in reducing climate forcing and improving human health 25

26 Summary (III) CPMA-electrometer system is a viable option for calibration of aerosol mass concentration instruments CPMA-electrometer measurements are highly linearly correlated with both types of mass instruments lower uncertainty, averaging 5.2% (k=2), and much quicker than NIOSH 5040 method CPMA resolution and presence or absence of a charge neutralizer do not appear to affect the measurements CPMA-electrometer system advantages have been realized more rapid than NIOSH 5040 filter experiments lower concentrations more readily achieved CPMA-electrometer system has potential for traceability 26

27 Thank you Dr. Gregory J. Smallwood Program Leader, Measurement Science for Emerging Technologies phone: web: