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BWP probe design – John Jayne Used during MCMA2003

BWP probe design – John Jayne Used during MCMA2003. Wire = 0.02” diameter = 0.508 mm. BWP calibration in MCMA2003. 57 steps from start to stop. Center = 52. BWP model.

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BWP probe design – John Jayne Used during MCMA2003

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  1. BWP probe design – John JayneUsed during MCMA2003 • Wire = 0.02” diameter = 0.508 mm

  2. BWP calibration in MCMA2003 • 57 steps from start to stop. • Center = 52

  3. BWP model • The model used the measured travel distance (4.81 mm) between the stops and the total number of steps (57) to derive a calibration of ~0.08 mm/step. • The model used this linear calibration to determine the “Val” positions used by the BWP. • The model (as shown here) shows the wire positions at the BWP plane, and not at the vaporizer plane. • As developed and operated, the model program was designed to fully cover the vaporizer center by matching the wire, side-by-side. The resulting transmission should add up to 100%. • Unfortunately, the actual operation resulted in gaps between the wire positions.

  4. La Merced Results

  5. Average Results for La Merced(two days) • Significant attenuation at the center (3) step and minor, though real, attenuation at the 2 and 4 steps. • IF we had operated the BWP as expected, the attenuation sum = 100% • NOTE: the sum of the attenuations do NOT add up to 100% • ( 0+0+10+60+10+0+0 = ~80%)

  6. BWP was steady during operation • Airbeam shows constant attenuation. • Wire positions did not change during measurements.

  7. BWP mechanism for motion Radius of rotation = 5 mm • Rotation of servo motor axis moves the arm in the horizontal plane. • The servo motor moves in discreet angular steps, however, the corresponding arm (attached to wire) does NOT move in a linear fashion. • The BWP program did NOT take this difference into account.

  8. Relation between servo motion and wire motion • The wire moved a total distance of ~4.8 mm in 57 constant angular steps. • John configured the wire setup such that the servo position was parallel to the particle beam when located in the center position. • Thus, for a symmetric system with a radius of rotation of 5 mm, the arm rotated ~30o in both directions from the center, sweeping out a total of 59o for a total horizontal distance of ~4.8 mm. • The projection of this motion onto the horizontal plane is NOT linear. • The horizontal steps of the wire (what we are really concerned with) are narrower at the edge and wider at the center. • The difference is ~10% per step at the middle.

  9. Results compared with Huffman et al. model • The center transmission was used to approximate the average particle beam width (black line = 0.38) • The white and red circles represent the nominal and actual transmissions of the wire positions (grey boxes show actual wire positions (at vaporizer plane – projection of 0.637 mm) • Note that the white (nominal) attenuations add up to 100%, but the actual do not. • Note the larger gaps at the center of the vaporizer • Note that due to resolution of BWP, the center wire position is not exactly on center line.

  10. Huffman et al. model results as a function of particle beam width for the actual positions of the MCMA2003 BWP wire • Grey box shows the measured particle transmission range and the yellow box shows the same as a function of sigma. • Shows that the 0.5 mm wire is nearly ideal for the ambient conditions • Shows that we should observe an inverse relationship between the center position and the first step positions away from the center over the observed range.

  11. Measured vs Predicted • Correlation plot between transmission at wire positions (steps) from center versus transmission at center wire position • Measured data was smoothed (gaussian) 2 points to minimize noise and binned with constant number of (center position) points • Plot shows the negative slope between the first step and center positions over the range of particle beam widths observed in ambient aerosol

  12. Correlation between Fraction Primary Organics and Particle Beam Width (transmission at center position) • Blue line is ‘Transmission at Center’ and Red line is ‘Fraction of Primary Organics’ • Data smoothed (gaussian) by 2 points.

  13. Obvious correlation • The more primary organics (e.g. vehicle soot) the wider the particle beam

  14. Conclusions • We now have a direct correlation between ambient wire data and Huffman et al. model. • We can now “measure” the particle beam width (limited by S/N and lack of significant attenuation at first wire positions from center) for the campaign • We have a correlation between primary organics and particle beam width (should really redo this to plot as a function of particle beam width, rather than center transmission AND should correlate as a function of particle size in addition to primary vs secondary)

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