Update on SMPS/CPC comparisons. As shown at 2011 AMS Users Mtg

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Clementine Preston
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Update on SMPS/CPC comparisons at BEACHON RoMBAS 212 Brett Palm, Jose Luis Jimenez University of Colorado

Deployed 5 different SMPSs and 3 stand alone CPCs at RoMBAS SMPS: TSI Kr, TSI Xray, Custom, BMI, Grimm

Basic check: compare total number concentrations 2. Reminder of where we stood at the end of campaign 3.

1 Update on SMPS/CPC comparisons at BEACHON RoMBAS 212 Brett Palm, Jose Luis Jimenez University of Colorado Boulder AMS Users Meeting 13 Oct Deployed 5 different SMPSs and 3 stand alone CPCs at RoMBAS SMPS: TSI Kr, TSI Xray, Custom, BMI, Grimm Often only 1 SMPS at a field site, used to determine CE Opportunity to see how well that may work out Basic check: compare total number concentrations 2. Reminder of where we stood at the end of campaign 3. Identification of some of the problems 4. Moral of the story 1 As shown at 211 AMS Users Mtg Factor of x5 between instruments None of SMPS agree with CPC! Number Concentration 2 1

As shown at 211 AMS Users Mtg Three different CPC models

#3 are too low 3 SMPS#1: CPCs have a lower size cutoff

2 As shown at 211 AMS Users Mtg Three different CPC models match taken to be true int. number density Compared to CPCs: SMPS #4 and #5 are too high SMPS #1 matches except for afternoons SMPS #2 and #3 are too low 3 SMPS#1: CPCs have a lower size cutoff Nucleation during afternoons Small particle losses in SMPS explain afternoon deviations 2

SMPS#1: CPCs have a lower size cutoff Nucleation during afternoons Small particle losses in SMPS explain afternoon deviations Investigating SMPS #2: dn/dlogd m scans compared to SMPS #1 Three

3 SMPS#1: CPCs have a lower size cutoff Nucleation during afternoons Small particle losses in SMPS explain afternoon deviations Investigating SMPS #2: dn/dlogd m scans compared to SMPS #1 Three different (and stable in time) size distributions on 8/12/11 Residence time in SMPS #2 inlet was much longer than in SMPS #1 inlet large losses of small particles in inlet dn/dlogd m D m 15x1 3 SMPS #1 SMPS #2 8/12/211 : 12x1 3 dn/dlogd m 8 4 8/12/211 21:56 8/12/211 15:16 1 D m dn/dlogd m D m 6 3

4 Empirical Correction Function for SMPS #2 dn/dlogd m 1..8 % Transmittance D m 7 SMPS #2: After size dependent correction dn/dlogd m SMPS #1 SMPS #2 8/12/211 : 12x1 3 dn/dlogd m 8 4 8/12/211 15: D m D m 15x1 3 8/12/211 21:56 dn/dlogd m D m 8 4

5 Integrated Number after SMPS #2 sizedependent correction 9 Integrated Volume after SMPS #2 sizedependent correction 1 5

6 As shown at 211 AMS Users Mtg Three different CPC models match taken to be true int. number density Compared to CPCs: SMPS #4 and #5 are too high SMPS #1 matches except for afternoons SMPS #2 and #3 are too low 11 Direct Comparisons of SMPS #1, #3 5 w/ CPC Ammonium sulfate from atomizer DMA set to a one size CPC SMPS #1, #3, #4, #5 Compare CPC counts to integrated SMPS counts Compare DMA selected particle size to measured SMPS size 12 6

7 SMPS #1 vs. CPC Decent agreement in size and integrated number Integrated SMPS Number Concentration (1nm - 1nm only) CPCcounts 15 5nm cm nm 5 25nm 28nm 4: PM 8/28/211 4:15 PM 4:3 PM 13 SMPS #4 vs. CPC Selected vs. measured size matches, but integrated number density does not 1nm 2nm 5nm 2nm 14 7

8 As shown at 211 AMS Users Mtg Three different CPC models match taken to be true int. number density Compared to CPCs: SMPS #4 and #5 are too high SMPS #1 matches except for afternoons SMPS #2 and #3 are too low 15 SMPS #5 vs. CPC Neither size nor integrated number density match Known problem: a TSI X Ray neutralizer was used, which produces a more symmetrical equilibrium charge distribution (see next slide). This means the software inversion is wrong, resulting in ~15 4% higher particle number density measured Unknown problem: why do selected and measured particle sizes not match? 16x Number Density (cm -3 ) nm selected by CU DMA (<14.6nm meas. by LANL) 5nm selected (37.2nm meas.) 1nm selected (73.7nm meas.) SMPS #5 CPC counts 28nm selected (216.7nm meas.) 6: PM 8/23/211 6:1 PM 6:2 PM 16 8

9 Slides from a TSI Webinar: X Ray vs Krypton Source 17 Slides from a TSI Webinar: X Ray vs Krypton Source 18 9

10 SMPS #3 vs. CPC Still working on this comparison, but there was definitely a software or user error in converting dn/dlogdp to integrated number. More to come What s going on? Nobody gets funded to bring an SMPS to a field campaign, or gets excited about its data (e.g. good luck recruiting a good PhD student to do SMPS measurements!) In a field study, people tend to take SMPS out of the box, set it up, and not pay much attention to it as they work on the more scientifically interesting instrument they really care about Unfortunately SMPSs can have many problems and still produce reasonablylooking concentrations and size distributions. Most users won t even notice! I d estimate the probability of a problem is ~9% for unattended SMPS AMS users need to be the exception because of the need of highquality SMPS measurements for 19 comparison Moral of the Story Always use 2+ independent measurements to compare to AMS (especially if trying to determine CE). Need to ALWAYS compare number and calibrate size on SMPS Even routine instruments are wrong more often than not. SMPS #5: known X Ray source problem + unknown size issue SMPS #4: Inversion routine error SMPS #3: software / user error? SMPS #2: Transmission loss + CPC problem SMPS #1: Not seeing nucleation particles 2 1

11 BACKUP SLIDES 21 Summary 5 SMPSs from 5 experienced groups at same location 1 working OK (not seeing nucleation particles, as expected) 1 losing particles < 2 nm due to both long inlet and CPC issues 1 likely has error in inversion software 1 has too many particles due to TSI X Ray charging efficiency, also unknown sizing problem 1 unclear, but maybe sofware / user error Moral of the story: you always want TWO independent measurements to compare to AMS 22 11

12 Integrated Volume after SMPS #2 sizedependent correction (zoom) 23 Number Comparison #1 vs #

13 Volume Comparison #1 vs #2 25 SMPS #2 now matches CPCs and SMPS #1 What about SMPS #3, #4, #5? 26 13

14 Slides from a TSI Webinar: X Ray vs Krypton Source 27 14

Calibration checks of particle counter using primary and other techniques at the laboratory level

Calibration checks of particle counter using primary and other techniques at the laboratory level Shankar G. Aggarwal, Ph.D. CSIR-National Physical Laboratory, New Delhi-110 012, India @ Particulate Workshop