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Note: Storm Peak Laboratory (Gannet and Ty)

Note: Storm Peak Laboratory (Gannet and Ty) Have done data quality control on all PSAP and Neph data from StormVEx i.e. removed all short term spikes due to snowmobiles, snowcats, etc…. Before providing data to Betsy . Comparison CAPS and Nephelometer+PSAP measurements

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Note: Storm Peak Laboratory (Gannet and Ty)

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  1. Note: Storm Peak Laboratory (Gannet and Ty) Have done data quality control on all PSAP and Neph data from StormVEx i.e. removed all short term spikes due to snowmobiles, snowcats, etc…. Before providing data to Betsy

  2. Comparison CAPS and Nephelometer+PSAP measurements – using Stormvex data from SPL CAPS measures aerosol light extinction at 630 nm we adjusted CAPS data to STP (T=0 C) using CAPS T and P Nephelometer measures aerosol light scattering at 450, 550, and 700 nm we adjusted nephelometer data to STP (T=0 C) using neph T and P we applied the correction suggested by Anderson and Ogren (1998) to account for instrument non-idealities (e.g., angular truncation) we applied a correction for instrument background due to problems with the hourly zero air measurement we adjusted the nephelometer scattering at 550 nm to 630 nm using the Ångström exponent. PSAP measures aerosol light absorption at 467, 530, and 660 nm data are reported at STP we applied the Bond et al. (1999) corrections for spot size, flow and scattering artifact. (Ogren, (2010) extends the Bond et al. corrections for 3-w PSAP.) we adjusted the PSAP absorption at 660 nm to 630 nm using the Ångström exponent.

  3. Instrument Set up • Instruments sampled off common manifold in Storm Peak Lab • CAPS and Neph+PSAP were next to each other on instrument bench and manifold • Period of data overlap CAPS with Neph+PSAP: Jan 30 – May 30, 2011 • Instrument issues result in only using data between Jan 30 – April 17, 2011 • PSAP transmittance <0.5 (filter overloaded) after ~May 20, 2011 • CAPS pressure jumps to ~80mb above ambient ~April 17, 2011 (see slide 3) • CAPS has extinction drops to zeros frequently throughout May, 2011 (see slide 4) • used hourly averaged values of CAPS and Neph+PSAP (10um size cut only) • CAPS had 5um inlet size cut • Neph+PSAP switched between 5um and 1um size cut every 30 min • Neph inlet RH was <40% over entire time period. CAPS does not have instrument RH measurement, but was probably similarly low (warm lab, cold outside air).

  4. CAPS instrument conditions change on April 27, 2010 Jump in CAPS pressure on April 27 Relationship between Neph and CAPS temperature also changes at this time It is unclear why this happened – nothing in field notes.

  5. CAPS extinction zeroes (happened frequently in May) May 17, 2011 CAPS extinct Neph scatter (10um) Plot shows 1min raw data (no corrections) for May 17. CAPS extinction has frequent excursions to zero, not seen by neph (or by other instruments on SPL manifold (e.g.,CPCs)). No explanation in field notes.

  6. Comparison of extinction measurements (Jan 30 – April 27, 2011) CAPS Neph+PSAP Ratio= • Instruments track each other nicely (except for blip around March 31) • Ratio of extinction (CAPS/(Neph+PSAP)) is noisy, but near 1

  7. Comparison of extinction measurements (Jan 30 – April 27, 2011) • CAPS extinction is ~93% of Neph+PSAP extinction • CAPS extinction is ~97% of Neph scattering

  8. Can ratio of extinction be related to properties of aerosol? Hard to say! Possibly a size effect – e.g., sub-micron fraction of scattering, but sub-um scattering fraction is pretty noisy at low loading.

  9. Comparison of absorption (extinction – scattering vs PSAP absorption) Blue lines are one-to-one lines Yuck! Upper plots do not suggest relationship between two methods of getting absorption. CAPS_ext-Neph_scat derived absorption is noisier than PSAP absorption would this be different if used 1 min data to calculate (CAPS_ext-Neph_scat)difference and then averaged, rather than averaging before differencing?

  10. Can ratio of absorption be related to properties of aerosol? Hard to say! Possibly a size effect – e.g., sub-micron fraction of scattering Possibly a loading effect – ratio of absorption decreases at higher extinction

  11. Conclusions Extinction from CAPS and extinction from Neph+PSAP are within 10%. Neph+PSAP extinction is slightly higher than CAPS extinction. Neph scattering is slightly higher than CAPS extinction. Unclear whether there are biases in extinction relationship due to aerosol properties. Difficult to compare absorption derived from extinction-scattering with measured absorption in this data set. clean air, relatively low loading used difference of averages not average of differences; this could create a bias due to size cut switching in neph+psap system Future Work Redo comparison using average of differences Potential for experiment in GMD lab with borrowed CAPS all instruments on same computer – same time stamp eliminate issues related to size cut switching generate aerosol with wide range of properties

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