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Uncertainties in AMS mass concentrations

Uncertainties in AMS mass concentrations. Roya Bahreini AMS Clinic 2012. Especially an important consideration when presenting AMS data to those outside the users’ community!. Calculating mass concentrations. Bahreini et al. , JGR , 2009. Error propagation.

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Uncertainties in AMS mass concentrations

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  1. Uncertainties in AMS mass concentrations RoyaBahreini AMS Clinic 2012 Especially an important consideration when presenting AMS data to those outside the users’ community!

  2. Calculating mass concentrations Bahreiniet al., JGR, 2009

  3. Error propagation John R. Taylor. (1997) An Introduction to Error Analysis: The study of uncertainties in physical measurements. (Second Edition) Sausalito, CA: University Science books.

  4. Overall uncertainty • Total AMS mass: Overall uncertainty of 20-35% • Note: uncertainty in the ratios may be better since some of the parameters cancel out (for example, NH4/SO4 has a better uncertainty since uncertaitny in IENO3, CE, and Q cancel out.

  5. Accuracy (uncertainty) vs. Precision Low Accuracy High Precision High Accuracy Low Precision • Precision: • Noise in the data • detection limit

  6. Mass Closure • Mass Ratio =(AMS mass+BC mass)/(volume×r) • AMS mass: 30% uncertainty • BC mass: 15% uncertainty • Volume: 30-45% uncertainty from UHSAS • mass weighted density (r): 7% uncertainty (10% uncertainty of rOA ) Mass Ratio: Overall uncertainty of 45%

  7. Mass closure:Mass Ratio x 2s circle of combined uncertainties Middlebrooket al., AST, 2012

  8. Aerosol Acidity Effect CEdry= max (0.45, 1.0 − 0.73 ×NH4/NH4,predict) [Eq. 4] • Acidity , CE “Apparent CE” (AMS w/ CE=1) NH4+,predict=18×(2×SO42-/96+NO3-/62+Cl-/35)

  9. AerosolNitrate Effect CEdry= max(0.45, 0.0833 + 0.9167×ANMF) [ Eq. 6] “Apparent CE” (AMS w/ CE=1) • ANMF , CE ANMF=80/62×NO3-/(SO42-+NO3-+Cl-+NH4++OA)

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