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

Calculating mass concentrations Parameter Uncertainty Procedure Reference IENO3 10% Routine NH4NO3 cals RIEspecies Jimenez et al., 2003; Alfarra et al., 2004; Canagaratna et al., 2007 NH4+ SO42- 15% Previous lab+ computational results OA 20% CE 30% Previous lab+ field results Matthew et al., 2008, Middlebrook et al., 2012 Q <0.5% Routine cals TE Lens transmission Bahreini et al., JGR, 2009

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.

Q, IE, CE, TE uncertainties Overall uncertainty Q, IE, CE uncertainties Q, IE, CE, TE uncertainties NH4+ 33% 34% NO3- SO42- 35% 36% OA 37% 38% 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.

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

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%

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

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

Aerosol Nitrate 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)