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

2. 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

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. 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.

5. Accuracy (uncertainty) vs. Precision
High Accuracy
Low Precision
Low Accuracy
High 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 Ratiox
2s circle of combined uncertainties
Middlebrook et al., AST, 2012

8. 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)

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