uncertainties in ams mass concentrations
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
Uncertainties in AMS mass concentrations
Roya BahreiniAMS Clinic 2012
Especially an important consideration when presenting AMS data to those outside the users’
community!
Calculating mass concentrations
QCERIEIEmass
speciesNOspecies
1111
3
Bahreini et al., JGR, 2009
Parameter Uncertainty Procedure Reference
IENO3 10% Routine NH4NO3 cals
RIEspecies Jimenez et al., 2003; Alfarra et al., 2004; Canagaratna et al., 2007
NH4+ 10% Routine NH4NO3 cals
SO42- 15% Previous lab+
computational resultsOA 20% Previous lab+
computational resultsCE 30% Previous lab+ field
resultsMatthew et al., 2008, Middlebrook
et al., 2012Q <0.5% Routine cals
TE 10% Lens transmission
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.
Overall uncertainty
Q, IE, CE uncertainties
Q, IE, CE, TE uncertainties
NH4+ 33% 34%
NO3- 33% 34%
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
• Precision: • Noise in the data • detection limit
High AccuracyLow Precision
Low AccuracyHigh Precision
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 )
8.1/25.1/75.1/)( 2434
2434
BCOASONONHBCOASONONH
r
Mass Ratio: Overall uncertainty of 45%
Mass closure:Mass Ratio
Middlebrook et al., AST, 2012
2s circle of combined uncertainties
x
Aerosol Acidity Effect
NH4+
,predict=18×(2×SO42-/96 +NO3
-/62 +Cl-/35)
“Apparent CE”(AMS w/ CE=1)
• Acidity , CE
CEdry = max (0.45, 1.0 − 0.73 ×NH4/NH4,predict) [Eq. 4]
Aerosol Nitrate Effect
ANMF=80/62×NO3-/(SO4
2-+NO3-+Cl-+NH4
++OA)
ANMF , CE
CEdry = max(0.45, 0.0833 + 0.9167×ANMF) [ Eq. 6]
“Apparent CE”(AMS w/ CE=1)