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)