Quantification of Aerosol Species with the AMS: Overview

Presented by Manjula Canagaratna

AMS Users Meeting, St. Louis

Sep 2018

3.0

2.5

2.0

1.5

1.0

0.5

0.0

Nitr

ate

Equi

vale

nt M

ass

Con

cent

ratio

n (µ

g m

-3)

1412010080604020m/z (Daltons)

Ammonium 4.8 ug/m3Nitrate 5.8Sulphate 9.4Organics 13.4Chloride 0.15

Mexico City 2/2002

How do we go from measured MS Ion intensities, to mass concentrations of species?

Ion

Inte

nsity

(Hz)

AMS Mass Quantification

Converting AMS ion signal to species mass concentrations

QCERIEIEmass

speciesNOspecies

1111

3

⋅⋅⋅∝

Ionization Efficiency (IENO3 )

Flow (Q)

Collection Efficiency (CE)

Relative Ionization Efficiency (RIES)

Collection Efficiency

Lens Transmission Overlap between particle beam and vaporizer

Particle Bounce on oven

Huffman et al., AS&T, 2005

Efficiency with which particles are transmitted to and collected at vaporizer

Collection Efficiency: ELStandard Lens: Liu et al. AS&T (2007)

EL: Size dependent Transmission through lens

PM2.5 Lens: Xu et al., AS&T (2017)

AMS, ACSM, SP-AMS: All use same Lens, same CEL effects

Collection Efficiency: Es

ES~1 (AMS and ACSM Thermal Vaporizers)

Most particles (even aspherical soot particles) are collected with greater that 95% efficiency

Huffman et al., AS&T, 2005

Es: Overlap between particle beam and Vaporizer

Collection Efficiency: Es

ES<1 (SP- AMS Laser Vaporizer)

Onasch et al. AS&T, 2012

SP2 Module: 1064 nm laser

Collection Efficiency: Eb

AMS and ACSM: SV Thermal Vaporizer•Bounce Loss is dominant

Eb<EL<Es• f(composition,phase, particle size ) AMS and ACSM: CV Thermal VaporizerEb = 1 SP-AMS: SP-mode (Laser Vaporizer)

No Bounce

Eb: Correction factor for particle bounce off Vaporizer

SV: Flash Vap

SV: Bounce

CV: Capture

Xu et al., AS&T 2017

Eb is dominant contribution to CE of SV and affected by particle bounce (depends on particle phase)

References: Matthew et al., AS&T, 2008 Quinn et al.,JGRAtm, 2006 Allan et al.,JGRAtm, 2003 Drewnick et al., Atm. Env, 2003

CE: Lab and Field Results

Typically, ambient CE=0.5 (+/-0.15) for all species with empirical composition dependence(Middlebrook et al.AS&T, 2012)Lab CES values are more variable since pure particles may not be identical in phase to complex, ambient particles (Matthew et al.,2008, Docherty et al. AS&T, 2013)

Composition Dependent CE ( CDCE) is incorporated into Squirrel/PIKA for ambient applicationsNeed to make sure that the input parameters (starred) are accurate before doing the calculations

AMS Mass Quantification

Converting AMS ion signal to species mass concentrations

QCERIEIEmass

speciesNOspecies

1111

3

⋅⋅⋅∝

Ionization Efficiency (IENO3 )

Flow (Q)

Collection Efficiency (CE)

Relative Ionization Efficiency (RIES)

RIE (Relative Ionization Efficiency)Inorganic SpeciesEarly lab calibrations on inorganics by Frank Drewnick, Ann

Middlebrook

RIENO3 - 1.1 (for ions other than m/z 30 and 46)RIENH4 - 3-5 RIE SO4 - 1.2

IENO3, RIENH4, are routinely calibrated for each instrumentRIE SO4 can be measured for each instrument.

(See later talk by Phil Croteau for information on inorganic RIE cals)

Determination of RIE for Organics (RIEOA)Complication: Ambient OA is made up of

thousands of individual organic species. What do we use as a calibrant?

Ambient Measurements: Usually CE*RIEOA= (0.5*1.4)=0.7- CE=0.5 assumes organic and inorganics

internally mixed- RIEOA = 1.4 is based on early laboratory work by

Silva et al. (See Jimenez et al., AS&T,2016 for more information)

Useful Discussion of AMS detection

Recent Lab work : Evaluating AMS RIE for organics

Recent Lab work : Evaluating AMS RIE for organics

Xu et al., AS&T (2018)1) What is variability in Organic RIEs across a

range of O/C (OSc) values?2) Can AMS organic RIEs be predicted from

theory?3) Is RIE of individual species significantly different

when in pure or mixed aerosol(i.e. Mixed alcohol/nitrate agree well with pure organics- could provide “simple” organic calibration method for RIEOrg)

Improved Calibration Protocol for RIEOA

Particle Source

(Atomize OA standards, Nucleation, PAM SOA)

Mobility Diameter Selection

(DMA)

Number Conc

(CPC)

Mass/Particle Selection

(CPMA)

Mass Conc

Q-AMS* (w/ LS)with standard

vaporizer and Capture Vaporizer (CE~1)

Particle Generation

Measurements

Input Mass= (CPMA Mass/particle)*CPC Number

AMS Mass = (1/CESRIES)*AMS NO3 Equiv. Mass

CES*RIES = NO3 Equiv. Mass/CPMA Input Mass

CES ~AMS pTOF Single Particle Counts/ CPCORAMS LS Particle Counts/ CPC

Data Processing

Data obtained by Wen Xu*, Xu et al. AS&T,(2018)

Particle size, mass selection

RIEOA vs OSc

CV and SV Measurements of Commercially available Organic Standards, PAM SOA show similar trends;

Lab RIEOA= 1.6 ± 0.5 (2σ) for OA with 1.0 < OSC < 0.5. This OSc range is consistent with most ambient OA except hydrocarbon-like organic aerosol (HOA) and cooking organic aerosol (COA).

The RIEOA typically used for ambient OA (1.4 ± 0.3) is within the laboratory RIEOA measurement uncertainty of oxidized organic species, but is a factor of 2 to 5 lower than that of reduced species.

Xu et al. AS&T,(2018)

Ambient OA trends do not show evidence for large differences in RIEPOA and RIESOA

Trends in SOA and POA RIE may be offset by their differences in CEL(POA sizes fall in small size range (<100 nm) where lens cutoff can be significant)

Jimenez et al. AS&T, 2016

Measured RIECOA is 1.56-3.06with CE=1

Agrees with expected RIE range for Osc ranges typical of COA

Xu et al. AS&T,(2017)

Summary• Difficult to get good laboratory surrogates of ambient

aerosol. (Lab RIEs and CEs can be different from ambient)

• Measurements and empirical parameterization must be used for RIE OA (Current theoretical predictions are not complete- see Xu et al., AS&T 2018, Jimenez et al.,AS&T 2016 for more details).

• More evaluations of AMS quantification (CEOA*RIEOA) with “real” ambient aerosol are needed (i.e. use ambient OA /filters as source for lab measurements)

• Intercomparison of AMS mass concentrations with other instruments are needed (see talks on sunday morning.)

• RIES - for other species should be measured: exotic metals, salts, inorganics (example: Drewnick et al, AMT, 2015)