Intercomparison of standard andcapture vaporizer in aerosol mass

spectrometer (AMS)

Weiwei Hu1, Pedro Campuzano-Jost1, Douglas A. Day1, Philip Croteau2,

Manjula R. Canagaratna2, John T. Jayne2, Douglas R. Worsnop2,

Jose L. Jimenez1

1 CIRES and Dept. of Chemistry, University of Colorado at Boulder, Boulder, CO, USA

2 Aerodyne Research, Inc., Billerica, Massachusetts, USA

1

Feature of standard vaporizer (SV) vscapture vaporizer (CV)

SV CV

Collection efficiency (CE) depends on :

Standard vaporizer temperature (Tv): 600℃

2Middlebrook et al., AST, 2012

Solid

Molybdenum

edge

Porous

Tungsten

Chemical composition: e.g. NH4NO3 fractions, Acidity of aerosol

Aerosol phase: e.g. Solid/semisolid/liquid particle, Relative humidity

Species: Organic aerosol, Sulfate

Typically contribute the most uncertainty for ambient aerosol measurement

Outlook of SV and CV

3

Temperature measurement for CV

4

Hu et al., submitted. 2016

Experiment setup：

5

SMPS

CPC

AMS with

CV

AMS with

SV

pump

pump

Atomizer

Nafion dryer

or silica gel

Bypass

Bypass(a)

Flow reactorSMPS

AMS with

CV

AMS with

SV

CPC

Nafion dryer

Nafion

dryer

Nafion

dryer

Bypass

(b)

Only exist in SOAS study

Other sampling line

P

PM2.5 cyclone

Lab

Ambient

Outline

•Does capture vaporizer make CE~1 ?

•Gas-phase CO2(g) formation in CV

•Does the capture vaporizer preserve or diminish the chemical and physical information from AMS?Fragmentation and OA source identification?

Size distributions?

6

AmbientLab

CE of standard inorganic species

7

Lab

Hu et al., submitted. 2016

NH4NO3 (NH4)2SO4NH4Cl

An improvement in CE of inorganic species in the CV

NaNO3

CE=AMS/CPC mass ratio

Shown results are carried out under medium vaporizer temperature 500-600C

Lens transimission corrections for NaNO3

dm=300nm→dva=670 nm

8

Hu et al., submitted. 2016

CE of ambient aerosols

9

Ambient

Hu et al., in prep. 2016

SV: CE: 0.5-0.7

CV: CE=1

Total OA SO4 NO3NH4

Multiple results support ambient CE in CV =1

10

Hu et al., in prep. 2016

Ambient

SV vs CV

AMS vs SMPS

SV

CV: CE=1

CV

SV: CDCE=0.5-0.7

Evaluation on chemical composition CE correction

11

Hu et al., in prep. 2016

Outline

•Does capture vaporizer make CE~1 ?

•Gas-phase CO2(g) formation in CV

•Does the capture vaporizer preserve or diminish the chemical and physical information from AMS?Size distributions?

Fragmentation and OA source identification?

Ambient

12

Lab

Production of CO2(g) is negligible for the CV for NH4NO3 and comparable to the SV for NaNO3.

13

Hu et al., submitted. 2016

Outline

•Does capture vaporizer make CE~1 ?

•Gas-phase CO2(g) formation in CV

•Does the capture vaporizer preserve or diminish the chemical and physical information from AMS?Fragmentation and OA source identification?

Size distributions?

Ambient

14

Lab

Fragmentation pattern of inorganic NH4NO3

15

SV

CV

Hu et al., submitted. 2016

Lab

Inorganic does not evaporate as intact salts E.g., NH4NO3(s)→NH4NO3(g)

but go through thermal decomposition.

E.g., NH4NO3(s)→NH3(g)+HNO3(g); HNO3(g)→NO2(g)+H2O(g)+O2(g)

(Drewnick et al., 2015)

Fragmentation pattern of organic species

16 Thermal decomposition is LARGER in CV (esp, for oxidizes species)!

CO enhancementHu et al., in prep. 2016

Lab

CxHy+ CxHyO

+

CxHy+ CxHyO

+ CxHyO2+ C6H8O7Citric acid

C30H50Squalene

Fragmentation pattern of organic species

17

CV

CxHy+ CxHyO

+ CxHyO2+ C18H34O2Oleic acid

Thermal decomposition is LARGER in CV (esp, for oxidizes species)!

CO enhancement

Where CO ion came from?

Lab

Measured isotope C13

labeled oleic acid

18

PToF show CO peak similar with aerosol phase

CO in aerosol

PToF

CO2 in

aerosol PToF

Squalene √ ×

Oleic acid √ √

Citric acid √ √

DOS √ √

Chamber SOA √ √

Isotope-

labeled Oleic

acid

√ √

19

Lab

j13CO+

j13CO2+

j13C3H5+

Chemical information in CV is not lost

20

Hu et al., in prep. 2016

Lab

F44=CO2/OA

Ambient

Ambient elemental ratio comparison

21

Hu et al., in prep. 2016

Ambient

SV

CV

Similar PMF results for SV vs CV

Hu et al., in prep. 2016

Ambient

IEPOX-SOA: Isoprene epoxydiols-derived SOA

SV

CV

22

Outline

•Does capture vaporizer make CE~1 ?

•Gas-phase CO2(g) formation in CV

•Does the capture vaporizer preserve or diminish the chemical and physical information from AMS?Fragmentation and OA source identification?

Size distributions?

Ambient

23

Lab

Size-resolved detection of inorganic ions

SV

CV

Lab

Hu et al., submitted. 201624

Size distribution of ambient aerosol in CV still work

25

Ambient

SV

Hu et al., in prep. 2016

Total

SO4

NO3

NH4

CV

Temperature dependent size distribution

26

Hu et al., submitted. 2016

Estimating vaporizer temperature for detecting species in size mode

27

Hu et al., submitted. 2016

SV CV

CE for ambient particles CDCE CE=1

CE for pure inorganics in lab Bounce <1 but better than SV

Impact of thermal decomposition Longer residence time

CE ~1 for ambient particles Substantial at high OA loading

Information for source apportionment (PMF)

Organic nitrate vs. ammonium nitrate Low S/N

OA elemental ratios

Single particle calibration

CPC-based calibration

Heater bias dependence of signal Sensitive Not sensitive

Nitrate Chloride artifact Vary with instrument history Vary with instrument history

CO2 signal decay lifetime faster than SV

CO2(g) formation from nitrates Minor for AN, comparable for SN

Lab & Chamber size distribution For monodisperse particles

Ambient size distribution Need AS calibration

SO4 UMR quantification under high OA For SO3+ and HSO3

+ ions

BadExcellent Better So-So

28

Faster CO2 decay in CV than SV

29

C6H8O7

Citric acid

τCO2 <3sτCO2 ≈11s

Summary• CE ~1 !

• Slower evaporation impacts size distributions

• Still OK for ambient air.

• Much broader for monodisperse lab exp.

• CO2 formation was neg

• Production of CO2(g) is negligible for the CV for NH4NO3 and

comparable to the SV for NaNO3.

• Mass spectra shifted to smaller fragments.

• But information content (e.g. OA sources and elemental ratios) not lost!!

• Further analysis: CO formation influences to the quantification of

OA.

Thanks for your attention.27