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