The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
A reanalysis of the capacity of PTRMS to uniquely identify and quantify VOCs in global background air
Ian Galbally, Erin Dunne, Sarah Lawson, Antonio Patti with collaborative data from Dennys Angove GAW Reactive Gases Workshop Helsinki June 2010
www.cawcr.gov.au
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
• Measuring VOCs using PTRMS • Introduction to PTRMS as a measurement technique • Review of suitability of PTRMS for measuring VOCs in background air
• Results from Cape Grim • VOC concentrations from two recent campaigns and comparison with other remote oceanic sites
Outline
ProtonTransferReaction Mass Spectrometer (PTRMS)
Proton Transfer: Proton Transfer: H H3 3O O + + + A + A → → AH AH + + + H + H2 2O O PA (A) > PA (H PA (A) > PA (H2 2O) O) Electric field ~50 V cm Electric field ~50 V cm 1 1 Pressure ~ 2 mbar Pressure ~ 2 mbar
Detection Limit: ~10 pptv Detection Limit: ~10 pptv Response Time: 100 ms Response Time: 100 ms
Compound identification: Compound identification: Capable of detecting 100s of Capable of detecting 100s of VOCs (mass range 1 VOCs (mass range 1 512amu) 512amu) Soft ionization reduces product Soft ionization reduces product ion fragmentation ion fragmentation
Compound quantification: Compound quantification: The product ion signal is The product ion signal is proportional to the mixing ratio of proportional to the mixing ratio of that compound in the air flow. that compound in the air flow.
PTRMS Identification and quantification of atmospheric volatile organic compounds
Current hypothesis: The PTRMS can be used to accurately identify and quantify VOCs in the atmosphere.
This hypothesis can be examined in 3 parts:
1. Can the PTRMS uniquely identify atmospheric VOCs?
2. Can the PTRMS accurately quantify the concentration of atmospheric VOCs?
3. What can be learnt of atmospheric VOCs from a substantial body of real atmospheric measurements?
PTRMS Limitations
PTR PTR MS Mass resolution: 1 amu MS Mass resolution: 1 amu PTR PTR MS cannot distinguish between product ions MS cannot distinguish between product ions with the same mass! with the same mass!
Identification and quantification require information on what Identification and quantification require information on what compounds are contributing to the ion signal at each mass channe compounds are contributing to the ion signal at each mass channel l
A signal at a given m/z may contain contributions from:
2 or more compounds with the same protonated mass Fragment or cluster ions Product ions from reactions with O2 + NO + and H3O + (H2O)
Laboratory fragmentation studies currently underway of VOCs by PTRMS
Alcohols Acids Esters Other OVOCs Alkanes/Alke nes
Methanol Formic acid Methyl formate Formaldehyde Toluene
Ethanol Acetic acid Ethyl formate Acetaldehyde 2methyl 1,3 butadiene
1propanol Propanoic acid Propyl formate Acetone
2propanol Oxalic acid Butyl formate 1hydroxy propanone
Organo nitriles
1butanol Methyl acetate 2butanone Acetonitrile
2butanol Ethyl acetate Methyl
isobutyl ketone
Tert. butyl alcohol
2oxo propanal*
Ethanedial*
Hydroxy acetic Acid*
Hydroxy acetaldehyde*
* to be completed
Case Study: Mass 75 Significant ion signal at mass 75 detected in semirural air near Sydney. 20 compounds with PA>H2O that would have a protonated mass of 75.
Significant correlations (r > 0.5) were observed between mass 75 and the following masses: 33, 43, 45 , 46, 47, 61, 71
The correlations and concentrations observed for m/z 75 and 43 indicate methyl acetate is prime candidate compound for the a majority of the signal observed at m/z 75
Mass spectra studies improve Mass spectra studies improve our ability to identify our ability to identify compounds in the atmosphere compounds in the atmosphere using PTR using PTR MS MS
E = V cm E = V cm 1 1
N = molec. N = molec. cm cm 3 3
Fragmentation studies of ethanol
Mass spectra studies can be Mass spectra studies can be used to optimize the used to optimize the instrument response to specific instrument response to specific compounds compounds
All analyses are on the same humidified air sample containing ethanol
PTRMS response to ethanol is optimal at E/N = 90Td
Low response at high E/N is likely due to fragmentation to H3O + unmeasurable!
E = V cm E = V cm 1 1
N = molec. cm N = molec. cm 3 3
CET Indoor Smog Chamber – D. Angove
• Teflon lined, airfilled chamber of 18 m 3 supported by an aluminium frame and lined with highly reflective aluminium
• Provides a low contaminant environment which permits studies at low reactant concentrations.
• UVA lights are used to simulate sunlight.
• Interfaced instruments allow measurement of reactant consumption and product formation.
• Facilities are available for the sampling of gaseous and aerosol samples.
• Observations are supported by complex chemical mechanism models such as the Master Chemical Mechanism.
CET Indoor Smog Chamber – External View
Formic acid during smog chamber runs with standard and ethanol containing fuels
0 100 200 300
2
0
2
4
6
8
10 ULP 362 ULP 363 E10 360 E10 361 E5 365 E5 366
Form
ic Acid Conc. (p
pb)
Time (min)
Formic acid measured using longpath FTIR (119 m) and spectrum fitting using the formic acid lines generated from the HITRAN database and MALT version 5.5 developed by David Griffiths (UOW). The errors are outputs from the fitting procedure.
Mass 47 (expressed in units of ethanol) during smog chamber runs with standard and ethanol containing fuels.
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ULP 362, ULP 363, E10 360, E10 361, E5 365, E5 366
Ethanol equiv. conc (ppb)
Time (min)
Water Injection
Fuel Injections
LIGHTS ON
Mass 47 increases in all experiments, in spite of the expected decrease in ethanol concentration – the influence of formic acid
There is indication of baseline offsets observed in all experiments with water injection. Is there either a water signal, or chamber wall desorption, at mass 47?
Aim: to determine whether PTRMS can unequivocally identify and quantify isoprene, terpenes, acetonitrile, methanol, ethanol, acetone, dimethyl sulphide, benzene and toluene in clean air.
Use mass spectral data to uniquely identify the PTRMS product ion signals of each of these VOCs in measurements from Cape Grim Tas. and rural site in WA.
e.g. acetonitrile measurements at Cape Grim. The contribution of propene must be removed from the signal at mass 42 for accurate quantification of acetonitrile.
H3O + + CH3CN → CH3CNH + + H2O m/z 42 O2 + + C3H6 → C3H6 + + O2 m/z 42
Ambient monitoring in the global atmosphere
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
The suitability of PTRMS to measure VOCs
VOC Protonated Mass
OK in background
air?
Issues at this mass Intercomparison studies
methanol 33 Y FTIR (Christian et al., 2004) (Karl et al., 2007)GCMS (de Gouw et al., 2003)
acetonitrile 42 Y O 2 + + propene but not significant when propene <100 ppt
GCMS (de Gouw et al., 2003)
ethanol 47 Challenging Formic acid Low sensitivity to ethanol due to fragmentation to H 3 O + (Inomata
Tanimoto, 2009b) Di methyl ether?
Saphir (Apel et al., 2008)
acetone 59 Y Propanal contributes (~10%) possibly glyoxal
GCMS (de Gouw et al., 2003) (Karl et al., 2007)
Saphir (Apel et al., 2008)
di methyl sulphide (DMS)
63 Y Hydrated acetaldehyde may contribute where [acetaldehyde] is
>> [DMS]
GCMS (de Gouw Warneke, 2007)
isoprene 69 Y (providing no biomass burning)
Furan C 5 H 8 hydrocarbons
GCMS(de Gouw et al., 2003) (Karl et al., 2007)
terpenes 81, 137 Y GCMS (de Gouw et al., 2003)
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Baseline Conditions at Cape Grim
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
VOC concentrations (ppt) at Cape Grim and other Oceanic sites
1. Galbally, I.E., et al., Environmental Chemistry, 2007. 4(3): p. 178182. 2. Ayres, G.P. and R.W. Gillett, Journal of Sea Research, 2000. 43: p. 275286. 3.Colomb, A., et al., Environmental Chemistry, 2009. 6(1): p. 7082. 4. Williams, J., et al., Environmental Chemistry, 2010 7(2): p. 171182. 5. Warneke, C. and J.A. de Gouw, Atmospheric Environment, 2001. 35(34): p. 59235933. 6 .Singh, H.B., et al., Journal of Gephysical Research, 2004. 109. 7. Williams, J., et al., Geophysical Research Letters, 2004. 31(23): p. 5.
Protonated Mass
Most Probable Compound
Lifetime in marine
boundary layer (days)
Cape Grim 2007
Cape Grim
2006 [1]
Cape Grim 19881993
[2]
Southern Hemisphere
Mid Latitude
Oceanic [3] [4]
Tropical Oceanic [5][6][7]
33 Methanol 15 633 476 546 575890
42 Acetonitrile 471 32 25 20 111142
45 Acetaldehyde 0.9 53 nd 290 204
59 Acetone 66 61 118 127 450 466530
63 DMS 1.5 95 ~80 110 77 5089
69 Isoprene 0.1 21 14 40 66
81 monoterpenes ~0.1 25 nd 10
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
DMS and isoprene diurnal cycles in clean air Dec 2007
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Concen
tration DM
S (ppt)
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100
Concen
tration isop
rene (p
pt)
DMS Isoprene
Radon data courtesy of Wlodek
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
DMS diurnal cycle – past and present
From: Ayers and Gillett, Journal of Sea Research 43 (2000) 275–286
10 days in December 2007 (PTRMS)
February 1996 (GCFPD)
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Con
centratio
n DMS (ppt)
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
Halogen chemistry?
0
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0 4 8 12 16 20 24 Hour of day
Con
centratio
n DMS (ppt)
From: Galbally et al, Geophysical Research Letters, 27 (2000), 38413844
DMS Dec 2007 O 3 DecJan 19851997
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
Thank you
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
Ian Galbally
Phone: +61 3 9239 4428 Email: [email protected] Web: www.cawcr.gov.au
Thank you www.cawcr.gov.au