Field Results from BEARPEX 2009 and the First Deployment of the Madison FILIF HCHO Instrument Josh...
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Transcript of Field Results from BEARPEX 2009 and the First Deployment of the Madison FILIF HCHO Instrument Josh...
Field Results from BEARPEX 2009 and the First Deployment
of the Madison FILIF HCHO Instrument
Josh DiGangi, Josh Paul, Sam Henry,
Aster Kammrath, Erin Boyle, Frank Keutsch
University of Wisconsin – Madison
06/21/10
2
Volatile Organic Compound (VOC) Oxidation
Processed via HOx/NOx
cycles
Results in O3 and CO2
production
HCHO is a major tracer of
VOC oxidation
3
HOx in Forest Canopies
Likely due to fast, in-canopy oxidation of unknown BVOCs Need a method of probing VOC oxidation in canopy…HCHO!!
Adapted from: DiCarlo et al., Science, 304, 722 (2004).
- Observed
- Modelled
HCHO Gradient & Flux Measurements
Multiple sampling heights allow measurement of vertical HCHO distribution (gradient)
4
HCHO Gradient & Flux Measurements
Multiple sampling heights allow measurement of vertical HCHO distribution (gradient)
Colocation of an inlet with a sonic anemometer allows calculation of mass transport (flux)
5
Eddy
HCHO Gradient & Flux Measurements
Multiple sampling heights allow measurement of vertical HCHO distribution (gradient)
Colocation of an inlet with a sonic anemometer allows calculation of mass transport (flux)
Combined, measurements provide insight into VOC oxidation above & inside canopy
6
Eddy
HCHO Gradient & Flux Measurements
Instrumental challenges– Field capable– High selectivity– High sensitivity– Fast time resolution (10 Hz)
No reported technique can meet all of these requirements
7
Eddy
8
LIF of HCHO
21
~
AA
11
~
A
353 nm vibronic
absorption
ν4
0
1
2
3
:
.
0
1
:
.
9
Absorption Spectrum of HCHO
Spectrum: J.D. Rogers, J. Phys. Chem., 94, 4011 (1990).
Assignment: Clouthier & Ramsay, Ann. Rev. Phys. Chem, 34, 31 (1983).
20
041
0 band
λ ≈ 353 nm
10
Dissociation of HCHO
1.0
0.8
0.6
0.4
0.2
0.0
Quantu
m Y
ield
360350340330320310300
Wavelength (nm)
(H + HCO)(H
2 + CO)
Total
* Data for plot from Finlayson-Pitts & Pitts, Chemistry of the Upper and Lower Atmosphere, Academic Press (2000).
† Möhlmann, G.R. App. Spectr. 39, 98 (1985).
No strong electronic absorption features at λ > 353 nm
~27% dissociation expected at 353 nm
11
LIF of HCHO
21
~
AA
11
~
A0
1
2
3
:
.
0
1
:
.
Radiative
De-excitation
(fluorescence):
~ 390 – 510 nm
ν4
12Selectivity throughRotational Transitions
Spectrum: Co et al., J. Phys. Chem. A, 109, 10675 (2005).
Assignment: Emery et al., J Chem. Phys., 103, 5279 (1995).
404 ← 413
13Selectivity throughRotational Transitions
Spectrum: Co et al., J. Phys. Chem. A, 109, 10675 (2005).
Assignment: Emery et al., J Chem. Phys., 103, 5279 (1995).
Online
Offline
Narrow Bandwidth UV Pulsed Fiber Laser14
• Bandwidth: < 300 MHz
• Fast tuning range: 1.5 cm-1
• Slow tuning range: 60 cm-1
• Repetition Rate: 300 kHz
• Power: ~ 13.5 mW
• Size/Weight: < 1 ft3
, < 10 lbs
• Power consumption: < 100 W
• Rugged and turnkey operation
15
FILIF Field Instrument
Based on design using Ti:Sapphire laser *
Compact design– < 4 ft3, ~ 250 lbs
High time resolution & low detection limit (3σ)– < 200 pptv / 1 s– < 1 ppbv / 0.1 s
* Hottle et al., Environ. Sci. & Tech., 43, 790 (2009).
BEARPEX 2009
Well-established meteorological pattern
> 10 research groups
16
Wind blows uphill
during day
Wind blows
downhill at night
BEARPEX 2009
Well-established meteorological pattern
> 10 research groups
17
Wind blows uphill
during day
Wind blows
downhill at night
17.8 m
8.7 m
3.3 m
2.4 m
Warm/Cold Diurnal Averages
8.7 m inlet
3.3 m inlet
17.8 m inlet
2.4 m inlet
warm
cold
18
* Isoprene + MBO and temperature measurements courtesy of the Goldstein group (UC-Berkeley)
Conc. Differential Diurnal Averages19
Conc. Differential Diurnal Averages20
Shows an inverted profile during daytime hours
Suggests in canopy production of HCHO
More HCHO in canopy during
day
21
HCHO Eddy Flux Measurements
Laser tunes from on to off peak in ≤ 10 ms
Slow/fast duality suggests improvements may make faster
Can measure @ 10 Hz with 90% duty cycle
Combined with high sensitivity should be capable of HCHO flux measurements
HCHO Eddy Flux Measurements HCHO Flux
measurements performed for ~10 days
22
HCHO Eddy Flux Measurements HCHO Flux
measurements performed for ~10 days
Covariance calculations result in no significant flux
Measurements believe to have failed due to incorrect air sampling
Will repeat measurements during BEACHON-ROCS: August 2010
23
Preliminary CalNex 2010 Flux24
25
Summary Successful first deployment of Madison FILIF
Instrument
Observed nighttime deposition of HCHO and daytime in-canopy HCHO production
New class of laser offers new opportunities in applied molecular spectroscopy
Interest in instrument reproduction by:– NASA (has already begun)– Max Planck Institute– University of Leeds
26
Acknowledgements
Keutsch Group NSF NASA Sierra Pacific Industries UW-Madison Chemistry NovaWave Technologies University of California System BEARPEX 2009 Science Team Blodgett Forest Research Station Wisconsin Alumni Research Fund The Camille & Henry Dreyfus Foundation, Inc.
27
28
Dispersed Emission of HCHODispersed Fluorescence of HCHO
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
350 400 450 500 550 600
Wavelength(nm)
Inte
nsi
ty (
A.U
.)
29Quantum Yield of HCHO Fluorescence
Mqdf
ff Pkkk
kΦ
*15f s102k
**16d s102.53k
Probability of a stimulated HCHO molecule to fluoresce
@ 100 torr, ≈ 4.5%
* Yeung & Moore. J. Chem. Phys. 58, 3988 (1973).
** Moortgat & Warneck. J. Chem. Phys. 70, 3639 (1979).
**114q sTorr101.7k
30
Contemporary HCHO Techniques
Hantzsch Derivitization*– Ex situ, insufficient time resolution– LOD: 75 pptv/min (3σ)
Proton Transfer Reaction – Mass Spectrometry (PTR-MS)*– Insufficient selectivity, bulky instrument– LOD: 300 pptv/2 s (3σ)
Tunable Diode Laser Absorption Spectroscopy (TDLAS)†
– Slow sampling, cannot measure fluxes– LOD: 180 pptv/1 s (3σ)
* Wisthaler et al. SAPHIR, Atmos. Chem. Phys., 8, 2189 (2008).† Weibring et al. Opt Exp., 15, 13476 (2007).
31