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