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 HO x /NO x cycles  Results in O 3 and CO 2 production  HCHO is a major tracer of VOC oxidation

3 HO x 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 353 nm vibronic absorption ν4ν :. 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) band λ ≈ 353 nm

10 Dissociation of HCHO * 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 :. 0 1 :. Radiative De-excitation (fluorescence): ~ 390 – 510 nm ν4ν4

12 Selectivity through Rotational Transitions Spectrum: Co et al., J. Phys. Chem. A, 109, (2005). Assignment: Emery et al., J Chem. Phys., 103, 5279 (1995) ← 4 13

13 Selectivity through Rotational Transitions Spectrum: Co et al., J. Phys. Chem. A, 109, (2005). Assignment: Emery et al., J Chem. Phys., 103, 5279 (1995). Online Offline

Narrow Bandwidth UV Pulsed Fiber Laser 14 Bandwidth: < 300 MHz Bandwidth: < 300 MHz Fast tuning range: 1.5 cm -1 Fast tuning range: 1.5 cm -1 Slow tuning range: 60 cm -1 Slow tuning range: 60 cm -1 Repetition Rate: 300 kHz Repetition Rate: 300 kHz Power: ~ 13.5 mW Power: ~ 13.5 mW Size/Weight: < 1 ft 3, < 10 lbs Size/Weight: < 1 ft 3, < 10 lbs Power consumption: < 100 W Power consumption: < 100 W Rugged and turnkey operation Rugged and turnkey operation

15 FILIF Field Instrument  Based on design using Ti:Sapphire laser *  Compact design –< 4 ft 3, ~ 250 lbs  High time resolution & low detection limit (3σ) –< 200 ppt v / 1 s –< 1 ppb v / 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 Averages 19

Conc. Differential Diurnal Averages 20  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 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

Preliminary CalNex 2010 Flux 24

25Summary  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

26Acknowledgements  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.

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28 Dispersed Emission of HCHO

29 Quantum Yield of HCHO Fluorescence  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).

30 Contemporary HCHO Techniques  Hantzsch Derivitization* –Ex situ, insufficient time resolution –LOD: 75 ppt v /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 ppt v /1 s (3σ) * Wisthaler et al. SAPHIR, Atmos. Chem. Phys., 8, 2189 (2008). † Weibring et al. Opt Exp., 15, (2007).

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