PHOTOPRODUCTION OF VOLATILE ORGANIC COMPOUNDS FROM SECONDARY ORGANIC AEROSOLS: AN UNEXPLAINED SOURCE?Kurtis Malecha

Nizkorodov Group

September 4, 2014

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INTRODUCTION TO ATMOSPHERIC AEROSOLS

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VOCs

O3,OH,NO

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Seed

ParticleSOA

POA

VOCs = Volatile Organic Compounds

SOA = Secondary Organic Aerosol

POA = Primary Organic Aerosol

SOA(Condensed

Phase)hν

VOCs

• Historical Assumption: formation and ageing of SOA exclusively in gas-phase2

• Emerging results: condensed-phase SOA photochemistry is important!3

• VOC Production – e.g., Formic Acid

2. Hallquist, M. et al. ACP, (2009).3. Nguyen, T. et al. ACP, (2014).

1. IPCC, 2007

FORMIC ACID

• Formic Acid present in atmosphere

• Global Production – up to 120 Teragrams Carbon/year4

• ~27 Tg C/year is from oxidation of Organic Aerosols4

• Contributes to acid rain in remote environments5

• Variety of sources exist:6

• Direct: Anthropogenic and Biogenic

• Exhaust, Vegetation, Forests, Biomass Combustion

• Indirect: Photooxidation of monoterpenes, Ozonolysis of alkenes

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4. Stavrakou, T et al. Nature geoscience (2012).

5. Chameides, W. & Davis, D.  Nature (1983).

6. Finlayson-Pitts, B., Pitts, J. Chemistry of the Upper and Lower Atmosphere (2000).

GOALS AND MOTIVATIONS• Climate models underpredict

HCOOH by up to 90 Tg C/year6

• Nature, 2012 – lack of laboratory experiments for formic acid production using monoterpenes and isoprene

• Large unidentified secondary biogenic source?

• Goal: test production rate of VOCs from condensed-phase SOA photolysis

• Initially: use Cavity Ring Down Spectroscopy (CRDS) for detection 4

CAVITY RING DOWN SPECTROSCOPY

( ) exp 1

( ) exp 1

o

o

tcI t I R L

L

t LI t I

c R L

= cavity ring down time with analyte; 0 = empty cavity ring down timec = speed of light = absorption coefficientR = mirror reflectivity; L = cavity length 5

0

1 1 1

c

0

Image adapted from: Wojtas, J. et al. Sensors (2013).

Equations adapted from: Berden, G. Cavity Ring Down Spectroscopy (2009).

METHODS USED

1. Nd:YAG pulsed laser

2. Optical Parametric Oscillator/Optical Parametric Amplifier (OPO/OPA) – IR Beam

3. Cavity with highly-reflective mirrors (>99.95%)

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1

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SPECIFIC SUMMER GOALS

• “Rebirth” the laser and associated components of the CRDS

• Fix the laser

• Begin scans of known compounds

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MY INITIAL SUMMER WORK

• Computer controlling CRDS instrument was nonfunctional• Extracted data and programs• Replaced computer and reloaded everything

• Optics in OPO were misaligned• Aligned them

• Mirror mount adjustments were not reproducible• Ordered new mounts

Research with lasers is slow-going initially with a steep learning curve.

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EXPERIMENTAL SETUP

9Image credit: Sergey Nizkorodov

BACK TO THE LASER…

• Laser was not seeding properly

• Consequence – unable to resolve ro-vibrational lines of CO

• Aligned seeder spatially• Better scan, but

Signal:Noise is poor

Aligning a seeder beam takes awhile.

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ABSORBANCE OF CO

The mirrors are not as good as they used to be.

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SUMMARY AND ACKNOWLEDGEMENTS

• Condensed-phase SOA photolysis for production of Formic Acid?

• Using CRDS for monitoring

• This summer:• Fixed Laser• Replaced Computer• Began scans of molecules

• Future: • Obtain new mirrors• Perform scans of Methane• Begin making SOA for photolysis

Thanks to:

• Nizkorodov Group

• Funding: NSF AGS-1227579, Photochemistry in Organic Aerosols 12