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PHOTOPRODUCTION OF VOLATILE ORGANIC COMPOUNDS FROM SECONDARY ORGANIC AEROSOLS: AN UNEXPLAINED SOURCE?Kurtis Malecha
Nizkorodov Group
September 4, 2014
1
INTRODUCTION TO ATMOSPHERIC AEROSOLS
2
VOCs
O3,OH,NO
3
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
3
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