Kurtis Malecha Nizkorodov Group September 4, 2014

1. Photoproduction of Volatile Organic Compounds from Secondary Organic Aerosols: an Unexplained Source? Kurtis Malecha Nizkorodov Group September 4, 2014

2. Introduction to Atmospheric Aerosols VOCs SOA (Condensed Phase) SOA • 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 • Hallquist, M. et al.ACP, (2009). • Nguyen, T. et al.ACP, (2014). Seed Particle hν VOCs = Volatile Organic Compounds SOA = Secondary Organic Aerosol POA = Primary Organic Aerosol POA VOCs O3,OH,NO3 • IPCC, 2007

3. 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 • Stavrakou, T et al.Nature geoscience(2012). • Chameides, W. & Davis, D.  Nature(1983). • Finlayson-Pitts, B., Pitts, J. Chemistry of the Upper and Lower Atmosphere (2000).

4. 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

5. Cavity Ring Down Spectroscopy 0  = cavity ring down time with analyte; 0 = empty cavity ring down time c = speed of light  = absorption coefficient R = mirror reflectivity; L = cavity length • Image adapted from: Wojtas, J. et al. Sensors (2013). • Equations adapted from: Berden, G. Cavity Ring Down Spectroscopy (2009).

6. Methods Used • Nd:YAG pulsed laser • Optical Parametric Oscillator/Optical Parametric Amplifier (OPO/OPA) – IR Beam • Cavity with highly-reflective mirrors (>99.95%) 1 3 2

7. Specific Summer Goals • “Rebirth” the laser and associated components of the CRDS • Fix the laser • Begin scans of known compounds

8. 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.

9. Experimental Setup • Image credit: Sergey Nizkorodov

10. 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.

11. Absorbance of CO The mirrors are not as good as they used to be.

12. 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