1 / 12

Kurtis Malecha Nizkorodov Group September 4, 2014

Photoproduction of Volatile Organic Compounds from Secondary Organic Aerosols: an Unexplained Source?. Kurtis Malecha Nizkorodov Group September 4, 2014. Introduction to Atmospheric Aerosols. VOCs. SOA (Condensed Phase). SOA.

becca
Télécharger la présentation

Kurtis Malecha Nizkorodov Group September 4, 2014

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

More Related