Glyoxal and Methylglyoxal; Chemistry and Their Effects on Secondary Organic Aerosol

1. Glyoxal and Methylglyoxal; Chemistry and Their Effects on Secondary Organic Aerosol Dasa Gu Sungyeon Choi

2. Glyoxal and Methylglyoxal • Glyoxal • Simplest alpha dicarbonyl organic compounds • Average life-time: ~1.3 hrs • Methylglyoxal

3. Motivation • Glyoxal can be an indicator for fast VOC chemistry in urban air, since it’s mainly formed from the oxidation of numerous VOCs and minor tailpipe emissions. (SCIENCE, 2005) • Glyoxal uptake accounts either forseveral 10 μg/m3 or several 10 μg/m3 of equivalent SOA mass in urban air. (Kroll et al, 2005; Liggio et al, 2005)

4. Sources of Glyoxal • Glyoxal is identified as a major primary product from the BTX-OH reaction. • Alkenes and acetylene are also precursors of glyoxal. (Volkamer et al, 2001)

5. Sinks of Glyoxal • Rapid photolysis and OH-reactions are main loss processes. (Wittrock et al, 2006) • Dry deposition and dilution in a rising planetary boundary layer are used in some models. (Volkamer et al, 2007) • Formation into Secondary Organic Aerosols is widely concerned. (Kroll et all, 2005; Liggio et al, 2005)

6. Monitoring (1) Chemical Derivatization • DNPH(2,4-dinitrophenylhydrazine) – HPLC (Munger et al,1995; Lee et al,1998) • PFPH – GCMS (Ho et al, 2002)

7. Monitoring (2) DOAS(Differential Optical Absorption Spectroscopy) CHO-CHO hour-by-hour: peaks between 1030h and 1300h CHO-CHO, HCHO diurnal variation; CHOCHO/NO2 (%)ratio (Volkamer et al,2005)

8. Monitoring (3) Satellites • SCIMACHY • OMI (Kurosu et al, AGU 2006)

9. Glyoxal and Secondary Organic Aerosol • Oxidation products from VOCs contribute to SOA formation • Growing evidence for glyoxal uptake to particles and cloud droplets despite its high volatility • Chemical reactions lead to formation of low-volatility products like oxalic acid Inorganic/ organic water Semivolatile products VOCs oxidation interaction

10. Glyoxal and SOA formation • Aerosol growth vs. glyoxal concentration is plotted • Highly dependent to RH value(water content in inorganic seed) • Dry seed, no growth Seinfeld, 2005, ASP Science Team Meeting

11. Gas-Phase GlyoxalConcentration in Mexico City • High-time resolution glyoxal measurement by long-path Differential Optical Absorption Spectroscopy were conducted as part of the Mexico City Metropolitan Area Field Campaign • Direct measurements of gas-phase glyoxal in Mexico City are compared to model prediction Volkamer et al, 2007

12. Gas-Phase Glyoxal Concentration in Mexico City Model - based on Master Chemican Mechanism(MCM) • Production • From oxidation of 26 VOCs listed • Including second and higher generation oxidation products • Loss • Photolysis • Reaction with OH-radicals • Dry deposition • Dilution in a rising planetary layer Volkamer et al, 2007

13. Gas-Phase Glyoxal Concentration in Mexico City • Observed glyoxal levels are significantly below those predicted • The difference is resolved by parameterization either of • Irreversible uptake to aerosol surface area • Reversible partitioning to aerosol liquid water • Reversible partitioning to oxygenated organic aerosol • A combination of above Volkamer et al, 2007

14. Uptake of Methylglyoxal on Acidic Media • Chamber study: Effective Henry’s law solubility coefficient(H*) is determined from measured uptake of methylglyoxal in sulfuric acid where Zhao et al, 2006

15. Uptake of Methylglyoxal on Acidic Media • Henry’s law solubility coefficient depends on acidity and temperature • H* increases at lower acidity & lower temperature • Implies that aqueous reaction in hydrate form is dominant Zhao et al, 2006

16. Aqueous Phase Reactions of Methylglyoxal • Possible aqueous reaction pathwayin acidic condition is provided • Hydration reaction and formation of various oligomers are shown • 2 and 3 are major forms in pure water solution, consisting of 56-62% and 38-44% respectively Zhao et al, 2006

17. Aqueous Phase Reactions of Methylglyoxal (Continued Mechanism) Zhao et al, 2006

18. Aqueous Photooxidation of Glyoxal to Form Oxalic Acid • Current aqueous-phase model assumes glyoxal is oxidized to glyoxylic acid and subsequently to oxalic acid (b) • Carlton et al. suggested more complex pathway (a), (c) Carlton el at., 2007

19. Aqueous Photooxidation of Glyoxal to Form Oxalic Acid • Aqueous-phase photooxidation of glyoxal is conducted at pH 4-5 • Oxalic acid formed from photooxidation of glyoxal • Involves rapid formation of formic acid followed by large multifunctional compounds • Glyoxalic acid is below the detection limit GLY + UV + H2O2 --> Oxalic acid Carlton el at., 2007

20. Reference • Carlton et al. (2007), Atmospheric oxalic acid and SOA production from glyoxal: Results of aqueous photooxidation experiments, Atmos. Environ., 41, 7500-7602 • Kroll, J. H. et al. (2005), Chamber studies of secondary organic aerosol growth by reactive uptake of simple carbonyl compounds, J. Geophys. Res., 110, D23207, doi: 10.1029/2005JD006004. • Liggio, J. et al.(2005a), Reactive uptake of glyoxal by particulate matter, J. Geophys. Res., 110, D10304, doi:10.1029/2004JD005113. • SCIENCE, June 3 2005, VOL 308, 1379 • Volkamer, R., et al. (2001), Primary and secondary glyoxal formation from aromatics: Experimental evidence for the bicycloalkyl-radical pathway from benzene, toluene, and p-xylene, J. Phys. Chem. A, 105, 7865– 7874. • Volkamer et al. (2007), A missing sink for gas-phase glyoxal in Mexico City: Formation of secondary organic aerosol, Geophys. Res. Lett., 45, L19807, doi:10.1029/2007GL030752 • Zhao et al. (2006), Heterogeneous Reactions of Methylglyoxal in Acidic Media: Implication for Secondary Organic Aerosol Formation, Environ. Sci. Technol., 40, 7682-7687