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

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

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/m 3 or several 10 μg/m 3 of equivalent SOA mass in urban air. (Kroll et al, 2005; Liggio et al, 2005)

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)

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)

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

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 (Volkamer et al,2005)

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

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 VOCs oxidation Semivolatile products Inorganic/ organic water interaction

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

Gas-Phase Glyoxal Concentration 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

Gas-Phase Glyoxal Concentration in Mexico City 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 Model - based on Master Chemican Mechanism(MCM) Volkamer et al, 2007

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

Chamber study: Effective Henry’s law solubility coefficient(H*) is determined from measured uptake of methylglyoxal in sulfuric acid Zhao et al, 2006 where 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

Aqueous Phase Reactions of Methylglyoxal Possible aqueous reaction pathway in 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

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

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

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 Aqueous Photooxidation of Glyoxal to Form Oxalic Acid Carlton el at., 2007 GLY + UV + H2O2 --> Oxalic acid

Reference Carlton et al. (2007), Atmospheric oxalic acid and SOA production from glyoxal: Results of aqueous photooxidation experiments, Atmos. Environ., 41, 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: /2005JD Liggio, J. et al.(2005a), Reactive uptake of glyoxal by particulate matter, J. Geophys. Res., 110, D10304, doi: /2004JD SCIENCE, June , 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– 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: /2007GL Zhao et al. (2006), Heterogeneous Reactions of Methylglyoxal in Acidic Media: Implication for Secondary Organic Aerosol Formation, Environ. Sci. Technol., 40,