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

Glyoxal and Methylglyoxal; Glyoxal and Methylglyoxal; Chemistry and Their Effects Chemistry and Their Effects

on Secondary Organic on Secondary Organic AerosolAerosol

Dasa Gu

Sungyeon Choi

Glyoxal and MethylglyoxalGlyoxal and Methylglyoxal• Glyoxal

• Simplest alpha dicarbonyl organic compounds• Average life-time: ~1.3 hrs

• Methylglyoxal

MotivationMotivation• 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)

Sources of GlyoxalSources 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 GlyoxalSinks 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)Monitoring (1)

Chemical Derivatization• DNPH(2,4-dinitrophenylhydrazine) – HPLC

(Munger et al,1995; Lee et al,1998)

• PFPH – GCMS

F F

NHNH2

FF

F + O C

F F

NH

FF

F

R2

R1

+ H2O

PFPH aldehyde orketone

hydrazone

F F

NH

FF

F NH Ck1

k-1

R1

OH

R2k2(s) (g) (s)

(s)N C

F F

NH

FF

F

N C

R1

R2

R1

R2

(s)

(Ho et al, 2002)

Monitoring (2)Monitoring (2)DOAS (Differential Optical Absorption Spectroscopy)

CHO-CHO hour-by-hour: CHO-CHO hour-by-hour: peaks peaks between 1030h and 1300hbetween 1030h and 1300h

CHO-CHOCHO-CHO, , HCHOHCHO diurnal variation; diurnal variation;CHOCHO/NO2 (%)CHOCHO/NO2 (%) ratioratio

(Volkamer Volkamer et al,2005et al,2005)

Monitoring (3)Monitoring (3)

Satellites• SCIMACHY

• OMI

(Kurosu et al, AGU 2006Kurosu et al, AGU 2006)

Glyoxal and Secondary Glyoxal and Secondary Organic AerosolOrganic 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

VOCsoxidation

Semivolatile products

Inorganic/organic waterinteraction

Glyoxal and SOA formationGlyoxal 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 GlyoxalGas-Phase GlyoxalConcentration in Mexico CityConcentration 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 Gas-Phase Glyoxal Concentration in Mexico CityConcentration 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 Gas-Phase Glyoxal Concentration in Mexico CityConcentration 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

(t)4kw

V

A

1/a bt1/ 2

bw

4H*RT(Dl / )1/ 2where

Uptake of Methylglyoxal on Uptake of Methylglyoxal on Acidic MediaAcidic Media

Uptake of Methylglyoxal on Uptake of Methylglyoxal on Acidic MediaAcidic 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 Aqueous Phase Reactions of MethylglyoxalMethylglyoxal

• 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 Aqueous Phase Reactions of MethylglyoxalMethylglyoxal

(Continued Mechanism)

Zhao et al, 2006

Aqueous Photooxidation of Aqueous Photooxidation of Glyoxal to Form Oxalic AcidGlyoxal 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 Aqueous Photooxidation of Glyoxal to Form Oxalic AcidGlyoxal to Form Oxalic Acid

Carlton el at., 2007

GLY + UV + H2O2 --> Oxalic acid

ReferenceReference• 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