Abstract
Abstract. We show that methylglyoxal forms light-absorbing secondary organic material in aqueous ammonium sulfate and ammonium nitrate solutions mimicking tropospheric aerosol particles. The kinetics were characterized using UV-Vis spectrophotometry. The results suggest that the bimolecular reaction of methylglyoxal with an ammonium or hydronium ion is the rate-limiting step for the formation of light-absorbing species, with kNH4+II=5×10−6 M−1 min−1 and kH3O+II≤10−3 M−1 min−1. Evidence of aldol condensation products and oligomeric species up to 759 amu was found using chemical ionization mass spectrometry with a volatilization flow tube inlet (Aerosol-CIMS). Tentative identifications of carbon-nitrogen species and a sulfur-containing compound were also made using Aerosol-CIMS. Aqueous solutions of methylglyoxal, with and without inorganic salts, exhibit significant surface tension depression. These observations add to the growing body of evidence that dicarbonyl compounds may form secondary organic material in the aerosol aqueous phase, and that secondary organic aerosol formation via heterogeneous processes may affect seed aerosol properties.
Highlights
Laboratory and field studies suggest that carbonyl-containing volatile organic compounds, when absorbed by aqueous aerosol particles or cloud droplets, participate in aqueousphase chemistry to form low-volatility secondary organic material (SOA)
In an aqueous aerosol particle, surface-active products may partition to the gas-particle interface, lowering the surface tension and acting as a barrier to mass transport between the gas and aqueous phases
Pendant drop tensiometry measurements show that aqueous solutions of methylglyoxal exhibit surface tension depression, and the effect is enhanced when NaCl or (NH4)2SO4 is present. These observations add to the growing body of evidence that dicarbonyl compounds form secondary organic material in the aqueous phase, and that SOA formation via heterogeneous processes may affect seed aerosol properties
Summary
Laboratory and field studies suggest that carbonyl-containing volatile organic compounds, when absorbed by aqueous aerosol particles or cloud droplets, participate in aqueousphase chemistry to form low-volatility secondary organic material (SOA) (Jang et al, 2002; Kroll et al, 2005; Liggio et al, 2005; Volkamer et al, 2006, 2007, 2009; Loeffler et al, 2006; Zhao et al, 2006; Gao et al, 2006; Altieri et al, 2008; Carlton et al, 2008; Noziere et al, 2009a, b; Gal-loway et al, 2009; Shapiro et al, 2009; Fu et al, 2009; El Haddad et al, 2009; De Haan et al, 2009a). Aldehydes have been reported to undergo aldol condensation in aqueous aerosol mimics to form π-conjugated species (Noziere et al, 2007; Noziere and Esteve, 2007; Casale et al, 2007). We recently reported the formation of light-absorbing, oligomeric molecules in aqueous aerosol mimics containing glyoxal and ammonium salts (Shapiro et al, 2009). We recently reported the formation of light-absorbing, oligomeric molecules in aqueous aerosol mimics containing glyoxal and ammonium salts (Shapiro et al, 2009). De Haan et al (2009a, b) observed browning upon the reaction of glyoxal with amino acids in aerosol and cloud droplet mimics
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