Relating carbon monoxide photoproduction to dissolved organic matter functionality.
Aqueous solutions of humic substances (HSs) and pure monomeric aromatics were irradiated to investigate the chemical controls upon carbon monoxide (CO) photoproduction from dissolved organic matter (DOM). HSs were isolated from lakes, rivers, marsh, and ocean. Inclusion of humic, fulvic, hydrophobic organic, and hydrophilic organic acid fractions from these environments provided samples diverse in source and isolation protocol. In spite of these major differences, HS absorption coefficients (a) and photoreactivities (a bleaching and CO production) were strongly dependent upon HS aromaticity (r2 > 0.90; n = 11), implying aromatic moieties are the principal chromophores and photoreactants within HSs, and by extension, DOM. Carbonyl carbon and CO photoproduction were not correlated, implying that carbonyl moieties are not quantitatively important in CO photoproduction. CO photoproduction efficiency of aqueous solutions of monomeric aromatic compounds that are common constituents of organic matter varied with the nature of ring substituents. Specifically, electron donating groups increased, while electron withdrawing groups decreased CO photoproductivity, supporting our conclusion that carbonyl substituents are not quantitatively important in CO photoproduction. Significantly, aromatic CO photoproduction efficiency spanned 3 orders of magnitude, indicating that variations in the CO apparent quantum yields of natural DOM may be related to variations in aromatic DOM substituent group chemistry.
Stubbins
Aron
A
Department of Chemistry and Biochemistry, Old Dominion University, Norfolk, Virginia 23529, USA. aron.stubbins@gmail.com
Hubbard
Vesper
V
Uher
Guenther
G
Law
Cliff S
CS
Upstill-Goddard
Robert C
RC
Aiken
George R
GR
Mopper
Kenneth
K
D002244:Carbon / Q000737:chemistry; D002248:Carbon Monoxide / Q000032:analysis / Q000737:chemistry*; D002625:Chemistry, Organic / Q000379:methods; D004583:Electrons; D004784:Environmental Monitoring / Q000379:methods; D006812:Humic Substances; D007659:Ketones / Q000737:chemistry; D008027:Light; D008956:Models, Chemical; D009930:Organic Chemicals / Q000737:chemistry; D010777:Photochemistry / Q000379:methods; D011789:Quantum Theory; D014466:Ultraviolet Rays; D014867:Water / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000737:chemistry
D006812:Humic Substances; D007659:Ketones; D009930:Organic Chemicals; D014874:Water Pollutants, Chemical; D014867:Water; D002244:Carbon; D002248:Carbon Monoxide