Environ. Sci. Technol. 1988, 22, 1284-1289
Kinetics of the Formation of Hydroxyacetaldehyde-Sulfur( I V ) Adducts at Low pH Terese M. Olson, Lori A. Torry, and Michael R. Hoffmann"
Environmental Engineering Science, W. M. Keck l,aboratories, California Institute of Technology, Pasadena, California 9 1125 ~~
The kinetics of the addition of hydroxyacetaldehyde and S(1V) was studied spectrophotometrically over the pH range of 0.7-3.3. Formation rates of the adduct 1,2-dihydroxy-l-ethanesulfonate(DHES) were consistent with the followine:three-term rate exmession: drDHESl ldt = (ko(H+lal/Kao + klal + kzaz)~CzH302lt[S(IV)1,where [CZH302]t = [CH,(OH)CHO] + [CH,(OH)CH(OH),], [S(IV)] = [HzO.S02] + [HSOB-] + [S03'-], al = [HSO3-]/ [S(IV)], and a2 = [S032-]/[S(IV)], and Kao is the acid dissociation constant for CH2(0H)C+HOH. The rate constant lzo corresponds to a proton-catalyzed pathway in which bisulfite reacts with the carbocation CH2(0H)C+HOH. A value for the constant ko/Kaowas determined as 5.4 (f2.0) M-, s-l (25 "C, p = 0.2 M). The intrinsic constants kl and k, are the respective rate constants for the reactions of HS0,- and SO3,- with unhydrated hydroxyacetaldehyde, where it was determined that k, = 1.74 (f0.16) M-l s-l and kz = 5.02 (f0.12) X lo4 M-l s-l. Because of the high intrinsic solubility of CH,(OH)CHO, calculated DHES formation rates in fogwater and cloudwater are faster than the addition rate of formaldehyde and S(1V). DHES is shown to satisfy the criteria of a significant S(1V) reservoir in atmospheric droplets.
for the hydroxyacetaldehyde-bisulfite adduct (1,2-dihydroxy-l-ethanesulfonate,hereafter referred to as DHES) as K1= [CH,(OH)CH(OH)SO3-]/[CH,(OH)CHO] [HSO,] = 2.0 X lo6 M-l. Since hydroxyacetaldehyde is approximately 90% hydrated in solution (13),the apparent adduct stability constant Kl,app = [CH,(OH)CH(OH)SO,-]/ ([CH,(OH)CHO] + [CH,(OH)CH(OH),])[HSO
