PARENT SESSION

1F - QSAR
Hall 13
8:30 AM - 12:30 PM, Tuesday, 29 April 2003
Chair: Schüürmann, G.¹, ¹
Co-chair: Verhaar, H.J.M.², Cronin, M.³, ^{2 3}

(TU13/2) Predicting abitotic transformation rates: QSARs vs. direct calculations.

Sabljic, Aleksandar¹, ¹ Institute Rudjer Boskovic, Zagreb, Croatia, Croatia

ABSTRACT- The reaction with the hydroxyl (OH) radical is the major chemical loss process for the organic compounds emitted into the troposphere. This removal process is critical for the ozone pollution in urban as well as rural areas, stratospheric ozone depletion, long range transport of chemicals, acid deposition, and global climate change. There are two general QSAR models for estimating tropospheric degradation of organic compounds, Atkinson's group contribution method (E.S.C. Kwok, R. Atkinson. Atmos. Environ. 29, 1685, 1995) and the MOOH method (A. Klamt. Chemosphere 26, 1273, 1993). An extensive evaluation has shown that Atkinson's method is far more accurate and consequently should be used as a method of choice. However, Atkinson's method should not be used to estimate tropospheric degradation of haloalkenes and haloalkanes with CX₃ (X=F, Cl, Br) groups, perhalogenated compounds and ethers (especially polyethers, cycloethers and halogenated ethers). Its application is also discouraged for chemical classes not used in its development. A viable alternative to Atkinson's and MOOH methods for estimating tropospheric degradation and tropospheric half-lifes of organic chemicals is the direct calculation of their reaction rate constants with hydroxyl radical. The dramatic developments in computing technology enabled the calculations of the energy profiles of gas-phase reactions to be performed almost routinely (S. Sekusak, K.R. Liedl, B.M. Rode, A. Sabljic, J. Phys. Chem. A 101, 4245, 1997). Recently, an affordable methodology was developed for calculating reaction rate constants at low computational cost. It is based on reliable semiempirical potential energy surfaces and the computed rate constants differ from experiment at most by a factor of 2 (S. Sekusak, A. Sabljic. J. Phys. Chem. A 105, 1968, 2001). This approach is particularly suitable for estimating tropospheric degradation of haloalkenes and haloalkanes with CX₃ (X=F, Cl, Br) groups.

Key words: reaction path, hydroxyl radical, reaction rate calculation, tropospheric degradation