B Acyclic Organic Acids

5-500 Torr). A least-squares fit of all the data to the Arrhenius expression yields k = 3.66 X 10 exp (50/r) cm molecule s . Alternatively, an unweighted average of the data leads to a temperature-independent value of k = 4.4 X 10 cm molecule s (298 45 K). Excluding the Zetzsch and Stuhl (1982) data from the fits leads to differences of 5% in the retrieved rate coefficients. This recommendation is very similar to those made by the JPL (Sander et al., 2006) and lUPAC (Atkinson et al., 2006) evaluation panels, = 4.0x 10 cm molecule s andA = 4.5x 10 cm molecule respectively, independent of temperature. Uncertainties in the data are estimated at 20% over the temperature range that has been studied. No data are available below 298 K, i.e., under conditions relevant for the free troposphere the JPL panel (Sander et al., 2006) recommends uncertainties of 30% near 250 K and 40% near 200 K. 

Kinetic data for the reaction of OH with DCOOH (Wine et al., 1985 Singleton et al., 1988) and for the reaction of OD with HCOOD and DCOOD (Singleton et al., 1988) have also been reported see table Vl-B-2 and figure VI-B-1. Values for 

The two studies of the Cl-formic acid reaction (Wallington et al., 1990a Li et al., 2000a), both conducted at ambient temperature, are in excellent agreement see table VI-B-3. An average of the two determinations yields a value of A = 1.9 x 10 cm molecule s , with an estimated uncertainty of 15%. Tyndall et al. (1991b) provide evidence that reaction occurs via abstraction at the formyl (C—H) site, rather than at the acidic (O—H) site, in contrast to the OH-formic acid reaction. 

VI-B-1.3. Summary of the Mechanism and End Products of Formic Acid Oxidation, and Summary of Its Atmospheric Fate 

The only significant gas-phase loss process for formic acid in the troposphere will be via reaction with OH. Even so, the lifetime of formic acid against OH loss is quite long, about 1 month for an assumed global [OH] of 10 molecule cm .  

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