Heterogeneous chemistry of trichloroacetyl chloride in the atmosphere

Abstract

The heterogeneous chemistry of trichloroacetyl chloride was studied using two different techniques allowing direct measurements of the uptake rate by water droplets and of the homogeneous aqueous phase hydrolysis rate. The first technique used was the droplet train technique for the study of the gas/liquid interaction which yielded uptake coefficients lower than 10−3 and estimates of the Henry's law constant H of 2 M atm−1 and of the hydrolysis rate constant kh of 500 s−1 for pH < 3.5. The second technique used was a stopped‐flow method for the homogeneous aqueous phase study. The results led to a hydrolysis rate constant of 150 s−1 in pure water for pH between 4.8 and 5.8 and strongly catalyzed by hydrogen and hydroxide ions. The results show that trichloroacetyl chloride can react readily with water leading to short residence time in the atmosphere.

Heterogeneous Atmospheric Chemistry of Alternative Halocarbon Oxidation Intermediates

“…These C0 2 0 results all agree reasonably well with the ARI/BC result and disagree strongly with the very high k hyd value measured by Ugi and Beck for this compound (10). This is significant because Mirabel and co-workers use the high k nyd values measured by Ugi and Beck for various halocarbonyls to lend credence to the similarly high values they obtain for Hk nyd 1/2 (and k hyd ) for CC1 2 0, CF 3 C(0)F, CF 3 C(0)C1 and CC1 3 C(0)C1 (3,4), as well as their high k hyd values obtained for CCl 3 C(0)Cl in stopped flow bulk measurements (3). These latter stopped flow measurements, which used mixed solvents, are also suspect because they indicate a strong acid catalyzed enhancement of the CC1 3 C(0)C1 hydrolysis rate, an effect we are unable to reproduce in our bubble column apparatus.…”

“…Also shown in Table II are the results, in the form of upper limits, from our previous, less sensitive droplet train uptake experiment (6). Table II also presents results for four of the target carbonyl compounds derived from droplet train uptake experiments performed by Mirabel and coworkers (3,4) as well as other measurements of H and k hyd available in the literature. Uptake parameter estimates prepared by Wine and Chameides (8) are also included.…”

“…Additional literature values of k hyd and H for CC1 2 0 (which has not yet been studied by the Mirabel group) are also listea (9)(10)(11)(12). The uptake parameters derived from the experimental results of Mirabel and coworkers (3,4) are significanUy larger than those deduced from the Aerodyne Research/ Boston College data (6,7). The degree of disagreement is illustrated in Figure 1, where actual bubble column uptake data (7) for CFaC(0)F and CC1 3 C(0)C1 are plotted along with the analytical fits to obtain Hk h y d !…”

“…* values of 3.8 and 6.9, respectively. Also plotted are analyses of how the nubble column data would have looked if the Hk hy(^/ 2 values of 37 and 45 measured by Mirabel and co-workers (3,4) were correct. (Note that reference 4 also quotes an Hk nyd 1/2 value of 60 obtained by an alternative analysis for CF 3 C(0)F; but we have chosen to compare with the lower, more conservative value derived from separate H and k hyd values quoted in the text.)…”

“…Mirabel and co-workers have recently developed a version of the droplet train method which measure the build-up of trace gases or their reaction products in the liquid phase by trapping and pooling the exposed droplets. This method extends the sensitivity of the droplet train technique to somewhat smaller values of y meas allowing them to use this method to measure uptake parameters for several of the compounds of interest to this study (3,4). Measurements of y meas as a function of contact time and other experimental parameters can be analyzed to yield a variety of fundamental physical and chemical parameters controlling uptake, including mass accommodation coefficients, Henry's law constants, reaction rate constants and liquid phase diffusion coefficients, depending on the actual parameter or parameters which control uptake for a given trace gas/liquid surface combination.…”