Experimental Studies of the Heterogeneous Kinetics of OH Radicals with terbuthylazine, Adsorbed on Self- Synthesized SiO2 Particles, in a Temperature Controlled Aerosol Smog Chamber

Atmospheric lifetimes of pesticides are limited by reactions with OH, which have been studied for a long time. Most studies were focused on the gas phase and only very few experiments on semivolatile pesticides investigated their OH reactions with aerosol-borne compounds. In this work, the reaction of gas-phase OH radicals with aerosol-borne terbuthylazine (TBA) has been investigated in the low temperature aerosol simulation chamber (LOTASC) at three temperatures. Self-synthesized, monodisperse SiO2 particles (diameter around 160 nm) were used as carrier particles in order to avoid any influence of agglomeration. The experimental results of second order rate constants showed a lower value than previous work on Aerosil 200 particles (Palm et al., 1997). However, results from this work correspond to the Langmuir-Hinshelwood mechanism, revealing the process of a reversible adsorption of OH on particle surfaces before chemical reaction. This is the first time to apply the Langmuir-Hinshelwood mechanism on the heterogeneous reaction of gas-phase OH radicals with aerosol-borne compounds. In this work, the Langmuir-Hinshelwood expression kIobs=(8.6±1.2)×10-12COH/ (1+(9.4±1.6)×10-8COH) was obtained at 25 °C, where the limiting slope for COH=>0 according to an Eley-Rideal mechanism leads to k(OH)Eley-Rideal = (8.6±1.2) ×10-12 cm3 s-1 (which is similar to the current views of structure/reactivity relations for gas-phase reactions). Chamber experiments were also performed at 6.5 °C and -10 °C. The experimental Langmuir-Hinshelwood expressions are kIobs=(8.5±1.6)×10-12 COH /(1+(1.07±0.24)×10-7 COH) and kIobs=(6.08±0.97)×10-12 COH / (1+(1.40±0.26)×10-7 COH), respectively. Based on the kinetic parameters, the atmospheric half-lives at different temperatures have been calculated. The results show that at 25°C and 6.5°C, the half-life of terbuthylazine is less than 2 days on plain mineral dust.

Level thesis:degree_level

thesis.doctoral

Grantor dc:publisher

Universität Bayreuth

Year

2013

Author dc:creator

• Han, Lei

Contributors dc:contributor

• Zetzsch, Cornelius

Repository record source_url

https://epub.uni-bayreuth.de/id/eprint/1675/

OAI identifier oai:identifier

oai:epub.uni-bayreuth.de:1675