Chemical kinetics and transport of tropospheric trace compounds - implications for environment and air quality

Abstract: Fourier transform infrared spectroscopy techniques were used to study the kinetics of gas-phase reactions of three lactones, γ-valerolactone (GVL), 2(5H)-furanone (2(5HF) and 3-methyl-2(5H)-furanone (3M2(5H)F) with Cl atoms, OH radicals and O3 respectively. The experiments were performed in a photochemical reactor at a total pressure of 700 Torr at room temperature (298±2 K). Both relative rate and absolute rate methods were used to determine the reaction rate constants (unit cm3molecule-1s-1) yielding kGVL+Cl = (4.56 ± 0.51)∙10-11, kGVL+OH = (2.94 ± 0.41)∙10-11, k2(5H)F+Cl = (2.94 ± 0.41)∙10-11, k2(5H)F+OH = (4.06 ± 0.073)∙10-12, k2(5H)F+O3 = (6.73 ± 0.18)∙10-20, k3M2(5H)F+Cl = (16.1 ± 1.8)∙10-11, k3M2(5H)F+OH = (12.6 ± 0.52)∙10-12 and k3M2(5H)F+O3 = (5.42 ± 1.23)∙10-19. Using atmospheric abundances of Cl, OH and O3 the lifetime of each lactone towards each of the reaction sinks was calculated. The largest sink for all three lactones is through the reaction with OH (lifetimes of tens of days). Removal by Cl atoms can become equally significant when abundant in high concentrations which could be locally important. The lifetime against removal by O3 (months-years) is relatively long on a tropospheric scale even at high concentrations. No significant reaction products were identified for experiments performed in N2. For experiments using an N2/O2 mixture the identified products are formic acid (HCOOH), formyl chloride (CHClO), maleic anhydride (C2H2(CO)2O) and phosgene (CCl2O). There are still unidentified reaction products. In addition to the kinetic studies a project was performed where a chemical transport model (GEOS-Chem) was used to study updated reaction rate constants and photolysis rate constants of bromoform (CHBr3) and bromine nitrate (BrONO2) in the troposphere. The effect on tropospheric inorganic bromine levels, and consequently ozone levels, was insignificant for bromoform and more significant for bromine nitrate.