TROPOSPHERIC DEGRADATION OF LONG-CHAIN ALDEHYDES INITIATED BY Cl ATOMS AND THEIR ATMOSPHERIC IMPLICATIONS

FABRICIO AGUIRRE; MARIANO TERUEL; MARIA BELEN BLANCO

Simposio; 26th International Symposium on Gas Kinetics and Related Phenomena; 2022

Introduction Aldehydes are ubiquitous gaseous chemical constituents in the atmosphere and are emitted by a variety of sources. They arise, for example, from incomplete fossil fuel combustion, are emitted by vegetation, are produced during biomass burning and the photochemical oxidation of most Volatile Organic Compounds (VOCs) in the atmosphere results in the formations of aldehydes to some degree.1-2Aldehydes can photolyze and/or react with typical atmospheric oxidants: OH and NO3 radicals and, in the marine boundary layer and coastal regions, react with Cl atoms.ObjectivesTo study the rate coefficients in the gas phase of the reactions of three saturated aldehydes with Cl atoms and to estimate their lifetimes in the troposphere. The compounds studied were heptanal (C7H14O), octanal (C8H16O), and nonanal (C9H18O). Materials and methodsThe experiments were carried out using a 405 L smog chamber coupled to Gas Chromatography with Flame Ionization Detection (GC-FID) to monitor the decrease in the concentration of aldehydes in relation to different reference compounds, using the relative method.ResultsThe following rate coefficients values were obtained for the reactions studied (cm3 molecule-1 s-1): k1 (Cl + CH3(CH2)5C(O)H) = (3.0 ± 0.5) × 10-10; k2 (Cl + CH3(CH2)6C(O)H) = (2.9 ± 0.5) × 10-10; k3 (Cl + CH3(CH2)7C(O)H) = (3.2 ± 0.6) × 10-10.In addition, the tropospheric lifetimes of the aldehydes were calculated according to the following equation Cl= 1/kCl [Cl]. Where [Cl]= 1×104 molecules/cm3.3Estimated atmospheric lifetimes were 93, 96, and 87 hours for heptanal, octanal, and nonanal, respectively.ConclusionsThe first kinetic study for the reactions of octanal and nonanal with Cl is presented. Aldehyde photolysis was not observed under the experimental conditions used.Tropospheric lifetimes of these aldehydes between 3 and 4 days indicate that they could be transported to other places producing local and regional impact.