Atmospheric photochemistry of alkyl nitrates

Abstract

Photoabsorption spectra of gaseous ethyl nitrate, n-propyl nitrate, 2-propyl nitrate, n-butyl nitrate and 3-methyl-1-butyl nitrate were quantitatively measured in the laboratory at room temperature for λ >185 nm. The spectra are continuous and exhibit low- and high-intensity absorption bands. The maximum for the high-intensity band occurs at 188 ± 2 nm. Atmospheric photodissociation rate coefficients for alkyl nitrates were estimated in the range 0 – 50 km and were found to have a strong dependence on altitude. Photodissociation lifetimes were on the order of days and hours for the proposphere and stratosphere respectively. Compared with reaction with OH, photodissociation is the dominant removal process for alkyl nitrates throughout the atmosphere.