PAM Time Constants

gas-phase OH oxidation lifetime (t_OH)

t_OH = 1/(k_OH_g*[OH]) = 1/(k_OH_g*OH_exposure*1/t_res)

• • t_res = average residence time (sec)

    • PAM volume = 13.3 L

    • flow rate (user-defined)

  • k_OH = OH rate constant (cm3/molec/s)

    • NIST chemical kinetics database: http://kinetics.nist.gov/kinetics/index.jsp

Example #1 ("low OH"): k_OH_g = 2e-11 cm3/molec/s, OH_exposure = 1e11 molec/cm3*s, t_res = 100 s: t_OH = 50 s

Example #2 ("high OH"): k_OH_g = 2e-11 cm3/molec/s, OH_exposure = 1e12 molec/cm3*s, t_res = 100 s: t_OH = 5 s

Table 1. k_OH for select compounds.

condensed-phase OH oxidation lifetime (t_OH)

t_OH = 1/(k_OH_p*[OH]) = 1/(k_OH_p*OH_exposure*1/t_res)

• • t_res = average residence time (sec)

  • k_OH_p = effective OH rate constant (cm3/molec/s)

Example #1 ("low OH"): k_OH_p = 2e-12 cm3/molec/s, OH_exposure = 1e11 molec/cm3*s, t_res = 100 s: t_OH = 500 s

Example #2 ("high OH"): k_OH_p = 2e-12 cm3/molec/s, OH_exposure = 1e12 molec/cm3*s, t_res = 100 s: t_OH = 50 s

UV photolysis lifetime (t_photol)

t_photol = 1/(sigma*UV_flux)

• • UV_flux = photon flux in PAM

    • 2e13 photons/cm2/s (max) at 185 nm

    • 2e15 photons/cm2/s (max) at 254 nm

  • sigma = absorption cross section (cm2)

    • Select absorption cross sections:

Example #1 ("low OH"): sigma = 1E-17 cm2, UV_flux_254 = 5.5e13 photons/cm2/s (lamps at 30V): t_OH = 1830 s

Example #2 ("high OH"): sigma = 1E-17 cm2, UV_flux_254 = 2e15 photons/cm2/s (lamps at 110V: t_OH = 50 s

Table 2. UV absorption cross sections for select compounds.