HIGH-RESOLUTION SPECTRAL FEATURES OF A SERIES OF AROMATIC-HYDROCARBONS AND BRO - POTENTIAL INTERFERENCES IN ATMOSPHERIC OH-MEASUREMENTS

Naphthalene (C10H8), several other hydrocarbons, mostly derivates naphthalene, and bromine oxide (BrO) were analyzed for narrow band (less-than-or-equal-to 0.01 nm) absorption lines in the wavelength range between 307.7 and 308.3 nm to study their potential impact on OH radical measurements by differential absorption spectroscopy. Only naphthalene showed narrow band absorption lines in this wavelength region. From nine naphthalene lines the differential absorption cross-section sigma' was determined. The strongest naphthalene line at 308.002 nm is close to the Q1(2)OH line, but about a factor of 200 weaker (sigma' = (65.2 +/- 15.3) x 10(-20) cm2/molec). The corresponding detection limit for naphthalene is about 15 ppt. We re-evaluated some spectra of our OH measurement campaign in July 1987 with respect to naphthalene and obtained an upper limit of 30 ppt for its concentration. BrO was recorded in the larger wavelength interval between 307.7 and 308.7 nm. Structured absorptions were only observed at wavelengths above 308.2 nm and no significant structures were found in the vicinity of the Q1(2) and Q1(3)OH lines.