Laser-induced phosphorescence for the in situ detection of glyoxal at part per trillion mixing ratios.

Glyoxal is a molecule of emerging importance to the atmospheric chemistry community because of its role in aerosol formation and utility as an indicator for oxidative chemistry. We describe the Madison laser-induced phosphorescence (LIP) instrument, an instrument based on LIP for direct, in situ measurement of gas-phase glyoxal with a S/N = 3 limit of detection (LOD) of 18 ppt(v)/min, with planned upgrades to reduce the LOD to 5 ppt(v)/min. By employing this technique, we have built an instrument with exceptional in situ limits of detection, tremendous selectivity, and the considerable advantage of direct, fast measurements that requires neither derivatization nor ex situ analysis. The instrument is equally well-suited for laboratory and field measurements. It was deployed for the first time to the BEARPEX 2007 field campaign in Georgetown, CA, producing nearly one month of continuous data with mixing ratios ranging from 20 to 250 ppt(v) glyoxal. To the authors' knowledge, this represents the first use of LIP for a field measurement.