Ambient measurements of N2O5 during SHARP using cavity ringdown spectroscopy

The formation of N₂O₅ provides the major pathway for NO_x removal at night, and the quantization of urban ambient concentrations will help to complete the total nitrogen budget. Nocturnal ambient measurements of N₂O₅ were performed during the SHARP field campaign from 15 April through 31 May 2009 in Houston, TX. Utilizing cavity ringdown spectroscopy (CRDS), N₂O₅ was detected through thermal decomposition to NO₂ and NO₃ followed by absorption of 662 nm radiation by the nitrate radical. Texas A&M's dual cell CRDS instrument was located on top of Moody Tower, an 18-story building approximately 5 km southeast of downtown Houston. Attempts were made to quantify NO₃ concentrations, however none was observed. Preliminary results show N₂O₅ was observed in varying concentrations ranging to a maximum of 300 ppt. Discussion of the results in the contexts of the SHARP scientific mission will be presented.