Photofragmentation two-photon laser-induced fluorescence detection of NO2 and NO: Comparison of measurements with model results based on airborne observations during PEM-Tropics A

Measurements of NO and NO2 are reported using a highly modified photofragme ntation two-photon laser-induced fluorescence (PF-TP-LIF) instrument. Avail able evidence suggests that the changes made substantially reduced wall dec omposition of labile NOy species. In sharp contrast to the results reported from NASA's 1991 PEM-West A program where the median value for the ratio ( NO2)(meas)/(NO2)(calc) was 3.36, the PEM-Tropics A observations produced a value for this ratio of 0.93. This represents the first time that remote up per tropospheric NO-NO2 data have shown a high degree of correspondence wit h current photochemical mechanisms.