Fast, high precision airborne formaldehyde (CH2O) measurements were made by TDLAS during the 2000 Texas Air Quality Study (TexAQS 2000). Measurement precisions of 300 and 100 pptv were estimated at the 2s level, for 1 and 10 second integration periods, respectively. TDLAS measurements were consistent with those of a ground based DOAS system at the La Porte site during seven overflights. Elevated concentrations of CH2O (up to 32 ppbv) produced largely by photochemistry, were measured in plumes. For individual plume transects, CH2O was well correlated with emitted species including CO and CO2, and secondary photoproducts such as O3 and HNO3. CH2O and O3 production per unit (NOY - NOX) was much higher in petrochemical plumes, due to the presence of large concentrations of highly reactive alkenes, than in power plant and urban (Houston and Dallas Ft. Worth) plumes. Good measurement-model agreement was achieved for isolated ethene and propene dominated petrochemical plumes, using observationally derived VOC emissions far higher than suggested by inventories. CH2O-acetaldehyde ratios in these plumes provided a check on the ratio of emitted ethene and propene. Measurements in the Houston Ship Channel plume of high CH2O, and O3 in excess of 200 ppbv, were also well replicated by model.