UV absorption cross sections of formaldehyde (HCHO) have been measured with a spectral resolution of 0.025 nm in the wavelength range 225--375 nm at 298 K using a diode array detector. At selected temperatures ranging from 223 to 323 K, measurements have been conducted to obtain temperature gradients in the wavelength range 250--356 nm. Error limits for the reported absorption cross sections are ¿5% but at least ¿3¿10-22 cm2 molecule-1. For the temperature gradients, uncertainties are <8%. Spectra and temperature gradients are compared with earlier measurements. ¿ 2000 American Geophysical Union