The absorption cross section of gaseous nitrous acid (HONO) in the actinic wavelength region (&lgr;≥290 nm) of the solar radiation is mapped through laser photodissociation experiments. HONO is photodissociated by a tunable ultraviolet beam, and the OH product is monitored through fluorescence induced by a frequency-doubled dye laser. The absorption of HONO is mapped by scanning the photolysis wavelength. Since this technique yields relative cross-sections, we calibrate our measurements with previous measurements of absolute cross-section at 354 nm (because there is reasonable agreement among previous measurements at this wavelength). The present experimental approach is insensitive to the presence of NO2, which apparently contributed to inaccuracies in some of the previous conventional measurements on HONO absorption. ¿American Geophysical Union 1990