Abstract: A solid-state light source photolytic NO2 converter including a reaction chamber made of a reflective material with diffuse reflective properties, whereby the reaction chamber includes a low volume gas cell wherein the gas sample residence time is less than 5 seconds is provided. The NO2 in the air sample is exposed to ultraviolet radiation at wavelengths less than 420 nm, whereby the NO2 is converted to NO. The NO is subsequently measured using an NO analyzer. The solid-state light source includes diode lasers and LED's that emit UV wavelength in the range of 350–420 nm. The use of a narrow wavelength range afforded by the solid-state light source results in an interference-free conversion of NO2 to NO at high efficiency.