Nitrogen oxides (NO_x) are important environmental air pollutants that pose a threat for cultural relics. NO_x does not only cause enormous damage, but it also enhances the corrosion induced by other pollutants such as sulfur oxides (SO_x) and organic acids. The rate of removal of low concentrations of NO_x by the adsorption onto biomass and by photocatalysis was studied. These studies have shown that although the direct use of biomass such a fir sawdust, larch sawdust and bamboo can remove moderate levels of NO_x, NO_x removal efficiency is increased 75% using bamboo charcoal made by carbonization at 520 C. The photooxidation efficiency of NO_x decreases with increasing flow rate, and the efficiency of NO_x removal changes slightly when organic acids are combined in the inlet stream of NO_x. Different combinations of photocatalysts and adsorbents were compared, and the optimal combination reduced the NO and NO₂ levels to 1.98 and 1.80μg/m³, respectively.