Reaction of NO in air with urea supported on activated carbons (AC) was examined in the range of 100-1000 ppm NO at room temperature to establish a basic scheme for its reduction in open atmosphere. NO in atmosphere containing 02 was found to be selectively reduced with urea supported on AC at the W/F of 2.5 x 10(-3) to 1.5 X 10(-3) ACF g min/ml and its reduction continued until the complete consumption of urea. The reduction of NO with urea supported on AC appears to proceed through the following steps. NO + 1/2O(2) → NO2 NO2 + NO + (NH2)(2)CO → 2N(2) + CO2 + H2O Combining (1) and (2) steps results in the followed reaction equation. 2NO + (NH2)(2)CO + 1/2O(2) → 2N(2) + CO2 + 2H(2)O Since (1) is rate determining, high NO oxidation activity is essential for AC to be active for the reaction. At the same time, activation of urea by AC is also necessary to reduce NO2. The present scheme for NO reduction with urea on the AC is very effective to remove NO, in the open atmosphere under ambient conditions. © 2004 Elsevier B.V. All rights reserved.