The co-adsorption and reaction of NO and O₃ on authentic Saharan dust surfaces was investigated in a Knudsen reactor at ≈296 K. NO was consumed on the dust surface in the presence of O₃ and thereby partially converted to NO₂, which was released to the gas-phase. An empirical expression for the dependence of NO₂ production, P_NO2, on the O₃ and NO concentrations and dust surface area could be formulated, allowing the importance of this process in the atmosphere to be assessed:

, where A_dust is the dust surface area per cubic centimetre of air, C^′_a = 1.4 × 10⁹ s⁻¹ cm⁻², b_O3 = 4.0 × 10⁻¹² cm³, and b_NO = 5.4 × 10⁻¹³ cm³. Even at high tropospheric dust concentrations, this production rate is too low to significantly supplement that from NO oxidation by O₃ and HO₂. Experiments to examine chemical ageing of dust by ozone showed that HNO₃ uptake was not influenced by the presence of 100 ppb O₃ (STP), and HNO₃ uptake coefficients were similar to those previously derived.