Silicon monoxide (SiO) is injected directly into the Earth’s upper atmosphere by ablating meteoroids. SiO is also produced by the reaction of atomic Si (another ablation product) with O₂ and O₃. The reactions of SiO with several atmospherically relevant oxidants have been studied by the pulsed laser photolysis of a Si atom precursor in the presence of O₂, followed by time-resolved non-resonant laser-induced fluorescence of SiO at 282 nm. This yielded: k(SiO + O₃, 190–293 K) = (4.4 ± 0.6) × 10⁻¹³ cm³ molecule⁻¹ s⁻¹; k(SiO + O₂ + He, 293 K) ≤ 3 × 10⁻³² cm⁶ molecule⁻² s⁻¹, k(SiO + O + He, 293 K) ≤ 1 × 10⁻³⁰ cm⁶ molecule⁻² s⁻¹, k(SiO + H₂O, 293 K, 4–20 Torr) ≤ 4 ×10⁻¹⁴ cm³ molecule⁻¹ s⁻¹, and k(SiO + OH, 293 K, 4–20 Torr) = (5.7 ± 2.0) × 10⁻¹² cm³ molecule⁻¹ s⁻¹. These results are explained by combining ab initio quantum chemistry calculations with transition state theory and RRKM theory. An upper limit of 5 × 10⁻¹³ cm³ molecule⁻¹ s⁻¹ for the reaction SiO₂ + O → SiO + O₂ was determined, but calculations indicate the existence of a high barrier (104.7 kJ mol⁻¹) which will make this reaction very slow at mesospheric temperatures.