While N2O3 has been observed previously in the gas phase, in solution and as a solid at low temperatures, it has not been reported adsorbed on solids at room temperature. However, the adsorbed species has been postulated as a precursor to HONO in the lower atmosphere. We report here the formation of N2O3 adsorbed on a porous glass surface at room temperature from the precursors NO and NO2 using transmission FTIR spectroscopy. The spectrum of the porous glass in the presence of NO and NO2 showed broad peaks at approximately 1870 and 1600 cm(-1) attributed to surface adsorbed asym-N2O3 (ONNO2). These peaks shifted by similar to 30-40 cm(-1) to lower wavenumbers when N-15-labeled NO was used, consistent with absorption bands previously assigned by other researchers to solid asym-N2O3 at low temperature. While the peaks assigned to surface-adsorbed asym-N2O3 did not decrease significantly on exposure to water vapor, measurable concentrations of gas-phase HONO were formed. The atmospheric implications are discussed.