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In Khadka et al. (2023), a sample of X-ray-detected reverberation-mappedquasars was presented and applied for the comparison of cosmologicalconstraints inferred using two well-established relations in AGN -- theX-ray/UV luminosity ($L_{X}-L_{UV}$) relation and the broad-line regionradius-luminosity ($R-L$) relation. $L_{X}-L_{UV}$ and $R-L$ luminositydistances to the same quasars exhibit a distribution of their differences thatis generally asymmetric and positively shifted for the six cosmological modelswe consider. We demonstrate that this behaviour can be interpretedqualitatively to arise as a result of the dust extinction of UV/X-ray quasaremission. We show that the extinction always contributes to the non-zerodifference between $L_{X}-L_{UV}$-based and $R-L$-based luminosity distancesand we derive a linear relationship between the X-ray/UV colour index$E_{X-UV}$ and the luminosity-distance difference, which also depends on thevalue of the $L_{X}-L_{UV}$ relation slope. Taking into account the median andthe peak values of the luminosity-distance difference distributions, theaverage X-ray/UV colour index falls in the range of$\overline{E}_{X-UV}=0.03-0.28$ mag for the current sample of 58 sources. Thisamount of extinction is typical for the majority of quasars and it can beattributed to the circumnuclear and interstellar media of host galaxies. Afterapplying the standard hard X-ray and far-UV extinction cuts, heavily extinctedsources are removed but overall the shift towards positive values persists. Theeffect of extinction on luminosity distances is more pronounced for the$L_{X}-L_{UV}$ relation since the extinction of UV and X-ray emissions bothcontribute.

Effect of extinction on quasar luminosity distances determined from UV and X-ray flux measurements