Single approach to carcinogen risk assessment from exposure to radiation and chemical environmental factors is developed on the base of multiplicative model. Existing methodology of environmental carcinogenic risk assessment is based on the additive risk model, so additional lifetime cancer rate depends only from carcinogenic hazard of chemicals and from the extent of human exposure to the hazardous chemicals. Medical and demographical features of the exposed population are not included in the model. To eliminate these limitations of the additive risk model, the multiplicative model for assessing environmental carcinogenic risk is developed. The distinguishing feature of this model is that the additional cancer rate in the result of exposure to carcinogenic chemicals in the environment changes with age as a value proportional to the natural (background) morbidity rate for cancer at this age. The similar conceptual approach is used in the world practice for assessing risks arising from ionizing radiation. The procedure is proposed for converting unit risks (slope factors) from the additive risk model, e. g. from the US EPA IRIS database, to the multiplicative risk model. For the main air pollutants that are routinely monitored in Russia, converted risk factor are calculated. Comparison of life-time carcinogenic risks from ionizing radiation and from the ambient air pollution is presented.