Abstract This paper presents a methodology for a systematic, robust and conservative ecological risk assessment for estimating environmental consequences and associated risk from ambient air concentrations of atmospheric pollutants and air toxics (also referred to as criteria pollutants and hazardous atmospheric pollutants in the United States legislation respectively), as arising from industrial activities. The paper details the main steps of the risk assessment process and makes a contribution in deriving conservative and safe Reference Concentrations (RfC) such as No Observed Adverse Effect Level (NOAEL) and Lowest Observed Adverse Effect Level (LOAEL) for fauna in their natural habitat, using published scientific dose-response toxicological studies with laboratory animals. It then uses these derived RfCs to determine step changes in consequence levels, from incidental to major, in order to complete the risk assessment. A similar approach is used to assess impacts on the marine environment. This methodology is repeatable and robust and can be applied as a screening level environmental risk assessment to establish conformance to legally postulated levels of acceptable environmental consequences, where available, or acceptable levels of environmental risk, associated with air quality.