This document establishes a classification system for GPACDs supplying single pass outdoor air to general ventilation systems using outdoor air polluted by local urban sources and/or long-distance pollution. The classification system is intended to aid in assessing molecular contamination in addition to the particulate contamination dealt with by ISO 16890-1.This document specifies four reference pollutants, i.e. ozone, sulphur dioxide, nitrogen dioxide and toluene, used for the classification due to their relevance to the intended application. This document further specifies three duty levels that are assigned for each pollutant reflecting the typical performance range of devices intended for the application. Since selection of reference pollutants and duty levels are specific and unique to the intended application, all other applications are excluded. In particular, this document does not apply to GPACDs in recirculation applications and/or dealing with pollution from indoor sources as well as pharmaceutical, microelectronic, nuclear, homeland security and military applications.