Forthcoming directives from European Commission will force homologation in altitude to approach standards to actual driving conditions in order to reduce the gap between regulated and real-life emissions. This work presents the use of a dedicated atmosphere simulator to analyse the impact of altitude on performance and emissions of a turbocharged diesel engine. The presented equipment provides engine intake and exhaust pressure to reproduce high-altitude conditions. The main advantages are related to cost savings with respect to round-robin testing campaigns ensuring controlled ambient conditions at the different altitudes. The paper shows the main features of the altitude simulator under steady-state and transient operation and the ability to control temperature at the same time that pressure according to International Standard Atmosphere (ISA) specifications. The experimental results highlight the need for specific testing facilities to perform calibration tasks as a key tool to comply with future emission standards in a cost-effective manner. In particular, regulated emissions measured at altitude are shown to clearly exceed that permitted at sea-level emphasizing the need to explore new dedicated engine control strategies for pollutant abatement under altitude operation.