Reducing air pollution and preventing climate change are major challenges for the future. The monitoring of atmospheric gas concentration and emissions that contribute to these effects is vital in assessing the impact of policies to reduce both air pollutant and greenhouse gas emissions. For this data to be reliable, calibration of monitoring instrumentation is required with gas standards with values traceable to Primary Reference Gas Mixtures. Such gas standards are produced by National Metrology Institutes. The paper describes the level of uncertainty and compatibility that can be achieved for a number of greenhouse gas and air quality gas standards based on the methods used to establish their values: CH₄ in air and NO in nitrogen (prepared by static gravimetry); NO₂ and HCHO (prepared by dynamic measurements); O₃ and impurities in NO_x gases (by spectroscopy); CO₂ and O₃ cross sections (by manometric methods).