“…Atlas, 1997;Atlas et al, 2003) and in the past 10 years have evolved for air quality applications (Timmermans et al, 2015). These OSSEs have focused on aerosols (Descheemaecker et al, 2018;Timmermans et al, 2009;Yumimoto and Takemura, 2013), carbon monoxide (CO) (Abida et al, 2017;Claeyman et al, 2011;Edwards et al, 2009;Yumimoto, 2013) and ozone (Hamer et al, 2011;Zoogman et al, 2011Zoogman et al, , 2014aZoogman et al, , 2014b from either LEO, GEO or a combination of both observing systems.. The review by Timmermans et al, (2015) provides a 5 framework and set of requirements for each step in the framework to ensure realistic evaluation of the benefit of the new instruments.…”