Since arriving at Goddard he has collaborated with scientists both at Goddard and elsewhere on a large range of topics, but primarily studies relating to atmospheric ozone. Since 1996 his main focus has been satellite retrieval of tropospheric ozone. He is currently an active science team member for both TOMS and EOS Aura OMI, and he contributes to SPARC, WMO, and UNEP reports. In recent years he has contributed significantly to developing algorithm schemes for deriving tropospheric ozone from Cloud Slicing and residual methods from satellite data.