Global cloud observations from CloudSat and Aura MLS are studied in combination with the new aerosol observations from CALIPSO and carbon monoxide (CO) measurements from Aura MLS to investigate global distribution and seasonal variation of clean and pollution contaminated clouds. Our study will focus on the cirrus cloud in the upper troposphere where MLS ice water content and CO measurements are available. Our approach is to use MLS CO to classify cirrus clouds as "clean" or "polluted", and to use CALIPSO aerosol to identify convective systems contaminated by aerosol particles. We define a "polluted" cloud by two criteria: one uses the coincident MLS CO measurements greater than a certain background value and the other uses the aerosol observations from CALIPSO. Surface emission source of CO and aerosol will be examined in parallel. This study compiles the climatologies of two sets of "polluted" clouds. These climatologies will be compared with that of the clean clouds to delineate how surface pollution alters the properties of upper tropospheric clouds. The results will be compared with model simulations as well. Preliminary analyses find high CO concentration co-exists with deep convective cores and cirrus anvils. Aerosols, however, are found collocated mostly with cirrus away from convective cores, where precipitation is not strongest. The spatial distribution and seasonal variation of "polluted" clouds will be presented at the meeting.