Observations by Satellites -- Air-Quality Study from Geostationary/High-Altitude Orbits -- Aerosol Forcing and the A-Train -- Total Ozone from Backscattered Ultraviolet Measurements -- The EOS Aura Mission -- MIPAS experiment aboard ENVISAT -- Aircraft and Ground-Based Intensive Campaigns -- Probing the Atmosphere with Research Aircraft-European Aircraft Campaigns -- MOZAIC -Measuring tropospheric constituents from commercial aircraft -- Uninhabited Aerial Vehicles: Current and Future Use -- U.S. Ground-Based Campaign -PM Supersite Program -- Ground-Based Networks -- Ozone from Soundings: A Vital Element of Regional and Global Measurement Strategies -- LIDAR Networks -- U.S. Federal and State Monitoring Networks -- Autonomous Systems and the Sensor Web -- Comparison of Measurements – Calibration and Validation -- Output of the Observational Web -- The Sensor Web: A Future Technique for Increasing Science Return -- Fundamentals of Modeling, Data Assimilation, and High-Performance Computing -- Inverse Modeling Techniques.