Air quality data are needed in many phases of air management. Air management itself involves the following 12 steps: (1) Determine the effects of various pollutant concentrations and exposure durations on people, plants, and property. (2) Decide which effects to prevent. (3) Select air quality goals or standards that will prevent these effects. (4) Measure and evaluate ambient air pollutant concentrations. (5) Calculate overall source reductions needed for an area to achieve selected ambient air quality goals. (6) Measure or estimate emissions from each source type in an area. (7) Decide how much each source can be permitted to emit and still achieve the desired ambient air quality goals, considering costs, social changes, and so forth. (8) Select or develop means for achieving the necessary source reduction. (9) Decide the date by which each source type should be controlled. (10) Set emission standards. (11) Enforce emission standards. (12) Continue monitoring sources and the ambient atmosphere to ensure that adequate air quality is being achieved. Air quality data are needed in Steps 1, 3, 4, 5, 7, and 12. The purpose of this section is to describe briefly how air quality data can be used to meet these needs; the references cited provide more detailed information.