Ambient air monitoring is an integral part of an effective air quality management system. Reasons to collect such data include to: assess the extent of pollution; provide air pollution data to the general public in a timely manner; support implementation of air quality goals or standards; evaluate the effectiveness of emissions control strategies; provide information on air quality trends; provide data for the evaluation of air quality models; and support research (e.g., long-term studies of the health effects of air pollution). There are different methods to measure any given pollutant. A developer of a monitoring strategy should examine the options to determine which methods are most appropriate, taking into account the main uses of the data, initial investment costs for equipment, operating costs, reliability of systems, and ease of operation. The locations for monitoring stations depend on the purpose of the monitoring. Most air quality monitoring networks are designed to support human health objectives, and monitoring stations are established in population centers. They may be near busy roads, in city centers, or at locations of particular concern (e.g., a school, hospital, particular emissions sources). Monitoring stations also may be established to determine background pollution levels, away from urban areas and emissions sources. Systems are needed to ensure that data are of acceptable quality, to record and store the data, and to analyze the data and present results.