The measurement of atmospheric pollutant concentrations can be performed using different approaches. The most commonly employed method consists of continuous monitoring at fixed stations integrated into air quality monitoring networks. Other approaches involve successive measurements at different locations within a defined grid over a specified period of time. Measurements may be manual or automatic. In manual methods, air samples are collected or pollutants are trapped in reactive solutions or filters, followed by laboratory analysis of the collected samples, solutions, or filters. In automatic methods, both sampling and analysis are carried out directly on site by the monitoring equipment. Measurements can also be classified as continuous or discontinuous. In continuous monitoring, analyses are performed either in real time or after a short sampling interval, depending on the selected integration time. In discontinuous monitoring, analyses are carried out after a relatively long sampling period. For practical reasons, continuous monitoring is generally associated with automatic methods. The choice between manual or automatic, and continuous or discontinuous monitoring depends on the characteristics of the monitoring equipment, the pollutants of interest — and consequently the mechanisms through which they exert harmful effects — as well as emission conditions and the magnitude and frequency of pollution episodes or peak concentrations.