manual methods) came into widespread use in air quality monitoring networks in the U.S. in the 1950s through early 1970s
both for PM and gases such as SO2 and nitrogen oxides (NOx). Intermittent sampling has the advantage of relatively low cost and provides reasonably useable data. It has the disadvantage of relatively long averaging times (typically 24 h)
historically viewed by regulators as undesirable for gas-phase pollutants. Intermittent sampling continues to be the sampling method of choice for PM10
PM2.5
Pb
and atmospheric deposition networks. Because of its relatively low cost
intermittent sampling is often used to supplement continuous monitoring systems. Intermittent sample collections at multiple locations may provide more useful data than a continuous record at a few locations. It is particularly useful where resources for pollutant monitoring are limited. Continuous monitoring devices provide instantaneous or near-instantaneous sampling results. Because data are acquired in real time
continuous monitors are the systems of choice in air quality monitoring programs. Their major disadvantages are high capital equipment and system maintenance costs and a need to reduce data to a manageable form. 7.1.1.3.1 Gas-Phase Pollutants Air quality 236
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