Page 259 - Fundamentals of Air Pollution

220 15. Air Pollution Monitoring and Surveillance

are often too slow to permit observation of rapid changes in concentration
as aircraft move in and out of a plume.
Despite these limitations, mobile monitoring systems have been used to
obtain useful information, such as the verification and tracking of the St.
Louis, Missouri, urban plume. The measurement of a well-defined urban
plume spreading northeastward from St. Louis is shown in Fig. 15-2 (7).
These data were collected by a combination of instrumented aircraft and
mobile vans. Cross-sectional paths were flown by the aircraft at increasing
distances downwind. Meteorological conditions of low wind speed in the
same direction helped to maintain this urban plume in a well-defined

Fig. 15-2. The St. Louis, Missouri, urban plume. Ozone and b scai profiles at four distances
downwind of St. Louis track a detectable urban plume for 150 km. Source: Wilson, W. E.,
Jr., Atmos. Environ. 12, 537-547 (1978).