Page 406 - Fundamentals of Air Pollution 3E

360 21. Air Pollution Climatology
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(less than 7 mi h" and greater than 7 mi h" ) superimposed. The average
pollutant concentrations are connected so as to be depicted as areas rather
than individual lines for each direction. Note that there is little seasonal
change for hydrocarbon concentrations and only minor directional varia-
tion. SO 2 , on the other hand, has very significant seasonal variation, with
very low concentrations in the summer. SO 2 also has considerable direc-
tional variation.
The behavior of these pollution roses is intuitively plausible, because
considerable hydrocarbon emissions come from motor vehicles which are
operated in both winter and summer and travel throughout the urban area.
On the other hand, sulfur dioxide is released largely from the burning of
coal and fuel oil. Space heating emissions are high in winter and low in
summer. The SO 2 emissions in summer are probably due to only a few
point sources, such as power plants, and result in low average concentra-
tions from each direction as well as large directional variability.
Concentrations resulting from dispersion models can also be depicted
using a form of pollution rose. Figure 21-11 is a concentration rose for a

Fig. 21-11. Contributions to the annual sulfur dioxide concentration from each direction
at a receptor in New York by area sources (lines) and point sources (rectangles) for 1969 using
the Climatological Dispersion Model.