The occurrence and nature of brown plumes in Ontario

• Published in: Atmospheric environment 1981, Vol.15 (12), p.2521-2529
• Main Authors: Melo, O.T., Stevens, R.D.S.
• Format: Article
• Language: English
• ISSN: 0004-6981; 1352-2310
• DOI: 10.1016/0004-6981(81)90067-6

A number of power plants have been located on the north shores of the Lower Great Lakes. These plants are equipped with high efficiency electrostatic precipitators which ensure invisible plumes most of the time. However, in spite of this effort, it was noticed that under certain circumstances the plumes would acquire a brown appearance 0.5–5 km from the power plant and remain visible for distances of up to 100 km. A study of the occurrence and nature of these brown plumes was undertaken using airborne plume sampling with an instrumented helicopter and ground based records of plume visibility, temperature and wind profiles, other aerometric parameters and power plant loading. On the basis of these studies, it has been estimated that under typical conditions about 90 ppm m of NO 2 is required to make a plume just visible against a blue horizon sky background, and NO 2 burdens larger than this value were measured frequently. Meteorological conditions are dominant in determining whether a brown plume will form or not. Stable layers in the lower atmosphere, generally induced by the cold lakes in spring and early summer, trap the plumes in shallow layers of 100–200 m thickness, 300–500 m above ground. Plume growth in the horizontal direction still takes place under these conditions and transports ambient O 3 into the plume thus leading to the conversion of NO to NO 2. A ground-level observer located off the axis of the plume perceives the plume as if it were undergoing no dilution. Good general visibility and a blue sky background enhance the brown appearance of the plume.