Sulfur dioxide visibility reduction

Harkins, I., and S. W. Nkksic. Studies on the role of sulfur dioxide in visibility reduction. J. Air Pollut. Control Assoc. 15 218-221, 1%5. 

Early work with sulfur dioxide showed a linear relationship between visible injury and reduction in yield for many crop species. The assessment was made that no reduction in yield would be found unless visible injury were noted. Definitive research with ozone, other oxidants, or mixtures of these pollutants with other gases has not been done. Thus, we do not know whether such relationships between visible injury and yield hold for the oxidants, but data in Table 11-3 suggest that for acute exposures there may be good correlations between injury and yield reductions. Many researchers have hypothesized that the oxidants may have an effect on plants that will produce a yield reduction with little or no visible injury. Such studies need to be designed in a more defmitive manner before it is concluded that yield reductions without visible symptoms are clearly acceptable. Projections of yield losses have made use of some of the data reported earlier. ... 

These data and those of others (1, 5, 6, 26, 27) indicate a change in growth rate and/or a reduction in leaf area after prolonged exposure to sulfur dioxide. These effects indicate possible alterations in the normal physiological functioning of the plant, and therefore probably have both a visible (ultrastructure) and biochemical basis. 

However, this does not preclude following the effects on plant growth of chronic exposure to low levels of sulfur dioxide. Injury is manifested in altered growth rates, reduction in plant size, and alteration in reproductive capacity, all of which are visible only if the plants can be compared with others of the same variety growing under nonpolluted condi-... 

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