1. Smithsonian Scientific Series;CG Abbot,1929
2. Alkezweeny, A. J. and Green, W. D.: ‘The Effect of Air Pollution on the Concentration of Ice and Condensation Nuclei’, J. Rech. Atmos. 4, 31–33 (1970).
3. Ashby, W. C. and Fritts, H. C.: ‘Tree Growth, Air Pollution and Climate near LaPorte, Indiana’, Bull Amer. Meteorol. Soc. 53, 246–251 (1972).
4. Barrett, E. W.: ‘Climate Change’, Science 173, 983 (1971).
5. Beebe, R. G.: ‘Changes in Visibility Restrictions over a 20 Year Period’, Bull. Amer. Meteorol. Soc. 48, 348 (1967).