Walker, N.P., R.H. Ellerbeck, and E. Kemeny. “NATIONAL SURVEY OF SMOKE AND SULPHUR DIOXIDE : QUALITY OF SMOKE MEASUREMENTS”. Clean Air Journal 7, no. 1 (June 3, 1986): 27–29. Accessed May 3, 2024. https://cleanairjournal.org.za/article/view/7346.