ABSTRACT
Sulfur dioxide is of great concern as an ambient air pollutant because of its deleterious effects on men, animals, plants and materials. Many methods for the determination of atmospheric sulfur dioxide abound in literature. They include the West-Gaeke method, the hydrogen peroxide method, the iodine method, the Tscherwenka et al method, the Mulik et al method etc.
Many of these methods have limitations especially when application to the Nigerian environment is concerned eg. The need for continuous supply of electricity, availability of ion chromatographic equipment etc.
In this research, a self-indicating (i.e. colour form in absorbing solution as the SO2 pollutant is absorbed by it) active method for the detection of sulfur dioxide (SO2) was developed.
Standard SO2 gas for the calibration of the method was generated in the laboratory from sodium bisulfite using simple experimental and quantification set up.
The generated SO2 gas was determined indirectly through its reduction of Ferric ion (from ferric ammonium sulphate) to ferrous ion.
The amount of ferrous ion produced was then determined spectrophotometrically with 1,10 – phenanthroline at 510nm.
The possible presence of other reductants was accounted for by carrying out a blank determination and subtracting its value from that for the sample.
The developed method was applied for the determination of SO2 in various locations in the atmosphere. The results showed a minimum SO2 concentration of 0.005 ± 0.001ppm at the Export Processing Zone (EPZ), Calabar and the highest concentration of 1.00±0.006ppm at the Crush Rock Industry, Akamkpa, Cross River State. Other results obtained were 1.55±0.06ppm at the Department of Chemistry, University of Benin (UNIBEN); 0.010 ± 0.001ppm at the Department of Electrical/Electronics of the University of Benin (UNIBEN); 0.150±0.020ppm at the Male Hostel (Malabor), Unical; 0.13±0.002ppm at the Female Hostel (Malabor), University of Calabar (Unical); 0.20±0.01ppm at Calabar Cement Company (CALCEMCO), Calabar; 0.04±0.004ppm at Government House, Uyo; 0.025±0.003 at Aluminum Smelting Company of Nigeria (ALSCON), Ikot Abasi; 0.37±0.003ppm at Calabar Round-about, Calabar; 0.005±0.02ppm at Export Processing Zone (EPZ), Calabar; 0.078±0.003ppm at Calabar Wood, Calabar; 0.446±0.02ppm at Unical Main gate/Etta-Agbor round-about, Calabar and 0.47±0.006ppm at Mary Slessor/Calabar road junction, Calabar.
The precision of the method expressed as coefficient of variation of the SO2 absorbing solution used ranged from 11-60%. The accuracy expressed as relative error from the reference West-Gaeke method ranged from 4.76- 20%.
