Sulphur dioxide

TCM/Pararosaniline―SO2 is absorbed from the air in a potassium tetrachloromecurate and formaldehyde in the following amounts by controlling the flow rate of sample and reagents. A pararosaniline methyl sulphuric acid dye is formed. The absorbance of the coloured solution is determined at about 550 nm in a spectrophotometer. Concentrations in the range of <25 to 1000 mg/m3 can be measured by this method [20] . This method requires relatively simple apparatus. It is essentially specific to SO2 since all known interference are minimised or eliminated, samples are relatively stable after collection. It has been used widely as a reference method and is covered by an international standard [21] .

Nitrogen dioxide

This method is intended for the manual determination of NO2 in the atmosphere in the concentration range of a few to about 9400 mg/m3 (5 ppm) for sampling periods of up to two hours and flow rate of up to 0.6/min. The principle of this method involve reacting NO2 with diazolizing-coupling reagents (Sulphanilic acid and N- (I-naphthyl)-ethylene diamine dihydrochloride) to produce a deeply coloured azo dye whose intensity is measured spectrophotometrically. It is sensitive enough to detect low concentration of NO2. This method has been used extensively in the United States and Europe, it has been tested by many workers and is highly recommended [20] [22] .

Carbon dioxide

Colorimetric chemical sensors―This detects emissions at their permissible exposure limit after some minutes of exposure. The sensors consist of disposable array of cross-responsive nanoporous pigments whose colours are changed by diverse chemical interaction with analytes. CO2 levels could range up to 10,000 ppm on the detector.

Carbon monoxide

Non-dispersive infrared―Non-Dispersive Infra-Red (NDIR) detectors are the industry standard method of measuring the concentration of carbon oxides. The constituent gas in a sample will absorb some infra-red at a particular frequency. By shining an infra-red beam through a sample cell (containing CO), and measuring the amount of infra-red absorbed by the sample at the necessary wavelength, a NDIR detector is able to measure the volumetric concentration of CO in the sample.

Hydrocarbons (total & BTEX)

An ultraviolet-visible spectrophotometer with automatic cell driver and spectrum design system equipped with quartz cells was used. With the spectrophotometer, the amount of a known chemical substance (concentrations) can be determined by measuring the intensity of light detected depending on the range of wavelength of light source.

Suspended Particulate Matter (SPM)

Gravimetric (non-destructive)―The sample is taken through continuous filtration of ambient air on glass fibre filtering material with a capturing capacity more than 99.5% and flow rate of 33 - 55 cm∙s−1. The filter head is turned with the open side down, at a distance of 1.5 - 3.0 m above the surface. The sampling time was for 24 hours. The sampling frequencies correspond to the character of the sampling site locations. The amount of sample captured on the filter (in µg) is determined gravimetrically as a difference between the weight of the filter prior to and after the exposure.

Heavy metals

Atomic absorption spectroscopy (AAS)―This method is very reliable and simple to use as it can analyze over 62 elements through atomic identification and quantification. Metals absorb ultraviolent lights in their elemental form when they are excited by heat and each metal has a characteristics wavelength that will be absorbed. The AAS instrument looks for a particular metal by focusing a beam of UV light at a specific wavelength through a flame and into a detector.