SOLID PHASE MICROEXTRACTION: MEASUREMENT OF VOLATILE ORGANIC COMPOUNDS (VOCs) IN DHAKA CITY AIR POLLUTION

Abstract

ABSTRACT A solid phase microextraction (SPME) technique was applied for the sampling of volatile organic compounds (VOCs) in ambient air polluted by two stroke autorickshaw engines and automobile exhausts in Dhaka city, Bangladesh. Analysis was carried out by capillary gas chromatography (GC) and GC-mass spectrometry (MS). The methodology was tested by insitu sampling of an aromatic hydrocarbon mixture gas standard with a precision of ±5% and an average accuracy of 1–20%. The accuracy for total VOCs concentration measurement was about 7%. VOC's in ambient air were collected by exposing the SPME fiber at four locations in Dhaka city. The chromatograms showed signature similar to that of unburned gasoline (petrol) and weathered diesel containing more than 200 organic compounds; some of these compounds were positively identified. These are normal hydrocarbons pentane (n-C5H12) through nonacosane (n-C29H60), aromatic hydrocarbons: benzene, toluene, ethylbenzene, n-propylbenzene, n-butylbenzene, 1,3,5-trimethylbenzene, xylenes, and 1-isocyanato-3-methoxybenzene. Two samples collected near an autorickshaw station contained 783 000 and 1 479 000 µg/m3 of VOCs. In particular, the concentration of toluene was 50–100 times higher than the threshold limiting value of 2000 µg/m3. Two other samples collected on street median showed 135 000 µg/m3 and 180 000 µg/m3 of total VOCs. The method detection limit of the technique for most semi-volatile organic compounds was 1 µg/m3.