Ozone Level Study at Major Traffic Stalling Points in the Federal Capital City, Abuja, Nigeria

Abstract

In the absence of a reference corpus on air pollution profiles at Nigeria’s capital city of Abuja, this study was designed to be a pilot in the hope that its structure would form the basis for further suchlike air pollution studies such that a reference corpus may be created. The part of Abuja chosen for this pilot study was the heavily built up Federal Capital City (FCC), the “heart” of the capital. Seventy-six major traffic stalling points were identified in the FCC: a traffic stalling point (TSP) is defined to be a road junction or node where all practical motor-mobiles (that is, cars, trucks, motor-cycles, motorized rickshaws, etc.) necessarily decelerate upon approaching the junction, for safety purposes, and accelerate to change velocity as they exit that junction; the process of acceleration involves revving of the engines of the motor-mobiles, with associated increase in the exhaust gaseous effluents. The first phase of this exercise involved the selection of appropriate stations to be occupied within the FCC; coordinate identification (plus corresponding elevation information) using a Global Positioning Systems (GPS) unit was incorporated in this phase. The second phase involved ozone (O3) levels measurements at the major traffic stalling points that were identified and these were carried out over a spread of 10 hours (that is, 7 a.m. to 5 p.m.) at the quarterly hour-mark interval (that is, 15 minutes): the GasAlert EXTREME Single Gas Detector (Ozone Mode) equipment was employed in this phase; thirty-seven sequences of measurements were taken for each day at each of the major traffic stalling points over the three-day period, resulting in a total of 37 x 3 = 111 individual measurements. 111 individual measurements over a spread of 76 major junctions resulted in 8436 targeted measurements for the period of survey; the full-bodied data set of this study represented these 8436 targeted measurements as much as possible. For the third and final phase, the data-set thus built was processed and interpreted in order that deductions on the prevailing nature of the ground-level ozone (O3) air pollution gas could be made. The targeted 111 individual measurements at the different major traffic stalling point were analysed to determine the number of “counts” of the time interval for ozone levels measurements greater than the acceptable threshold of 0.1 ppm. Below the threshold of 0.1 ppm, ozone levels are classified as “tolerable;” between 0.1 ppm and 9 ppm, ozone levels are classified as “hazardous;” above 9 ppm, ozone levels are classified as “critical.” Thus, the “counts” frequency indicated in this analysis applies only to ozone levels above 0.1 ppm, with no descriptive bar on the upper limit of the ppm magnitude, even if this goes beyond 9 ppm, where possible. This result of this study shows that risk to ozone exposure for road users within the FCC is greatest in the hours after midday, beginning from just at lunch time to the early evening rush-hour of 5 p.m. (the timeframe of intense sunshine in Nigeria). Thus, this principal observation has corroborated the prevailing scientific notion that vehicular effluents released during periods of intense sunshine are the mechanism for the formation of ozone. A Geographic Information System (GIS) scheme was implemented for this study in order to have the results of this survey available to the general public: since the “mother ship” of a GIS already exists as the Abuja Geographic Information System (AGIS), the logical approach here was to create an ozone pollution layer that was a veritable subset of the AGIS.