Fabrication of Passive Air Samplers for Measurement of Atmospheric Inorganic Gases

Atmospheric pollution is a global challenge due introduction of substances in the atmosphere in concentrations above their normal ambient levels to the extent that they produce measurable effects on human, wildlife and vegetation. The major causes of atmospheric pollution include burning of fossil fuels, agricultural activities, exhaust from factories and industries, motor vehicles, mining operations and indoor air pollution.

To control atmospheric pollution, it is necessary to develop stringent policies that safeguard the environment, and also to ensure enforcement of these policies. Monitoring the levels of pollutants in the atmosphere plays integral part in terms of evaluating the effectiveness of the mitigation measures employed. The two main ways to implementing monitoring are: through active sampling and passive sampling.  Active sampling involves collection of actual volumes of air followed by measurement of pollutant concentrations, whereas passive sampling involves trapping the air pollutants on suitable sorbents installed in a suitable stationary housing over an extended period of time. Whereas active sampling this is the most preferred way of air quality monitoring, but it is expensive and unaffordable to roll out consistent national monitoring in most developing countries. Therefore, development of passive samplers is necessary to achieve consistent sampling of pollutants. Currently, monitoring activities in Kenya rely on imported passive samplers which is expensive and unsustainable over a long period of time. Therefore, the goal of this project was to fabricate and test passive sampler for trapping nitric acid using locally available materials.

The passive sampler adsorbent was fabricated from Whatman filter paper No. 40 impregnated with sodium hydroxide methanol trapping solution for nitric acid. The samplers installed on the roof top of chemistry department on a metallic standard at a height of 1.5 m. The samples collected periodically after 0, 2, 4 and 6 week for analysis of nitric acid trapped. Analysis was conducted using nitrate ion selective electrode.

The concentration of nitric acid measure increased with time but stabilized after the fourth week, suggesting attainment of the breakthrough volume and establishment of equilibrium with the atmospheric levels. The results suggest that the fabricated sampler was effective at trapping atmospheric Nitric acid. Further studies will be required to establish the sampling rate and to calibrate the sampler against the active sampler.

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