Abstract:
While several studies have reported on the utility of low-cost sensors for air
quality campaigns in advanced countries including the development of data
correction and quality improvement mechanisms thereby using them to
complement regulatory monitors, there is, in contrast, limited information on the
use of low-cost sensors for air pollution applications in Ghana and wider parts of
Sub-Saharan Africa. This PhD study presented a proof of concept approach on
the feasibility of factory calibrated Alphasense OPC-N2 for two main purposes.
Firstly, the suitability of low-cost sensors for high-density ground-based air
pollution studies and the applicability of the high-resolution data for quantification
of atmospheric emissions. Pearson’s correlation analysis was applied to establish
the reproducibility of the selected sensors for high-density ground-based air
quality monitoring specifically for PM species due to the spatial and temporal
variability and suitability of PM for developing urban air quality standards. Trend
analysis, calendar plots and sectorial plots in the components of wind were
experimented using the high-resolution data to quantify particulate matter (PM)
and its sources. Hourly averaged data from the selected sensors have
demonstrated the reproducibility of low-cost OPC-N2 for use in the selected
environments for PM with correlation coefficients (Pearson’s, R) between 0.97
and 0.98 for PM₁ , PM₂.₅ and PM₁₀. For quantification of the species monitored,
PM₁ 0 values were 500 µg/mᶟ; PM₂.₅ were a little below 90 µg/mᶟ and PM₁ values
were a little below 60 µg/mᶟ. These levels though preliminary, agree with PM
pollution reported from these types of environments. It was also found that PM
pollution was locally characterised with low wind speed (≤ 2 ms⁻¹) tied to
background activities and the surrounding environment which includes traffic,
wind-blown dust and roadside food cooking and vending activities. The statistical
difference in mean values (t-values of 17.3, 11.4 and 4.2 for PM₁ , PM₂.₅ and PM₁₀
respectively) of the reported PM species have shown that the sensors are better
suited for PM₁₀ monitoring. Findings from this study provide a benchmark for
future (AQ) studies in Ghana, particularly in the selected exemplar urban areas.
It demonstrates the feasibility of the current generation of relatively low-cost PM
sensors for a high-density ground-based air quality monitoring in environments
typical of large parts of West and Sub Saharan Africa.
