O-105 Ambient particulate matter ratio as an indicator of Saharan dust intrusion: a pilot study in Grenada

Methods: Ambient PM2.5 and PM10 data were collected from three fixed-site low-cost monitors in Grenada which continuously captured particulate matter mass using optical sensors. Meteorological correlates were obtained from the Grenada Meteorological Service. Summary statistics were calculated and a time series analysis of the daily PM2.5/PM10 ratio with locally estimated scatterplot smoothing (LOESS) smoothing was constructed. Daily PM2.5/PM10 ratios were modeled as a function of the meteorological correlates.

Results: The mean PM2.5 (4.50 µg m–3) and PM10 (6.55 µg m–3) levels indicate that Grenada’s baseline air quality generally meets the WHO recommendations of 5 µg m-3 and 41 µg m-3, respectively. However, there were periods during the year when concentrations exceeded the 24-hour thresholds set by the WHO, 15 µg m–3 and 45 µg m–3 respectively, highlighting a public health risk. The calculated PM2.5/PM10 ratio, with an annual mean of 0.68 and a range of 0.31 to 0.92, reflected the significant variability in particle size distribution throughout the year. Lower ratios, indicative of dust intrusions, and generally coinciding with dust advisories, were observed at the start and again at the end of the dry season.

Conclusion: The estimation of the PM2.5/PM10 ratio confirms that periods of poor air quality in Grenada is associated with Saharan dust events. The study highlights the practical value of low-cost monitors in generating crucial air quality data to improve public health messaging in resource-limited settings, such as Grenada and the Caribbean.