Synoptic influences on air pollution events in the Durban South Basin, 2006 to 2010.

Abstract

This study aimed to assess the relationships (if any) between air pollutant measurements in the Durban South Basin (DSB) and (i) local meteorology, (ii) community reports of pollution incidents in Durban, and (iii) air quality and meteorology in Cape Town on the days preceding the Durban South Basin events. With the use of daily synoptic charts and various meteorological variables at an hourly resolution, it was established that air pollution events were better associated with local meteorological events than a community complaint database. Visual analyses of graphed meteorological conditions during the course of air pollution events revealed three clear meteorological scenarios associated with these: 1. A pre-frontal scenario; 2. A scenario showing inversion conditions but no approaching front, and generally low wind speeds; and 3. A post-frontal scenario, likely to be associated with stack downwash under higher wind speeds with the passing of a front. ANOVA revealed significant differences between peak PM10 and average PM10 across scenarios, with Scenario 3 showing highest average and peak PM10. At the Wentworth monitoring station, 24.4% of pollution incidents fell under Scenario 1, 64.2% under Scenario 2, and 5.7% under Scenario 3 between 2006 and 2010. A further 5,7% of the air pollution incidents did not fall under these three scenarios. The latter were not associated with fronts, and did not show inversion conditions, and are likely to be associated with intermittent industrial pollution events. Further statistical analysis assessed the relationships (if any) between various meteorological variables, traffic levels and air pollution concentrations at the Wentworth station between 2006 and 2010. Findings show that delta temperature (change in temperature with height) is the strongest explanatory variable with respect to PM10, wind speed the second strongest, and traffic levels the third strongest. On average, PM10 concentrations increased with increasing delta temperature, decreasing wind speed, and increasing traffic levels. The pressure minimum at Durban associated with an approaching front showed a negative relationship with PM10 during pre-frontal events, but this variable was not significant at the 95% confidence level. This tentatively suggests that even when controlling for frontal influences on delta temperature, lower pressure minima (i.e. stronger frontal systems) are associated with higher pollution levels. Pollution maxima at various Cape Town stations and pressure minima in Cape Town prior to the incident in the DSB showed no relationships with incident PM10 levels at Wentworth. As such, pollution concentrations and meteorology in Cape Town as a front approaches do not appear to be effective predictors of pollution conditions in the DSB when the front approaches there.