The Spatial and Temporal Variability of Airborne Pollutants in Stormwater Runoff

Atmospheric deposition is increasingly being recognised as a significant source of total suspended solids (TSS) and heavy metals in urban runoff. However, many uncertainties and challenges remain with measuring and managing these pollutants in runoff. Impermeable concrete boards were deployed in a residential, industrial, and airside landuse area in Christchurch for almost one year in 2013 to determine the spatial and temporal variability of airborne pollutant loads (principally TSS, Cu, Pb, and Zn) in runoff. Results showed that each land-use area displayed similar trends of increasing/decreasing pollutant loads throughout the monitoring period, suggesting that the pollutants originated from a similar source. Consistently higher pollutant loads were found for the industrial area, which was attributed to local topographic conditions rather than land-use activity. All pollutants had a statistically significant relationship with antecedent dry days, illustrating its importance on pollutant build-up. Pollutants dominated by their particulate-phase were influenced by peak rainfall intensity, which was explained by the energy from an intense rainfall event dislodging more particulate pollutants; however, this relationship was weak. Dissolved-phased pollutants displayed a greater relationship to rain depth showing that the quantity of rain influences the dissolution of pollutants from a surface.