Spatial analysis and evolution of four air pollutants in England and Wales

Pollution control is based on an exhaustive knowledge of concentration distributions. This study analyses a detailed database of NO₂, O₃, PM₁₀ and PM_2.5 in England and Wales over the period 2007-2011. Daily and annual means were considered in a 1-km spatial resolution. Histograms revealed a shape like a sawtooth. The interval was wide for NO₂ and O₃, although with a gap, whilst the particulate matter range was narrow. Spring provided the peak for the O₃ annual cycle, whereas minima for the other pollutants were reached in summer. A trend for the annual medians of particulate matter was observed, with a minimum in the period analysed. However, the pattern was uniform for NO₂ and O₃. Cities appeared as NO₂ hot spots and O₃ cold spots. Wales stood out as an NO₂ clean country, although with high O₃ levels. Sources or sinks of particulate matter were not observed, suggesting that more detailed analysis is required. Two NO₂ pollution axes were sometimes seen, one in the south from London to Bristol, and the second in the north, from Liverpool to Kingston Upon Hull. No annual spatial pattern was seen for the remaining pollutants beyond the contrast between cities and country sites for O₃. Consequently, spatial analysis allows the real impact of pollutant sources be known, although it must be performed with a detailed temporal resolution in order to investigate the extension, quantity, and length of the concentrations calculated.