that shifted from “Low” to “Medium”. For a short time only, high
levels of NOx at the street canyon (253 mG/m3
) lowered the AQI
value and dominated the LHC. At midday, high values of O3 at all
three sites caused a decrease in AQI value, and consequently,
shifted the LHC from “Low” to “Medium”. This episode was more
pronounced in the urban park for a longer duration. It should be
noted that although PM10 values in the park were sometimes
higher than those in the urban square (Table 5, Fig 2(b)), they
were not high enough to change the AQI values. Extremely high
values of O3 at that time were the dominant pollutant that
lowered the LHC.