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Table 2 Statistics for urban air pollutant, weather variables, and distribution of the absolute differences between the daily levels of each pollutant ("event days") and the average concentrations over the "control days".

From: Urban air pollution and emergency room admissions for respiratory symptoms: a case-crossover study in Palermo, Italy

Parameter Unit Mean Percentiles
    10 25 50 75 90
Pollutants        
   PM10 μg/m3 36.0* 21.6 26.3 33.2 41.5 52.6
   NO2 μg/m3 41.5 24.8 32.7 40.8 49.7 58.6
   SO2 μg/m3 3.4 0.6 1.2 2.6 4.5 6.9
   CO mg/m3 1.1 0.4 0.6 0.9 1.5 2.1
Differences "event-control" days        
   PM10 μg/m3 11.8 1.4 4.2 8.9 15.6 24.1
   NO2 μg/m3 10.8 1.7 4.1 9.0 15.2 22.1
   SO2 μg/m3 2.2 0.3 0.6 1.4 2.8 5.0
   CO mg/m3 0.4 0.0 0.1 0.3 0.6 0.9
Weather variables        
   Air temperature °C 18.6 10.7 13.3 18.7 23.8 26.7
   Relative humidity % % 58.8 44.2 51.3 59.8 66.9 72.1
   Atmospheric pressure mbars 994.2 987.6 990.7 993.9 997.8 1001.3
   Precipitation mm 0.1 0.0 0.0 0.0 0.0 0.3
   Wind speed m/s 3.2 1.6 2.0 2.6 4.1 6.1
  1. January 2005 - December 2007
  2. * on a cumulative basis, about 45% of the daily observations exceeded threshold.