Table 2

 Descriptive statistics for environmental variables, Boston, Massachusetts, USA, between 1998 and 2002

Parameter (units; all are 24 h means)Number of observationsArithmetic mean (SD)RangeInterquartile range
AT, apparent temperature; BC, black carbon; PM2.5, particles <2.5 μm in aerodynamic diameter, known as fine particles; SO42−, sulphate.
*Particulate matter <2.5 μm in aerodynamic diameter measured by the Upright & Patashnik Tapered Element Oscillating Microbalance sampler.
†BC measured by aethalometer (Magee Scientific).
‡SO42− measured by the Harvard Annular Denuder System or by ion chromatography.
AT (°C)927.1 (10.0)(−7.9, 33.1)16.5
PM2.5* (μg/m3)9211.4 (5.9)(0.07, 33.7)7.6
BC† (μg/m3)921.1 (0.8)(0.2, 5.8)0.6
SO42−‡ (μg/m3)593.0 (2.0)(0.5, 9.6)2.2