Table 3 Associations between incident wheezing symptoms and single-day and 3-day mean concentrations (lag 2–4) of air pollutants with maximum data available for each pollutant (12 December 1998 to 19 December 2004)
Age 0–1Age 1–2Age 2–3Age 0–3
OR* (95% CI)OR (95% CI)OR (95% CI)OR (95% CI)
PM10 (μg/m3)
    n†189171155195
    Lag 01.05 (0.88 to 1.25)1.00 (0.86 to 1.15)0.87 (0.72 to 1.06)0.97 (0.87 to 1.08)
    Lag 11.00 (0.82 to 1.22)1.02 (0.87 to 1.19)0.95 (0.78 to 1.15)0.99 (0.89 to 1.10)
    Lag 21.01 (0.83 to 1.23)1.05 (0.93 to 1.19)0.99 (0.82 to 1.17)1.01 (0.92 to 1.12)
    Lag 31.20 (0.98 to 1.46)0.96 (0.84 to 1.09)1.03 (0.84 to 1.25)1.03 (0.93 to 1.14)
    Lag 41.23 (1.02 to 1.48)‡1.04 (0.90 to 1.21)0.89 (0.74 to 1.09)1.04 (0.94 to 1.15)
    3-day mean§1.21 (0.99 to 1.48)1.03 (0.88 to 1.22)0.94 (0.74 to 1.19)1.04 (0.92 to 1.17)
UFPNC§ (particles/m3)
    n144157151179
    Lag 00.71 (0.44 to 1.16)0.82 (0.62 to 1.09)1.00 (0.67 to 1.49)0.85 (0.68 to 1.05)
    Lag 10.88 (0.56 to 1.38)0.92 (0.70 to 1.21)0.93 (0.68 to 1.26)0.91 (0.75 to 1.10)
    Lag 21.60 (0.92 to 2.67)0.88 (0.67 to 1.16)1.03 (0.73 to 1.44)1.00 (0.81 to 1.24)
    Lag 31.07 (0.67 to 1.73)0.79 (0.59 to 1.06)0.89 (0.63 to 1.27)0.84 (0.70 to 1.02)
    Lag 41.50 (0.89 to 2.54)0.99 (0.76 to 1.29)0.62 (0.44 to 0.89)0.88 (0.73 to 1.05)
    3-day mean1.92 (0.98 to 3.76)0.83 (0.58 to 1.17)0.72 (0.49 to 1.04)0.85 (0.68 to 1.07)
NO2 (ppb)
    n190171155196
    Lag 00.78 (0.61 to 1.00)0.99 (0.85 to 1.17)1.00 (0.82 to 1.22)0.93 (0.82 to 1.05)
    Lag 10.82 (0.67 to 1.01)1.03 (0.86 to 1.24)0.94 (0.78 to 1.13)0.95 (0.84 to 1.06)
    Lag 21.12 (0.88 to 1.42)1.07 (0.90 to 1.26)1.12 (0.94 to 1.36)1.09 (0.97 to 1.21)
    Lag 31.42 (1.15 to 1.77)‡0.99 (0.80 to 1.22)1.20 (0.98 to 1.46)1.13 (0.99 to 1.30)
    Lag 41.33 (1.06 to 1.68)‡1.06 (0.89 to 1.26)1.00 (0.82 to 1.21)1.09 (0.96 to 1.23)
    3-day mean1.45 (1.08 to 1.95)‡1.09 (0.85 to 1.40)1.19 (0.98 to 1.45)1.19 (1.01 to 1.30)‡
NOx (ppb)
    n190171155196
    Lag 00.84 (0.68 to 1.02)0.98 (0.85 to 1.12)1.00 (0.84 to 1.19)0.94 (0.85 to 1.04)
    Lag 10.82 (0.69 to 0.98)1.02 (0.87 to 1.19)0.90 (0.77 to 1.05)0.92 (0.84 to 1.02)
    Lag 21.05 (0.87 to 1.28)1.06 (0.92 to 1.22)1.11 (0.95 to 1.30)1.07 (0.97 to 1.17)
    Lag 31.30 (1.09 to 1.53)‡0.99 (0.83 to 1.18)1.12 (0.95 to 1.33)1.09 (0.98 to 1.22)
    Lag 41.26 (1.03 to 1.54)‡1.03 (0.89 to 1.19)1.01 (0.85 to 1.19)1.07 (0.96 to 1.19)
    3-day mean1.30 (1.03 to 1.65)‡1.09 (0.89 to 1.32)1.14 (0.97 to 1.35)1.14 (1.00 to 1.30)‡
CO (ppm)
    n190172154196
    Lag 00.82 (0.61 to 1.10)1.04 (0.80 to 1.36)1.04 (0.75 to 1.44)0.96 (0.80 to 1.15)
    Lag 10.77 (0.57 to 1.04)1.05 (0.79 to 1.40)0.94 (0.68 to 1.29)0.92 (0.77 to 1.10)
    Lag 21.05 (0.77 to 1.42)1.10 (0.86 to 1.42)1.16 (0.90 to 1.50)1.08 (0.92 to 1.28)
    Lag 31.47 (1.10 to 1.96)‡0.89 (0.67 to 1.18)1.08 (0.80 to 1.46)1.07 (0.90 to 1.26)
    Lag 41.19 (0.86 to 1.64)0.94 (0.72 to 1.22)1.04 (0.76 to 1.43)1.02 (0.84 to 1.23)
    3-day mean1.33 (0.94 to 1.90)0.97 (0.70 to 1.34)1.13 (0.81 to 1.55)1.07 (0.87 to 1.32)
  • CI, confidence interval; CO, carbon monoxide; COPSAC, Copenhagen Prospective Study on Asthma in Childhood; IQR, interquartile range; OR, odds ratios; NOx, nitrogen oxide; NO2, nitrogen dioxide; PM10, particulate matter <10 μm in diameter; UFPNC, ultrafine particles.

  • *Odds ratios estimated per IQR of a pollutant in a single-pollutant model adjusted for age, gender, smoking, paternal asthma history, temperature and season.

  • †Number of COPSAC children in the model.

  • ‡p<0.05.

  • §Total concentration of ultrafine particles 10–700 nm in diameter (95% of total concentration comes from particles <100 nm).