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Does chronic exposure to high levels of nitrogen dioxide exacerbate the short-term effects of airborne particles?
  1. Annunziata Faustini,
  2. Massimo Stafoggia,
  3. Matteo Renzi,
  4. Giulia Cesaroni,
  5. Ester Alessandrini,
  6. Marina Davoli,
  7. Francesco Forastiere
  1. Department of Epidemiology, Lazio Regional Health Service, Rome, Italy
  1. Correspondence to Dr Annunziata Faustini, Department of Epidemiology, Lazio Regional Health Service, via Cristoforo Colombo 112, Rome 00147, Italy; a.faustini{at}


Background Long-term exposure to air pollutants has been hypothesised as a factor in susceptibility to short-term exposure to particulate matter (PM), but results are not coherent. We studied the short-term effects of PM10 on mortality and assessed whether long-term exposure to nitrogen dioxide (NO2) modifies this association.

Methods We used a case-crossover design to evaluate daily PM10-related mortality among 124 432 35+ year-old participants who died in Rome between 2001 and 2010 and maintained the same address for at least 5 years before death. Modification of PM10-related mortality by long-term NO2 exposure was determined by two-way interaction, while a three-way interaction was used to assess effect modification of high NO2 levels in population groups defined by sociodemographic position and pre-existing diseases.

Results Mortality increased by 0.82% (0.23–1.41%) for each 10 µg/m3 increase in PM10. Mortality rose by 1.22% (0.17–2.38%) in participants exposed to NO2 levels ≥50 µg/m3 and by 0.69% (0.03–1.34%) in those exposed to levels <50 µg/m3 with no effect modification (p-interaction 0.378). A suggestion of effect modification was seen in 85+-year-olds (3.10%; p-interaction 0.043), as well as in those with a pre-existing arrhythmia (3.26%; p-interaction 0.014) and chronic obstructive pulmonary disease (3.52%; p-interaction 0.042).

Conclusions Long-term exposure to NO2 is not likely to induce susceptibility to short-term PM10 exposure in the overall population. However, an effect modification of NO2 is probable in the elderly and in those suffering from arrhythmias and chronic obstructive pulmonary disease.

  • short-term PM exposure
  • mortality
  • long-term NO2
  • effect modification
  • additive effect

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  • Competing interests None declared.

  • Provenance and peer review Not commissioned; externally peer reviewed.