Does chronic exposure to high levels of nitrogen dioxide exacerbate the short-term effects of airborne particles?

The short-term effects of PM10 on mortality and whether long-term exposure to NO2 modifies this association were investigated 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 employed to assess effect modification of high NO2 levels in population groups defined by socio-demographic position and pre-existing diseases. An overall increase in mortality for each 10 μg/cu m increase in PM10 was observed. Short-term PM10-related mortality increased among people exposed to both high and low NO10 levels, but a clear effect modification was not detected. However, effect modifications of short-term PM10-related mortality were observed among those exposed to long-term NO2 for people over the age of 85-years, for those with pre-existing arrhythmias, and for those with pre-existing chronic obstructive pulmonary disease.