Further complicating is the fact that there is also overlap in health effects between PM2.5 and N02. It is not clear to what extent health effects are different when people are exposed to a combination or cocktail of different pollutants. In real life, exposure to such a cocktail is the most likely situation. Important to note is that there is no doubt that PM2.5 has significant negative impacts on health and should be kept as a representative tracer of such effects.