Pollution pumped out into the air decades ago could still be causing deaths today, a study suggests.
More recent exposure to pollutants had a greater effect on health, the researchers from Imperial College found, prompting them to warn there is an "imperative" to act now on air pollution to deliver both swift and long term benefits.
The study used data from 368,000 people over a 38-year period, estimating black smoke and sulphur dioxide in the areas they lived in 1971, 1981, 1991 and, as a result of new ways of measuring pollution, microscopic particles known as PM10s in 2001.
For every increased level of black smoke and sulphur dioxide people were exposed to in 1971, produced mostly by burning fossil fuels, they had a 2% higher risk of dying in 2002 to 2009, the long-running study published in the journal Thorax showed.
For each increased level of PM10s people were exposed to in 2001, including particles from fossil fuels but also from the breaking up of road surfaces and tyres as vehicles drive along and brake, they had a 24% increase in risk of death in 2002 to 2009.
Although pollution levels have fallen dramatically across the country since the 1970s, those living in a polluted area in 2001 still had a 14% higher risk of death than those in the least polluted places - the same as in 1971.
This could be because the pollution people in the UK face is more toxic now than in the past, the researchers suggested.
While they said action should be taken to tackle air pollution, the study's authors also said the effects of poor air quality were small compared to other risk factors such as smoking and obesity.
A switch to diesel has been widely blamed for continued problems with air pollution in some towns and cities such as London.
But tackling PM10s, 50% of which come from road surfaces, tyres and braking, would also need a focus on lighter cars, report author Dr John Gulliver suggested.
The study was not able to calculate how many deaths today were down to historic air pollution, but lead author Dr Anna Hansell said Public Health England had warned pollutants caused some 29,000 early deaths a year.
"What this study is showing is that the effects of air pollution persist for a very long time, over 30 years in this particular study, and may actually be persisting longer than that.
"It's also shown that the more recent exposures appear to be the more harmful to health.
"In a way there's a good and a bad message, there's an imperative there that because the effects are so long-lasting, we really ought to act on it.
"The good news is that if most of the risk is related to recent exposure there's even more of an imperative to act because we'll have an important short term - in the next few years - benefit if we act now."