Pollution from traffic fumes can be as bad for people's happiness as bereavement or divorce, according to a study.
Academics at the University of York have said the effect of nitrogen dioxide (NO2) on life satisfaction is comparable to that of significant events in people's lives.
In a paper - titled Can clean air make you happy? Examining the effect of nitrogen dioxide (NO2) on life satisfaction - Sarah J Knight and Peter Howley write that "the welfare gains to society from reductions in exposure to NO2 can be substantive".
They wrote: "Our results suggest a significant and negative association between mean annual ambient NO2 and life satisfaction, and moreover that these effects are substantive and comparable to that of many 'big hitting' life events."
The paper says: "We find that NO2 is significantly related with subjective wellbeing, albeit much smaller in magnitude than previous estimates after controlling for a variety of important spatial controls.
"That being said, the effect size is substantive and comparable to that of many other widely studied determinants of subjective wellbeing.
"For example, our standardised coefficients suggest that the effect of NO2 on life satisfaction is equivalent to approximately half that of unemployment, and equivalent to that of marital separation and widowhood, factors commonly associated with some of the largest wellbeing reductions in the literature to date.
"Given that the effect of NO2 is, to some extent, experienced by everyone (ie not everyone is unemployed but everyone is subject to a certain level of NO2 exposure) this suggests that the welfare gains to society from reductions in exposure to NO2 can be substantive."
Concerns over the impact of diesel cars on NO2 levels were raised by the Volkswagen emissions scandal in September 2015.
And this week, MP Neil Parish, the chairman of an influential Commons committee, is expected to tell ministers that owners of old diesel cars should be able to scrap their vehicles for cash in pollution hotspots.
Following the Volkswagen emissions scandal in 2015, a Department for Transport investigation found that 37 top-selling diesel cars exceeded the legal limit required for laboratory pollution tests when driven for 90 minutes on normal roads.
Drivers were encouraged to switch away from petrol under Tony Blair's government and Prime Minister Theresa May has said that would be taken "into account" in future plans.
During a recent trip to the Middle East, Mrs May said: "In relation to the issue of diesel cars, obviously we will be producing a new air quality plan, we've been required to do that by the courts.
"Decisions will be taken when we produce that plan - obviously we will take final decisions as to what we do.
"But I'm very conscious of the fact that past governments have encouraged people to buy diesel cars and we need to take that into account when we're looking at what we do in the future."