Total emissions from motor vehicles fell 12% from 2012 to 2016, according to the Office for National Statistics.
However, the UK remains in breach of European limits for nitrogen oxides (NOx) in 16 cities.
Nonetheless, environmentalists have welcomed the overall drop in pollutants from cars and lorries. The reduction is thought to have been propelled by tightening restrictions.
The one emission going in the wrong direction is ammonia from farming.
Jon Bennett from the green group ClientEarth told BBC News: “We very much welcome the reduction in emissions.
"But the concentrations of NO₂ (nitrogen dioxide) in towns and cities are at illegal and harmful levels.
“So government policy needs to focus on bringing these down with clean air zones, diesel-scrappage and other initiatives.”
The news is contained in the ONS annual national emissions data (PDF). This records a decades-long general trend downwards in all pollutants in the UK – except for ammonia.
Emissions from ammonia – mostly from farming – actually increased over the year from 2015.
The gas is produced by activities like muck-spreading from dairy farms, and causes a problem in cities as well as the countryside.
When ammonia blows into urban areas it can react to form harmful particles that get breathed deep into the lungs.
Air pollution is estimated to contribute to shortening the lives of 40,000 people a year in the UK. It undermines the health of people with heart or lung problems.
The UK has been given a final warning from Brussels about its failure to bring down NOx levels in cities to acceptable levels.
The UK's overall national emissions of NOx are within legal limits, and many parts of the UK enjoy reasonable air quality.
But the roadside concentrations of NOx in many local sites – especially near to busy roads – are regularly in breach of EU limits.
The government has registered significant progress, though, in reductions of another gas, SO₂. The report says SO₂ emissions decreased by 29% from 2015 to 2016, dropping to a new low.
This is mainly thanks to the steady closure of coal-fired power stations.
NOx emissions from the energy industries also fell by 45% between 2012 and 2016. That was the greatest change for any emissions source group.