That's the warning from Dearman, which says the problem is caused by the increase in temperature-controlled transport and the fact that diesel-powered units are unregulated.
The clean technology company says its research shows there are 84,000 transport refrigeration units on UK roads, emitting almost 50,000 tonnes of CO2, 163 tonnes of NOx and 22 tonnes of PM every year.
This "hidden polluter" continues to be ignored, says Dr Tim Fox (pictured), Dearman's international ambassador and fellow of the IMechE.
"Until now, nobody has given transport refrigeration units a thought. We all shop at food stores, eat in restaurants or have chilled food delivered, but the impact of transport refrigeration units has never been investigated, let alone addressed," he says.
"Although refrigerated vehicles make up a small proportion of the vehicles on the road, they are unregulated, use outdated fossil-fuelled technology and are disproportionately polluting. What's worse, that pollution is concentrated on city streets where it does the most damage to our health."
Bringing refrigeration units up to modern emissions standards, or making them zero emission, could have a significant impact, he adds.
Dearman is developing applications for its engine, a piston model that uses the rapid expansion of liquid air (or liquid nitrogen) to produce zero-emission power and cooling.
The most advanced is a zero-emission transport refrigeration system, which is currently undergoing on-vehicle trials. It will enter commercial trials later this year and will begin multi-country trials next year.