REGARDING air pollution in Winchester, Andrew Beadle (Letters, January 5) sensibly says that “everyone wants the minimum possible pollution with a vibrant city centre”. 

Unfortunately, emissions from internal combustion engines, as are found in cars and buses, come at a cost. 

They all emit the greenhouse gas carbon dioxide, without doubt a major cause of climate change, and poisonous carbon monoxide.

Petrol engines also emit nitrogen oxide gases including nitrogen dioxide (NO2) which aggravates heart and lung disease.

Diesel engines likewise emit NO2 (but at least 4.5 times as much) and tiny soot particles which can get dangerously deep inside lungs and even enter the blood stream.

Although diesel engines are more efficient than petrol engines in terms of miles per gallon, and hence are better for climate change and the pocket over long journeys, their more harmful impact on human health means that most diesel vehicles should be discouraged from entering densely populated cities.

It’s wrong to blame buses for most of Winchester’s pollution. A report written for the city council in February 2016 calculated that cars and other vehicles deliver about four times more pollution in the form of NO2 in central Winchester than buses.

New Euro 6 buses are less polluting largely because of EU directives that drive higher standards. Older diesel cars are worse.

Clearly Winchester needs to ensure that fewer and smaller cars enter the city centre so that it becomes a healthier place for all.

Walking and cycling, which are cheap to enable and encourage, and are non-polluting, must be a major part of the solution as well as more frequent buses.

Bob Whitmarsh

Winchester.