URGENT solutions are needed to Oxford's congestion problems before the Westgate opens, it has been warned, as it is revealed the city's air quality has deteriorated for the first time in five years.

More than 2,000 extra daily journeys are expected once the £440m centre opens in October and both Oxford Bus Company and city council environment leaders have called for an end to 'bus jams' increasing emissions and polluting Oxford.

Options for how to implement a zero emissions zone could be published later this year but a rise in nitrogen dioxide levels in 2016 has led to more urgent calls for Oxfordshire County Council to come up with a plan.

The average nitrogen dioxide concentration in High Street and St Aldate's rose last year, having fallen year-on-year since 2011.

Bus companies had warned the temporary closure of Queen Street would increase congestion and therefore emissions.

Managing director of Oxford Bus Company, Phil Southall, said the data proved their concerns and it would only get worse come October unless the county council found a solution.

He said: "One of the many concerns we raised with the County Council before the temporary closure of Queen St is that it will simply move congestion and pollution to other areas.

"The additional mileage that our vehicles have to cover whilst Queen St is unavailable for use means that overall it will result in more emissions and longer journey times.

"This new air quality data appears to support our concerns and we would urge the County Council to consider this in advance of the opening of the new Westgate centre when we expect passenger and vehicle movement numbers to increase dramatically."

Oxford City Council approved the Westgate plans in 2014 along with assessments on how it would impact on air quality - it found it would be 'unlikely' to increase pollution but the county council is the transport authority.

Nitrogen dioxide levels had fallen from 58 ug/m3 (micrograms per cubic metre of air) to 44 ug/m3 in High Street from 2011 to 2015 but jumped back up to 47 ug/m3 last year.

The same pattern occurred at the other city centre monitoring station in St Aldate's.

The county council said its officers were working an experimental traffic regulation order that would pedestrianise Queen Street and address the concerns surrounding its impact.

It also said it was working on a 'parking guidance system' to ensure drivers know when city centre car parks are full and use the Park and Ride instead.

But Oxford City Council's board member for a clean and green Oxford, John Tanner, said he wanted to see more and urgently.

He said: "We have got to the stage where there are so many buses we are getting bus jams in the city centre.

"We need more bus priority and a better system through the city - the only way the Westgate won't increase pollution is if most people travel to it by bus or bike.

"Drivers won't ditch their cars unless the bus will get them into the city quickly.

He added: "I have yet to see anything from the county council and it has now become urgent."

Air quality consultant Chris Dore it was 'disappointing' pollution was worsening when Oxford's bus fleet was one of the cleanest in the country.

He said: "I'm sympathetic to the city council, they made some difficult decisions - such as moving parking out of the centre - but decisions were made for the right reasons.

"With the Westgate centre due to open there will be a lot more challenges ahead to control air pollution and more certainly needs to be done."

County council spokesman Martin Crabtree said: "We recognise that the bus network in Oxford is vital to the life of the city and its future growth.

"For example, over 60% of the new staff and visitors to the Westgate centre will be arriving by bus.

"Without a good bus and Park & Ride network the development wouldn’t be happening at all."

He added: "The intention is for the experimental traffic order to be in place in time for the Westgate Centre opening."