Campaigners fighting to overturn a road closure in Hounslow claim it has caused a major spike in pollution in surrounding streets.
They say NO2 levels in parts of Twickenham Road, Isleworth , are up to 77.72 micrograms per cubic metre (μg/m3) - nearly twice the legal limit - following the closure of nearby Church Street.
But supporters of the decision to close Church Street have questioned the accuracy of the latest readings.
They also insist the closure will in time help reduce the number of cars on local roads, leading to a fall in overall pollution.
Opponents say it has led to a huge increase in traffic along Twickenham Road, where they have installed their own monitors to record the effect on air pollution.
The initial readings for the period January 3-31 this year, show NO2 levels ranging from 39.21μg/m3 to 77.72μg/m3.
These figures do not include the junction at Busch Corner, where supporters of the closure say traffic is not affected by Church Street being shut.
'Our children's health is being put at risk'
Tamsin Turner, who is campaigning for Church Street to be reopened, said: "Just 10 weeks since the closure of Church Street next to the River Thames, pollution levels in Isleworth have spiked above legal limits.
"The health of our children is being put at risk. Community cohesion lies in tatters. And council leaders refuse to engage with the mounting evidence being presented to them.
"The local community and numerous small businesses are suffering deeply. We are not lab rats. This unconscionable traffic experiment has to stop now."
The monitors were funded by the campaigners and analysed by Gradko, which they say is the same company used by Hounslow Council.
The council's own figures show NO2 levels in Twickenham Road, at the junction with South Street, have been hovering around the 40μg/m3 over the past four years but rose sharply to 74.9μg/m3 at Busch Corner, where Twickenham Road meets London Road, in 2014.
In Church Street itself, NO2 levels were recorded at 35.3μg/m3 in 2014, prior to its closure.
'Re-opening street will make things worse'
Supporters of the closure say this is particularly high for a narrow residential road, which shows how much traffic it accommodated.
They have questioned the accuracy of the latest readings and say campaigners are missing the point anyway, which is that the closure will reduce the total number of cars on the borough's streets.
Chris Sainty, who has lived in Church Street for more than 21 years, said research had shown a direct correlation between the number of roads and the amount of traffic in an area.
"Re-opening Church street will not cure congestion or pollution, but keeping it closed will help this borough to reduce its potential capacity for through traffic and in doing so reduce pollution across Hounslow," he said.
"There is the proposition that opening Church Street will cure congestion and pollution – it won't, it'll actually make things worse."
A council spokesperson said: "All guidance and best practice says that the potential impact of a traffic management scheme on air quality needs to be monitored for a minimum of six months or preferably over a full calendar year; to take into consideration seasonal variations.
"Results of just one reading will not offer much insight. The relevant data is published on our website and will be reported to the Isleworth and Brentford area forum as part of the interim report on the trial closure in September and again in spring 2017 prior to any final decisions being taken."