The gauges are used to monitor water and pollutant levels.

WSJ: Susquehanna River commission wants gauge funding

The researchers Katherine Ensor and Loren Raun cross referenced the time and place of the cases against air pollutant levels recorded by the extensive network of air monitors throughout the Houston area.

FORBES: Researchers Prove Air Pollution Causes Heart Attacks

Two Surrey councils have said they will be working together to improve air quality as readings showed levels of a pollutant above government targets.

BBC: Air pollutants in Woking above government target levels

In Edinburgh, 18 out of 38 air quality monitoring sites breached acceptable levels of the pollutant, while Aberdeen Council expressed concern over meeting the target near busy roads, the charity said.

BBC: Valley 'most polluted area'

The main pollutant, sulphur dioxide, was linked to coal burning which was said to have reached exceptional levels.

BBC: News, London