Nitrogen dioxide, which has been linked to increases in breathing problems and heart disease, has doubled in parts of the county.
The dangerous levels, which have peaked way above the Government guidelines, have been blamed on the hot, still air which has sat across the UK for the past few weeks.
The heatwave took its toll yesterday when a girl collapsed in the Peace Gardens in Sheffield city centre as the temperatures soared and had to receive medical help before being taken to hospital by ambulance.
Care4Air, the South Yorkshire air quality campaign group, confirmed nitrogen dioxide levels are "higher than usual" and urged people with conditions such as asthma or lung or heart disease who develop problems to contact their GP.
Nitrogen dioxide levels in the east end of Sheffield have averaged 50 micrograms per cubic metre during the past few weeks - above the Government's daily average target of 40 micrograms.
And during the hottest days levels have even peaked briefly at above 100 micrograms.
Neil Parry, of the East End Quality of Life Initiative project, said: "Levels of nitrogen dioxide are certainly higher this year than last year because of the hot still air.
"It is worrying because hot weather like this is predicted to become more common and this could lead to consistently high pollution levels in places such as Tinsley. The asthma rate for Tinsley is double the city average and so higher pollution could have a serious impact on people with health problems."
Levels in parts of Rotherham have also peaked at way above the national target, with a pollution station in Bradgate recording 70 micrograms of nitrogen per cubic metre yesterday.
Rotherham town centre recorded a peak of 60 micrograms per cubic metre at the same time, although levels generally were thought to be around Government targets.
Care4Air, the South Yorkshire air quality campaign, is encouraging people to take steps to reduce congestion in the coming weeks, after hot weather conditions caused air pollution levels to rise.
PA Weather Centre spokesman Rob Hutchinson said South Yorkshire would be sunny again today but cooler later with rain predicted tonight. Temperatures are due to fall next week.
Last winter abnormally low temperatures, coupled with still air, pushed levels of nitrogen dioxide to almost 245 micrograms per cubic metre
Mr Parry said: "Although levels are high at the moment they are nothing compared to what happened last winter."