You can watch all four reports of our special Pollution Investigation here:
Peaks of pollution outside some city schools are seven times higher than others a Meridian investigation has shown.
We monitored air quality on the morning and afternoon school runs at 4 different schools in Southampton using specialist equipment from expert scientists.
Watch the next report by our Social Affairs Correspondent Christine Alsford:
Every morning seven year old Titas walks to school with his mum from his home in St Mary's.
While Iman, who lives in Shirley, takes the car with her Dad.
Their 2 journeys to St John's Primary School in Southampton take roughly the same amount of time - around 35 minutes. But we discovered the amount of air pollution they're experiencing can vary enormously.
Both agreed to wear testing equipment to measure the microscopic amounts of a tiny sooty particle called black carbon that they are breathing in.
Black carbon is emitted from diesel engines and burning fossil fuels.
5.24 black carbon has been linked to a number of health effects - especially on the lungs and the cardiovascular system.
With no legal limit or guideline for black carbon in place, scientists class any reading over 10,000 as a peak.
The school run for Titas means leaving home to cross busy roads. There are underpasses, roadworks and delivery lorries to contend with. Their route goes via a park and the city centre shopping area before arriving at school.
For Iman it's a drive through residential streets before taking the dual carriageway into town and wending through inner city streets to the gates in time for the bell.
But our snapshot results show the levels Iman recorded within the car are far greater with much higher and more frequent peaks - the average exposure for her was more than double that of Titas walking along the street.
His highest reading at the end of his journey when he arrived at the school gates at peak dropping off time.
Dr Matthew Loxham from University of Southampton tells us about soot:
Our volunteers were shocked and surprised at what we found.
Adam Goulden from The Environment Centre tells us a bit more about HOW commuting in a car is worse for your health: