You can watch all four reports of our special Pollution Investigation here:
Peak pollution levels outside some of our city schools are more than 7 times higher than others. That's the finding of our special ITV Meridian investigation.
We measured air quality at infant and primary schools and found big variations in the levels of a sooty black material associated with asthma and heart problems.
In the second of her special reports our social affairs correspondent Christine Alsford looks at what our children are breathing in on the busy school run:
Southampton is regularly included in lists of the most polluted cities in the UK by the World Health Organisation.
And that's why we chose to base our investigation there into air quality at the school gates .
Using specialist monitoring equipment provided by scientists at Queen Mary University in London we measured the level of tiny microscopic particles called Black Carbon which can be harmful to human health when breathed in.
We monitored the air quality outside four schools in Southampton- one right by the docks, one close to a railway, another on the outskirts of city and the last on a busy road where several schools are sited within a few hundred yards.
The 2 schools we measured at afternoon pickup time recorded levels of black carbon that were relatively low and constant.
But one of the schools at morning drop off recorded much higher results - Sholing Juniors had 12 so-called peak exposures.
One - recorded at the time a diesel car was idling very close by - was more than seven times that recorded in the streets outside other schools.
We took our findings to experts at the council. We spoke to Steve Guppy- Scientific Officer at Southampton City Council:
Sholing is one of the most active schools in the city in encouraging pupils to walk and scoot to school.
Leading scientists in the field say more research is very much needed.
We spoke to Professor Jonathan Grigg at Queen Mary University:
Our results just a snapshot and could well have been impacted by differing weather conditions and other factors.
But our findings do give some clues to the huge challenges we face in places where improving air quality still has a long way to go.