York research: pollution reduced LESS in latest lockdown compared to first
Experts think it's because of central heating being used more.
The latest lockdown did not have as big an impact on air pollution levels as the first lockdown in 2020, according to new York University research.
Across the UK, nitrogen dioxide decreased by 52% on average during the first lockdown, compared to 28% during the winter months of 2021.
The greatest difference between lockdowns was recorded in Leeds and London.
Researchers say the disparity was probably partly caused by those commuting to work starting their cars in colder conditions.
Dr Will Drysdale, from the department of Chemistry, said: "If you start your car up in the summer, everything's much warmer and it can get up to temperature much quicker, which means a lot of the pollution control technologies in there also work more efficiently.
"If you're just doing your commute in the winter, often your car doesn't really get up to that temperature and it'll be more polluting for the same journey."
Another cause was more people using central heating at homes, with more nitrogen dioxide recorded near homes than on roads.
Dr Drysdale added: "Within the same city we've been able to look at two different types of monitoring station. Some of them are by the roadside, whereas some of them are more likely residential areas.
"As you'd expect, you see those greater reductions by the roadside, more at home you don't see that as strongly there.
Large cities record bigger change
The greatest change between lockdowns was recorded in large cities, like Leeds and London.
During the first period of restrictions, nitrogen dioxide fell by 59% during the Spring 2020 restrictions.
In winter 2021, Leeds recorded a 25% decrease, and London 30%.
Masters student Rhianna Evans said: "We think they've been occurring due to changes in traffic, people have been working from home, and I think a lot of public transport systems as well have been quite reduced.
"As expected, these larger urban areas had larger drops because they have a greater working population which are staying at home.