I've got F'all qualifications, but I can read and remember which means I also know Ozone (O3) levels can trap heat[1], and heat is Infra-Red (IR), a large part of the electromagnetic light spectrum [2] and ozone happens to be considerably higher in built up in areas[3], also contributing to the Heat Island Effect seen in towns and cities.

So whilst I cant find a copy of the study, and I recognise your comment on the modelling and approach being simplistic, the above also demonstrates that other factors like increased number of vehicles on the road, can be a factor as they contribute to ground level ozone and many also come with an air conditioning unit built into the car as standard today.

[1] https://uk-air.defra.gov.uk/research/ozone-uv/moreinfo?view=...

[2] https://en.wikipedia.org/wiki/Light#/media/File:EM_spectrum....

[3] https://www.gov.uk/government/statistics/air-quality-statist....