Ecological disaster made most areas on Earth uninhabitable. Air quality is toxic without some kind of filtration. Most city centers have Carbon Macrofilters that purify the air within a certain radius, but their maintenance has been generally neglected by the governments that put them up due to regulatory capture by private interests decades ago. So the filters become sort of a core of the Sprawl communities, as volunteers pool resources to keep them running. It's not uncommon for neighborhoods to form public collectives (Filter Gangs) in order to organize that effort. And given the stakes in play, those collectives don't always play nice to keep the filters running.
(A note on aesthetics: Why so many neon street signs? It looks cool, but in a world of AR, they'd be unnecessarily expensive to maintain. In PL, street signage is at a minimum.)