The 'CO2 Scraper' by Nectar Product Development is a carbon-positive building that will actually purify the surrounding air cleaner. It's meant for high-pollution areas like factories, but I could see several of these in global metropolitan areas noted for their pollution like Los Angeles and Beijing.
The 'CO2 Scraper' is a giant skyscraper that is essentially a vertical forest. It can hold 200-400 large trees, which naturally absorb carbon dioxide and convert it into oxygen. A windmill-powered irrigation system fertilizes and waters the trees; the only outside electricity Nectar Product Development says the 'CO2 Scraper' needs is for an elevator so that maintenance workers can ascend the tower.