The plants I'm a cure-all against it smog, but it should not be forgotten that they too suffer from polluted air. In choosing the plants from the garden, especially in the city, therefore, the aspect of their resistance to harmful substances contained in the air at the risk of smog and in acid rain.
Between plants large and fast growing resistant to smog there are for example: the tulip tree (liriodendron tulipifera) with its beautiful blue flowers; many varieties of magnolia, resistant even to cold; ginco biloba (ginkgo biloba) of which, however, it is advisable not to crush the fruits because they are malodorous; some American oaks such as holm oak (quercus ilex) or real American oak (quercus rubra); and locust trees which are so resistant as to become infesting at times.
If you are looking for resistant shrubs instead smog you can focus on osmanthus with a very intense scent, mahonia and privets. Between plants shrub suitable to form resistant hedges smog there are the pyracanthas and the crataegus, some varieties of philadalpus and the very common lauro ceraso.
Between plants resistant to smog there are also little known botanical species, some with many advantages that make them particularly suitable for a garden in the city: they are rustic (ie resistant and easy to cultivate), resistant to parasites, decorative and floriferous. If they are not very widespread, it is only because of the product uniformity that simplifies the work of nurserymen, which however risks extinguishing them by removing them from the attention of the market.
The plants resistant to smog little known are numerous, have particular characteristics and it would be simplistic to list them here. The advice we give is to go to a nursery where you work with passion, there are many, and consult detailed catalogs. The search for plants details should not necessarily be oriented towards exotic essences, just look closely at the local varieties of which Italy is very rich. You will find pleasant surprises and perhaps the opportunity to start a new form of collecting.