Just read this article about Mexico City and one effort to reduce air pollution there. http://www.banderasnews.com/1304/nb-mexicocityhospitaleatssmog.htm A local hospital installed an ‘air-pollution-eating’ wall that’s supposed to break down the worst of the pollution into less toxic particles. That always makes one pause… but hey, it might work. Seems like vertical gardens on all the buildings would be helpful, too.