Naturation of Mexico City: cost benefit analysis of an air quality improvement proposal

The naturation project consist in adapting plants (crasulaceae) to roofs and other concrete surfaces in order to reduce, among others, particulate matter levels in air. Particulate matter of less than 10 microns can cause severe respiratory disease and minor symptoms. In this work we assess the impact of particles in public health, relating that impact to costs of hospitalization and reduction of productivity in the Mexico City Metropolitan Area (MCMA), based on works for another countries, while better data are obtained. On the other hand, an estimation of the effect in reducing particles by the naturation project is made in order to assess the savings in costs due to public health damage, regarding them as benefits. The particle's mean level concentrations would decrease 15 percent. A cost analysis is performed in order to estimate a costhenefit ratio through different periods of time, using three different scenarios. With US $ 621 million of benefits per year, we obtained the recovery of the investment, measured in social terms, in a 25-year period. The time of recovery could be reduced if cheaper, but high quality material could be developed for the project. Additional risk analysis showed that a 30 year period is a good horizon when random cash flows between optimistic and pessimistic scenarios are considered. When compared to reforesting, this project results very expensive to cany out. Reforesting, for the case of optimal planning, is recommended, as naturation can be a complementary program for a far future.