Ozone concentrations in situ in the Mexico City basin forests and influence of elevation

Abstract

The presence of photochemical pollutants in the Mexican Basin is a reality and the damage they cause to human health and vegetation is evident. Lack of data on ozone concentrations in the forests of the Mexico City Basin was the main reason to carry out this survey in three forested areas: El Ajusco (AJU), Desierto de los Leones (DDL) and Izta-Popocatépetl (IZP). CanOxy PlateTM monitors were used and exposed for three-weekly periods during 14 months (November 10th, 2004 to January 20th, 2006), in nine monitoring plots. The ozone concentrations recorded in the three forested areas were between 15.41 and 53.8 ppb. Two peaks with higher ozone concentration were identified, one in August and second one in November, 2005. The average ozone concentration for each area was 32.87 ppb for AJU, 28.34 for DDL and 28.60 ppb for IZP. The DDL and IZP ozone concentrations recorded were lower, in spite of the proximity to the emission source in the case of the first area; the reason was due to two of the monitoring plots were located leeward, it means, they were not exposed to the polluted air masses from Mexico City. For IZP, ozone concentrations were similar to the ones from the DDL, highlighting winds direction. Ozone concentrations were higher in the way that altitude increased. Exposure to the polluted air masses, wind and altitude roles were tested.