Summary of Air Pollution Impacts on Forests in the Mexico City Air Basin

Abstract

Oxidant air pollution symptoms were first reported in bioindicator plants in the Mexico City Air Basin (MCAB) in 1971 (de Bauer 1972). Classic injury symptoms on well-known bioindicator plants strongly supported the presumption that symptoms were caused by photochemical oxidants, of which ozone (O3) is the primary pollutant. Symptoms in indicator plants characteristic of injury caused by peroxyacetyl nitrate (PAN), ethylene, and sulfur dioxide (SO2) were also reported (de Bauer 1972; de Bauer and Hernández-Tejeda 1986). These discoveries were followed in 1976 by the observation of O3 injury symptoms in native pine species in forests in Ajusco (AJ), just south of Mexico City (de Bauer and Hernández-Tejeda 1986; Krupa and de Bauer 1976). Then in the 1980s, a dramatic and severe decline occurred in sacred fir (Abies religiosa) stands in the highly polluted area of the Desierto de los Leones (DL) National Park southwest of Mexico City (Alvarado-Rosales and Hernández-Tejeda 2002). Thousands of trees died, leaving dead zones called cemeteries. Air pollution was widely believed to be an important causal factor in the widespread mortality of sacred fir within the park (Ciesla and Macias-Samano 1987). Topographic conditions, including volcanic mountain ranges circumscribing much of the Basin, thermal atmospheric inversions, and prevailing winds which carry pollutants from the urban zone to forested areas to the south-southwest (SSW), create conditions favoring high pollution exposure for these forests (Bravo and Torres 2002; Jáuregui 2002). BT - Urban air pollution and forests