Variaciones de largo periodo de la visibilidad en la ciudad de México

Abstract

Visibility data for a 43 year period is used to determine changes in the transparency of air in Mexico City. On the average a general decrease in visibility is observed. During the 1940's average visibilities (at noon) were from 4 to 10 km decreasing steadily to 1 to 2 km up to the fust half of the seventies. However, the fJve year average variation of visibility for the second half of the seventies shows a marked increase. When fJve year average frequency of various visibility categories was determined, a signfficant decrease in the frequency of low (bad) visibilities during the 197 5-79 period was observed. Also, an increase in the frequency of intermedia te (1 to 10 km) visibilities was noted for the above mentioned period. The observed changes in visibility toward a better air quality, could be related to actions taken by sanitation authorities in reducing pollution.