Mexico City has one of the world’ s most serious air pollution problems.
The city is located atop a high plain at an altitude of 2200 meters, and is
surrounded on three sides by mountains and snow-capped volcanoes. Since incident
solar radiation does not vary significantly with season at tropical latitudes,
photochemical smog is produced much of the year. In winter, air quality can
worsen significantly when thermal inversions keep polluted air masses close to
Atmospheric particulates (aerosols) are readily visible at oblique view
angles, and differences in aerosol amount on two days are indicated by these
images of central Mexico from the Multi-angle Imaging SpectroRadiometer (MISR).
The images at left and center are natural color views acquired by MISR’ s
70-degree forward-viewing camera on April 9 and December 5, 2001, respectively.
Mexico City can be identified in the center panel by the large area of haze
accumulation above image center. Two small brighter patches within the hazy area
indicate low fog. In the left-hand panel, the city basin appears significantly
clearer, but some haze remains apparent across the Sierra Madre mountains in the
lower portion of the images. On the right is an elevation field corresponding to
the December 5 view. Automated MISR stereoscopic retrievals reveal the clouds at
lower right to be at very high altitudes, in contrast to the low-lying haze and
fog near Mexico City. When the stereo retrieval determines that a location is
not covered by clouds, digital terrain elevation data are displayed instead.
High clouds appear as the orange and red areas, and mountainous areas appear
light blue and green. The position of the clouds within the 70-degree image are
slightly southward of their location in the elevation map as a consequence of
Major sources of air pollutants within the basin enclosing the Mexico City
urban area include exhaust from 3.5 million vehicles, thousands of industries,
and mineral dust. The ancient lakebed valley in which Mexico City is situated
became a major source of dust when it was drained in the 16th century. The city
basin stretches approximately 70 kilometers wide; it is reported that the local
air quality causes the surrounding mountains to be rarely visible from the urban
The Multi-angle Imaging SpectroRadiometer views almost the entire Earth every
9 days. These images cover an area of 330 kilometers x 464 kilometers.