Guatemala City is notoriously polluted by old, recycled U.S. school buses, the basis of its public transportation network, which belch out diesel fumes in the form of black clouds. A promising recent development is a revamping of the city’s public transportation system to include newer vehicles and stop older buses from circulating in the city center. In addition to auto exhaust, pollution from industrial facilities and burning garbage from the city dump combine to form a thick haze often hanging over the city.

The worst days occur when thermal inversions cause the haze to hang in a low-altitude pollution gulag, much like a pineapple-upside-down cake. Concentrations of particulates, ozone, and nitrogen dioxide often exceed World Health Organization safety standards, particularly on these days. During the rainy season, the haze is washed away by the afternoon rains, after which the atmosphere is amazingly free of pollutants.

Elsewhere, smoke and ash from occasional volcanic eruptions can make the atmosphere somewhat hazy, though the worst pollution comes from dry-season agricultural burning and forest fires. When one considers that more than half of all energy consumption comes from burning firewood, the reasons behind the thick haze hanging over much of the country during March and April begin to emerge.