MEXICO CITY (Reuters) -- Mexico City's air is among the worst in the
                  world but the Mexican government said Wednesday it had made progress in
                  cleaning it up.

                  Mexico City Secretary of Environment Alejandro Encinas Rodriguez said
                  that in the past three years the city has reduced average ozone levels from
                  189 points to 145 points on the overall air quality index, known as the
                  Imeca.

                  While Mexico City has declared environmental emergencies in recent years
                  when the Imeca reached 250 points, many urban areas use 100 as a
                  threshold indicating pollution is at dangerous levels.

                  Mexico spent at least $5 billion during the 1990s in a bid to clean up the air
                  in its capital. Measures have included producing cleaner gasoline, barring
                  most car owners from driving one day a week, shuttering a Mexico City
                  refinery, planting new trees and replacing diesel buses.

                  Mexico City and the surrounding metropolitan area -- one of the largest
                  population centers in the world with more than 20 million people and 3.5
                  million vehicles -- has long been notorious for its toxic air.

                  Last year, the World Resources Institute, funded by the World Health
                  Organization, named the city as the most dangerous in the world for children
                  in terms of air pollution.

                  Despite progress, the Mexico City metropolitan area still has work to do
                  before it resolves its pollution problem, Encinas said.

                  "Obviously the problem isn't resolved. We have an enormous challenge
                  ahead because we want every day to be within the norms of air quality,"
                  Encinas told reporters at an environmental conference.

                  At the conference, Sherwood Rowland, a Nobel Prize winning chemist, said
                  data showed the capital's air was indeed getting better.

                  "This does indicate there has been progress in Mexico City," he said.

                  The World Resources Institute study, released in March 1999, showed that
                  Mexico City ranked worst for three pollutants: sulfur dioxide, nitrogen
                  dioxide and total suspended particulates (TSPs).

                     Copyright 2000 Reuters.