SANTIAGO — Six-year-old Juan Covarrubias just paints what he sees. His watercolor skies are always a muddy, murky brown. He never chooses any shade of blue; after all, he is a budding realist, not a surrealist.

"When young kids paint the sky brown it means we have a serious problem with air pollution here in Santiago," said Juan's father, Jorge, a 39-year-old antiquarian based in the smog-smothered Chilean capital.

Santiago, which boasts awesome views of jagged snow-capped Andean peaks on days when wind or rain has dispersed the smog, competes with Mexico City and So Paulo for the ignominious title of Latin America's most polluted city.

Pollution stirs up such political controversy that reliable statistics are in short supply, unlike smog, so it is difficult to work out which city is more of a health hazard.

But in terms of population, Santiago has the most acute pollution problem. Only 5 million people live here vs. 18-20 million in Mexico City and its surrounding urban sprawl and 16 million in the metropolitan area of Brazil's So Paulo.

As Chile slips into the Southern Hemisphere winter, lines of coughing children and pensioners in hospitals grow longer. TV ads switch to flogging bronchial remedies and vitamin C, replacing beer spots aimed at slaking summer thirsts.

Santiago's pollution soars in winter as cooler temperatures press ozone — smog's main component — and suspended particles closer to the ground. Pollution makes residents' eyes sting and gives them a tongue-drying taste of dirt.

Making matters worse is Santiago's geographical location. Little wind reaches the city, which lies in a valley. With the Andes rising to the east and another range of coastal mountains to the west, the smog is, quite literally, trapped.

Due mainly to a cocktail of vehicle fumes and industry emissions that have mushroomed as Chile's economy has grown 7 percent per year in the past decade, Santiago has fought a long-standing but losing battle against smog.

Drugstores do a roaring trade in surgical face masks during the winter, and schools are banned from holding physical education classes when air quality levels slump.

Spanish tenor Placido Domingo called off a concert in a Santiago theater after just two arias in 1997. Some 1,500 fans were left with unthrown flowers as the opera star blamed bronchitis brought on by pollution for his inability to sing.

Ecologists say conditions are not improving despite annual drives to curtail smog. With industry gradually switching to cleaner-burning fuels such as natural gas, the finger of blame has turned to Santiago's 1 million cars and trucks.

Such is the desperation that cleanup ideas and inventions have begun to show eccentric streaks.

Last month the city unveiled a 15-foot high chimney connected to an air-sucking "washing machine" that filters smog in water and spews out clean air onto the downtown streets. But critics say the contraption is pure "hot air."

Bicycle lovers in Santiago have formed the "Furious Cyclists Movement" and stage monthly pedal pow wows, invading the streets of what they dub Santiasco — loosely translatable as Smogiago — to urge the government to build cycle paths.

President Ricardo Lagos, a socialist who took over the reins of this nation of 15 million people in March, faces a vote-losing option to rid the city of its No. 1 scourge: a wider ban on cars when pollution levels rise.

Bans are already in place on older gas guzzlers in the winter, restrictions that broaden under complicated formulas to affect more cars when pollution levels climb. Lagos is pondering extending the ban to cars with catalytic converters to promote more use of public transport, even though he faces a political backlash.

Meanwhile, when pollution levels hit critical levels last week, private cars were banned on six major roads, causing mayhem on side streets while leaving buses and taxis the run of the road on the city's six main boulevards.

"The idea was to increase a 30-minute car drive to 60 minutes and decrease a 40-minute bus journey to 20 minutes," said Gianni Lopez, head of the Santiago office of the government's National Environment Commission (Conama).

Lopez hailed the ban as a success as 25 percent of car owners did not use their vehicles that day. But experts say Lagos has an uphill struggle to convince car owners to flag down a bus or ride the subway, especially without first upgrading the image and the reality of public transport.

Santiago has a slick state-run underground system known as the metro, but there are only five lines, limiting its reach.

Some 10,000 private buses ply crisscross routes around the city, but constant dogfights to pick up passengers have handed the bus drivers a reputation as dangerous and reckless.

"Cars are a status symbol. Whatever the restrictions, people who can will still drive," said Rodrigo Garrido, professor in transport engineering at Chile's Catholic University. "The metro is an acceptable option, even top managers will ride the metro, but not buses," he added.

But subway expansion is costly — about $500 million per line, or 0.6 percent of Chile's annual gross domestic product — so Lagos is left with no option but clamping down on cars to improve the air, even if that includes cleaner-running cars with catalytic converters.

"It is not that cars with converters pollute, but that they kick up the pollution into the air," Garrido said. "The more movement on the roads, the worse the pollution becomes."

In coming years, restricting cars with converters might not be enough. Experts say Chile might have to charge for the use of public roads.

For the moment, experts say the government must concentrate on improving public transport policy, which is uncoordinated at best and contradictory at worst. One district of the capital is reducing the number of lanes on major roads to discourage car use, while a neighboring district is building parking lots.

Juan's thin brown line at the top of his paintings is a child's-eye perspective of the problem. His father, Jorge, worries more about his son's health. "It is not the clouding his mind but the choking his lungs — that's the real problem."