The calls to the city of Houston's 311 help line came in the early morning and the middle of the night - complaints of red smoke, yellow smoke, explosions, fire, a child having trouble breathing.

Reports like these--189 of them over the last five years--led Houston air authorities to discover a previously unrecognized and dangerous source of air pollution: metal recyclers and car crushers, according to interviews and documents obtained by the Houston Chronicle.

The smoke comes from cutting metal with torches and from fire when vehicle gas tanks aren't drained properly. Explosions can occur when propane tanks are fed into the maw of the crushers.

Descriptions of shattering noise, cracked walls and smoke were significant enough that the city had to "dedicate a good amount of effort responding to these complaints," said Arturo Blanco, chief of the city's Bureau of Pollution Control and Prevention.

Subsequent testing outside five Houston metal recycling operations found dangerous levels of hexavalent chromium. Chrome VI, as it's also called, is a high priority for air experts.

"People were complaining about smoke, and it turns out there were carcinogenic metals," said Loren Roan, an environmental statistician at Rice University. "And we found them only around these facilities, not in other areas we tested, not even in other industrial areas of the city."

At the Department of Chemistry atmospheric chemist Matthew Johnson invented and patented the air cleaning method which is based on the natural ability of the Earth atmosphere to clean itself. In a process triggered by sunlight, polluting gasses rising into the sky start forming particles when they come across naturally occurring compounds such as ozone.

The newly formed particles are washed out of the atmosphere by rain. Once the rain hits the ground, the atmosphere is clean again. In other words the whole process is nature's own purifications works, explains Professor Johnson.  

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Until she read a newspaper article about pesticide use on school grounds, Marla Zando of Scarborough was unaware that chemicals used on playgrounds or ballfields could hurt children.

"I really, really never had thought about it," she said. "And I sort of think of myself as being environmentally aware," but "wow, it was really eye-opening. I really was clueless, very, very clueless.

"Kids love to play in the dirt," said Zando, the mother of a 4-year-old son. "You don't know when (pesticides) are there; you can't see them. I find it very scary."

Zando began asking questions of physicians, members of the town council, even bird watchers-- people she knew would be knowledgeable about the subject--to find out about synthetic pesticides and their potential health effects.