A resident is subjected to a medical test of carbon monoxide in his lungs at a stand placed by the Buenos Aires city's government on the Florida pedestrian walkway, in Buenos Aires, capital of Argentina, on May 31, 2013. The campaign was held under the framework of the World No Tobacco Day. (Xinhua/Martin Zabala)

Residents wait to be subjected to a medical test of carbon monoxide in their lungs at a stand placed by the Buenos Aires city's government on the Florida pedestrian walkway, in Buenos Aires, capital of Argentina, on May 31, 2013. The campaign was held under the framework of the World No Tobacco Day. (Xinhua/Martin Zabala)

A resident is subjected to a medical test of carbon monoxide in his lungs at a stand placed by the Buenos Aires city's government on the Florida pedestrian walkway, in Buenos Aires, capital of Argentina, on May 31, 2013. The campaign was held under the framework of the World No Tobacco Day. (Xinhua/Martin Zabala)

An employee checks the carbon monoxide level at a stand placed by the Buenos Aires city's government on the Florida pedestrian walkway, in Buenos Aires, capital of Argentina, on May 31, 2013. The campaign was held under the framework of the World No Tobacco Day. (Xinhua/Martin Zabala)

Students participate in a march to mark the World No Tobacco Day, in Tegucigalpa, capital of Honduras, May 31, 2013. (Xinhua/Rafael Ochoa)

Students participate in a march to mark the World No Tobacco Day, in Tegucigalpa, capital of Honduras, May 31, 2013. (Xinhua/Rafael Ochoa)

Students participate in a march to mark the World No Tobacco Day, in Tegucigalpa, capital of Honduras, May 31, 2013. (Xinhua/Rafael Ochoa)