RADON LEVELS SURVEY IN THE UNDERGROUND TRANSPORT METRO SYSTEM IN MEXICO-CITY

The Metro underground transport system moves more than 8 million peopl e daily across Mexico city. The Metro is the most popular mass transpo rt system. The average time a traveller remains inside the underground stations and tunnels is more than two hours. The airborne radon level s were measured, during the three months of summer, at 20 different st ations, including the more deeply located halls. Stations were in diff erent zones of the city. The radon concentration in underground corrid ors and stations varied from 60 Bq.m(-3) to 350 Bq.m(-3). The environm ental factors, such as outside temperature, humidity, and days of rain were compiled in order to understand radon entry and transport better . Travellers inside the Metro system are, of course, exposed to airbor ne contaminants from several other sources.