The number of passengers traveling through Rhode Island’s main airport fell about 6 percent last year. Statistics released Tuesday show that more than 3.6 million passengers traveled through T.F. Green Airport in 2012. More than 3.8 million used it the year before. The airport had about 289,000 passengers in December, roughly the same as in 2011. The airport in Warwick has seen fewer passengers overall since the economic downturn began in 2008. More than 5 million people used the airport in 2007. People who make round trips are counted twice.