Korea is expected to become the world's fourth largest mobile ad market this year.

According to a report by U.S.-based researcher eMarketer, Korea's estimated spending on mobile advertisements this year is US$450 million (US$1=W1,129), up 40 percent from a year before.

The U.S. will top the list by spending $2.4 billion, almost double the amount of 2011, to overtake last year's leader Japan. Total spending worldwide is estimated at around $6.4 billion, over 60 percent more than last year, thanks to the rapid adoption of smartphones and mobile Internet use. Despite the huge gains, however, mobile ads will only represent 1 percent of total ad spending worldwide this year.