The number of passengers using Des Moines International Airport grew 0.1 percent in May. Airport officials are hoping to keep an annual growth rate of more than 3 percent to set the stage for the construction of a new terminal building over the next decade or so. The rolling 12-month total was up 3.8 percent, to 2,333,171 from 2,246,981. The May passenger count was 210,890, up from 210,575 a year ago.