U.S. stocks fell sharply Tuesday, turning negative for the year. The Dow Jones industrial average fell 551.80, or 2.2 percent, to 24,465.64. The broader Standard & Poor's 500 index fell 48.84, or 1.8 percent, to 2,641.89. The technology-heavy Nasdaq composite index fell 119.65, or 1.7 percent, to 6,908.82.