Air pollution in Beijing reached its highest level on Tuesday as a sandstorm from the north shrouded the capital in dust, choking pedestrians and delaying flights, the government and reports said. Air pollution measured between levels four and five at monitoring stations throughout the capital, according to the Beijing Environmental Protection Bureau's website. Level five represents the worst air quality under the bureau's monitoring system and automatically triggers warnings for people to stay indoors and refrain from outdoor activities. "Preparations must be made to guard against the sandstorms, close doors and windows, wear face masks and carry tissue to avoid...