Intense smog shrouded the metropolitan area of Iran’s capital, Tehran, on Monday in what local health authorities called the worst air pollution in months. They warned all residents of the area — roughly 14 million people — to stay indoors if possible because of the poor air quality. The semiofficial Tasnim News Agency said air contaminants were seven times the maximum level recommended by the World Health Organization. Air pollution is a chronic issue in Tehran, which is surrounded by mountains that trap atmospheric pollutants. Exhaust fumes from vehicles account for most of the problem, which typically worsens in colder weather.