STORY: The Taj Mahal was obscured as a toxic mix of smoke and fog shrouded the Indian capital.Smog caused a sharp drop in visibility in Delhi this week, causing a raft of delays at the city's airport.More patients flocked to hospitals, particularly children. One pediatrician told a new agency he'd seen a spike in asthma attacks.:: What caused the smog?Officials blamed high pollution, combined with humidity, low wind speed, and a slight drop in temperature.Daily air quality in the region crossed into the 'severe' category for the first time this season.Air-quality monitoring group IQAir ranked New Delhi the second-most polluted major city on Thursday, behind Lahore, in neighboring Pakistan.:: How far has it spread?Dense smog has engulfed other parts of northern India, such as the states of Punjab and Uttar Pradesh, where visibility fell to zero in some areas on Thursday.Neighboring Pakistan's Punjab province, which shares a border with India, also faces similar conditions.Doctors in Lahore said many children were…