Thick smog is blanketing New Delhi after Diwali celebrations with fireworks sent air pollution levels soaring. Revelers burst firecrackers late into Monday night, filling the air with smoke and fine particles. By Tuesday morning, air quality in several neighborhoods ranked as severe. Last week, India's top court eased a ban on firecrackers, allowing limited use of "green firecrackers" that emit fewer pollutants. Pollution spikes due to firecrackers are common after Diwali, which coincides with cooler weather and crop residue fires. New Delhi and its metropolitan region — home to more than 30 million people — routinely ranks among the world's most polluted cities during winter.