The Congress on Monday targeted Prime Minister Narendra Modi over the alarming pollution levels in Delhi, saying that the city was facing "pollution emergency" and he kept silent on the issue.Speaking to the media here, Congress spokesperson Abhishek Manu Singhvi also targeted Delhi Chief Minister Arvind Kejriwal on the issue, saying there was a mutual blame game in which people in the national capital were suffering.Targeting Modi, Singhvi said he keeps talking of "Swachch Bharat" but the air quality of Delhi and several other cities was going down. "What is the point of talking of 'Swachch Bharat' when the most important aspect should be tackling pollution. How can the Prime Minister be quiet? "There is an emergency as far as pollution is concerned. Delhi is the world's most polluted mega city," he added.Singhvi said Delhi had been ranked "greenest capital of the world" when Sheila Dikshit was the Chief Minister. Delhi and its neighbouring region on Monday experienced first smog of the season with air pollutants many folds higher than the permissible limit. The air quality was in the "severe-plus" or "emergency" category.