The air quality in Delhi-NCR deteriorated further, slipping to 'severe' category on Friday.
The Air Quality Index in the national capital was 411.
The satellite cities of Ghaziabad (426), Greater Noida (426) and Noida (423) also recorded air quality in the severe category.
An AQI between 0-50 is considered 'good', 51-100 'satisfactory', 101-200 'moderate', 201-300 'poor', 301-400 'very poor' and 401-500 'severe'. An AQI above 500 falls in the 'severe plus' category.
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