Delhi's air quality continued to improve on November 17. According to Central Pollution Control Board's National Air Quality Index, most parts of the national capital recorded moderate category on air pollution index. Some of the areas like RK Puram poor and Ashok Vihar recorded 'Poor' category. Wazirpur and North Campus recorded 'Satisfactory' category. The dip in air pollution levels is due to evening showers on November 15th, followed by increased wind speed. According to National Air Quality Index, an air quality index (AQI) between 0-50 is marked good, 51-100 is satisfactory, 101- 200 is moderate, 201- 300 is poor, 301-400 is very poor and 401-500 is considered severe.