The air quality of the national capital deteriorated to the 'poor' category on Friday but will improve sharply by Saturday as heavy surface wind is expected, according to the Ministry of Earth Sciences.

Delhi's air quality index (AQI) stood at 263 micrograms per cubic meter. AQI within the limit of 0-5 is regarded as good, 51-100 satisfactory, 101-200 moderate, 201-300 poor, 301-400 very poor and 401-500 is considered severe.

The concentration of ultra-fine PM2.5 particulates is 268 while PM10 is 112. The normal level of PM2.5 should be 60 micrograms cubic meter and PM10 level should be 100 microgram cubic meter.

Out of 39 pollution monitoring stations in the capital city, the one in Narela recorded the highest AQI at 341, followed by Mundka at 328, Dwarka at 317, Bawana at 316 and Vivek Vihar at 309 micrograms per cubic meter.

"Overall Delhi air quality is in the poor category. Surface winds are high and forecast to increase. AQI is forecast to sharply improve to the moderate category by tomorrow," stated the Ministry's System of Air Quality and Weather Forecasting and Research on Friday.

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The air quality is likely to further improve and remain in the moderate to the satisfactory category for March 7 and marginally deteriorate to moderate to a poor category on March 8, the SAFAR said. The officials have advised sensitive people to consider reducing prolonged or heavy exertion and take it easy if symptoms such as coughing or shortness of breath occur.

Residents of Delhi's neighbouring regions -- Ghaziabad, Noida, Gurugram, Faridabad and Greater Noida are also breathing poor quality of air. Ghaziabad has the worst air quality amongst all at 287 micrograms per cubic meter.