The air quality in Delhi today deteriorated beyond the "severe" level because of a ground-level dust storm in western India that had increased coarser particles in the air, the Central Pollution Control Board (CPCB) data showed. The CPCB data showed that the PM10 (particles with diameter less than 10mm) level was beyond "severe" at 778 in Delhi-NCR area and 824 in Delhi particularly, leading to hazy conditions and limiting visibility.