The air quality in Delhi on Wednesday deteriorated beyond the “severe” level due to a ground-level dust storm in western India, the Central Pollution Control Board said, according to PTI.

The board’s data showed that the level of PM 10 particles – the concentration of particulate matter of diameter less than 10 microns – was 778 in Delhi and the National Capital Region on Wednesday morning. An Air Quality Index reading up to 50 is considered “good” and up to 100 is considered “satisfactory”. A reading between 401 and 500 is ranked “severe” on the index, which means the air is dangerously filled with pollutants.

“There was a ground-level dust storm in the western part of the country that increased coarser particles in the air, causing a spike in pollution levels in Delhi,” said Gufran Beig, a scientist at the state-run System of Air Quality and Weather Forecasting and Research institute.

A massive dust storm hit Delhi on Saturday evening. Rain showers were reported in several parts of the national capital immediately afterwards. Wind speeds of between 70 and 80 km per hour were recorded.

“Due to the high wind speeds, dust particles are being transported from Rajasthan,” said VK Shukla, a scientist in-charge of the air lab at the Central Pollution Control Board, according to Reuters. Shukla also said the situation is likely to remain the same for the next two days.