A haze covered the Gunnedah area for much of yesterday as a cool change brought dust from the west, bringing hazardous conditions to some parts of the state.
Air quality assessments showed that, on average for the day, Gunnedah, Narrabri and Tamworth on the North-West Slopes had some of the poorest air quality in NSW.
The Office of Environment and Heritage (OEH) air quality data listed one pollutant - PM10, meaning particles less than 10 micrometers in diameter - as being at "hazardous" levels.
The local readings were at least twice as bad as almost everywhere else in NSW.
By 11am today, those readings for Gunnedah remained "poor", while Narrabri and Tamworth were still "hazardous".
Gunnedah's rating was 91.7, Narrabri's 126.6 and Tamworth's was 150.1.
The highest reading elsewhere was at Muswellbrook with 78.4.
Effect of drought
The dust was being moved on by a strong cold front moving north and east across the south-east of Australia.
OEH climate and atmospheric science director Matthew Riley said more of the same could be on the way.
"This is the effect of the drought," Mr Riley said.
"It is very, very dry across the entire western part of the state and there is very little ground cover.
"This means whenever a front comes through, we're expecting dust storms."
Mr Riley said the air pollution figures were not affected by the intense fires raging in Tingha and Tabulam.
He said the dust was being picked up from the Mallee region in Victoria and the Eyre basin in South Australia by a cold front moving across eastern Australia.
The dust was being dragged from the south-west right up to Queensland.