A spokesman from the Rural Fire Service NSW said it was mainly fog, though a large hazard reduction burn in the Nattai National Park, west of Bargo, was contributing to the atmosphere.

“The majority of it is fog this morning,” he said. “The smoke that’s affecting most of [the region] is from a 4440 hectare burn out in the western Wingecarribee area.

“[The hazard reduction burn] was undertaken by the RFS, National Parks and Wildlife Service. That will still be burning for a number of days.”

Another hazard reduction burn further west at Kowmung Mountain in Wollondilly may also be contributing, with 4600 hectrares so far burnt.

The spokesman said a “low weather inversion” (whereby air at higher altitudes becomes warmer than at lower altitudes) was making it look worse than what it is.

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