Ozone Gas Warning Issued As Temperatures Near 50 Degrees In NSW

Two days into a severe heatwave, health authorities have urged those with respiratory issues to be extra vigilant as high ozone air pollution sets in around Sydney.

It's hot -- very hot --  and sunny across the state, which means ozone levels are rising.

While ozone in the atmosphere is important to shield us from the sun's UV radiation, at ground level the gas can be a harmful pollutant.

Excess ozone is created when nitrogen oxides -- from things like our car exhausts and air conditioners -- chemically react with oxygen in sunshine and hot temperatures.

In simple terms, more heat and more sun means more ozone and more breathing problems.

As NSW Health director of environment health Dr Richard Broome explained, it can irritate the lungs and trigger multiple health conditions. “Ozone levels are higher outdoors than indoors, and generally highest in the afternoon and early evening," he said in an advisory.

"So limiting time outdoors during the heat of the day and in the evening helps people to not only keep cool but to limit their exposure to ozone pollution."

Broome urged people with asthma and chronic respiratory diseases to seek immediate medical help should they feel effects during the heatwave, while those with asthma should remember to keep their medication close by.

It's the second warning Broome has given NSW residents this week, after urging people to keep physical activity to a minimum and be extra aware of those more vulnerable to the heat including older family members.

Meanwhile in Sydney, the western suburbs will cop the brunt of the heatwave, with Penrith -- which hit 41 degrees on Wednesday -- gearing up for a 45 degree Friday.

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The hottest temperatures in the state will be in the Riverina and Lower Western region. Hay, Ivanhoe, Wentworth and Lake Mungo are all forecast to hit 47 degrees on Wednesday and remain in the 40s until the weekend.