NSW Health has issued an air pollution alert as Sydney prepares to swelter through another summer day, warning that an increased level of ozone in the atmosphere is likely to affect residents with respiratory problems.
Sydney's air quality is forecast to be poor on Tuesday, when the mercury is expected to hit a top of 31 degrees in the city and 37 degrees in the western suburbs.
The Bureau of Meteorology is forecasting a top of 38 degrees in the city on Wednesday, dipping to 27 degrees on Thursday, but rising again to 33 degrees on Friday and 31 degrees on Saturday.
Richmond and Penrith are both forecast to reach 40 degrees on Wednesday, dipping to 30 degrees on Thursday before rising to a sweltering 42 on Friday.
Spare a thought for the residents in Bourke, in north-western NSW, which is expecting a maximum of 45 degrees on both Wednesday and Thursday, rising to 47 degrees on Friday.
The Bureau of Meteorology's forecast states that NSW Health has issued an air quality alert for poor air quality in Sydney on Tuesday.
"Those with respiratory diseases such as asthma should follow their action plan and use their relieving medication where necessary. If respiratory symptoms worsen, they should seek medical advice," the alert states.
Ozone forms in the lower levels of the atmosphere on sunny days by chemical reactions between reactive organic gases and oxides of nitrogen, according to the NSW Office of Environment and Heritage.
It is not a pollutant in the upper atmosphere, where it absorbs harmful UV radiation, but when near the ground is one of the irritants in photochemical smog. Ozone forms more readily in summer and reaches its highest concentrations in the afternoon or early evening.
NSW Health said ozone can cause eye, nose, throat and lung irritations, coughing and shortness of breath, and may worsen chronic respiratory diseases such as asthma.
Dr Ben Scalley, from NSW Health, said ozone levels usually were at their highest about 7pm on a hot, still day.
"Ozone levels are higher outdoors than indoors, so parents should limit the time their children with asthma play outside as they are more susceptible to the effects of ozone pollution," Dr Scalley said.
"Ozone levels reach their peak around 7pm in the evening and tend to be lowest in the morning, so it's best to plan outdoor play in the morning when the day is cooler."
