Melbourne, Jan 18 (AFP) Australian Open organisers Saturday introduced a scaled air quality rating to determine when play can be suspended following stinging criticism after days of toxic smoke during qualifying.

Air quality in Melbourne was among the worst on the planet on Tuesday and only marginally better Wednesday because of smoke from bushfires that have devastated huge swathes of the country.

It was recommended that people and their pets stay indoors, but qualifying for the opening Grand Slam of the year went ahead regardless.

Slovenian Dalila Jakupovic was forced to retire from her match after a distressing coughing fit, while Britain's Liam Broady claimed "multiple" players needed asthma medication.

Broady also was seething over what he considered a lack of clarity on the decision-making process about when to suspend play.

"The more I think about the conditions we played in a few days ago the more it boils my blood," he said.

In the wake of the backlash, organisers Saturday unveiled a five-step "air quality rating" based on pollutants measured by monitoring stations throughout Melbourne Park.

Play will be suspended if the particulate matter rating (PM2.5) -- the solid and liquid particles suspended in the air -- hits 200, or five on the air quality scale.

Between 97 and 200 -- a four rating -- will trigger a discussion between medical staff and officials about whether play should continue with the match referee able to suspend a match if he sees fit.

The rules will apply to all outside courts and the Grand Slam's three arenas with retractable roofs, where play will be halted until the roof is closed.

Matches will continue until an even number of games in the set has been played, or at the end of a tiebreak, if applicable.

"I do think air quality for sport and for tennis is a conversation we're going to have more of in the future, Australian Open chief Craig Tiley told reporters on Thursday in seeking to diffuse the backlash.

"Absolutely we understand the anger," he added.

"We've invited the players to come in at any time and have a conversation."

The Australian Open gets underway on Monday, when rain is forecast. Air quality in Melbourne on Saturday was rated 'moderate', one step below 'good'. (AFP)

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