Lewis Hamilton will be hoping his march towards a sixth Formula One world title around the streets of hazy Singapore this week is not affected by smoke from wildfires raging in neighbouring Indonesia.
The National Environment Agency is forecasting pollution at the "low end of the unhealthy range" for Sunday's showpiece night race after dense smog last weekend.
Formula One bosses are reported to have a contingency plan in place should the "highly changeable" air quality deteriorate, though the race weekend is still scheduled to go ahead as planned.
Hamilton, who has a 63-point lead in the title race over teammate Valterri Bottas after winning eight grands prix this season, and Mercedes have prospered in the past at the Marina Bay Circuit.
But they could do little to prevent Ferrari's Charles Leclerc from storming to consecutive victories on power-friendly layouts in Belgium and Italy in the two races since the summer break.
Hamilton has taken four of Mercedes' five victories at the demanding 23-turn city-centre street circuit and is looking for a third consecutive triumph in race that even without the threat of smog is traditionally draining because of heat and high humidity.
More From This Section
But Hamilton remains wary of Leclerc, who has outshone his error-prone Ferrari teammate Sebastian Vettel since joining the Italian team at the start of the season.
"I am not looking forward to the next race thinking it will swing our way," Hamilton said of the 21-year-old from Monaco.
"I hope that it is competitive between us -- I want this battle to continue."
"But I have no doubt that Ferrari will have learned and will have a good package."