unhealthy air quality??

i was thinking of popping down for a week before Christmas. but when I check the weather on my iPhone it keeps showing unhealthy air quality. after doing some searches I can't seem to find any info on this. what's going on?

All I can say is how absurd. We enjoy some of the best air quality on the planet throughout the year with the exception of the burning season in April and May, and the burning season itself is only bad during the end of May, right before the first rains of the rainy season.