Northern Thailand was once a paradise. Now forest fires have made the air worse than Beijing’s. Black ash is falling from the sky.

In mid-March, the city with the worst air pollution in the world wasn’t an industrial powerhouse populated by millions. It was Chiang Mai, the tourist-friendly cultural center in northern Thailand.

And for Chiang Mai and its environs, that was the beginning, not the end, of northern Thailand’s trouble with air pollution.

The air pollution was caused in part by forest fires, notably the practice of the area’s farmers of starting fires to clear land for new harvests. Some Chiang Mai residents said the poor air quality showed that the government’s efforts to stop farmers from exacerbating northern Thailand’s seasonal haze problem were not working.

And aside from the health hazards to humans and animals alike, there was another smog side effect. Chiang Rai, also in Thailand’s north, faced a similar problem. And the hotel industry lamented that spending during Songkran, the Thai new year festival in mid-April, was down about 20 percent, according to TTR Weekly, a Southeast Asian tourist website. Hazardous smog was thought to be behind the drop.

Residents of once picturesque Chiang Rai are suffering with sore throats, persistent coughs and have witnessed black ash falling from the sky.

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