Helicopters dumped water on fires that were started illegally on two mountains in northern Thailand.

The Forest Fire Operation Centre dispatched two helicopters - an army MI-17 helicopter and a KA-32 helicopter from the Department of Disaster Prevention and Mitigation - to douse the blaze at the Suthep Scout Camp in Doi Suthep-Pui National Park in Chiang Mai on April 18. 

The aircraft assisted more than 50 staff that had been battling the inferno since April 17 evening.

Meanwhile, two helicopters from the Ministry of Natural Resources and Environment flew to Doi Luang Chiang Dao mountain at the Chiang Dao Wildlife Sanctuary as the fire there was inaccessible to ground teams.

The operation marked the first successful fire extinguishing effort on the mountain, with support from the 3rd Army and the Suea Fai operation teams to prevent major fires.

Doi Chiang Dao was declared a UNESCO biosphere reserve in 2021. It is the only place in the country that contains sub-alpine vegetation, and it serves as a habitat for several protected wild animals.

According to Swiss air company IQAir, the air quality in Chiang Mai reached an unhealthy level at 171 AQI with 94.6 µg/m³ of PM2.5 fine dust on April 18.

Dangerous levels of deadly PM 2.5 particles - which cause cancer and other debilitating illnesses - are recorded every year in Thailand between December and April when farmers across Southeast Asia burn waste crops to clear their land.

The rudimentary method, known as 'slash and burn', is quicker and cheaper than modern machinery, leaving relatively poor landowners unwilling to heed environmental and health concerns over economic necessity.

Despite paying lip service for several years, politicians have failed to stop individuals from burning their land due to it being cheaper and easier than modern farming methods.

In March 2023, the Public Health Ministry of Thailand reported that around 1.3 million people in the country had been unwell due to the rising levels of air pollution. Officials said 200,000 residents were hospitalised in a single week.

Researchers from Peking University in Beijing, China, found that exposure to PM 2.5 air pollution is associated with an increased risk of lung cancer.

In December, Dr Krittai Thanasombatkul from Chiang Mai - one of the world's worst cities for air pollution - died of lung cancer. He had previously blamed PM 2.5 microdust particles for his condition.

The New York State Department of Health says PM 2.5 also increases the risk of heart disease, asthma, and low birth weight.

Medics from South Korea published research in the National Institute of Health in the United States that said the pollutant increases the risk of stroke, ischemic heart disease, chronic obstructive pulmonary disease (COPD), lung cancer, and other illnesses such as immune deficiency and even obesity.