In March of 2019, Chiang Mai was struck by its worst smoke crisis to date, ranking the city almost continuously as the number one most polluted place in the world. This impacted not only the tourism industry but also the health of all residents. On March 30th, the AQI (Air Quality Index) readings from the AirVisual website rose up to 520 US AQI. Furthermore, Chiang Mai had been constantly ranked among the top 10 most polluted places in the world since the end of February 2019. A rise in the values of PM2.5 - Particulate Matter small enough to deeply penetrate into the lungs - can create major health risks in the long run. Intense and persistent smog caused these tiny particles to descend over the streets. This seriously impaired the visibility of our surroundings and passed into people’s households, both day and night.
Because most of the areas in Northern Thailand is surrounded by mountains especially Chiang Mai city, its topography resembles the shape of a bowl. During the change from winter to the summer season, the weather is very dry and there is no wind. These factors - combined with high air pressure and low morning temperatures - bring smog into the lower parts of the Chiang Mai valley, actively retaining it there. This meteorological phenomenon is called a temperature inversion.
Man-made forest fires are major causes of the haze, especially at this time of the year. People set forests on fire so as to increase harvestable surface and stimulate the growth of rare and expensive mushrooms. Moreover, they are always used as traps for wild animals. Others practice a ‘slash and burn’ crop-rotation system on the mountain slopes to clear land for new plantations, mainly growing corn for the livestock industry. Both of these practices have always caused problems in the past. But they'll become inevitably more severe in the near future as demand for these agricultural products is on the rise.