| Resumo: | In the dry season, the north of Thailand always experiences reduced air quality, reduced visibility, and public health exposure from the burning of biomass domestically and in surrounding countries. The purpose of this research was to investigate the distribution and the meteorological control of PM<sub>2.5</sub> accumulation, as well as its effect on visibility in northern Thailand in 2020. The Geographic Information System (GIS) was applied for the analysis of the spatial distribution, while Pearson’s correlation coefficient was utilized to examine the association between PM<sub>2.5</sub> and meteorological variables. The results showed that the PM<sub>2.5</sub> concentrations were in the range of 16–195 μg/m<sup>3</sup> in 2020. The high level of PM<sub>2.5</sub> in Lampang, Chiang Rai, and Chiang Mai provinces was in the range of 150 to 195 μg/m<sup>3</sup> from January to May. Favorable meteorological conditions included low wind and relative humidity, and high temperatures contributed to high PM<sub>2.5</sub> concentrations in northern Thailand. Domestic burning and burning in neighboring countries contribute to huge amounts of smoke that cause low visibility in northern Thailand, especially at 1 km above ground level, with a reduced visibility in the range of 70–90% for all provinces in April.
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