The objective of this research is to study the effects of thermal hotspots on PM2.5 concentrations in the upper northern of Thailand during 1 January–31 May 2019. The number and the density of fire hotspots of the examined and adjacent areas was investigated. The time-series relationships between PM2.5 concentrations, the number of satellite-based fire hotspots, and meteorological factors derived from 9 stations were analyzed. As results, the greater number of hotspots was correlated with increased levels of PM2.5 concentrations. Such conditions exhibit considerable impacts on health. High PM2.5 concentrations were specifically found around provincial boundaries, in forests, agricultural areas, as well as in Thailand’s neighboring countries. As for the surrounding areas, the areas that have high density of fire hotspots were found near investigated areas in the north region. Provincial fire hotspots were correlated to high PM2.5 concentration, with a lower r-value. The thermal hotspot locations from the surrounding areas have effects on provincial PM2.5 concentrations. Finally, the effect of meteorological factors on PM2.5 concentrations was analyzed. As a result, precipitation and wind speed have inverse effects on PM2.5 concentrations.