Long-term exposure to airborne fine particulate matter or PM2.5 is associated with an increase in the long-term risk of premature death that creates critical concerns for public health. This study uses twenty years (2002-2021) of daily remotely sensed data with multi-spatial resolution of 1 km to 3 km to examine the long-term spatiotemporal distribution of PM2.5 across Thailand. Good agreement is found between the in-situ measurements of PM2.5 and instantaneous estimates made from the satellite data with correlation coefficients of 0.51. Based on data analysis during the year 2002- 2021, the region with the highest yearly averaged concentration level of PM2.5 was a central region of Thailand (19.91 μg.m-3) followed by northern (19.11 μg.m-3), northeastern (18.92 μg.m-3), eastern (18.76 μg.m-3) and southern (16.16 μg.m-3) region, respectively. The period with the highest PM2.5 levels were during March and April with monthly averages 23.74 to 26.72 μg.m-3. For the 20-year record, monthly-mean PM2.5 concentration in northern Thailand showed statistically significant increase at the rate of 0.14 μg.m-3 month-1 in dry season, the same as in the northeastern (0.126 μg.m-3month-1), eastern (0.12 μg.m-3 month-1) and Central region (0.083 μg.m-3 month-1). While the southern region has a negative trend (-0.018 μg.m-3 month-1) which is different from other regions. The spatiotemporal variation and changing of PM2.5 concentrations were a result of both changing in meteorological factors and anthropogenic activities. Here, we discuss and present possible explanations for long-term spatiotemporal variation of PM2.5.
This study has investigated the physical processes of energy exchange between the water surface and atmosphere over Lake Huron. The four components of surface energy balance, including net radiation, latent heat, sensible heat, and heat storage, were estimated using the eleven years (2002-2012) daily MODIS data together with in-situ measurements. Good agreement was found between the seasonal turbulent heat fluxes calculated from satellite data and those from the direct measurements (eddy covariance method) with correlation coefficients of 0.94 and 0.95 for sensible heat and latent heat, respectively. There were temporal, spatial heterogeneities, and strong seasonal pattern for all of the four components, which were very high in summer and low in winter for net radiation and heat storage. In contrast, latent heat and sensible heat were very high in the winter and very low in the summer. Trend analysis revealed long term changes for each of the energy balance components, particularly the increase in latent heat which was equivalent to evaporation rate of 0.017 mm m-2 per year, indicating that lake evaporation increased by 0.19 mm m-2 over the eleven years observation period. This was possibly a result of a smaller amount of over lake ice cover and an increase in surface water temperature of Lake Huron.
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