A combination of terahertz (THz) absorption and 2D correlation spectroscopy (2DCOS) has been used to identify the concentration and pollution sources of PM2.5 (particulate matter less than 2.5 µ in diameter) in the Beijing-Tianjing-Hebei region of China. The THz-2DCOS analysis revealed that samples with high PM2.5 were related to higher THz absorption at selected frequencies. This information was used to determine appropriate emergency measures needed to relieve haze pollution. This is a terahertz-2DCOS analysis of PM2.5 during red alert period (a) and normal condition (b). 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