The indoor-outdoor characteristics of water-soluble ion in PM2.5 in Tianjin wintertime.

The indoor and outdoor PM2.5 mass concentration, water-soluble ion by filter sampler was analyzed on December 3-21, 2015 during wintertime in Tianjin, China. The results indicate that high humidity conditions result in the accumulation of atmospheric pollutants and reduce atmosphere visibility. The I/O ratio for PM2.5 concentration in dormitory and lab are less than 1 in haze days. Indoor PM2.5 concentration increases rapidly with outdoor PM2.5 concentration increasing in haze days. The filtration factors of the dormitory and lab indicate nearly half of the outdoor PM2.5 enters indoor environment. The human activities in dormitory could cause more the formation of PM2.5 than those in lab. The concentration of SO42- is the highest ion in water-soluble ion for outdoor PM2.5. The SO42-, NO3-, NH4+, and Cl- are generated mainly by outdoor sources; however, the Na+, Ca2+, and Mg2+ are generated mainly by indoor sources. The NH4NO3, (NH4)2SO4, and NH4Cl accounts for 20.2~41.8%, 32.0~51.4%, and 6.4~10.6% of the total water-soluble ion in different indoor-outdoor environment. The total secondary aerosols including NH4NO3, (NH4)2SO4, and NH4Cl in PM2.5 are 28.3, 42.1, 28.2, 31.0, and 33.9% in outdoor environment for haze days, outdoor environment for non-haze days, dormitory for haze days, dormitory for non-haze days, and lab for haze days, respectively.