The indoor-outdoor characteristics of water-soluble ion in PM 2.5 in Tianjin wintertime

Abstract

The indoor and outdoor PM_2.5 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 PM_2.5 concentration in dormitory and lab are less than 1 in haze days. Indoor PM_2.5 concentration increases rapidly with outdoor PM_2.5 concentration increasing in haze days. The filtration factors of the dormitory and lab indicate nearly half of the outdoor PM_2.5 enters indoor environment. The human activities in dormitory could cause more the formation of PM_2.5 than those in lab. The concentration of SO₄²⁻ is the highest ion in water-soluble ion for outdoor PM_2.5. 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 PM_2.5 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.