Temporal and Spatial Pollution Characteristics of Main Water-soluble Ions of Atmospheric PM_2.5 in Wuhan

Objectives To investigate the temporal and spatial pollution characteristics of major water-soluble ions in atmospheric PM_2.5 in Wuhan.

Methods For the whole year of 2016 from January to December, PM_2.5 was continuously sampled from 5 monitoring sites in Wuhan, and the main water-soluble ions in PM_2.5 were analyzed via Ion Chromatography. The seasonal variation and spatial distribution difference were also examined in this study.

Results It showed obvious seasonal variations on PM_2.5 mass concentration in Wuhan. Meanwhile, the mass concentration and proportion of other ions (except for Cl^-) in PM_2.5 also had obvious seasonal variation. From the perspective of spatial distribution, the SO₄^2- concentration was the highest in all 5 monitoring sites, followed by NO₃^- and NH₄⁺ and Cl^- concentration was the lowest. However, the total ion concentrations in Wuchang district and Qingshan district were relatively higher, while the concentration in Jiang'an district was the lowest. The ion proportions were consistent, that is, the proportion of SO₄^2- was much larger than that of other ions. Cl^- was the lowest, and NO₃^- and NH₄⁺ were at the same level. The acidity of PM_2.5showed that PM_2.5 was acidic all over the year (R=0.83). The NOR trend was:winter > autumn > spring > summer, and the SOR trend was the highest value appeared in summer and lowest value appeared in winter. The seasonal variation of NO₃^-/SO₄^2- was obvious with an annual average < 1, indicating that sulfur and nitrogen in the atmosphere are mainly from stationary sources.

Conclusions The major water-soluble ions in atmospheric PM_2.5 in Wuhan showed obvious seasonal variations and spatial distribution variations.