Characteristics of water-soluble inorganic aerosol pollution and its meteorological response in Wuhan, Central China

Due to the rapid economic development in Central China, PM2.5 (particles not larger than 2.5 mu m) pollution is serious in recent years. To fully understand the causes of PM2.5 in this region, we conducted a long-term tracking (2015-2018) on water-soluble inorganic ions (WSIIs) in PM2.5, including sulfate (SO42-), nitrate (NO3-), ammonium (NH4+), chlorine (Cl), potassium (K+), calcium (Ca2+), sodium (Na+), and magnesium (Mg2+). Results indicate that each ion has significant seasonal variations, with the maximum concentration in winter and minimum in summer. The secondary inorganic aerosols (SIAs) have remarkably higher concentrations in haze periods than non-haze periods, which indicates that the outbreak of haze is closely related to the massive generation of SIAs. Moreover, each ion shows a different response to the variation of meteorology, implying the different formation mechanisms. Generally, high pollution levels of Ca-2(+), Mg-2(+), K+, Cl-, and Na+ are correlated to prevailing winds, suggesting the significant contribution of regional transport. High concentrations of SIAs are usually accompanied by the low temperature (T < 15 degrees C), high relative humidity (RH > 60%), and calm wind, which means they are mainly locally generated. Under conditions with low T and high RH, more gaseous sulfur and nitrogen tend to be converted into solid inorganic salts, proved by the higher oxidation efficiency. Different to NO3-, SO42- is also easily generated at high T through photochemical oxidization. This study interprets fine particle pollution from the perspective of particle composition, and the results provide an reference for regional air pollution prevention.

Automated summary

The study found that PM2.5 pollution in Central China is mainly caused by water-soluble inorganic ions, with significant variations in different ions during seasons and haze periods. The outbreak of haze is closely related to the generation of secondary inorganic aerosols. Different ions have varying responses to meteorological changes, implying different formation mechanisms.