[Pollution Characteristics, Source Apportionment, and Meteorological Response of Water-soluble Ions in PM_2.5 in...

Pollution variation, source characteristics, and meteorological effects of water-soluble inorganic ions (WSIIs) in PM_2.5 were analyzed in Xinxiang city, Henan Province. PM_2.5 samples and their chemical components were monitored online by using URG-9000 in four seasons:winter (January, 2022), spring (April, 2022), summer (July, 2022), and fall (October, 2022). The results showed that the TWSIIs had the same seasonal fluctuations as PM_2.5. The average seasonal concentrations of WSIIs ranged from 19.62-72.15 μg·m^-3, accounting for more than 60% of PM_2.5, demonstrating that WSIIs were the major components of PM_2.5. The annual concentration value of NO₃^-/SO₄^2- was 2.11, which showed an increasing trend, suggesting predominantly mobile sources for secondary inorganic aerosols (SNA). Further, the molar concentration value [NH₄⁺]/[NO₃^-] was 1.95, demonstrating that agriculture emissions were the dominant contributors to atmospheric nitrogen. Furthermore, the backward trajectory analysis showed that the concentrations of Ca²⁺ and Mg²⁺ were higher when the northeasterly wind prevailed and the wind speed was high. High values of SOR and NOR were correlated with low temperatures and high relative humidity (T < 8℃, RH > 60%), demonstrating that more gaseous precursors were converted into sulfate and nitrate. At high temperatures (T > 24℃), there was no apparent high NOR value like that for SOR, mainly due to the decomposition of NH₄NO₃ at high temperatures. Finally, backward trajectories associated with the PMF-resolved results were used to explore the regional transport characteristics. The results illustrated that dust sources in the study areas were mainly influenced by air trajectories originating from the northwest regions, whereas secondary sulfate, secondary nitrate, and biomass sources contributed more to WSIIs when wind speed and altitude air masses were low in the area surrounding the observation site.