The wet deposition of the inorganic ions in the 320 cities across China: spatiotemporal variation, source apportionment, and dominant factors

Abstract

<p><strong>Abstract.</strong> The acid deposition has been considered to be a severe environmental issue in China. The pH, electrical conductivity (EC), and the concentrations of the water soluble ions (NO<sub>3</sub><sup>−</sup>, Cl<sup>−</sup>, Ca<sup>2+</sup>, K<sup>+</sup>, F<sup>−</sup>, NH<sub>4</sub><sup>+</sup>, Mg<sup>2+</sup>, SO<sub>4</sub><sup>2−</sup>, and Na<sup>+</sup>) in the precipitation samples collected from the 320 cities during 2011–2016 across the whole China were measured. The mean concentrations of F<sup>−</sup>, NO<sub>3</sub><sup>−</sup> and SO<sub>4</sub><sup>2−</sup> were in the order of winter (6.10, 19.44 and 45.74 μeq/L) > spring (3.45, 13.83, and 42.61 μeq/L) > autumn (2.67, 9.73, and 28.85 μeq/L) > summer (2.04, 7.66, and 19.26 μeq/L). The secondary ions (SO<sub>4</sub><sup>2−</sup>, NO<sub>3</sub><sup>−</sup> and NH<sub>4</sub><sup>+</sup>), and F<sup>−</sup> peaked in Yangtze River Delta (YRD) and Sichuan basin (SB). The crustal ions (i.e., Ca<sup>2+</sup>, Mg<sup>2+</sup>), Na<sup>+</sup>, and Cl<sup>−</sup> showed the highest concentrations in the semi-arid regions and the coastal cities, respectively. The statistical methods confirmed that the mean anthropogenic contribution ratios to SO<sub>4</sub><sup>2−</sup>, F<sup>−</sup>, NO<sub>3</sub><sup>−</sup>, and NH<sub>4</sub><sup>+</sup> at a national scale were 46.12 %, 71.02 %, 79.10 %, and 82.40 %, respectively. However, Mg<sup>2+</sup> (70.51 %), K<sup>+</sup> (77.44 %), and Ca<sup>2+</sup> (82.17 %) were mostly originated from the crustal source. Both Na<sup>+</sup> (70.54 %) and Cl<sup>−</sup> (60.42 %) were closely linked to the sea-salt aerosols. On the basis of the stepwise regression (SR) analysis, it was proposed that most of the secondary ions and F<sup>−</sup> were closely related to gross industrial production (GIP), total energy consumption (TEC), vehicle ownership, and N fertilizer use, but the crustal ions (Ca<sup>2+</sup> and K<sup>+</sup>) were mainly controlled by the dust events. The influence of dust days, air temperature, and wind speed on ions increased from Southeast China (SEC) to Central China, and then to Northwest China (NWC), whereas the influence of socioeconomic factors on acid ions (SO<sub>4</sub><sup>2−</sup> and NO<sub>3</sub><sup>−</sup>) displayed the higher value in East China.</p>