The composition, seasonal variation, and potential sources of the atmospheric wet sulfur (S) and nitrogen (N) deposition in the southwest of China
2016
Liu, Lei | Zhang, Xiuying | Lu, Xuehe
The composition, seasonal variation, and potential sources of sulfate (S) and nitrogen (N) deposition in precipitation in the southwest of China from 2003 to 2013 were investigated. The results showed that the concentration of SO₄²⁻, NO₃⁻, and NH₄⁺ in rainwater were 10.57–1360, 7.16–523.71, and 7.54-1020 μeq l⁻¹, with an annual volume-weighted mean (VWM) concentration of 103.99, 46.73, and 97.30 μeq l⁻¹, respectively. The annual wet deposition of SO₄²⁻, NO₃⁻, and NH₄⁺ was 21.66, 8.16, and 17.49 kg S (N) ha⁻¹, respectively. The temporal variations of the ions showed that the abrupt decreasing breakpoints were in 2008 for SO₄²⁻ and in 2009 for NO₃⁻ and NH₄⁺, and increasing trends were observed after 2010 for the three ions. These trends reflected the effect of economy recession and the policy of controlling SO₂ and NOₓ emissions. The acid rain type of precipitation was shifted from sulfur to a mixed one. The ions of SO₄²⁻, NO₃⁻, and NH₄⁺ presented high values in winter and spring and low values in autumn and summer. A highly positive linear correlation between SO₄²⁻ and NO₃⁻ (R ² = 0.71), SO₄²⁻ and NH₄⁺ (R ² = 0.74), and NO₃⁻ and NH₄⁺ (R ² = 0.84) existed while a strong negative correlation was found between the three main ionic concentrations and precipitation. The SO₄²⁻ was mainly from fossil fuel combustion (60.53 %), aged sea salt (19.03 %), agriculture (11.38 %), crust (6.66 %), and biomass burning (2.40 %); the NO₃⁻ was mainly from fossil fuel combustion (75.41 %), biomass burning (9.67 %), aged sea salt (7.97 %), and agriculture (6.96 %); and the NH₄⁺ was mainly from agriculture (86.38 %), fossil fuel combustion (10.52 %), and aged sea salt (3.09 %).
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