Wet deposition of sulfur and nitrogen in Jiuzhaigou National Nature Reserve, Sichuan, China during 2015–2016: Possible effects from regional emission reduction and local tourist activities

In order to understand the impacts of regional emission changes and local tourism on sulfur and nitrogen wet deposition in Jiuzhaigou National Nature Reserve of southwestern China, wet deposition was monitored at a background site (Rize) and a tourist-affected site (PE: park entrance) in the reserve during 2015–2016. The observation data were compared between Rize and PE and between 2010–2011 and 2015–2016 monitoring campaigns. Also, the observation data were used in the Positive Matrix Factorization (PMF) model to identify the major sources of sulfur and nitrogen wet deposition. The results show that although local tourism emissions had considerable contributions to NH₄⁺, NO₂⁻, NO₃⁻, and SO₄²⁻ concentrations in wet deposition (p < 0.05), most of the annual Volume Weighted Mean (VWM) concentrations of these four ions were likely from emissions outside Jiuzhaigou. Annual wet deposition fluxes of the four ions were also affected more by precipitation and regional emissions than by local emissions. Although annual precipitation was higher at Rize (818 mm) during 2015–2016 than at another background site near Long Lake (LL: 752 mm) during 2010–2011, the annual concentrations and fluxes of SO₄²⁻ and NO₃⁻ wet deposition decreased by 77% and 74% for SO₄²⁻ and by 12% and 19% for NO₃⁻, respectively, most likely due to regional emission reductions. Similar large reductions in SO₄²⁻ and NO₃⁻ concentrations have been also found in some other sites in southwestern China. In contrast, the annual concentration and flux of NH₄⁺ wet deposition at Rize during 2015–2016 were 1.4 and 1.2 times of that measured at LL during 2010–2011, respectively. The results of source apportionment analysis and tour bus emission estimates suggest that elevated NH₄⁺ wet deposition was possibly related to NH₃ emissions from local tour buses, but additional studies on NH₃ emissions from tour buses in the reserve are needed to confirm this.