Atmospheric wet deposition of sulfur and nitrogen in Jiuzhaigou National Nature Reserve, Sichuan Province, China

Science of the Total Environment 511 (2015) 28–36

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Atmospheric wet deposition of sulfur and nitrogen in Jiuzhaigou National Nature Reserve, Sichuan Province, China Xue Qiao a, Weiyang Xiao b, Daniel Jaffe c, Sri Harsha Kota d, Qi Ying d, Ya Tang a,⁎ a

Department of Environment, College of Architecture and Environment, Sichuan University, Chengdu 610065, China Jiuzhaigou Administration Bureau, Jiuzhaigou County 623407, Sichuan Province, China Department of Atmospheric Sciences, University of Washington, Seattle 98117, USA d Zachry Department of Civil Engineering, Texas A&M University, College Station, TX 77843, USA b c

H I G H L I G H T S • • • • •

was 8.06 kg S ha− 1. Annual wet deposition flux of SO2− 4 Annual wet deposition flux of TIN was 2.68 kg N ha−1. and TIN into JNNR. Wet deposition dominated annual total inputs of SO2− 4 and TIN in JNNR. Human sources dominated wet deposition fluxes of SO2− 4 Acid rain and elevated deposition of S and N would deteriorate ecosystems in JNNR.

a r t i c l e

i n f o

Article history: Received 22 August 2014 Received in revised form 29 November 2014 Accepted 1 December 2014 Available online xxxx Editor: Xuexi Tie Keywords: Tourism Acid rain Ecological impacts World Natural Heritage Site National Park Regional air pollution

a b s t r a c t In the last two decades, remarkable ecological changes have been observed in Jiuzhaigou National Nature Reserve (JNNR). Some of these changes might be related to excessive deposition of sulfur (S) and nitrogen (N), but the relationship has not been quantified due to lack of monitoring data, particularly S and N deposition data. In this study, we investigated the concentrations, fluxes, and sources of S and N wet deposition in JNNR from − + April 2010 to May 2011. The results show that SO2− 4 , NO3 , and NH4 concentrations in the wet deposition −1 were 39.4–170.5, 6.2–34.8, and 0.2–61.2 μeq L , with annual Volume-Weighted Mean (VWM) concentrations − + of 70.5, 12.7, and 13.4 μeq L−1, respectively. Annual wet deposition fluxes of SO2− 4 , NO3 , and NH4 were 8.06, 1.29, and 1.39 kg S(N) ha−1, respectively, accounting for about 90% of annual atmospheric inputs of these species at the monitoring site. The results of Positive Matrix Factorization (PMF) analysis show that fossil fuel combusand tion, agriculture, and aged sea salt contributed to 99% and 83% of annual wet deposition fluxes of SO2− 4 + NO− 3 , respectively. Agriculture alone contributed to 89% of annual wet deposition flux of NH4 . Although wet deposition in JNNR was polluted by anthropogenic acids, the acidity was largely neutralized by the Ca2+ from crust and 81% of wet deposition samples had a pH higher than 6.00. However, acid rain mainly caused by SO2− 4 continued to occur in the wet season, when ambient alkaline dust concentration was lower. Since anthropogenic emissions have elevated S and N deposition and caused acid rain in JNNR, further studies are needed to better quantify the regional sources and ecological effects of S and N deposition for JNNR. © 2014 Elsevier B.V. All rights reserved.

1. Introduction Abbreviations: S, Sulfur; N, Nitrogen; NPS, U.S. National Park Service; MEP, Ministry of Environmental Protection of China; EANET, Acid Deposition Monitoring Network in East Asia; JNNR, Jiuzhaigou National Nature Reserve; QTP, Qinghai–Tibetan Plateau; a.s.l, Above Sea Level; NTN, National Trend Network; NADP, U.S. National Atmospheric Deposition Program; VWM, Volume-Weighted Mean; NF, Neutralization Factor; PMF, Positive Matrix Factorization; EPA, U.S. Environmental Protection Agency; BGMEDSPC, Bureau of Geology and Mineral Exploration and Development of Sichuan Province, China; TSP, Total Suspended Particles; TIN, Total Inorganic Nitrogen; NTN, U.S. National Trend Network. ⁎ Corresponding author. E-mail address: [email protected] (Y. Tang).

http://dx.doi.org/10.1016/j.scitotenv.2014.12.028 0048-9697/© 2014 Elsevier B.V. All rights reserved.

Fossil fuel combustion and agricultural practices have increased NO2, NH3, and SO2 emissions from North America, Europe, and Asia by more than a factor of ten in the 20th century (van Aardenne et al., 2001). As a result of the high emissions, the deposition fluxes of sulfur (S) and nitrogen (N) have increased significantly, and excessive deposition of S and N has caused detrimental effects on human health (Kampa and Castanas, 2008), infrastructures (Kucera and Fitz, 1995), forests (Bytnerowicz et al., 2007), crops (Cao, 1989), soil (Stevens et al.,

X. Qiao et al. / Science of the Total Environment 511 (2015) 28–36

2009), and aquatic ecosystems (Bergström and Jansson, 2006; Stoddard et al., 1999). S and N deposition are of particular concern for protected areas, such as national parks and nature reserves, as critical loads of ecosystems, i.e. the maximum levels of pollutant exposure without significant detrimental effects on sensitive elements of the environment (Nilsson and Grennfelt, 1988), in these areas are usually low (Ellis et al., 2013; Sullivan et al., 2014). The ecological impacts of S and N deposition have been extensively studied for many protected areas in Europe and North America, and stringent legislations and regulations have been developed to preserve the natural resources in these regions (U.S. National Park Service (NPS), 2001). In China, the annual fluxes of S and N deposition are 12–160 kg S ha−1 (Larssen et al., 2006) and 2– 117 kg N ha−1 (He et al., 2010; Li et al., 2012; Pan et al., 2012), respectively. These values are in the same ranges of the observations in Europe and North America in the 1980s when peak acid deposition occurred in the two continents (Larssen et al., 2006; Liu et al., 2013), and 10.6% of China's land is identified as acid rain affected zones (Ministry of Environment Protection of China (MEP), 2014). Although a number of studies have reported the effects of enhanced S and N deposition on China's ecosystems (Acid Deposition Monitoring Network in East Asia (EANET), 2012; Cao, 1989; Chen and Mulder, 2007; Fang et al., 2009; Larssen et al., 1999, 2006; Liu et al., 2011), there is still a paucity of observation for China's nature reserves, many of which are located in acid rain affected zones and/or in those regions with high deposition fluxes of S and N (MEP, 2014; Zhao et al., 2009; Fig. A1). Close to the acid rain affected zone in southwestern China, Jiuzhaigou National Nature Reserve (JNNR), also a World Biosphere Reserve and UNESCO-designated World Natural Heritage Site, has experienced remarkable ecological changes in the last two decades, such as tree dieback, increased algal productivity, and tufa degradation (Fig. A2) (Gu et al., 2013). These changes may be partially caused by excessive inputs of S and N into the ecosystems through deposition or direct exposure to air pollutants. In a previous study, chemically resolved aerosol concentrations in JNNR were monitored (Qiao et al., 2014a), allowing estimations of S and N inputs through dry deposition for the period from April 2010 to May 2011. Bulk deposition, which is a mixture of dry and wet deposition collected in open areas without trees, was also measured for N and phosphorus from May 2011 to May 2012 (Qiao et al., 2014b). Although wet deposition has long been postulated to be a significant source of S and N inputs in the region, there is a lack of relevant observation. Thus, the main objectives of this study are: (1) monitoring the acidity and ionic composition of wet deposition, (2) determining the fluxes of S and N wet deposition, and (3) estimating the contributions of anthropogenic sources to S and N wet deposition.

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limited. Shuttle buses are used to transport visitors between the park entrance and various vista points within the reserve along a 50 km route, located at the bottom of the Shuzheng, Rize, and Zechawa Valleys (Fig. 1b). JNNR opens to visitors every day from 0700 to 1800 local time, and overnight stays are not permitted. The wastes generated by tourists and local residents are carefully collected and transported out of the reserve. These make JNNR one of the best-managed nature reserves in China (Gu et al., 2013). 2.2. Sample collection and analysis Weekly or bi-weekly wet deposition samples were collected from April 2010 to May 2011 at the Long Lake Meteorological Station (33.04°N, 103.93°E, 3100 m a.s.l.) (Fig. 1b), following the National Trends Network (NTN) Site Operation Manual (U.S. National Atmospheric Deposition Program (NADP), 1999). The sampling site was located

2. Materials and methods 2.1. Study area JNNR is located in a mountainous region in the eastern rim of Qinghai–Tibetan Plateau (QTP) (32.88°–33.33°N, 103.77°–104.08°E), encompassing an area of 650 km2 and spanning from about 2000 to 4880 m above sea level (a.s.l.) (Fig. 1). JNNR is a headwater watershed, with precipitation as the sole water source. Annual precipitation is 539– 771 mm, and 90% of precipitation falls during the rainy season (April to October) (Fig. A3). Approximately 1000 residents live in six villages within JNNR and three of these villages are located in the Rize, Zechawa, and Shuzhang Valleys (Fig. 1b). JNNR is one of the most popular tourist destinations in China, visited by 3.6 million tourists in 2012. To protect JNNR from local anthropogenic activities, a number of regulatory measures have been enforced (Gu et al., 2013). Farming and grazing have been banned since 2001 and logging has been barred since 1978. Electricity is used for household heating and cooking, and local biomass burning is expected to be

Fig. 1. Locations of JNNR, the sampling site, and the tourist areas. (a) Location of JNNR and (b) locations of the sampling site and the tourist areas (at the bottom of the Rize, Shuzheng, and Zechawa Valleys).

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upstream of the tourist and residential areas, and chemical composition of wet deposition at this site should be mainly influenced by regional processes. Wet deposition samples were collected using a wet deposition sampler equipped with a polyethylene bucket (ADS/NTN Atmospheric Precipitation Sampler, N-CON Systems Co., Inc., U.S.). An infrared detector sensed the rain and automatically kept the cover of the sample collector open using an internal drive motor until precipitation stopped. Before each sampling, the bucket, cover, and sealing pad were cleaned with tap water, and then rinsed thoroughly with ultrapure water. A total of 36 samples were collected, including 32 weekly and 4 biweekly samples. After each sampling, conductivity, pH, volume, and temperature were measured immediately. Conductivity and pH were determined using a conductivity meter (Hach Sens ION5) and a pH meter (Milwaukee SM102), respectively. Prior to ionic analysis, each sample was filtrated through a Teflon membrane filter (pore size: 0.45 μm) to remove insoluble particles and preserved in polyethylene bottles at 4 °C. Concentrations of K+, Ca2+, Na+, Mg2+, Cl−, F−, SO2− 4 , + NO− 3 , and NH4 were measured using ion chromatography (Dionex ICS-900). Each sample was measured three times and the percent relative standard deviation was less than 2.5% for each ion. Analysis of blank samples (one per month) showed that contamination during sampling, transport, and treatment was negligible. Analysis of simulated rainwater showed that the percent bias was less than 10% for each ion. The sample specific ionic concentrations were used to calculate monthly and annual Volume-Weighted Mean (VWM) concentrations ( C ) using Eq. (1). The monthly and annual VWM pH values were calculated using the monthly and annual VWM concentrations of H+, respectively. C¼

XN

XN

CQ= i¼1 i i

i¼1

Qi

ð1Þ

where Qi is the volume of the ith sample (mL) and Ci is the measured conductivity (μS cm−1) or the measured concentration of a given ion (μeq L−1). − + Wet deposition fluxes of SO2− 4 , NO3 , and NH4 were calculated using Eq. (2), and the overall wet deposition fluxes during the month or the year were calculated by adding the fluxes of each sample. F i ¼ KP i C i

ð2Þ

where F i is the flux of a given ion (kg S(N) ha − 1 ) during the ith sampling period; C i is the measured concentration of a given ion (μeq L− 1 ) in the ith sample; P i is the precipitation amount (mm) during the ith sampling period; and K is a unit conversion factor (K is 1.6 × 10− 6 for S and is 1.4 × 10− 6 for N species). 2− − The equivalent ratio of ([Ca2+] + [NH+ 4 ]) to ([SO4 ] + [NO3 ]) was calculated as a measure of the extent of acid neutralization in wet deposition (Huang et al., 2009). Neutralization factor (NF) was also calculated using Eq. (3) to compare the contributions of different alkaline species to acid neutralization in wet deposition (Huang et al., 2009): i h  2− − þ ½NO3  NFx ¼ ½X= SO4

ð3Þ

where X is the cation of interest (μeq L−1). 2.3. Source apportionment of ionic species The Positive Matrix Factorization (PMF) model (version 5.0, downloaded from http://www.epa.gov/heasd/research/pmf.html) developed by the U.S. Environmental Protection Agency (EPA) was used to analyze the major sources of ions in wet deposition. PMF has been extensively used to study sources of volatile organic compounds (Yuan et al., 2009), airborne particulate matter (Pražnikara et al., 2014), as well as wet deposition (Gratz et al., 2013). The PMF analysis

of wet deposition is based on the following chemical mass balance equation for a given chemical species in a wet deposition sample:

C i; j ¼

p X

f i;k g k; j þ ei; j

ð4Þ

k¼1

where Ci,j is the concentration of the ith species in the jth sample (μeq L−1); p is the number of sources that contribute to the measured concentration in the sample; fi,k is the relative fraction of the ith species in the kth source (μeq μeq−1); gk,j is the contribution of the kth source to the jth sample (μeq L−1); and ei,j is the residual error of the ith species in the jth sample (μeq L−1). The PMF analysis utilizes all available observation data to determine the optimal number of sources and the relative contribution of each source to each ion. In PMF, Eq. (4) represents a system of N × M equations, where N is the number of chemical species analyzed for each sample and M is the number of samples used in the PMF analysis. The source profile (f) and source contribution (g) matrixes are simultaneously determined using an iterative optimization technique that seeks to minimize the sum of the residual errors weighted by the uncertainty of each sample keeping positivity of the elements in the f and g matrixes. The advantage of the PMF model (and other receptor-oriented source apportionment models) to chemical transport modeling based source apportionment techniques (Kleeman and Cass, 2001) is that the PMF model is based on statistical analysis of observation data alone and thus avoids the uncertainties associated with modeling or parameterizing the physical and chemical processes that determine the pollutant concentrations from their emission source locations to receptor sites. 3. Results and discussion 3.1. Acidity, chemical composition, and flux of wet deposition The pH of samples varied from 5.06 to 8.01, with an annual VWM value of 5.95 (Table 1). The pH was lower in the wet season (from April to October) than in the dry season (from November to March). All the four samples with a pH lower than 5.60, which points to the pH of precipitation at equilibrium with atmospheric CO2 (Charlson and Rodhe, 1982), were collected in the wet season (Fig. 2b). Compared to the average pH of natural precipitation (Miller and Brewer, 2008), the pH in JNNR was higher, with 81% of samples having a pH above 6.00 (Fig. 3a). This high pH was associated with the ionic concentrations (Table 1). The ionic balance showed that a large amount of anion was not measured (Fig. 3b). Since limestone is the main bedrock of JNNR (Bureau of Geology and Mineral Exploration and Development of Sichuan Province, China (BGMEDSP), 2006), this anion deficiency was most likely related to the exclusion of HCO− 3 in ionic measurement and similar phenomena were found in other regions (Li et al., 2007). Among all the ions measured, Ca2+ occurred in the highest concentration, ranging from 28.9 to 812.2 μeq L−1 and with annual VWM and meoccurred in the dian concentrations both about 150 μeq L−1. SO2− 4 second highest concentration, ranging from 39.4 to 170.5 μeq L− 1 and with an annual VWM concentration of 70.5 μeq L−1. The annual + −1 , reVWM concentrations of NO− 3 and NH4 were 12.7 and 13.4 μeq L 2− spectively, much lower than the corresponding values of SO4 and − Ca2 +. The annual VWM equivalent ratios of [SO2− 4 ] to [NO3 ] and 2− − ([Ca2+] + [NH+ 4 ]) to ([SO4 ] + [NO3 ]) were 5.6 and 2.0, respectively. The annual VWM values of NFCa2 + and NFNH4 + were 1.8 and 0.2, respectively. All the above suggest that most of the time the acidity was largely neutralized mainly by Ca2 +, but JNNR still experienced acid in the wet season. rain mainly caused by SO2− 4 Table 1 also shows the concentrations of Na+, Cl−, K+, and F−. The annual VWM concentrations of Na+ and Cl− were 38.0 and 37.2 μeq L− 1, respectively. The existence of Na+ and Cl− in the wet

X. Qiao et al. / Science of the Total Environment 511 (2015) 28–36 Table 1 Conductivity, pH, and ionic composition of wet deposition in JNNR between April 2010 and May 2011. Concentrations of the ions are in unit of μeq L−1.

Sample volume (mL) pH Conductivity (μS cm−1) Cl− Na+ K+ NO3− NH+ 4 SO2− 4 2+ Ca Mg2+ F− NF2+ Ca + NFNH4 − a [SO2− 4 ]:[NO3 ] ½Ca2þþ½NH4þ a ½SO42−þ½NO3−

Total anion Total cation a

Range

Median

Annual VWM

80.0–3200.0 5.06–8.01 3.43–155.30 6.8–1003.2 7.7–304.3 0.9–767.6 6.2–34.8 0.2–61.2 39.4–170.5 28.9–812.2 30.6–71.7 11.5–59.2 0.4–6.6 0.0–0.6 2.4–12.9 0.5–6.9

1255 6.75 13.86 17.3 37.0 6.9 12.5 9.6 71.0 157.1 40.0 19.5 1.9 0.1 4.8 2.1

5.95 12.67 37.2 38.0 21.2 12.7 13.4 70.5 149.8 41.1 21.0 1.8 0.2 5.6 2.0

71–1198 85–1801

132 247

141 264

Equivalent ratio.

deposition was probably due to long-range transport of sea salt aerosols. K+ is usually considered as a tracer of biomass burning (Zunckel et al., 2003), and its concentration varied significantly from 0.9 to 767.6 μeq L− 1 in this study. The existence of a significant amount of F− (11.5–59.2 μeq L− 1) in the wet deposition may be an indication of coal combustion impact, as fluorine concentration is high in coals from China and no particular control is applied to remove fluorine (Dai et al., 2012).

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Precipitation amount, conductivity, and ionic concentrations showed pronounced seasonal variations (Fig. 2). Conductivity and concentrations of all the ions except NH+ 4 were lower in the wet season than in the dry season. This may be partially related to the higher dilution effect of precipitation on ionic concentrations in the wet season and associated with the longer residency time of ambient aerosols in the dry season. This explanation is supported by the findings that concentrations of total suspended particles (TSP) and the particulate concentra+ − 2− were lower in the wet tions of Ca2 +, K+, NO− 3 , Na , Cl , and SO4 + season (Qiao et al., 2014a). NH4 concentrations of wet deposition were lower in the dry season and this was probably related to lower NH3 emissions from agricultural activities in winter. Annual deposition fluxes of S and N are shown in Fig. 4. The annual + − wet deposition fluxes of SO2− 4 , NH4 , NO3 , and total inorganic nitrogen (TIN) were 8.06, 1.39, 1.29, and 2.68 kg S(N) ha−1, respectively. About 90% of these wet deposition fluxes occurred in the wet season. In parallel with the wet deposition observation, dry deposition was also monitored at the same site, and the results showed that annual dry + − deposition fluxes of SO2− 4 , NH4 , NO3 , and TIN were 0.61, 0.22, 0.14, and 0.36 kg S(N) ha−1, respectively (Qiao et al., 2014b; Fig. 4). These indicate that wet deposition accounted for about 90% of annual atmospheric inputs of the four species into JNNR. Larger amounts of precipitation and associated lower pH in the wet season suggest that the ecological effects of S and N wet deposition would be more severe in the wet season. 3.2. Comparison with remote sites 3.2.1. Wet deposition of S and N Chemical composition of wet deposition was compared between JNNR and five global background sites: Amsterdam Island in the

Fig. 2. Temporal variations of the amount, pH, conductivity, and ionic concentrations of wet deposition in JNNR between April 2010 and May 2011.

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Fig. 3. Frequency distribution of pH (a) and ionic balance (b) in the wet deposition samples collected in JNNR between April 2010 and May 2011.

Indian Ocean, Poker Plat in Alaska, Katherine in Australia, San Carlos de Rio Negro in Venezuela, and St. Georges in Bermuda (Galloway et al., 1982). These five sites had similar annual VWM pH, ranging from 4.78 − to 4.96 (Fig. 5a). The annual VWM concentrations of SO2− 4 , NO3 , and at these five sites were 2.9–36.3, 1.7–5.5, and 1.1–3.8 μeq L − 1, NH+ 4 respectively (Fig. 5a, b). Although chosen as a global background site, St. Georges in Bermuda was primarily controlled by anthropogenic emissions and had the highest annual VWM concentrations of SO2− 4 −1 (36.3 μeq L−1) and NO− ) among the five sites (Galloway 3 (5.5 μeq L et al., 1982). The composition and acidity of wet deposition at the other four sites were controlled by unknown mixtures of natural or anthropogenic processes (Galloway et al., 1982). Compared to these five global background sites, the annual VWM concentrations of SO2− 4 , + NO− 3 , and NH4 in JNNR were 1.94–24.3, 2.31–7.47, and 3.53–12.2 times higher, respectively, reflecting an apparent influence of anthropogenic emissions on wet deposition in JNNR. Since JNNR is located in the eastern rim of QTP, we also compared the chemical composition of wet deposition between JNNR and other sites in the plateau (Fig. 5), including Lhasa city and three nearby towns (Zhang et al., 2003), Nam Co (Li et al., 2007), Waliguan (Tang et al., 2000), and Xixabangma Peak of the central Himalayas (Kang and NO− et al., 2002). The concentrations of SO2− 4 3 in JNNR were 4.5– 100.7 and 1.2–11.5 times of the observations at the other QTP sites, respectively (Fig. 5a, b). The NH+ 4 concentration in JNNR was much higher than that in Xixabangma Peak, similar to the observations in Lhasa city and three nearby towns, and lower than that in Nam Co and Waliguan (Fig. 5b). Chemical fertilizers and coal were not intensively used in − QTP, and the higher concentrations of SO2− 4 and NO3 in JNNR may indicate that JNNR was more polluted by fossil fuel combustion compared to the other QTP sites. The concentrations and fluxes of S and N wet deposition were also compared between JNNR and the U.S. national protected areas (e.g., national parks, national wildlife refuges, and national grasslands) and NO− (Fig. 5). SO2− 4 3 concentrations in wet deposition showed declining trends in many U.S. protected areas since the late 1980s or

− + Fig. 4. Annual wet and dry deposition fluxes of SO2− 4 , NO3 , NH4 , and TIN in JNNR between April 2010 and May 2011. (Data source of dry deposition: Qiao et al., 2014b).

early 1990s (NPS, 2010), thus we included the data of the U.S. national protected areas collected in 1990 and 2013 (NTN, 2014). The annual + VWM concentrations and annual fluxes of NO− 3 , NH4 , and TIN in JNNR were in the same ranges of the observations in the U.S. protected areas (Fig. 5b, c), but the SO2− 4 concentration in JNNR was 2–20 times of the corresponding values in the U.S. protected areas. Despite the difference in precipitation amount, annual wet deposition flux of SO2− 4 was also higher in JNNR than in most U.S. protected areas (Fig. 5c). The an− nual equivalent ratio of [SO2− 4 ] to [NO3 ] was 5.6 in JNNR, much higher than the ratios in the U.S. protected areas but close to the ratios in Chongqing and Xi'an (EANET, 2012) (Fig. 6). The sites in Chongqing and Xi'an are hundreds of km away from JNNR, reflecting that high − ratio of SO2− 4 to NO3 in wet deposition was a regional phenomenon. 3.2.2. Acid neutralization in wet deposition Compared to the remote sites mentioned in Section 3.2.1, JNNR was and NO− much more polluted by acids (SO2− 4 3 ) but had higher pH (Fig. 5a), indicating that wet deposition in JNNR was well neutralized by alkaline species. Charlson and Rodhe (1982) reported that 0.38– 1.12 mg per liter of CaCO3 was sufficient to buffer natural rainwater with pH of 4.4–6.2 to alkaline rain. Ca2+ was the main acid neutralizer in JNNR, with concentrations of 28.9–812.2 μeq L−1 (1.44–40.6 mg of CaCO3 equivalent) (Table 1). As limestone is the main bedrock in JNNR (BGMEDSPC, 2006), most of the Ca2 + in JNNR was likely from the CaCO3 and CaO weathered from local crust. This explanation is supported by the results of PMF analysis (see Section 3.3). Although most of the time alkaline dust largely neutralized the acidity of wet deposition, acid rain continued to occur during the wet season (Fig. 2b), when concentrations of ambient alkaline dust were lower due to wet scavenging, as reflected by the lower concentrations of Ca2 + in wet deposition (Fig. 2i) and in TSP (Qiao et al., 2014a). 3.3. Source apportionment of the ionic species in wet deposition Supported by the literature, the analysis of the chemical composition data can give a general idea of the possible sources that can affect the chemical composition of wet deposition in JNNR. Fossil fuel combustion and agricultural activities were likely the main anthropogenic sources − + for SO2− 4 , NO3 , and NH4 wet deposition in JNNR, but their relative contributions cannot be determined from concentration analysis alone. This lack of detailed source contribution data makes it difficult for policy makers to develop effective emission controls to protect JNNR. In this study, a PMF source apportionment analysis revealed the contributions of different sources to ions in wet deposition. Fig. 7 shows a comparison of the observed and PMF predicted concentrations of chemical components for each sample. Excellent agreement was found for most of the ions, giving confidence that the PMF model captured the major sources and correctly quantified their contributions. The PMF analysis resolved five distinct sources (Fig. 8). The first source had high loadings of Na+ followed by Cl−, a clear signal of sea salt impact (Fig. 8a). However, the profile also contained a significant 2− amount of NO− 3 and SO4 , a typical characteristic of aged sea salt. Sea

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Fig. 5. Comparison of wet deposition in JNNRi with that in global background sitesii, the U.S. protected areasiii, and other QTP sites (Lhasa city and three nearby townsiv, Nam Cov, Waliguanvi, and 2+ − + 2− concentration and the equivalent ratio of Xixabangma Peak of central Himalayasvii). (a) SO2− 4 concentration and pH, (b) NO3 and NH4 concentrations, (c) SO4 and TIN fluxes, and (d) Ca i ii iii iv v vi vii 2− − ([Ca2+] + [NH+ 4 ]) to ([SO4 ] + [NO3 ]). ( This study; Galloway et al., 1982; NTN, 2014; Zhang et al., 2003; Li et al., 2007; Tang et al., 2000; and Kang et al., 2002).

salt aerosols were “aged” when they were transported from source regions to receptors by interacting with atmospheric H2SO4 and HNO3 from anthropogenic sources, replacing the more volatile acid HCl (Song and Carmichael, 1999). The second source had high loadings of K+ and Cl−, indicating a biomass burning source (Fig. 8b). Since biomass burning was strictly controlled locally, a significant fraction of the biomass burning signal must come from long-range transport. The third source had a high loading of Ca2+, representing a crustal or windblown dust source (Fig. 8c), as discussed in Section 3.2.2. The fourth − − source was enriched with SO2− 4 , NO3 , and F (Fig. 8d), indicating a fossil fuel combustion source. The large fraction of F− in the fourth factor indicates that it likely represents high sulfur fossil fuel combustion sources, especially coal-fired power plants, which are known to be a major source of atmospheric F− in China (Feng et al., 2003). The fifth source was dominated by NH+ 4 , suggesting an agricultural source (Fig. 8e). A clear secondary inorganic aerosol factor did not show up in the analysis. The percentage contributions of each source to annual fluxes of S and N wet deposition are shown in Fig. 9. Fossil fuel combustion was − − 2+ the main contributor to SO2− 4 (59%), NO3 (42%), F (85%), and Mg (71%). In addition to its significant contributions to the fluxes of Na+

(77%) and Cl− (25%), aged sea salt also contributed to 25% of SO2− 4 + flux and to 19% of NO− 3 flux. NH4 flux was mainly from agriculture (89%) and fossil fuel combustion (6%). NH3 existed in the exhaust from vehicles equipped with three-way catalysts designed to reduce NOx and VOC emissions (Kean and Harley, 2000). The PMF analysis also revealed that biomass burning could significantly contribute to the fluxes of K+ (78%) and Cl− (57%). Several episodes of high K+ and Cl− concentrations were identified in January and November, and these episodes were believed to be related to nearby wildfire and/or straw combustion, some of which are documented by the global fire inventory (Wiedinmyer et al., 2011). The existence of aged sea salt in the wet deposition agreed with the general understanding of the long-range transport patterns in this region. In summer and fall, air masses of precipitation in JNNR are mainly from the South China Sea, the Bay of Bengal, and the western Pacific Ocean (Zhou et al., 2006). Before arriving at JNNR, these air masses may gain a considerable amount of air pollutants from southern and western China, some regions of which have the highest emission densities of SO2, NO2, and NH3 in the world (Kurokawa et al., 2013). Paulot et al. (2013) also found that the Asia Summer Monsoon could push N from Southeast Asia and India to southwestern China where JNNR is

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i − Fig. 6. Comparison of the equivalent ratio of SO2− 4 to NO3 in wet deposition in JNNR with that at four sites in Xi'an and Chongqing (two EANET cities)ii, global background sitesiii, other sites in QTPiv, and the U.S. protected areasv. (iThis study; iiEANET, 2012; iii Galloway et al., 1982; ivZhang et al., 2003; and vNTN, 2014.).

located. Overall, wet deposition in JNNR may be considerably affected by the high emissions of SO2, NO2, and NH3 from some regions in China and South Asia, and relevant quantitative studies will be presented in future papers.

4. Conclusions Chemical composition of wet deposition was monitored in JNNR from April 2010 to May 2011. The results show that the annual − + VWM concentrations of SO2− 4 , NO3 , and NH4 were 70.5, 12.7, and 13.4 μeq L−1, respectively. The annual wet deposition fluxes of SO2− 4 , + −1 , respecNO− 3 , NH4 , and TIN were 8.06, 1.29, 1.39, and 2.68 kg S(N) ha tively, accounting for about 90% of annual atmospheric inputs of these species into JNNR. SO2− 4 was the main source of acidity and its annual VWM concentration in JNNR was much higher than the observations from global background sites, the U.S. protected areas, and other sites in QTP. However, about 80% of wet deposition samples collected

Fig. 7. Comparison of PMF predictions with observations for ionic concentrations (μeq L−1) in the wet deposition samples collected in JNNR.

Fig. 8. Predicted source profiles of PMF for wet deposition data collected in JNNR. The bars indicate source profiles (left y-axis), and the filled dots indicate percentage of species (right y-axis) attributed to that source.

in JNNR had a pH above 6.00 due to the high acid neutralization capacity from Ca2 +, most of which is from local limestone. When ambient alkaline dust concentration was low in the wet season, acid rain continued to occur.

Fig. 9. Percentage contributions of aged sea salt, crust, agriculture, fossil fuel combustion, and biomass burning to annual wet deposition flux of each ion in JNNR between April 2010 and May 2011.

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The acidity, ionic concentrations, and fluxes of wet deposition showed pronounced seasonal variations. In addition to pH, concentrations of all the ions except NH+ 4 were lower in the wet season, but − + about 90% of annual wet deposition fluxes of SO2− 4 , NO3 , and NH4 occurred in this period. These seasonal variations of wet deposition chemistry were associated with the seasonal variations in precipitation amount, air pollutant emissions, the residency time of ambient alkaline species, and the dilution effect of precipitation on ionic concentrations. Larger amounts of precipitation and associated lower pH in the wet season suggest that the ecological effects of S and N wet deposition would be more severe in the wet season. Anthropogenic sources have dominated the wet deposition fluxes of − + SO2− 4 , NO3 , and NH4 in JNNR. Specifically, fossil fuel combustion, agriculture, and aged sea salt contributed to 99% and 83% of annual wet deposition fluxes of SO24 − and NO− 3 , respectively. Agriculture alone contributed to 89% of annual wet deposition flux of NH+ 4 . Since anthropogenic emissions have elevated S and N deposition and caused acid rain in JNNR, further studies are needed to better quantify the regional sources and ecological effects of S and N deposition for JNNR. Supplementary data to this article can be found online at http://dx. doi.org/10.1016/j.scitotenv.2014.12.028. Acknowledgments This study is sponsored by the International Program of the Ministry of Science and Technology of China (2010DFA91280) and the Program of Introducing Talents of Discipline to Universities (B08037). We thank Amanda Schmidt, Josh Schmidt, Hui Jin, Jie Du, Xiaoyan Shangguan, and Yan Wang for their assistance during the field sampling. We thank Thomas Hinckley for language editing. References Bergström, A., Jansson, M., 2006. Atmospheric nitrogen deposition has caused nitrogen enrichment and eutrophication of lakes in the northern hemisphere. Glob. Change Biol. 12, 635–643. BGMEDSPC, 2006. Geological Environment and Water Recycling in the Key Scenery Regions of Jiuzhaigou and Huanglong: Monitoring, Protection, and Roles in Scenery Formation. Bureau of Geology and Mineral Exploration and Development of Sichuan Province, China; Chengdu. Bytnerowicz, A., Omasa, K., Paoletti, E., 2007. Integrated effects of air pollution and climate change on forests: a northern hemisphere perspective. Environ. Pollut. 147, 438–445. Cao, H.F., 1989. Air pollution and its effects on plants in China. J. Appl. Ecol. 26, 763–773. Charlson, R.J., Rodhe, H., 1982. Factors controlling the acidity of natural rainwater. Nature 295, 683–685. Chen, X.Y., Mulder, J., 2007. Atmospheric deposition of nitrogen at five subtropical forested sites in South China. Sci. Total Environ. 378 (3), 317–330. Dai, S.F., Ren, D., Chou, C.L., Finkelman, R.B., Seredin, V.V., Zhou, Y.P., 2012. Geochemistry of trace elements in Chinese coals: a review of abundances, genetic types, impacts on human health, and industrial utilization. Int. J. Coal Geol. 94, 3–21. EANET, 2012. Data report on the acid deposition in the East Asian region 2010. Acid Deposition Monitoring Network in East Asia. Available at:. http://www.eanet.asia/ product/datarep/datarep10/datarep10.pdf. Ellis, R.A., Jacob, D.J., Payer, J.M., Zhang, L., Holmes, C.D., Schichtel, B.A., Blett, T., Porter, E., Pardo, L.H., Lynch, J.A., 2013. Present and future nitrogen deposition to national parks in the United States: critical load exceedances. Atmos. Chem. Phys. 13, 9151–9178. Fang, Y.T., Gundersen, P., Mo, J.M., Zhu, W.X., 2009. Nitrogen leaching in response to increased nitrogen inputs in subtropical monsoon forests in southern China. For. Ecol. Manag. 257, 332–342. Feng, Y.W., Ogura, N., Feng, Z.W., Zhang, F.Z., Shimizu, H., 2003. The concentrations and sources of fluoride in atmospheric depositions in Beijing, China. Water Air Soil Pollut. 145, 95–107. Galloway, J.N., Likens, G.E., Keene, W.C., Miller, J.M., 1982. The composition of precipitation in remote areas of the world. J. Geophys. Res. 87, 8771–8786. Gratz, L.E., Keeler, G.J., Morishita, M., Barres, J.A., Dvonch, J.T., 2013. Assessing the emission sources of atmospheric mercury in wet deposition across Illinois. Sci. Total Environ. 448, 120–131. Gu, Y., Du, J., Tang, Y., Qiao, X., Bossard, C., Deng, G.P., 2013. Challenges for sustainable tourism in Jiuzhaigou World Natural Heritage site, western China. Nat. Resour. Forum 37, 103–112. He, C.E., Wang, X., Liu, X.J., Fangmeier, A., Christie, P., Zhang, F.S., 2010. Nitrogen deposition and its contribution to nutrient inputs to intensively managed agricultural ecosystems. Ecol. Appl. 20, 80–90. Huang, D.Y., Xu, Y.G., Peng, P.A., Zhang, H.H., Lan, J.B., 2009. Chemical composition and seasonal variation of acid deposition in Guangzhou South China: comparison with precipitation in other major Chinese cities. Environ. Pollut. 157, 35–41.

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