Department of Geography, National Taiwan University, No. 1, Sec. 4, Roosevelt Rd., Taipei 10617, Taiwan.
Taiwan Forestry Research Institute, 53 Nanhai Rd., Taipei 10066, Taiwan.
Sci Total Environ. 2017 Dec 15;605-606:88-98. doi: 10.1016/j.scitotenv.2017.06.158. Epub 2017 Jun 27.
Long-term monitoring of precipitation chemistry provides a great opportunity to examine the evolution of air pollutant emissions and effectiveness of air pollution control measures. We evaluated the characteristics and trends of precipitation chemistry at both annual and seasonal scales based on the records of 1994-2013 at Fushan Experimental Forest (FEF) of northeastern Taiwan. The results showed that 77% of the weekly precipitation had pH<5.0. The two-decadal average annual pH was 4.62, without a significant inter-annual trend, possibly due to the concurrent declines of both acidic pollutants and base cations. There was a significant positive relationship between [SO+NO] and [Ca+NH] indicating that their deposition was likely dominated by NHNO, (NH)SO, Ca(NO), and CaSO. There was a significant negative relationship between precipitation pH and the difference between [SO+NO] and [Ca+NH], not just [SO+NO], suggesting that precipitation acidity was not solely determined by acidic pollutants but by the balance between acidic pollutants and base cations. We also found temporal decreases of Ca and NH concentrations in precipitation which contributed to the low acid neutralization capacity of precipitation. Annual deposition of NO and SO was 23 and 55kghayr, which is much higher than most forest sites in the industrialized countries suggesting that acid deposition is still a major environmental issue in Taiwan. Annual deposition of NH, Ca and NO showed significant decreasing trends during the 20-year period, which was mostly due to the decreases in the summer deposition associated with air pollution mitigation strategies. Winter deposition showed no decreasing patterns for the same period. The high contribution to annual acid deposition from autumn-winter and spring rains (50%) associated with northeast monsoon implies that long-range transport of anthropogenic emissions from East Asia played a key role on acid depositions at FEF and possibly many areas in the region. Therefore, intergovernmental cooperation is urgently needed to effectively mitigate the threat of acid deposition in East Asia.
长期监测降水化学提供了一个很好的机会来检验空气污染物排放的演变和空气污染控制措施的有效性。我们根据台湾东北部福山实验林（FEF）1994-2013 年的记录，在年际和季节尺度上评估了降水化学的特征和趋势。结果表明，每周有 77%的降水 pH 值<5.0。二十年平均年 pH 值为 4.62，没有显著的年际趋势，这可能是由于酸性污染物和碱性阳离子同时下降所致。[SO+NO]和[Ca+NH]之间存在显著的正相关关系，表明它们的沉积可能主要由 NHNO、(NH)SO、Ca(NO)和 CaSO 控制。降水 pH 值与[SO+NO]和[Ca+NH]之间的差值呈显著负相关，而不仅仅是[SO+NO]，这表明降水酸度不仅由酸性污染物决定，还由酸性污染物和碱性阳离子之间的平衡决定。我们还发现，降水酸度呈下降趋势，这是由于降水酸度呈下降趋势，导致降水的中和能力较低。NO 和 SO 的年沉降量分别为 23 和 55kg ha yr，远高于工业化国家的大多数森林地区，这表明酸沉降仍然是台湾的一个主要环境问题。在 20 年期间，NH、Ca 和 NO 的年沉降量呈显著下降趋势，这主要是由于与空气污染缓解策略相关的夏季沉降量减少所致。同期冬季沉降量没有下降趋势。与东北季风相关的秋冬春雨（50%）对年酸沉降的高贡献意味着东亚人为排放的长程传输对 FEF 及该地区许多地区的酸沉降起着关键作用。因此，迫切需要政府间合作，以有效减轻东亚酸沉降的威胁。
