Atmospheric wet deposition, in the forms of precipitation or snow, is considered the most effective approach to removing pollutants from the atmosphere.1 The components of atmospheric wet deposition, such as nitrogen (N), phosphorus (P), sulfate, heavy metal, and volatile organic compound (VOC), vary which depend on the source of emission and the intensity of human activities in a specific area.2-3 In recent decades, atmospheric wet deposition aroused concerns not only because it became an important source of bioavailable nutrient (e.g., N and P) input to natural ecosystems, but also an input of toxic heavy metal and acid deposition which deteriorated environment pollution.
Previous researches on atmospheric precipitation chemistry largely focused on urban site, while natural ecosystems in suburban or remote areas received less attention. For example, in 1992, the National Acid Deposition Monitoring Network of China was built to monitor and control acid rain (observation parameters include pH and conductivity). Later on, an N Pollution Monitoring Network was established to observe nitric oxides (NOX) and N dioxide (NO2) in city. Most of these monitoring sites were located in China’s eastern developed areas, and much fewer in the western remote areas.4 Meanwhile, relatively singular monitoring parameters were employed.5 However, as our economy and technology develop, the environmental problems we face also evolve. In these circumstances, the relatively singular monitoring parameters cannot reflect the actual status of environment, and a systematic, comprehensive observation system is in need. Therefore, it is vital to build a systematic network for atmospheric wet deposition observation, which covers urban, natural and agricultural ecosystems.
In 2013, based on stations from the Chinese Ecosystem Research Network (CERN)6, we constructed a China Wet Deposition Observation Network (ChinaWD). ChinaWD network can monitor atmospheric N, P, sulfate, base cations, and heavy metal depositionsynchronously,2-3, 7-9and monitoring of VOCs and precipitation isotope can be expected in near future. By the end of 2018, ChinaWD network had run stably for 6 years and there were 54 stations in the network (from 41 stations in 2013 to 54 stations in 2018).The sites cover all major terrestrial ecosystems in China, including forest, grassland, desert, lake, marsh and karst ecosystems, and encompass eight ecological regions according to climate and vegetation types (Figure1). This study mainly introduced the performance, metrics, and data services of ChinaWD network., and included information on wet nitrogen (N), phosphorus (P), and acid deposition from 41 sites across China in 2013.
Fig.1
China Wet Deposition Observation Network (ChinaWD) 
