Abstract:As a primary basic gas in the atmosphere, atmospheric ammonia (NH 3 ) plays an important role in determining air quality, environmental degradation, and climate change. However, the limited ground observation currently presents a barrier to estimating ground NH 3 concentrations on a regional scale, thus preventing a full understanding of the atmospheric processes in which this trace gas is involved. This study estimated the ground NH 3 concentrations over China, combining the Infrared Atmospheric Sounding Interferometer (IASI) satellite NH 3 columns and NH 3 profiles from an atmospheric chemistry transport model (CTM). The estimated ground NH 3 concentrations showed agreement with the variability in annual ground NH 3 measurements from the Chinese Nationwide Nitrogen Deposition Monitoring Network (NNDMN). Great spatial heterogeneity of ground NH 3 concentrations was found across China, and high ground NH 3 concentrations were found in Northern China, Southeastern China, and some areas in Xinjiang Province. The maximum ground NH 3 concentrations over China occurred in summer, followed by spring, autumn, and winter seasons, which were in agreement with the seasonal patterns of NH 3 emissions in China. This study suggested that a combination of NH 3 profiles from CTMs and NH 3 columns from satellite obtained reliable ground NH 3 concentrations over China.
Soil mercury (Hg) pollution in some areas of China is a serious problem and has aroused a lot of attention on a local scale. However, there are few studies on Hg pollution on a national scale. This study collected 444 published papers during 2005-2015 on Hg concentrations in agricultural soil throughout China, under seven land uses, namely: dry land, paddy field, vegetable field, tea garden, orchard, traditional Chinese medicine field and tobacco field, to assess the spatial distribution of Hg concentration and evaluate its influence on food safety. The averaged Hg concentration (0.108 mg/kg) was higher than its background (0.065 mg/kg), but much lower than the guidelines (GB15618-1995 II) for crop production. The spatial distribution of Hg throughout China showed great variability, with some hotspots due to Hg related mining and smelting activities. According to the Environment Quality Standard for soil in China (GB15618-1995 II), 4.2% of agricultural soil should be abandoned due to Hg pollution, and 2.0% faced a high risk of Hg pollution.
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