Aohan Tang

Enhanced nitrogen deposition over China

China is experiencing intense air pollution caused in large part by anthropogenic emissions of reactive nitrogen. These emissions result in the deposition of atmospheric nitrogen (N) in terrestrial and aquatic ecosystems, with implications for human and ecosystem health, greenhouse gas balances and biological diversity. However, information on the magnitude and environmental impact of N deposition in China is limited. Here we use nationwide data sets on bulk N deposition, plant foliar N and crop N uptake (from long-term unfertilized soils) to evaluate N deposition dynamics and their effect on ecosystems across China between 1980 and 2010. We find that the average annual bulk deposition of N increased by approximately 8 kilograms of nitrogen per hectare (P < 0.001) between the 1980s (13.2 kilograms of nitrogen per hectare) and the 2000s (21.1 kilograms of nitrogen per hectare). Nitrogen deposition rates in the industrialized and agriculturally intensified regions of China are as high as the peak levels of deposition in northwestern Europe in the 1980s, before the introduction of mitigation measures. Nitrogen from ammonium (NH4+) is the dominant form of N in bulk deposition, but the rate of increase is largest for deposition of N from nitrate (NO3−), in agreement with decreased ratios of NH3 to NOx emissions since 1980. We also find that the impact of N deposition on Chinese ecosystems includes significantly increased plant foliar N concentrations in natural and semi-natural (that is, non-agricultural) ecosystems and increased crop N uptake from long-term-unfertilized croplands. China and other economies are facing a continuing challenge to reduce emissions of reactive nitrogen, N deposition and their negative effects on human health and the environment.

Concentrations and isotopic characteristics of atmospheric reactive nitrogen around typical sources in Beijing, China

With rapid economic growth in China, anthropogenic reactive nitrogen (Nr) emissions have more than doubled over the last two or three decades. Atmospheric Nr pollution is an environmental concern in China especially in megacities such as Beijing. In order to identify the impact of emission sources on atmospheric Nr pollution, we measured atmospheric Nr concentrations and their isotopic composition (δ15N) dynamics at three typical sites: landfill, pig farm and road traffic sites in Beijing from April 2010 to March 2011. Passive samplers were used for monitoring ammonia (NH3) and nitrogen dioxide (NO2), two major Nr species, while their δ15N values were measured by a diffusion method combined with mass spectrometer approach. The raw water pool of the landfill and fattening house of the pig farm were important NH3 sources with mean NH3 concentrations being 2,829 and 2,369 µg/m3, respectively, while the road traffic site was a minor NH3 source (10.6 µg/m3). NH3 concentrations at sites besides the landfill and roads were high in summer and low in winter due to the annual variation of temperature and the change of emission source intensity. In contrast, the NH3 concentrations inside the pig farm house were high in winter and low in summer, for the barn windows were open in summer and closed in winter. The mean NO2 concentrations were 89.8, 32.9 and 23.0 µg/m3 at the road traffic, the landfill and pig farm sites, respectively. Due to vehicle fuel combustion, NO2 concentration at the road traffic was the highest among the three sources, and the road traffic was a main NO2 emission source. PM10, pNH4+ and pNO3–concentrations in particulate matter were higher in summer than in winter (except PM10 for the pig farm). The δ15NH3 values ranged from–19.14‰ to 7.82‰, with an average of–0.05‰ for the landfill site, and the lowest values were observed in June and July. The δ15NH3 values for the pig farm site ranged from–29.78‰ to–14.05‰ with an average of–24.51‰, and the δ15NH3 values were more negative in summer than in the other seasons. The δ15NO2 values were–9.63‰ to 7.04‰ with an average of–3.72‰ for the road traffic site. The δ15NO2 values were more negative in summer than those in the other seasons. The different δ15N values for the various Nr species in different sources may serve as important indicators for identifying atmospheric Nr sources in megacities. The results may also provide the theoretical basis for research on the atmospheric N deposition and its sources.

Erratum to: Atmospheric Nitrogen Emission, Deposition, and Air Quality Impacts in China: an Overview

In the recently published review paper BAtmospheric Nitrogen Emission, Deposition, and Air Quality Impacts in China: an Overview,^ the following author name and affiliation were inadvertently omitted from the author list: Yunhua Chang, Yale-NUIST Center on Atmospheric Environment, Nanjing University of Information Science and Technology, Nanjing, 210044, China. Dr. Chang was responsible for writing the section, BNH3 Emission^. The authors acknowledge Dr. Chang’s equal contribution to the paper. The citation of the paper should be as follows: LiuX.J., XuW., Duan L., Du E.Z., PanY.P., LuX.K., Zhang L., Wu Z.Y., Wang X.M., Zhang Y., Shen J.L., Song L., Feng Z.Z., Liu X.Y., Song W., Tang A.H., Zhang Y.Y., Zhang X.Y., Collett Jr. J., Chang Y.H., 2017. Atmospheric nitrogen emission, deposition and air quality impacts in China: An overview. Current Pollution Reports, doi:10.1007/s40726-017-0053-9.

Atmospheric deposition of inorganic nitrogen in a semi-arid grassland of Inner Mongolia, China

Due to increasing global demand for crop production and energy use, more and more reactive nitrogen (Nr) has been generated and emitted to the environment. As a result, global atmospheric nitrogen (N) deposition has tripled since the industrial revolution and the ecological environment and human health have been harmed. In this study, we measured dry and wet/bulk N deposition from July 2013 to December 2015 in a semi-arid grassland of Duolun County, Inner Mongolia, China. The samples of dry and wet/bulk N deposition were collected monthly with a DELTA (DEnuder for Long Term Atmospheric sampling) system and with Gradko passive samplers and a precipitation gauge. The measured results show that the annual mean concentrations of NH3, NO2, HNO3, particulate NH4+ (pNH4+) and particulate NO3− (pNO3−) in atmosphere were 2.33, 1.90, 0.18, 1.42 and 0.42 μg N/m3, respectively, and that the annual mean volume-weighted concentrations ofNH4+-N and NO3−-N in precipitation were 2.71 and 1.99 mg N/L, respectively. The concentrations of Nr components (including NH3, NO2, HNO3, pNH4+, pNO3−,NH4+-N and NO3−-N) exhibited different seasonal variations. Specifically, NO2 and HNO3 exhibited higher concentrations in autumn than in summer, while the other Nr components (NH3, pNH4+, pNO3−,NH4+-N and NO3−-N) showed the highest values in summer. Based on measured concentrations of Nr components and their deposition velocities estimated using the GEOS-Chem global atmospheric chemical transport model, the calculated annual mean dry deposition fluxes were 3.17, 1.13, 0.63, 0.91 and 0.36 kg N/(hm2•a) for NH3, NO2, HNO3, pNH4+ and pNO3−, respectively, and the calculated annual mean wet/bulk deposition fluxes were 5.37 and 3.15 kg N/(hm2•a) forNH4+-N and NO3−-N, respectively. The estimated annual N deposition (including dry N deposition and wet/bulk N deposition) reached 14.7 kg N/(hm2•a) in grassland of Duolun County, approaching to the upper limit of the N critical load (10–15 kg N/(hm2•a)). Dry and wet/bulk deposition fluxes of all Nr components (with an exception of HNO3) showed similar seasonal variations with the maximum deposition flux in summer and the minimum in winter. Reduced Nr components (e.g., gaseous NH3 and pNH4+ in atmosphere andNH4+-N in precipitation) dominated the total N deposition at the sampling site (accounted for 64% of the total N deposition), suggesting that the deposited atmospheric Nr mainly originated from agricultural activities. Considering the projected future increases in crop and livestock production in Inner Mongolia, the ecological and human risks to the negative effects of increased N deposition could be increased if no mitigation measures are taken.