Spatial–temporal patterns of inorganic nitrogen air concentrations and deposition in eastern China

Abstract

Abstract. Five-year (2011–2015) measurements of gaseous NH3, NO2, and HNO3 and particulate NH4+ and NO3− in air and/or precipitation were conducted at 27 sites in the Nationwide Nitrogen Deposition Monitoring Network (NNDMN) to better understand spatial and temporal (seasonal and annual) characteristics of reactive nitrogen (Nr) concentrations and deposition in eastern China. Our observations reveal annual average concentrations (16.4–32.6 µg N m−3), dry deposition fluxes (15.8–31.7 kg N ha−1 yr−1), and wet/bulk deposition fluxes (18.4–28.0 kg N ha−1 yr−1) based on land use, ranked as urban > rural > background sites. Annual concentrations and dry deposition fluxes of each Nr species in air were comparable at urban and background sites in northern and southern regions, but were significantly higher at northern rural sites. These results, together with good agreement between spatial distributions of NH3 and NO2 concentrations determined from ground measurements and satellite observations, demonstrate that atmospheric Nr pollution is heavier in the northern region than in the southern region. No significant inter-annual trends were found in the annual Nr dry and wet/bulk N deposition at almost all of the selected sites. A lack of significant changes in annual averages between the 2013–2015 and 2011–2012 periods for all land use types suggests that any effects of current emission controls are not yet apparent in Nr pollution and deposition in the region. Ambient concentrations of total Nr exhibited non-significant seasonal variation at all land use types, although significant seasonal variations were found for individual Nr species (e.g. NH3, NO2, and pNO3−) in most cases. In contrast, dry deposition of total Nr exhibited a consistent and significant seasonal variation at all land use types, with the highest fluxes in summer and the lowest in winter. Based on sensitivity tests by the GEOS-Chem model, we found that NH3 emissions from fertilizer use (including chemical and organic fertilizers) were the largest contributor (36 %) to total inorganic Nr deposition over eastern China. Our results not only improve the understanding of spatial–temporal variations of Nr concentrations and deposition in this pollution hotspot, but also provide useful information for policy-makers that mitigation of NH3 emissions should be a priority to tackle serious N deposition in eastern China.

Spatial and seasonal patterns of atmospheric nitrogen deposition in North China

“…In addition, the areas with highest N deposition (>80 kg N ha −1 yr −1 ) were dotted (such as the megacities of Beijing and Jinan) or zonal (such as the city belt from Shijiazhuang to Zhengzhou); the lowest N deposition areas (<40 kg N ha −1 yr −1 ) were mostly concentrated in forests and grasslands ( Figure S2). This spatial distribution of N deposition is consistent with the conclusions reported by Xu et al (2018) based on ground monitoring; that is, the total N deposition in urban areas is higher than that in rural areas, and that in rural areas is higher than at background sites.…”

Impacts of climate change and emissions on atmospheric oxidized nitrogen deposition over East Asia

“…For models showing agreement with the ensemble mean, if more than half of the models show statistical significance at 95% level, then the ensemble mean change for that particular grid is considered to be statistically significant. likely caused by the high deposition velocity (Zhang et al, 2017) and wet deposition due to larger precipitation in summer, consistent with previous studies (Liu et al, 2017;Zhang et al, 2017;Xu et al, 2018). Over the ocean such as Yellow Sea and East China Sea, the notably higher NOy deposition (first row of Fig.…”

Impacts of climate change and emissions on atmospheric oxidized nitrogen deposition over East Asia

“…2a) from eastern China to the coastal areas. Seasonal variations show that over mainland China summer is the season with the highest dry and wet NO y deposition, with high dry deposition likely caused by the high deposition velocity and wet deposition due to more precipitation in summer, consistent with previous studies ; Zhang et al, 2017;Xu et al, 2018). Over the Yellow Sea and East China Sea, the notably higher NO y deposition (first row of Fig.…”