Abstract
Abstract. With the rising anthropogenic emissions from human activities, elevated concentrations of air pollutants have been detected in the hemispheric air flows in recent years, aggravating the regional air pollution and deposition issues. However, the regional contributions of hemispheric air flows to deposition have been given little attention in the literature. In this light, we assess the impact of hemispheric transport on sulfur (S) and nitrogen (N) deposition for six world regions: North America (NA), Europe (EU), South Asia (SA), East Asia (EA), Middle East (ME) and Russia (RU) in 2010, by using the multi-model ensemble results from the 2nd phase of the Task Force Hemispheric Transport of Air Pollution (HTAP II) with 20 % emission perturbation experiments. About 27 %–58 %, 26 %–46 % and 12 %–23 % of local S, NOx and NH3 emissions and oxidation products are transported and removed by deposition outside of the source regions annually, with seasonal variation of 5 % more in winter and 5 % less in summer. The 20 % emission reduction in the source regions could affect 1 %–10 % of deposition in foreign continental regions and 1 %–14 % in foreign coastal regions and the open ocean. Significant influences are found from NA to the North Atlantic Ocean (2 %–14 %), and from EA to the North Pacific Ocean (4 %–10 %) and to western NA (4 %–6 %) (20 % emission reduction). The impact on deposition caused by short-distance transport between neighboring regions (i.e., from EU to RU) occurs throughout the whole year (slightly stronger in winter), while the long-range transport (i.e., from EA to NA) mainly takes place in spring and fall, which is consistent with the seasonality found for hemispheric transport of air pollutants. Deposition in the emission-intensive regions such as US, SA and EA is dominated (∼80 %) by own-region emissions, while deposition in the low-emission-intensity regions such as RU is almost equally affected by foreign exported emissions (40 %–60 %) and own-region emissions. We also find that deposition of the coastal regions or the near-coastal open ocean is twice more sensitive to hemispheric transport than the non-coastal continental regions, especially for regions in the downwind direction of emission sources (i.e., west coast of NA). This study highlights the significant impacts of hemispheric transport of air pollution on the deposition in coastal regions, the open ocean and low-emission-intensity regions. Further research is proposed to improve the ecosystem and human health, with regards to the enhanced hemispheric air flows.
Highlights
The increasing consumption of energy by human activities has largely increased the deposition of nitrogen (N) over the terrestrial and marine ecosystem (Kim et al, 2011; Galloway et al, 2008; Duce et al, 2008)
What are the contributions of hemispheric transport and own-region emissions on local deposition? In line with the analysis for other pollutants, to this purpose we evaluate the so-called response to extraregional emission reduction (RERER) metric
This study assesses the impact of hemispheric transport on S and N deposition for six regions: North America (NA), Europe (EU), South Asia (SA), East Asia (EA), Russia (RU) and Middle East (ME), by using multi-model ensemble results from 11 models of Hemispheric Transport of Air Pollution (HTAP II), with simulations under base case and 20 % emission perturbation scenario for each region
Summary
The increasing consumption of energy by human activities has largely increased the deposition of nitrogen (N) over the terrestrial and marine ecosystem (Kim et al, 2011; Galloway et al, 2008; Duce et al, 2008). The NOx emissions have increased by about 10 Tg(N) from 2001 to 2010, due to the large increase in Asian regions (Tan et al, 2018), while recent studies have reported the year 2011 as the turning point for NOx emissions from China (Li et al, 2017; Liu et al, 2016). The SO2 emission in China experiences increases from 2000 to 2005 due to energy consumption and decreases after 2006 thanks to the implementation of flue-gas desulfurization systems on power plants. The prevention and control of exceeding deposition have become growing worldwide concerns
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