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Discussion papers
https://doi.org/10.5194/acp-2019-418
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2019-418
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 25 Jun 2019

Research article | 25 Jun 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Decoding long-term trends in the wet deposition of sulfate, nitrate and ammonium after reducing the perturbation from climate anomalies

Xiaohong Yao1 and Leiming Zhang2 Xiaohong Yao and Leiming Zhang
  • 1Key Lab of Marine Environmental Science and Ecology, Ocean University of China, Qingdao 266100, China
  • 2Air Quality Research Division, Science and Technology Branch, Environment and Climate Change Canada, Toronto, Canada

Abstract. Long-term trends of wet deposition of inorganic ions are affected by multiple factors, among which emission changes and climate conditions are dominant ones. To assess the effectiveness of emission reductions on the wet deposition of pollutants of interest, contributions from these factors to the long-term trends of wet deposition must be isolated. For this purpose, a two-step approach for preprocessing wet deposition data is presented herein. This new approach aims to reduce the impact of climate anomalies on the trend analysis so that the impact of emission reductions on wet deposition can be revealed. This approach is applied to a two-decade wet deposition dataset of sulfate (SO42−), nitrate (NO3) and ammonium (NH4+) at rural Canadian sites. Analysis results show that the approach allows for robustly identifying inflection points on decreasing trends in the wet deposition fluxes of SO42− and NO3 in northern Ontario and Québec. The inflection points match well with the three-phase mitigation of SO2 emissions and two-phase mitigation of NOx emissions in Ontario. Improved correlations between the wet deposition of ions and their precursors' emissions were obtained after reducing the impact from climate anomalies. Furthermore, decadal climate anomalies were identified as dominating the decreasing trends in the wet deposition fluxes of SO42− and NO3 at a western coastal site. Long-term variations in NH4+ wet deposition showed no clear trends due to the compensating effects between NH3 emissions, climate anomalies, and chemistry associated with the emission changes of sulfur and nitrogen.

Xiaohong Yao and Leiming Zhang
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Status: open (until 20 Aug 2019)
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Xiaohong Yao and Leiming Zhang
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Latest update: 19 Jul 2019
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Short summary
An innovative approach is developed to preprocess monitored wet deposition data of inorganic ions for generating their decadal trends. Differing from traditional approaches which directly apply annual or seasonal averaged data to trend analysis tools, the proposed new approach makes use of slopes of regression equations between a series of study years and a climatology (base) year in terms of monthly averaged data. The new approach yields more robust results than the traditional tools.
An innovative approach is developed to preprocess monitored wet deposition data of inorganic...
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