Preprints
https://doi.org/10.5194/acp-2020-1179
https://doi.org/10.5194/acp-2020-1179

  28 Dec 2020

28 Dec 2020

Review status: a revised version of this preprint is currently under review for the journal ACP.

Insights into seasonal variation of wet deposition over Southeast Asia via precipitation adjustment from the findings of MICS-Asia III

Syuichi Itahashi1,2, Baozhu Ge3,4,5, Keiichi Sato6, Zhe Wang3,5,7, Junichi Kurokawa6, Jiani Tan8,9, Kan Huang9,10, Joshua S. Fu9, Xuemei Wang11, Kazuyo Yamaji12, Tatsuya Nagashima13,14, Jie Li3,4,5, Mizuo Kajino2,14, Gregory R. Carmichael15, and Zifa Wang3,4,5 Syuichi Itahashi et al.
  • 1Environmental Science Research Laboratory, Central Research Institute of Electric Power Industry (CRIEPI), Abiko, Chiba 270–1194, Japan
  • 2Meteorological Research Institute (MRI), Tsukuba, Ibaraki 305–0052, Japan
  • 3State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry (LAPC), Institute of Atmospheric Physics (IAP), Chinese Academy of Sciences (CAS), Beijing 100029, China
  • 4Collage of Earth Science, University of Chinese Academy of Sciences, Beijing 100049, China
  • 5Center for Excellence in Urban Atmospheric Environment, Institute of Urban Environment, Chinese Academy of Sciences (CAS), Xiamen 361021, China
  • 6Asia Center for Air Pollution Research (ACAP), 1182 Sowa, Nishi-ku, Niigata, Niigata 950–2144, Japan
  • 7Research Institute for Applied Mechanics (RIAM), Kyushu University, Fukuoka 816-8580, Japan
  • 8Multiphase Chemistry Department, Max Planck Institute for Chemistry, Mainz 55128, Germany
  • 9Department of Civil and Environmental Engineering, University of Tennessee, Knoxville, TN 37996, USA
  • 10Department of Environmental Science and Engineering, Fudan University, Shanghai 200433, China
  • 11Institute for Environment and Climate Research, Jinan University, Guangzhou 510275, China
  • 12Graduate School of Maritime Sciences, Kobe University, Kobe, Hyogo 658–0022, Japan
  • 13National Institute for Environmental Studies (NIES), Tsukuba, Ibaraki 305–8506, Japan
  • 14Faculty of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305–8572, Japan
  • 15Center for Global and Regional Environmental Research, University of Iowa, Iowa City, IA 52242, USA

Abstract. Asia has attracted research attention because it has the highest anthropogenic emissions in the world, and the Model Inter-Comparison Study for Asia (MICS-Asia) Phase III was carried out to foster our understanding on the status of air quality over Asia. This study analyzed wet deposition in Southeast Asian countries (Myanmar, Thailand, Lao People's Democratic Republic (PDR), Cambodia, Vietnam, the Philippines, Malaysia, and Indonesia) with the aim of providing insights into the seasonal variation of wet deposition. Southeast Asia was not fully considered in MICS-Asia Phase II due to a lack of observational data; however, the analysis period of MICS-Asia III, namely, the year 2010, is covered by ground observations of the Acid Deposition Monitoring Network in East Asia (EANET), and the coordinated simulation domain was extended to cover these observation sites. The analyzed species are wet depositions of S (sulfate aerosol, sulfur dioxide (SO2), and sulfuric acid (H2SO4)), N (nitrate aerosol, nitrogen monoxide (NO), nitrogen dioxide (NO2), and nitric acid (HNO3)), and A (ammonium aerosol and ammonia (NH3)). The wet deposition simulated with seven models driven by unified meteorological model in MICS-Asia III was used with the ensemble approach, which effectively modulates the differences in performance among models. By comparison with EANET observations, although the seven models generally captured the wet depositions of S, N, and A, there were difficulties capturing these in some cases. This failure of models is considered to be related to the difficulty in capturing the precipitation in Southeast Asia, especially during the dry and wet seasons. To overcome this, a precipitation-adjusted approach which scaling the modeled precipitation to the observed value was applied, and it was demonstrated that the model performance was improved. Satellite measurements were also used to adjust for precipitation data, which worked well to account for spatio-and-temporal precipitation patterns, especially in the dry season. As the statistical scores were mostly improved by this adjustment, the estimation of wet deposition with precipitation adjustment was considered to be superior. To utilize satellite measurements, the spatial distribution of wet deposition was revised. Based on this revision, it was found that Vietnam, Malaysia, and Indonesia were upward-corrected and Myanmar, Thailand, Lao PDR, Cambodia, and the Philippines were downward-corrected; these corrections were up to ±40 %. The improved accuracy of precipitation amount was key to estimating wet deposition in this study. These results suggest that the precipitation-adjusted approach has the potential to obtain accurate estimates of wet deposition through the fusion of models and observations.

Syuichi Itahashi et al.

 
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Syuichi Itahashi et al.

Syuichi Itahashi et al.

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Short summary
This study presents the detailed analysis of acid deposition over Southeast Asia based on the Model Inter-Comparison Study for Asia (MICS-Asia) phase III. Simulated wet deposition is evaluated with observation data from the Acid Deposition Monitoring Network in East Asia (EANET). The difficulties of models to capture observation are related to the model performance on precipitation. The precipitation-adjusted approach was applied, and the distribution of wet deposition was successfully revised.
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