Project No: 16305921

Title: Estimation and spatiotemporal analysis of wet deposition of long-term non-sea-salt-sulfate, nitrate, ammonium, and calcium in Northern Hemisphere

Principal Investigator: Prof. Jimmy FUNG

Co-Investigator: Prof. David SIMPSON


Air pollution is one of the most pressing environmental issues, with potentially severe adverse effects on human health. As one of the major natural processes for the removal of atmospheric pollutants, wet deposition plays an important role in decreasing the pollution level. Once washed down to terrestrial and aquatic ecosystems, some chemical components of atmospheric origin, such as non-sea-salt (nss)-sulfate (SO4 2- ), nitrate (NO3 - ), ammonium (NH4 + ), and calcium (Ca2+), can provide important nutrients for these ecosystems. However, excessive wet deposition of nss-SO4 2- and NO3 - can lead to acidification of soil and water bodies, and excessive budgets of NO3 - and NH4 + can lead to eutrophication of aquatic systems. Therefore, it is vital to understand the spatial patterns and long-term trends of the wet deposition of these four chemical components in various ecosystems. Ground observation data are limited by the number of available stations and cannot provide accurate spatial patterns of wet deposition on regional and global scales. Meanwhile, parameterization and emission errors may lead to uncertainties in the simulation of long-term trends of wet deposition by 3D chemical transport models. The spatial patterns and long-term trends of the wet deposition of these four chemicals have not been well quantified in hemispheric scale.

In this proposed project, in combination with remote sensing satellite data, reanalysis data, and ground observation data, a convolutional neural network deep learning framework will be developed and applied to estimate the long-term wet deposition of nss-SO4 2- (2005–2018), NO3 - (2001–2017), NH4 + (2007–2017), and Ca2+ (2005–2018) at a spatial resolution of 0.5°×0.5° over the Northern Hemisphere. The spatial patterns, long-term trends, and hotspots of the wet deposition of these four chemical species will be analyzed thoroughly. Attention will be paid to the monthly difference in wet deposition between climate zones (e.g., tropical monsoon climate and humid continental climate) and evolution of the acid rain types in different countries over the Northern Hemisphere. In addition, the wet deposition budgets of the four chemical species in various ecosystems and in comparison with the critical load values will be studied. The results of this study will help scientists and policymakers understand if it is necessary to further tighten the emission standards for the purpose of the ecosystems protection. The public will also benefit from the results of this study by gaining a deeper understanding of the wet deposition conditions in ecosystems of interest.