Reviewing global estimates of surface reactive nitrogen concentration and deposition using satellite retrievals

Since the industrial revolution, human activities have dramatically changed the nitrogen (N) cycle in natural systems. Anthropogenic emissions of reactive nitrogen (N-r) can return to the earth's surface through atmospheric N-r deposition. Increased N-r deposition may improve ecosystem productivity. However, excessive N-r deposition can cause a series of negative effects on ecosystem health, biodiversity, soil, and water. Thus, accurate estimations of N-r deposition are necessary for evaluating its environmental impacts. The United States, Canada and Europe have successively launched a number of satellites with sensors that allow retrieval of atmospheric NO2 and NH3 column density and therefore estimation of surface N-r concentration and deposition at an unprecedented spatiotemporal scale. Atmosphere NH3 column can be retrieved from atmospheric infra-red emission, while atmospheric NO2 column can be retrieved from reflected solar radiation. In recent years, scientists attempted to estimate surface N-r concentration and deposition using satellite retrieval of atmospheric NO2 and NH3 columns. In this study, we give a thorough review of recent advances of estimating surface N-r concentration and deposition using the satellite retrievals of NO2 and NH3, present a framework of using satellite data to estimate surface N-r concentration and deposition based on recent works, and summarize the existing challenges for estimating surface N-r concentration and deposition using the satellite-based methods. We believe that exploiting satellite data to estimate N-r deposition has a broad and promising prospect.