Estimating 40 years of nitrogen deposition in global biomes using the SCIAMACHY NO2 column

Owing to human activity, global nitrogen (N) cycles have been altered. In the past 100 years, global N deposition has increased. Currently, the monitoring and estimating of N deposition and the evaluation of its effects on global carbon budgets are the focus of many researchers. NO₂ columns retrieved by space-borne sensors provide us with a new way of exploring global N cycles and these have the ability to estimate N deposition. However, the time range limitation of NO₂ columns makes the estimation of long timescale N deposition difficult. In this study we used ground-based NO_x emission data to expand the density of NO₂ columns, and 40 years of N deposition (1970–2009) was inverted using the multivariate linear model with expanded NO₂ columns. The dynamic of N deposition was examined in both global and biome scales. The results show that the average N deposition was 0.34 g N m^–2 year^–1 in the 2000s, which was an increase of 38.4% compared with the 1970s’. The total N deposition in different biomes is unbalanced. N deposition is only 38.0% of the global total in forest biomes; this is made up of 25.9%, 11.3, and 0.7% in tropical, temperate, and boreal forests, respectively. As N-limited biomes, there was little increase of N deposition in boreal forests. However, N deposition has increased by a total of 59.6% in tropical forests and croplands, which are N-rich biomes. Such characteristics may influence the effects on global carbon budgets.