Improved ammonia emission inventory of fertilizer application for three major crops in China based on phenological...

NH₃ has an important impact on atmospheric chemistry, and its reduction has become a potential pathway to alleviate haze pollution. The existing NH₃ emission inventories still have significant uncertainties in terms of their temporal distributions. In this study, we combined satellite remote-sensing phenological data with ground-station phenological data to develop a method for the temporal allocation of NH₃ emissions from fertilizer application. A high-resolution dataset for fertilizer application in China was established. We developed NH₃ emission inventories for the fertilization of three major crops in China, with a resolution of 1/12° × 1/12°. The results showed that there was a significant temporal variation in fertilizer application dates across the country, mainly concentrated in June (17.16 %), July (19.08 %), and August (18.77 %). The majority of fertilizer application for the three major crops occurred during the spring and summer months, with a particular emphasis on April (5.72 Tg), May (7.05 Tg), and June (4.29 Tg). The total NH₃ emission from the three major crops in China in 2019 was 2.73 Tg. The North China Plain (762.23 Gg) and Middle and Lower Yangtze River Plain (606.85 Gg) were identified as the primary regions for high NH₃ emissions from fertilizer application. The results also showed that NH₃ emissions from the three major crops were predominantly observed during summer, with a peak value in July (606.99 Gg), mainly because of the high proportion of topdressing fertilizers. Areas with high fertilizer application generally coincided with areas of high NH₃ emissions. This study may be the first to utilize remote-sensing phenological data to establish the NH₃ emission inventory, which is of great significance for further improving the accuracy of the NH₃ emission inventory.