Seasonal Variability in Atmospheric Ammonia in the Last Decade across the United States

In the last decades, Strategic Plan for Clean Air in USA have played a huge role in reduction of SO ₂ and NO _x,which cause atmospheric ammonia increase in large percentage due to decreasing chemical loss. Seasonal trends of ammonia and total ammonia defined as ammonia plus ammonium during the most recent 11 years were analysed at 12 sites aross the United States using the monitored data obtained from AMoN networks.In warm season,ammonia at all sites and total ammonia at 8 sites show increasing trends.Ammonia and total ammonia show increasing trends at 9 and 3 sites during fertilization,respectively.Both of ammonia and total ammonia at all sites without obviously increasing trend comparing warm season and fertilization. The large percentage increases in the annual NH ₃ concentration cannot be fully explained by all the identifified causes.