Ammonia emissions from an avian-rich island in the Great Barrier Reef: Environmental drivers and observational insights

Ammonia, a key alkaline gas in the atmosphere, plays a significant role in new particle formation and cloud condensation nuclei activity, particularly in marine environments. On islands rich in avian fauna, ammonia emissions often exceed those in urban areas and are influenced by environmental factors such as temperature and precipitation. This study investigated the NH₃ emissions on Heron Island in the Great Barrier Reef using three different methods, namely offline active sampling, offline passive sampling, and online nitrate chemical ionization mass spectrometry (NO₃-CIMS). The average NH₃ mixing ratio of active sampling, passive sampling, and NO₃-CIMS during the sampling period was 29 ± 23 ppb, 29 ± 22 ppb, and 39 ± 19 ppb. Results from the three methods revealed consistent NH₃ mixing ratio trends. Changes in NH₃ mixing ratio were highly correlated with precipitation events. During precipitation periods, the NH₃ mixing ratio increased significantly within 30 min to a few hours after the rain started. Laboratory bird guano experiments further proved that NH₃ emissions are more influenced by precipitation than temperature. Besides, the δ¹⁵N-NH₃ values (−19.5 ‰ to −11.7 ‰) measured by passive samplers negatively correlated with NH₃ levels, confirming seabird guano as the primary NH₃ source. These findings highlighted the dynamic behavior of NH₃ emissions and their sensitivity to environmental factors, shedding light on the potential importance of the Great Barrier Reef ecosystem for atmospheric processes relevant to aerosol formation.