Ammonia, the dominant base in the remote marine troposphere: a review

Ammonia appears to be the dominant base in the remote marine troposphere, yet its røle in atmospheric acid-base chemistry is not well understood. The physical and chemical interactions of ammonia with acidic species is complicated by its presence in the gas and particle phases and in cloud-, rain- and seawater. This review summarizes the reported ammonia concentration data in these 5 phases as well as existing sampling and analysis methods. An attempt is made to compare these data using equilibrium and scavenging calculations. The lowest measured ammonia gas phase concentrations appear to be consistent with reported sulfate and ammonium concentrations in the particulate phase. The high gas phase concentrations of ammonia found in older data appear to be a result of sampling artifacts. Reported ammonium particle and rainwater data also appear to be consistent with each other. Calculations suggest that ammonia may be in equilibrium between the gas phase and the Ocean surface. To confirm or refute these conclusions, the simultaneous measurement of ammonia and relevant acidic species in all 5 phases is needed.