Atmospheric concentration of ammonia in Massachusetts and deposition on vegetation

Abstract

Ammonia has an important role in atmospheric chemistry and the soil nitrogen cycle, and it has long been suggested that terrestrial ecosystems may be important sources and sinks for atmospheric ammonia in both gaseous and particulate form^1–4. But there is relatively little information on the average atmospheric concentrations of NH₃ gas and particulate NH⁺₄ and their fluxes to and from ecosystems. Furthermore, much existing data are unreliable because of difficulties in separating gaseous NH₃ from particulate NH⁺₄ (refs 1, 5). We have used a new method^5,6 which overcomes these difficulties and have made continuous measurements for a 1-yr period at a rural location in Massachusetts. From these data and from measurements of the rate of deposition of ammonium on plastic and natural leaves, we conclude that particulate NH⁺₄ can be a significant nitrogen source for ecosystems, especially pine forests. In contrast, gaseous NH₃ is probably of little importance as its concentration is very low.