Nitrogen Isotope Fractionation from Ammonia Gas to Ammonium in Particulate Ammonium Chloride

The nitrogen stable isotope ratios of NH₃ gas (δ¹⁵N-NH_3(g)) and particulate NH₄⁺ (δ¹⁵N-NH₄⁺_(p)) have been used to determine the sources and elucidate the environmental dynamics of NH_3(g) and NH₄⁺_(p). Some studies have determined the sources from δ¹⁵N-NH₄⁺_(p) in the ambient environment by using the nitrogen isotope fractionation value (Δδ¹⁵N). Studies of Δδ¹⁵N are limited and estimated the Δδ¹⁵N by theoretical calculation or laboratory experiments in closed systems. Here, we produced actual submicron-sized particles and exposed them to NH_3(g) in a dynamic chamber under various experimental conditions of temperature and NH_3(g) turnover rate. Δδ¹⁵N was lower when temperature was higher. For low turnover rates (about 0.9 per day), the Δδ¹⁵N was 31.6 ± 2.0‰ (mean ± 1SD), almost equal to the Δδ¹⁵N from theoretical calculations and laboratory tests in closed systems. Also, the relationship between Δδ¹⁵N, the temperature, and the turnover rate can be described in the equation form. This relationship can help to explain the discrepancies between Δδ¹⁵N values in closed and open systems. Our results could help to clarify the sources and mechanisms of particle formation.