Ammonia and NOx in Seeded and Unseeded Snowfall – An Australian Perspective

The Snowy Precipitation Enhancement Research Project is a six year cloud seeding trial currently in progress in the Snowy Mountains region of south-eastern Australia. The trial commenced in the winter of 2004 and targets a study area of approximately 1000 square kilometers within the Kosciuszko National Park.

Cloud seeding is undertaken using a series of generator pairs releasing minute particles of a seeding agent (silver iodide), and an inert tracer (indium sesquioxide).

Potential ecological impacts of the trial are monitored through an extensive environmental monitoring program. However concerns have been raised by some stakeholders over the possibility that cloud seeding may increase concentrations of NOx and ammonia in snowfall, resulting in potential adverse increases in nutrient levels in the lakes of the Park.

Snowy Hydro Ltd has undertaken a program of monitoring concentrations of ammonia and NOx in seeded and unseeded snowpack from five sites. No significant differences were identified between concentrations of ammonia and NOx in seeded and unseeded snowpack. Concentrations of ammonia varied from 0.046 mg/L to 0.062 mg/L in seeded snow samples, and 0.042 mg/L to 0.078 mg/L in natural snow. NOx concentrations varied from 0.025 mg/L to 0.037 mg/L in seeded snow samples, and from 0.028 mg/L to 0.043 mg/L in natural snow. Differences in concentrations were typically greater between sites than between seeded and natural snow samples within the same site.