Measurements of Ammonia and Related Species at IL11 (Bondville)

Between 1999 and 2003, the Illinois Water Survey has sampled ambient atmospheric gases and fine particles as part of an atmospheric fine particle (PM-2.5) characterization project at the NADP station near Bondville, IL (IL11). Gas phase ammonia, nitric acid, and sulfur dioxide were sampled for 24 hours every 6 days using coated denuders. The denuders were backed up by a filterpack with Teflon and nylon filters to collect PM-2.5. Fine particles were analyzed for sulfate, nitrate, and ammonium ions. Beginning in spring 2003, a continuous ion chromatography sampler was put in operation at IL11. This device measures the same species as the 24-hour denuder/filterpack system on a 30-minute cycle. In summer 2003, a separate commercial ammonia analyzer that measures gas-phase ammonia every 35 seconds was added to the instrumentation at IL11.

The concentration of ambient ammonia is typically around 1 ppb with fall maximum values as high as 10 ppb. Nitric acid averages about 0.3 ppb with summer maximum values of about 1.5 ppb. The average concentration of sulfur dioxide at IL11 is about 1.5 ppb. Maximum sulfur dioxide concentrations of up to 9 ppb were measured in the winter. The average concentration of PM-2.5 at IL11 is about 13 µg/ m3. Most of the year, PM-2.5 is dominated by ammonium sulfate, which accounts for an average of 35% of the PM-2.5 mass and up to 80% of PM-2.5 mass in the summer. Ammonium nitrate accounts for about 20% of PM-2.5 on an annual basis. This species can make up more than half the ambient PM-2.5 when average ambient temperatures are below 5C.

Preliminary evaluations of the continuous samplers deployed at IL11 indicate that they can provide data equivalent to the denuder/filter method with time resolution under one minute. Continuous measurements will make it easier to evaluate the correlation of chemical parameters and meteorological data, which usually vary on a time scale much shorter than 24 hours.