Continuous measurements of nitric acid and ammonia at a rural New York site

Continuous low-level measurement of gaseous ammonia and nitric acid has been demonstrated for a three month period at a rural site in southwestern New York State. Nitric acid is measured by denuder difference and chemical conversion using heated molybdenum converters and chemiluminescence detection of nitric oxide (NO). Ammonia is measured with a commercial Ion Mobility Spectrometer (IMS). Both techniques provide adequate sensitivity to detect and quantify the sub-ppb levels of these species often encountered at the measurement site. Measurements show that nitric acid and ammonia are often elevated during the same overall time periods, but peak concentrations are always offset, such that maximum nitric acid occurs while ammonia is minimum (or decreasing), and vice versa. For this ammonia analyzer the issue of time response, and more specifically, the ability of the analyzer to accurately track rapid up and down changes in ammonia concentrations, requires further evaluation.