Environ. Sci. Technol. 2007, 41, 8412–8419
A Laboratory Intercomparison of Real-Time Gaseous Ammonia Measurement Methods J A M E S J . S C H W A B , * ,† Y O N G Q U A N L I , † MIN-SUK BAE,† K E N N E T H L . D E M E R J I A N , † J I A N H O U , ‡,§ X I A N L I A N G Z H O U , ‡,§ B J A R N E J E N S E N , | AND SARA C. PRYOR⊥ Atmospheric Sciences Research Center, University at Albany, State University of New York, Environmental Health Sciences, School of Public Health, University at Albany, State University of New York, and Wadsworth Center, New York State Department of Health, Albany, New York 12203, Department of Atmospheric Environment, National Environmental Research Institute, DK-4000 Roskilde, Denmark, and Atmospheric Science Program, Department of Geography, Indiana University, Bloomington, Indiana 47405
Received February 12, 2007. Revised manuscript received August 22, 2007. Accepted October 04, 2007. Received December 15, 2007
Six different measurement methods (and seven instruments) for the measurement of gaseous ammonia at low part-per-billion levels were compared simultaneously in a laboratory setting. The instruments were the tunable diode laser (TDL) absorption spectrometer, the wet scrubbing long-path absorption photometer (LOPAP), the wet effusive diffusion denuder (WEDD), the ion mobility spectrometer (IMS), the Nitrolux laser acousto-optical absorption analyzer, and a modified chemiluminescence analyzer. With the exception of the modified chemiluminescence analyzer, the instruments performed well and, under stable calibration conditions, generally agreed to within about 25% of the expected calibration value. Instrument time response is shown to be sensitive to measurement history as well as the sample handling materials and is shortest for the TDL. The IMS and Nitrolux are commercial instruments used without modification from the manufacturer. These two instruments have significantly slower time response than the TDL (especially in the case of the Nitrolux) and exhibited measurement biases of approximately +25% (IMS) and -25% (Nitrolux). The LOPAP and WEDD instruments, both research instruments using wet chemical methods, performed well in the calibration tests in terms of the absolute accuracy of measured concentrations, but the WEDD instrument suffered from significantly slower time response than the LOPAP.
Introduction Ammonia (NH3) gas plays a number of important roles in atmospheric chemistry, aquatic chemistry, and terrestrial * Corresponding author e-mail:
[email protected]. † Atmospheric Sciences Research Center, State University of New York. ‡ School of Public Health, State University of New York. § New York State Department of Health. | National Environmental Research Institute. ⊥ Indiana University. 8412
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ecosystems (1–3). As a result, many measurement methods for NH3 have been developed (4–8), though with few exceptions, ambient measurement of NH3 has remained a “research activity”, requiring equipment that is often delicate and expensive, and labor-intensive. Nevertheless, the United States Environmental Protection Agency has designated gaseous NH3 as a target pollutant for measurement at roughly 75 multipollutant sites nationwide (9). This poses a significant challenge since ambient NH3 levels vary from background levels of
