A Continuous Analyzer for Soluble Anionic Constituents and Ammonium in Atmospheric Particulate Matter

Abstract

A new continuous soluble particle collector (PC) that does not use steam is described. Preceded by a denuder and interfaced with an ion chromatograph, this compact collector (3 in. o.d., approximately 5 in. total height) permits collection and continuous extraction of soluble components in atmospheric particulate matter. The PC is mounted atop a parallel plate wetted denuder for removal of soluble gases. The soluble gas denuded air enters the PC through an inlet. One version of the PC contained an integral cyclone-like inlet. For this device, penetration of particles as a function of size was characterized. In the simpler design, the sampled air enters the PC through a nozzle, and deionized water flows through a capillary tube placed close to the exit side of the nozzle by Venturi action or is forcibly pumped. Some growth of the aerosol occurs in the highly humid mist-chamber environment, but the dominant aerosol capture mechanism involves capture by the water film that forms on the hydrophobic PTFE membrane filter that constitutes the top of the PC and the airflow exit. Water drops coalesce on the filter and fall below into a purpose-machined cavity equipped with a liquid sensor. The water and the dissolved constituents are aspirated by a pump onto serial cation and anion preconcentrator columns. NH4+ captured by the cation preconcentrator is eluted with NaOH and is passed across an asymmetric membrane device. NH3 diffuses from the alkaline donor stream into a deionized water flowing countercurrent; the conductivity of the latter provides a measure of ammonium. The anions on the anion preconcentrator column are eluted and measured by a fully automated ion chromatography system. The total system thus provides automated semicontinuous measurement of soluble anions and ammonium. With a 15 min analytical cycle and a sampling rate of 5 L/min, the limit of detection (LOD) for ammonium is 8 ng/m3 and those for sulfate, nitrate, and oxalate are < or = 0.1 ng/m3. The system has been extensively field tested.

Semicontinuous PM2.5and PM10Mass and Composition Measurements in Lindon, Utah, during Winter 2007

“…Anion analysis is performed using an IonPac AG11-HC guard column and an IonPac AS11-AC column with 30-min chromatographic cycles largely following protocols described previously. 19,20 The system can collect particles down to 100-nm aerodynamic diameter with high efficiency. This technology was field tested in Philadelphia, PA, in the summer of 2001; in Tampa, FL, in the summer of 2002; and in Fresno, CA, in the winter of 2003.…”

Evaluation and application of a semi-continuous chemical characterization system for water soluble inorganic PM&lt;sub&gt;2.5&lt;/sub&gt; and associated precursor gases

“…The limits of detections were established as 100 ng m −3 for all particle anion species, 25 ng m −3 for all gas anion species and 100 ng m −3 for both gas and particle cation constituents. Further details regarding this instrument's design have been previously described by Al Horr et al (2003) and Ullah et al (2006). The measurement uncertainty for individual GPIC species was determined over a period of stable operating conditions and concentrations.…”

Laboratory and Field Evaluation of Instrumentation for the Semicontinuous Determination of Particulate Nitrate (and Other Water-Soluble Particulate Components)

“…Calibration of the TTU prototype instrument was monitored by daily control standard injections. The TTU prototype instrument and its operation are described in Al-Horr et al 20 Instrumentation based on similar principles is described by Weber et al 21 and Simon et al 22,23 Because of manufacturer's quality assurance issues associated with concentrator columns of the TTU prototype instrument, limited data were obtained from this instrument during the 3-week Rubidoux field sampling period. Over time, highpressure conditions present in the IC system and the continued sample loading/back-flushing process in the concentrator columns resulted in loosening of the column frits, loss of resin from the columns, and eventual column failure.…”