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

Abstract

Studies conducted at the U.S. Environmental Protection Agency facility in Research Triangle Park, NC, and at a field study in Southern California have demonstrated the capability for the semicontinuous determination of particulate nitrate (and other water-soluble ionic species). Two instruments, an R&P Series 8400N Ambient Particulate Nitrate Monitor (8400N) and an ion chromatography (IC)-based prototype monitor developed at Texas Tech University, were evaluated both in the laboratory using aqueous standards and simulated ambient aerosols and in the field during a 3-week (July 1-21, 2003) joint ambient comparison study with Brigham Young University and the South Coast Air Quality Management District (SCAQMD). The field study was conducted at the SCAQMD Rubidoux field site near Riverside, CA. During initial (before the field study) laboratory studies, both instruments were responsive to changes in the simulated aerosol concentration. However, potential problems were discovered involving both instruments during the laboratory-based studies both before and after the Rubidoux study, and these problems are currently being addressed. During the 3-week field study period, 15-minute average particulate nitrate concentrations approaching 30 g/m 3 were observed. Because of malfunctioning IC components (concentrator columns) of the Texas Tech University prototype monitor, limited data were obtained from this instrument during the 3-week sampling period. Initial ambient comparisons show general agreement between the 8400N and IC-based prototype instrument for the semicontinuous determination of ambient particulate nitrate at lower nitrate concentrations (Ͻ15 g/m 3 ) and an underdetermination by the 8400N at higher concentrations (Ͼ15 g/m 3 ). A decreased molybdenum converter efficiency in the pulse analyzer of the 8400N discovered during postfield study laboratory evaluation may explain the negative bias observed at higher nitrate concentrations. Semicontinuous results obtained from U.S. Environmental Protection Agency-operated instruments were averaged and compared with integrated sampler results obtained by Brigham Young University and SCAQMD.

Evaluation and application of a semi-continuous chemical characterization system for water soluble inorganic PM<sub>2.5</sub> and associated precursor gases

“…Comparable underprediction of the 8400N as compared to other measurement techniques (noted as the slope in Table 2) has been cited previously at various US urban and rural centers Wittig et al, 2004;Grover et al, 2006;Long and McClenny, 2006;Rattigan et al, 2006). A summary of in- strument intercomparison relationships is presented in Table 2 where all centres were urban environments with the exception of Whiteface Mountain, NY.…”

“…Low efficiency may have resulted in incomplete NO 2 to NO conversion causing nitrate measurement underestimations. It is also worth noting that Long and McClenny (2006) observed only a negative bias with the 8400N as compared to the GPIC during ambient sampling; the 8400N accurately measured high nitrate concentrations when operating under controlled laboratory conditions. These results suggested that interfering species may have contributed to the divergence between measurement techniques at high nitrate concentrations.…”

“…Toronto experienced a period of high temperature (T >30 • C) and elevated relative humidity (RH>85%) from 25 July 2006 to 2 August 2006 and on 27 August 2007. The R&P 8400N may have suffered from incomplete flash volatilization resulting in underpredicted measurements during these times (Long and McClenny, 2006).…”

“…Moreover, each summarized study reported a similar mass concentration range as that observed in the current study. Nitrate measurement loss by the 8400N may have been in part due to decreased Molydenum converter efficiency which was located in the system's pulse analyzer (Long and McClenny, 2006). Low efficiency may have resulted in incomplete NO 2 to NO conversion causing nitrate measurement underestimations.…”

Measurement of Both Nonvolatile and Semi-Volatile Fractions of Fine Particulate Matter in Fresno, CA

“…The most significant differences were observed during a persistent inversion at the beginning of the sampling period, which was associated with ground level fog and high humidity. Incomplete flash volatilization by the R&P Nitrate Monitor under conditions of high humidity (Long and McClenny 2006) may explain the differences observed between the two monitoring techniques. Unfortunately, PC-BOSS data were not obtained during this time period of the sampling campaign.…”