Intercomparison of near real time monitors of PM2.5 nitrate and sulfate at the U.S. Environmental Protection Agency Atlanta Supersite

Abstract

[1] Five new instruments for semicontinuous measurements of fine particle (PM2.5) nitrate and sulfate were deployed in the Atlanta Supersite Experiment during an intensive study in August 1999. The instruments measured bulk aerosol chemical composition at rates ranging from every 5 min to once per hour. The techniques included a filter sampling system with automated water extraction and online ion chromatographic (IC) analysis, two systems that directly collected particles into water for IC analysis, and two techniques that converted aerosol nitrate or sulfate either catalytically or by flash vaporization to gaseous products that were measured with gas analyzers. During the one-month study, 15-min integrated nitrate concentrations were low, ranging from about 0.1 to 3.5 mg m À3 with a mean value of 0.5 mg m À3 . Ten-minute integrated sulfate concentrations varied between 0.3 and 40 mg m À3 with a mean of 14 mg m À3 . By the end of the one-month study most instruments were in close agreement, with r-squared values between instrument pairs typically ranging from 0.7 to 0.94. Based on comparison between individual semicontinuous devices and 24-hour integrated filter measurements, most instruments were within 20-30% for nitrate ($0.1-0.2 mg m À3 ) and 10-15% for sulfate (1-2 mg m À3 ). Within 95% confidence intervals, linear regression fits suggest that no biases existed between the semicontinuous techniques and the 24-hour integrated filter measurements of nitrate and sulfate;, however, for nitrate, the semicontinuous intercomparisons showed significantly less variability than intercomparisons amongst the 24-hour integrated filters.

Aerosol Inorganic Composition at a Tropical Site: Discrepancies Between Filter-Based Sampling and a Semi-Continuous Method

“…Good agreement was found for aerosol NO − 3 measured with filter samplers, a PILS and an AMS in New York City (Hogrefe et al 2004). A reasonable overall comparability between semi-continuous and integrating samplers was also observed for aerosol during several other studies in the United States (e.g., Weber et al, 2003;Wittig et al 2004;Rattigan et al 2006). However, on individual days Weber et al (2003) observed differences of a factor of two to three between semi-continuous and integrating samplers.…”

“…A reasonable overall comparability between semi-continuous and integrating samplers was also observed for aerosol during several other studies in the United States (e.g., Weber et al, 2003;Wittig et al 2004;Rattigan et al 2006). However, on individual days Weber et al (2003) observed differences of a factor of two to three between semi-continuous and integrating samplers. Results from Pittsburgh (Wittig et al 2004) and New York (Rattigan et al 2006) showed differences of a factor of two or more between R&P semi-continuous aerosol NO -3 and 24-h integrated measurements for individual days.…”

“…Differences between semi-continuous techniques and filter-based methods had been found to be smaller than 30% at Northern Hemisphere extratropical sites (e.g., Drewnick et al 2003;Lee et al 2003;Schaap et al 2004;Slanina et al 2001;Weber et al 2003). This study will show that these findings may not always hold under tropical conditions.…”

Automated Measurement of the Size and Concentration of Airborne Particulate Nitrate

“…In Riverside, Mira Loma, and Bakersfield, California, measurements with our original single stage system yielded regression slopes between 0.96 and 1.06 in comparison to integrated filter systems (Stolzenburg and Hering 2000). In Atlanta the single stage ICVC gave regression slope of 0.94 ± 0.05 by comparison to the mean of other automated nitrate measurement methods (Weber et al 2003).…”

“…Time-resolved measurements of inorganic ions can be made using on-line ion chromatographic systems, such as those of Dasgupta (1993, 1995), Khlystrov et al (l995), Slanina et al (2001), and Weber et al (2001). Although these ion chromatographic systems do not offer size resolution, they show precision comparable to that obtained from integrated filter methods (Weber et al 2003). …”