Skip directly to search Skip directly to A to Z list Skip directly to page options Skip directly to site content

NIOSHTIC-2 Publications Search

Search Results

Highly time resolved fine particle nitrate measurements at the Baltimore Supersite.

Harrison-D; Park-SS; Ondov-J; Buckley-T; Kim-SR; Jayanty-RKM
Atmos Environ 2004 Oct; 38(31):5321-5332
Nitrate in particles smaller than 2.5 m was measured at 10-min intervals at the Baltimore Supersite in east Baltimore from 14 February through 30 November 2002, using the R&P 8400N semicontinuous monitor to determine its contributions to fine-particle aerosol mass concentrations. Comparison with 24-h filter-based measurements, revealed a discrepancy of 33% between the 24-h averages derived from the two methods, for most of the 9.5 month study period, despite corrections for conversion efficiency and Reaction Cell Pressure deviations, suggesting a true conversion efficiency of 68%. Estimates of precision in individual 10-min measurements averaged 8.7% and ranged from 6.3% to 23%, excluding uncertainty encompassing dissociation losses. Uncertainties in 24-h averages of the 10-min measurements were generally larger (median of 9.1%) owing to missing or invalid values. The detection limits for 24-h averaged and 10-min concentrations were typically 0.17 and 0.24 g m-3, respectively, during the study (both after slope correction to achieve agreement with 24-h speciation measurements). Regression slopes were statistically equivalent for all months except February and October (an outlier not understood). Intercepts were generally small and insignificant. Good agreement between the 24-h data sets was achieved after the monthly mean regression slopes were applied to the 10-min data. In February, when flat flash strips were used and instrument compartment/outdoor ambient temperature differences were often severe, the regression slope was statistically larger than the average for the remaining months and the intercept was positive and significant. Results of a nonlinear least squares model used to estimate dissociation losses suggest that the largest errors occurred when concentrations are near the detection limit, instrument-outdoor temperature differences were large, and ambient RH low (<40%), i.e., conditions which most frequently and severely occurred in February and March. In February, dissociation losses as large as 1.65 g m-3 (100% of the slope-corrected measured value) may have occurred and such losses were predicted to be >30% in 63.5% of the 10-min measurements for that month. However, model predictions for the other months, when new ridged-flash strips were used, suggest that dissociation losses were much less significant, i.e., <15% in >95% of the measurements. Our experience suggests that the semicontinuous monitor can produce reliable 24-average concentrations when instrument-outdoor differences are kept small, an independent measurement is used to correct the data, and are improved when grooved flash strips are used.
Particulates; Measurement-equipment; Monitoring-systems; Monitors; Aerosol-particles; Air-contamination; Air-quality; Air-quality-control; Air-quality-measurement; Air-quality-monitoring; Air-samples; Air-sampling; Air-sampling-equipment; Airborne-dusts; Airborne-fibers; Airborne-particles; Nanotechnology; Author Keywords: Nitrate; R&P8400N; Semicontinuous nitrate monitor
John Ondov, Department of Chemistry and Biochemistry, University of Maryland, College Park, MD, USA
Publication Date
Document Type
Journal Article
Email Address
Funding Type
Fiscal Year
NTIS Accession No.
NTIS Price
Identifying No.
Issue of Publication
Source Name
Atmospheric Environment
Performing Organization
Johns Hopkins University