 |
| Titel |
An assessment of the performance of the Monitor for AeRosols and GAses in ambient air (MARGA): a semi-continuous method for soluble compounds |
| VerfasserIn |
I. C. Rumsey, K. A. Cowen, J. T. Walker, T. J. Kelly, E. A. Hanft, K. Mishoe, C. Rogers, R. Proost, G. M. Beachley, G. Lear, T. Frelink, R. P. Otjes |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1680-7316
|
| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 14, no. 11 ; Nr. 14, no. 11 (2014-06-06), S.5639-5658 |
| Datensatznummer |
250118778
|
| Publikation (Nr.) |
 copernicus.org/acp-14-5639-2014.pdf |
|
|
|
|
|
| Zusammenfassung |
| Ambient air monitoring as part of the US Environmental Protection Agency's
(US EPA's) Clean Air Status and Trends Network (CASTNet) currently uses
filter packs to measure weekly integrated concentrations. The US EPA is
interested in supplementing CASTNet with semi-continuous monitoring systems
at select sites to characterize atmospheric chemistry and deposition of
nitrogen and sulfur compounds at higher time resolution than the filter
pack. The Monitor for AeRosols and GAses in ambient air (MARGA) measures
water-soluble gases and aerosols at an hourly temporal resolution. The
performance of the MARGA was assessed under the US EPA Environmental
Technology Verification (ETV) program. The assessment was conducted in
Research Triangle Park, North Carolina, from 8 September to 8 October
2010 and focused on gaseous SO2, HNO3, and NH3 and
aerosol SO42-, NO3-,
and NH4+. Precision of the
MARGA was evaluated by calculating the median absolute relative percent
difference (MARPD) between paired hourly results from duplicate MARGA units
(MUs), with a performance goal of ≤ 25%. The accuracy of the MARGA
was evaluated by calculating the MARPD for each MU relative to the average
of the duplicate denuder/filter pack concentrations, with a performance goal
of ≤ 40%. Accuracy was also evaluated by using linear regression,
where MU concentrations were plotted against the average of the duplicate
denuder/filter pack concentrations. From this, a linear least squares line
of best fit was applied. The goal was for the slope of the line of best fit
to be between 0.8 and 1.2. The MARGA performed well in comparison to the
denuder/filter pack for SO2, SO42−,
and NH4+, with
all three compounds passing the accuracy and precision goals by a
significant margin. The performance of the MARGA in measuring NO3-
could not be evaluated due to the different sampling efficiency of coarse
NO3- by the MUs and the filter pack. Estimates of "fine"
NO3- were calculated for the MUs and the filter pack. Using this
and results from a previous study, it is concluded that if the MUs and the
filter pack were sampling the same particle size, the MUs would have good
agreement in terms of precision and accuracy. The MARGA performed moderately
well in measuring HNO3 and NH3, though neither met the linear
regression slope goals. However, recommendations for improving the
measurement of HNO3 and NH3 are discussed. It is concluded
that SO42-, SO2, NO3-,
HNO3, NH4+,
and NH3 concentrations can be measured with acceptable accuracy and
precision when the MARGA is operated in conjunction with the recommendations
outlined in the manuscript. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|