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| Titel |
Multi-year objective analyses of warm season ground-level ozone and PM2.5 over North America using real-time observations and Canadian operational air quality models |
| VerfasserIn |
A. Robichaud, R. Ménard |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 14, no. 4 ; Nr. 14, no. 4 (2014-02-17), S.1769-1800 |
| Datensatznummer |
250118405
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| Publikation (Nr.) |
 copernicus.org/acp-14-1769-2014.pdf |
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| Zusammenfassung |
| Multi-year objective analyses (OA) on a high spatiotemporal resolution for
the warm season period (1 May to 31 October) for ground-level ozone and for
fine particulate matter (diameter less than 2.5 microns (PM2.5)) are
presented. The OA used in this study combines model outputs from the
Canadian air quality forecast suite with US and Canadian observations from
various air quality surface monitoring networks. The analyses are based on
an optimal interpolation (OI) with capabilities for adaptive error
statistics for ozone and PM2.5 and an explicit bias correction scheme
for the PM2.5 analyses. The estimation of error statistics has been
computed using a modified version of the Hollingsworth–Lönnberg (H–L)
method. The error statistics are "tuned" using a χ2 (chi-square) diagnostic, a semi-empirical procedure that provides
significantly better verification than without tuning. Successful
cross-validation experiments were performed with an OA setup using 90%
of data observations to build the objective analyses and with the remainder
left out as an independent set of data for verification purposes.
Furthermore, comparisons with other external sources of information (global
models and PM2.5 satellite surface-derived or ground-based
measurements) show reasonable agreement. The multi-year analyses obtained
provide relatively high precision with an absolute yearly averaged
systematic error of less than 0.6 ppbv (parts per billion by volume) and 0.7 μg m−3 (micrograms per cubic meter) for ozone and PM2.5,
respectively, and a random error generally less than 9 ppbv for ozone and
under 12 μg m−3 for PM2.5. This paper focuses on two
applications: (1) presenting long-term averages of OA and analysis increments
as a form of summer climatology; and (2) analyzing long-term (decadal) trends
and inter-annual fluctuations using OA outputs. The results show that high
percentiles of ozone and PM2.5 were both following a general decreasing trend
in North America, with the eastern part of the United States showing the
most widespread decrease, likely due to more effective pollution controls.
Some locations, however, exhibited an increasing trend in the mean ozone and
PM2.5, such as the northwestern part of North America (northwest US
and Alberta). Conversely, the low percentiles are generally rising for
ozone, which may be linked to the intercontinental transport of increased
emissions from emerging countries. After removing the decadal trend, the
inter-annual fluctuations of the high percentiles are largely explained by
the temperature fluctuations for ozone and to a lesser extent by
precipitation fluctuations for PM2.5. More interesting is the economic
short-term change (as expressed by the variation of the US gross domestic
product growth rate), which explains 37% of the total variance of
inter-annual fluctuations of PM2.5 and 15% in the case of ozone. |
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