Publication: Assessing the value of air stagnation indices to reproduce PM10 variability in Europe
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2021-01-15
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Elsevier Science Inc
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Abstract
Different air stagnation indices (ASIs) have been proposed to measure the atmospheric diffusion conditions. This paper undertakes a comparative analysis of three ASIs and explores their ability to capture the conditions conducive to elevated PM10 (particulate matter ≤ 10 µm) at 306 background sites in Europe for the winter and summer months of 2000–2012. Despite the similar spatial patterns of stagnation frequency found for the three ASIs, the use of different meteorological variables to characterize the dilution capacity of the atmosphere (wind speeds at 10 m and 500 hPa, boundary layer height and ventilation in the boundary layer) leads to important differences in the seasonal cycles. Moreover, the response of the PM10 concentrations to stagnation varies with the ASI. Winter PM10 anomalies under stagnant conditions are of the same order of magnitude (on average 17.2 to 18.6 μg m^(-3) , around 60 % of the mean values) for the three ASIs. The anomalies are considerably smaller (3.8–5.7 μg m^(-3), around 19–28 %) in summer, when one of the indices outperforms the others at most locations. The dependence of the PM10 concentrations on the ASI components is also evaluated by using correlations and generalized additive models. The results indicate that the consideration of the large-scale circulation is particularly relevant in summer, explaining the different ASI performances during this season. We have also identified some potential improvements that could be made to two of the ASIs. Nevertheless, since the three ASIs are based on fixed thresholds, they cannot deal with non-linear relationships, which limits their ability to explain PM10 variability.
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© 2021 Elsevier B.V. This work was supported by the Spanish Ministerio de Educación, Cultura y Deporte [grant number FPU16/01972]; the Spanish Ministerio de Economía y Competitividad [grant number RYC-2014-15036]; and the Spanish Ministerio de Economía, Industria y Competitividad [grant numbers CGL2017-83198-R and RTI2018- 096402-B-I00]. The authors are grateful to the European Environment Agency, the EU member states and collaborating countries for collecting and providing PM10 data through the Air-Base air quality database. ERA5 data are provided by ECMWF. We are also thankful to Mateusz Taszarek for helpful discussions on the calculation and use of CAPE and CIN in Europe. Three anonymous reviewers helped improve the original manuscript.