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Analysis of summer O3 in the Madrid air basin with the LOTOS-EUROS chemical transport model

Author: Escudero, M. · Segers, A. · Kranenburg, R. · Querol, X. · Alastuey, A. · Borge, R. · Paz, D. de la · Gangoiti, G. · Schaap, M.
Type:article
Date:2019
Publisher: Copernicus GmbH
Source:Atmospheric Chemistry and Physics, 22, 19, 14211-14232
Identifier: 871705
doi: doi:10.5194/acp-19-14211-2019
Keywords: Air quality · Atmospheric chemistry · Atmospheric transport · Concentration (composition) · Data set · Oxygen · Seasonal variation · Troposphere · Environment & Sustainability · Urbanisation

Abstract

Tropospheric <span classCombining double low line"inline-formula">O3</span> remains a major air-quality issue in the Mediterranean region. The combination of large anthropogenic emissions of precursors, transboundary contributions, a warm and dry aestival climate, and topographical features results in severe cases of photochemical pollution. Chemical transport models (CTMs) are essential tools for studying <span classCombining double low line"inline-formula">O3</span> dynamics and for assessing mitigation measures, but they need to be evaluated specifically for each air basin. In this study, we present an optimisation of the LOTOS-EUROS CTM for the Madrid air basin. Five configurations using different meteorological datasets (from the European Centre for Medium-Range Weather Forecast, ECMWF; and the Weather Research and Forecasting Model, WRF), horizontal resolution and number of vertical levels were compared for July 2016. LOTOS-EUROS responded satisfactorily in the five configurations reproducing observations of surface <span classCombining double low line"inline-formula">O3</span> with notable correlation and reduced bias and errors. However, the best-fit simulations for surface <span classCombining double low line"inline-formula">O3</span> were obtained by increasing spatial resolution and using a large number of vertical levels to reproduce vertical transport phenomena and the formation of reservoir layers. Using the optimal configuration obtained in the evaluation, three characteristic events have been described: recirculation (REC) episodes and northern and southern advection (NAD and SAD, respectively) events. REC events were found to produce the highest <span classCombining double low line"inline-formula">O3</span> due to the reduced ventilation associated with low wind speeds and the contribution of reservoir layers formed by vertical transport of <span classCombining double low line"inline-formula">O3</span> formed near the surface in the previous days of the event. NAD events, usually associated with higher wind speeds, present the lowest ground-level <span classCombining double low line"inline-formula">O3</span> concentrations in the region. During SAD episodes, external contributions along with low wind speeds allow <span classCombining double low line"inline-formula">O3</span> to increase considerably but not as much as in REC events because steady southerly winds disperse local emissions and hinder the formation of reservoir layers. © Author(s) 2019. This work is distributed under the Creative Commons Attribution 4.0 License.