Study of CO surface pollution in Europe based on observations and nested-grid applications of GEOS-CHEM global chemical transport model

Abstract

Carbon monoxide (CO) is studied over Europe for 2001 using measurements from 31 rural-background stations and the nested-grid application of the global CTM GEOS-CHEM. The model reveals lowest (highest) biases in warm (cold) periods, tracking observations in most cases more closely than the global model. The role of CO production and destruction processes and the atmospheric conditions are investigated. A rotated Principal Component Analysis is applied to all stations, based on daily CO modelled concentrations in 2001, yielding three principal components (PCs) with stations of common characteristics. CO concentrations are studied for these groups in relation to the circulation patterns prevailing over Europe in 2001, at mean sea level and 850 hPa. The nested-grid model improves results in comparison to those calculated by the global model by up to ∼22% for first principal component subregion, where emissions are high and elevation is low. Improvement reaches∼17 and∼7%, respectively, for second and third principal component subregions, where emissions are lower and altitudes are higher. Better performance is achieved for patterns associated with westerly flow, whereas poor skills are revealed during stagnant conditions. During pollution events, the nesting model’s ability in capturing CO surface concentrations improves by up to ∼40% in comparison to the global simulation.