Abstract
Abstract. The evaluation of chemical transport models, CTMs, is essential for the assessment of their performance regarding the physical and chemical parameterizations used. While regional CTMs have been widely used and evaluated over Europe, their validation over Greece is limited. In this study, we investigate the performance of the Long Term Ozone Simulation European Operational Smog (LOTOS-EUROS) v2.2.001 regional chemical transport model in simulating nitrogen dioxide, NO2, over Greece from June to December 2018. In situ NO2 measurements obtained from 14 stations of the National Air Pollution Monitoring Network are compared with surface simulations over the two major cities of Greece, Athens and Thessaloniki. Overall the LOTOS-EUROS NO2 surface simulations compare very well to the in situ measurements showing a mild underestimation of the measurements with a mean relative bias of ∼-10 %, a high spatial correlation coefficient of 0.86 and an average temporal correlation of 0.52. The CTM underestimates the NO2 surface concentrations during daytime by ∼-50 ± 15 %, while it slightly overestimates during night-time ∼ 10 ± 35 %. Furthermore, the LOTOS-EUROS tropospheric NO2 columns are evaluated against ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) NO2 measurements in Athens and Thessaloniki. We report that the CTM tropospheric NO2 column simulations over both urban and rural locations represent the diurnal patterns and hourly levels for both summer and winter seasons satisfactorily. The relative biases range between ∼ −2 % and −35 %, depending on season and relative NO2 load observed. Finally, the CTM was assessed also against space-borne Sentinel-5 Precursor (S5P) carrying the Tropospheric Monitoring Instrument (TROPOMI) tropospheric NO2 observations. We conclude that LOTOS-EUROS simulates extremely well the tropospheric NO2 patterns over the region with very high spatial correlation of 0.82 on average, ranging between 0.66 and 0.95, with negative biases in the summer and positive in the winter. Updated emissions for the simulations and model improvements when extreme values of boundary layer height are encountered are further suggested.
Highlights
Nitrogen oxides (NOx = NO+NO2) adversely affect human health, the environment and the ecosystems
From the comparison with measurements by air quality stations in Athens and Thessaloniki, we found that overall the LOTOS-EUROS NO2 surface simulations compare very well to the in situ measurements over the two major cities of Greece between June and December 2018, showing a mild underestimation of the measurements with a mean relative bias of −11 %, a median relative bias of −10 %, a high spatial correlation coefficient equal to 0.86 and an average temporal correlation of 0.52
We evaluate tropospheric NO2 surface simulations over Greece from the LOTOS-EUROS regional CTM against in situ surface concentrations from 14 air quality stations during June and December 2018
Summary
Nitrogen oxides (NOx = NO+NO2) adversely affect human health, the environment and the ecosystems. Exposure to NO2 is linked with high mortality rates and premature deaths (Crouse et al, 2015). NO2 dominates the formation of ozone and inorganic aerosols in the troposphere I. Skoulidou et al.: Evaluation of the LOTOS-EUROS NO2 simulations dis, 1998) with detrimental effects on the climate and human health. The deposition of nitrogen leads to eutrophication and acidification (Bouwman et al, 2002). While NOx sources can be either natural (soils, wildfires and lightning) or anthropogenic (fossil fuel combustion, industrial emissions, and emissions from road and non-road transport) (Miyazaki et al, 2017), it is estimated that human activities are responsible for 65 % of the global annual NOx flux (Müller and Stavrakou, 2005)
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