## 5 Conclusions  
A wide variety of observational data (satellite and ground based measurements) has been used to evaluate the ability of the chemistry transport model CHIMERE to simulate dust outbreaks through the Northern Hemisphere in March 2014. The novelty of this work is to use a regional chemistry transport model (CHIMERE) at such a large scale with a high resolution (about 10 km), focusing on several places in the world for the same short period, and evaluating simultaneously the ability of the model to simulate these episodes. The CHIMERE model can simulate the main patterns of the dust concentrations compared to previous modeling studies and produces much more detailed structures due to the very fine horizontal  
Figure 29: Evolution of the different dust plumes toward the Pacific Ocean simulated by CHIMERE for 19 March 2014 00:00 UTC. (**Top**) Longitudinal cross section of total dust concentrations fields (altitude versus longitude) at 39.9\({}^{\circ}\) N (Beijing latitude) from longitude 110\({}^{\circ}\) E to 179\({}^{\circ}\) E passing over Beijing (BJ), North Korea (NK) and Japan (JP) on 19 March 2014 00:00 UTC and travelling over the Pacific Ocean in a westerly flux. The dotted line represents the height of the boundary layer, the dashed lines represent the fraction of fine dust in percent. (**Middle, bottom**) Dust concentrations in the boundary layer (BL) and the free troposphere (FT) on 19 March 2014 00:00 and 15:00 UTC. resolution. Over mid latitudes, the transport of dust in low free troposphere is confirmed particularly over the Pacific Ocean while the transatlantic transport of dust from Sahara to the Caribbean area mainly occurs within the boundary layer. Close to the equatorial Pacific and Atlantic Oceans the fine fraction of dust concentration is dominating due to heavy precipitations which efficiently remove the biggest particles by sub-cloud scavenging. The background dust concentrations seem overestimated by the model when comparing the data at high latitude sites. A specific pattern is simulated with high dust concentrations over the pole at about 2-3 km in altitude, which is certainly the result of dust accumulation issued from long-range transport. In the model, the effect of sedimentation for the biggest particles and the condensation and coagulation of the smallest aerosols shows a narrowing of the size aerosol distributions toward the upper levels of the atmosphere. Several dust outbreaks have been identified in March 2014; some of them, already studied in previous works, are very well captured by the model with a good timing. In China, the three main events are very well simulated, the model outputs showing a sharp increase of PM concentrations over the Beijing area due to dust issued from the Gobi Desert. Over the USA, three dust storms have been identified and analyzed with several observational datasets and CHIMERE is able to simulate these events with a rather good timing. The evolution of the plumes toward Mexico and particularly Baja California is confirmed by available observations. Europe is mainly affected during end of March with a dust plume that is mainly located in the free troposphere at the beginning with some intrusions within the boundary layer; this episode affects later in April the UK [87]. The Caribbean area is affected by a long-range transport of dust from the Sahara and again the model rather well captures the arrival timing of the plume but with a clear overestimation while the concentrations and AOD are in rather good agreement on African stations. The transport of dust in the low troposphere is confirmed by CALIPSO retrievals. Over Asia, several dust episodes are also identified and rather well captured by the model. Unfortunately, the difficulty to obtain PM measurements in Siberia and the impossibility to use satellite data due to the presence of clouds makes difficult the evaluation of the model, however the SYNOP manned measurements confirmed the evolution of the dust plumes in Central Asia.