## 4 Discussion on Regional Dust Events
### Dust Outbreaks over China  
The major source areas of the Asian dust events affecting China are Gobi Desert, Taklimakan desert, and Loess Plateau [130; 131; 132]. Two major dust outbreaks affecting the region of Beijing are identified in 12-13 and 16-18 March 2014, another episode also identified end of March. Figure 24 shows a comparison between CHIMERE concentrations and CALIPSO qualitative data passing over the east part of China. The shape of dust concentrations is very well reproduced by CHIMERE and extends up to 5 and 6 km in altitude then largely ventilated into the free troposphere. Figure 23: Evolution of daily mean total surface dust concentrations from 16 to 21 March with manned “dust” SYNOP observations at WMO stations (“star” symbol), a symbol is plotted if at least one observation is reported for a given day. Figure 24: Cross section of CHIMERE dust concentrations (**right**) for two dates zoomed over the highest values area versus the corresponding CALIPSO qualitative data (**left**) showing in yellow the dust load and in orange the polluted dust, for the CALIPSO trajectories CNA4 (**top**) and CNA5 (**bottom**) as reported in Figure 2. The dotted line represents the height of the boundary layer, the dashed lines represent the fraction of fine dust in percent. The March 2014 episodes were discussed in previous studies [133; 134], to understand the long-range transport processes of bioaerosols over the Asian-dust source regions. The mid-March episode was also studied with satellites data issued from CALIPSO to track the trans-Pacific transport of dust from Asia to North America [135]. These episodes were also studied by using a global model [136]; they confirmed the importance of coarse-mode dust-nitrate as evidence of \"polluted dust\" event. The model analysis showed that the formation of dust-nitrate occurred over the Yellow Sea and East China Sea before arriving in Japan. The mid-March episode was studied with the on-line coupled Weather Research and Forecasting-Chemistry (WRF-Chem) model over the Nanjing area focusing on the interactions between the dust load with the photochemistry [137]. Combined with observational data, the WRF-chem model has been recently used in a recent study [138] at \(1^{\circ}\times 1^{\circ}\) to analyze the transport of a dust plume from Asia to North America for an episode in March 2015. They show the dust plume located in the altitudes ranging from 1 km to 7 km over the source region, then ascended to 2-9 km over the Pacific Ocean. High wind speed enhancing the height of planetary boundary layer (PBL) tend to occur in spring over northern China [139], which are favorable for the dust particles to be lofted into the free troposphere. These events were also analyzed in terms of emissions size distributions in Yinchuan, China close to Inner Mongolia [140], showing a bi-modal emission shape of the mass particle size distributions (PSD), but very different according their emission conditions (background, floating dust, blowing dust, and dust storm), these two modes are located at 3-4 \(\upmu\)m and around 10 \(\upmu\)m in diameter. However, from in situ measurements compiled close to North African source regions [141], an emission mode is usually observed around 10 \(\upmu\)m. From campaign to campaign the PSD are very different [142] since they depend on the location of measurements and meteorological conditions. Other studies report particle size distribution curves of Asian dust often extending over 10 \(\upmu\)m. In a previous study [143], a mean diameter of about 9 \(\upmu\)m by using a cascade impactor in Seoul was reported. CHIMERE (Figure 25) displays only one mode around 10 \(\upmu\)m in Yinchuan, the missing first peak could be explained by an underestimation of the anthropogenic fraction of PM\({}_{2.5}\) in the model due to a lack of emissions in the model for this city.