CMS physics technical design report : Addendum on high density QCD with heavy ions

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Analysis of the causes of heavy aerosol pollution in Beijing, China:A case study with the WRF-Chem model

The causes and variability of a heavy haze episode in the Beijing region was analyzed. During the episode, the PM2.5 concentration reached a peak value of 450 g/kg on January 18, 2013 and rapidly decreased to 100 g/kg on January 19, 2013, characterizing a large variability in a very short period. This strong variability provides a good opportunity to study the causes of the haze formation. The in situ measurements (including surface meteorological data and vertical structures of the winds, temperature, humidity, and planetary boundary layer (PBL)) together with a chemical/dynamical regional model (WRF-Chem) were used for the analysis. In order to understand the rapid variability of the PM2.5 concentration in the episode, the correlation between the measured meteorological data (including wind speed, PBL height, relative humidity, etc.) and the measured particle concentration (PM2.5 concentration) was studied. In addition, two sensitive model experiments were performed to study the effect of individual contribution from local emissions and regional surrounding emissions to the heavy haze formation. The results suggest that there were two major meteorological factors in controlling the variability of the PM2.5 concentration, namely, surface wind speed and PBL height. During high wind periods, the horizontal transport of aerosol particles played an important role, and the heavy haze was formed when the wind speeds were very weak (less than 1 m/s). Under weak wind conditions, the horizontal transport of aerosol particles was also weak, and the vertical mixing of aerosol particles played an important role. As a result, the PBL height was a major factor in controlling the variability of the PM2.5 concentration. Under the shallow PBL height, aerosol particles were strongly confined near the surface, producing a high surface PM2.5 concentration. The sensitivity model study suggests that the local emissions (emissions from the Beijing region only) were the major cause for the heavy haze events. With only local emissions, the calculated peak value of the PM2.5 concentration was 350 g/kg, which accounted for 78% of the measured peak value (450 g/kg). In contrast, without the local emissions, the calculated peak value of the PM2.5 concentration was only 100 g/kg, which accounted for 22% of the measured peak value

Effects of meteorology and secondary particle formation on visibilityduring heavy haze events in Beijing, China

The causes of haze formation in Beijing, China were analyzed based on a comprehensive measurement, including PBL (planetary boundary layer), aerosol composition and concentrations, and several important meteorological parameters such as visibility, RH (relative humidity), and wind speed/direction. The measurement was conducted in an urban location from Nov. 16, 2012 to Jan. 15, 2013. During the period, the visibility varied from N20 km to less than a kilometer, with a minimum visibility of 667 m, causing 16 haze occurrences. During the haze occurrences, the wind speeds were less than 1 m/s, and the concentrations of PM2.5 (particle matter with radius less than 2.5 &mu;m) were often exceeded 200 &mu;g/m3. The correlation between PM2.5 concentration and visibility under different RH values shows that visibility was exponentially decreased with the increase of PM2.5 concentrations when RH was less than 80%. However, when RH was higher than 80%, the relationship was no longer to follow the exponentially decreasing trend, and the visibility maintained in very low values, even with low PM2.5 concentrations. Under this condition, the hygroscopic growth of particles played important roles, and a large amount of water vapor acted as particle matter (PM) for the reduction of visibility. The variations of meteorological parameters (RH, PBL heights, and WS (wind speed)), chemical species in gas-phase (CO, O3, SO2, and NOx), and gas-phase to particle-phase conversions under different visibility ranges were analyzed. The results show that from high visibility (N20 km) to low visibility (b2 km), the averaged PBL decreased from 1.24 km to 0.53 km; wind speeds reduced from 1 m/s to 0.5 m/s; and CO increased from 0.5 ppmv to 4.0 ppmv, suggesting that weaker transport/diffusion caused the haze occurrences. This study also found that the formation of SPM (secondary particle matter) was accelerated in the haze events. The conversions between SO2 and SO4 _ as well as NOx to NO3 &minus; increased, especially under high humidity conditions. When the averaged RH was 70%, the conversions between SO2 and SO4 _ accounted for about 20% concentration of PM2.5, indicating that formation of secondary particle matter had important contribution for the haze occurrences in Beijing.</p

A study of elevated pollution layer over the North China Plain using aircraft measurements

An elevated pollution layer (EPL) at altitude &sim;1700 m was observed over the North China Plain (NCP) in November 2016. The vertical profiles of aerosol loadings, chemical compositions and meteorological parameters were in-situ measured at both ground and aircraft platforms. The EPLs were observed simultaneously over Beijing and Baoding city (&sim;150 km distance between) with similar aerosol concentration and size distribution, indicating the impact of the EPL at regional scale. The synoptic and remote sensing analysis suggest the pollutants in the EPL may result from regional transport from the polluted southwest, and then elevated by the influence of anticyclone circulation and surrounding terrain. The descent air mass next day may lead to EPL entrainment and contribute to increased aerosol concentration at lower level. The non-refractory compositions measured by aerosol mass spectrometer showed more significant fraction of nitrate and secondary organics in the EPL compared to the other layers. The pollutants in the EPL was then mixed into the developed planetary boundary layer (PBL), leading to uniform distribution of aerosol composition. Such atmospheric stratification at high level and its subsequent impact on the lower level needs to be considered for the future radiative forcing study over this region.</p

A budget analysis of the formation of haze in Beijing

During recent winters, hazes often occurred in Beijing, causing major environmental problems. To understand the causes of this &ldquo;Beijing Haze&rdquo;, a haze episode (from Oct. 21 to Oct. 31, 2013) in Beijing was analyzed. During the episode, the daily mean concentration of fine particulate matter (PM2.5) reached a peak value of 270&nbsp;&mu;g/m3 on Oct. 28, 2013, and rapidly decreased to 50&nbsp;&mu;g/m3 the next day (Oct. 29, 2013). This strong variability provided a good opportunity to study the causes of a &ldquo;Beijing Haze&rdquo;. Two numerical models were applied for this study. The first model is a chemical/dynamical regional model (WRF-Chem). This model is mainly used to study the effects that weather conditions have on PM2.5 concentrations in the Beijing region. The results show that the presence of high air pressure in northwest Beijing (NW-High) generally produced strong northwest winds with clean upwind air. As a result, the NW-High played an important role in cleaning Beijing&#39;s PM. However, the NW-High&#39;s cleaning effect did not occur in every situation. When there was low air pressure in southeast Beijing (SE-Low) accompanied by an NW-High, an air convergent zone appeared in Beijing. The pollutants became sandwiched, producing high PM2.5 concentrations in the Beijing region. The second model used in this study is a box model, which is applied to estimate some crucial parameters associated with the budget of PM2.5 in the Beijing region. Under calm winds, the calculations show that continuous local emissions rapidly accumulate pollutants. The PM2.5 concentrations reached 150&nbsp;&mu;g/m3 and 250&nbsp;&mu;g/m3 within one (1) day and two (2) days, respectively. Without horizontal dilution, this estimate can be considered as an upper time limit (the fastest time) for the occurrences of haze events in the Beijing region. The wind speed (WSb) is calculated for the balance between the continuous emissions and atmospheric clean processes. The results show that the WSb is strongly dependent on the planetary boundary layer (PBL) height and the wind direction. Under SE-Low weather conditions, the WSb is 2&nbsp;m/s with a higher PBL height (700&nbsp;m). However, under lower PBL heights, the WSb rapidly increases, reaching 4.5&nbsp;m/s and 7.0&nbsp;m/s with PBL heights of 300&nbsp;m and 200&nbsp;m, respectively. In contrast, under NW-High weather conditions, the WSb reduces to 2.5&nbsp;m/s and 4.0&nbsp;m/s. These results suggest that when the prevailing wind in Beijing is a northwest wind (with wind speeds of &gt;4&nbsp;m/s), particulate matter (PM) begins to decrease.</p

Analyse experimentale des mecanismes de coercivite dans les aimants Nd-Fe-B frittes

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc