| In accompany of urbanization and industrialization process, air pollution in and surrounding the Shandong province is getting worse in recent decades. As a coastal province in eastern China, Shandong province connects the Yangtze River Delta and Jing-Jin-Ji region (Beijing, Tianjin and Hebei), which is an indispensable region for haze research. In this study the characteristics of haze in and surrounding the Shandong province were analyzed from the climate observation and numerical simulation separately.To assess the influences of different haze standards on haze analysis in Shandong Province, we compared statistical characteristics of haze with the haze standards based on daily mean,14 local time and diurnally anytime visibility and humidity as well as the 2010 haze standard issued by China Meteorological Administration, by using the meteorological observation data at 74 stations over Shandong province during 1980-2013 and the PM2.5 measurements of 2013. The results indicated that the averaged relative humidity threshold of haze by using all the standards is less than 71%. The threshold of humidity between inland and coastal stations might be different when haze is identified. The daily mean standard is still a more appropriate method to study the long-term characteristic of haze over Shandong.By using the daily mean standard and the surface observation data (1961—2013) at 80 meteorological stations over Shandong Province, the inter-annual and inter-decadal variations in haze seasonality and distributions over Shandong Province in recent 53 years were analyzed with several statistical methods. The results indicated that the seasonal characteristics of haze occurrence in the last century have become indistinct going in the 21th century, the frequent periods of haze days have been spreading from winter to autumn, summer and even spring. Seasonally, the inter-annual increase rates peaked in summer with the values of higher than 4.5%·a-1, and then followed by autumn and spring, and dived in winter with the increase rate of lower than 1.5%·a-1. Haze pollution in Shandong Province, has tended to be a frequently occurring phenomenon in all over the year.The air quality model Weather Research and Forecasting/Chemistry (WRF/Chem) was applied to simulate a PM2.5 pollution process occurred in Shandong Province over February 21-26,2014. To explore the characteristics of PM2.5 of haze over Shandong Province, the analysis was focused on the evaluation of simulation results, temporal and spatial variations of PM2.5 concentration, and its relationship with meteorological conditions. The results showed that in the process of PM2.5 accumulation, the weak southerly wind was prevailing; while the northwest wind was promoted to clean the PM2.5 in the process of PM2.5 dissipation. In addition, when the Beijing-Tianjin-Hebei region had a more severe polluted phenomenon in the meantime, the northwest wind was helpful to drive another high peak of PM2.5 to some areas of Shandong before PM2.5 dissipation. The modeling capacities were best in the southern Shandong in terms of the pollution period, followed by peninsula, middle and southwestern region. During the pollution period, the Shandong’s averaged simulation values of PM2.5 concentration was 125μg·m-3, with the wind speed of 3.0m/s, boundary layer height of 370m and relative humidity of 70% respectively, and the results also indicated that the modeling PM2.5 concentration was strongly dependent on the boundary layer height. There might be some limitations of PBL scheme in describing the PM2.5 variations between daytime and nighttime.Therefore, to explore the impacts of different PBL schemes on the simulation of high PM2.5 concentrations during severe haze, three PBL schemes [Yonsei University (YSU), Mellor-Yamada-Janjic (MYJ), and Bougeault-Lacarrere (Boulac)] were employed to simulate the same haze period in and surrounding theBeijing-Tianjin-Hebei region. The results showed that the three schemes all showed similar guidance for the observed inter-annual variations of PM2.5 concentration. The simulated area averaged values by YSU, MYJ and Boulac schemes were 174.4μg·m-3, 182.4μg·m-3 and 176.9μg·m-3 respectively, with difference no more than 5%. After the comprehensive analysis of statistics, the Boulac scheme was found to be the best among the schemes in terms of its representation of the polluted period, followed by the YSU and MYJ scheme. The diurnal variations of surface PM2.5 simulated using the three schemes were not as reasonable as their reflection of daily averaged variation. The lower ability of PBL schemes in distinguishing the diffusion between haze and clean days in the complex topography area in China is an important problem for PM2.5 forecasting, which is worthy of being studied in detail. |
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