Yanyan Yang

Formation and evolution mechanism of regional haze: a case study in the megacity Beijing, China

The main objective of this study is to investigate the formation and evolution mechanism of the regional haze in megacity Beijing by analyzing the process of a severe haze that occurred 20–27 September 2011. Mass concentration and size distribution of aerosol particles as well as aerosol optical properties were concurrently measured at the Beijing urban atmospheric environment monitoring station. Gaseous pollutants (SO 2, NO-NO2-NOx, O3, CO) and meteorological parameters (wind speed, wind direction, and relative humidity) were simultaneously monitored. Meanwhile, aerosol spatial distribution and the height of planetary boundary layer (PBL) were retrieved from the signal of satellite and LIDAR (light detection and ranging). Concentrations of NO, NO2, SO2, O3, and CO observed during 23–27 September had exceeded the national ambient air quality standards for residents. The mass concentration of PM 2.5 gradually accumulated during the measurement and reached at 220 μg m −3 on 26 September, and the corresponding atmospheric visibility was only 1.1 km. The daily averaged AOD in Beijing increased from∼ 0.16 atλ = 500 nm on 22 September and reached∼ 3.5 on 26 September. The key factors that affected the formation and evolution of this haze episode were stable anti-cyclone synoptic conditions at the surface, decreasing of the height of PBL, heavy pollution emissions from urban area, number and size evolution of aerosols, and hygroscopic growth for aerosol scattering. This c se study may provide valuable information for the public to recognize the formation mechanism of the regional haze event over the megacity, which is also useful for the government to adopt scientific approach to forecast and eliminate the occurrence of regional haze in China.

East Asian dust storm in May 2017: observations, modelling and its influence on Asia-Pacific region

A severe dust storm event originated from the Gobi Desert in Central and East Asia during 2–7 May 2017. Based on Moderate Resolution Imaging Spectroradiometer (MODIS) satellite products, hourly environmental monitoring measurements from Chinese cities and East Asian meteorological observation stations, and numerical simulations, we analysed the spatial and temporal characteristics of this dust event as well as its associated impact on the AsiaPacific region. The maximum observed hourly PM10 (particulate matter with an aerodynamic diameter ≤ 10 μm) concentration was above 1000 μg m−3 in Beijing, Tianjin, Shijiazhuang, Baoding, and Langfang and above 2000 μg m−3 in Erdos, Hohhot, Baotou, and Alxa in northern China. This dust event affected over 8.35 million km2, or 87 % of the Chinese mainland, and significantly deteriorated air quality in 316 cities of the 367 cities examined across China. The maximum surface wind speed during the dust storm was 23– 24 m s−1 in the Mongolian Gobi Desert and 20–22 m s−1 in central Inner Mongolia, indicating the potential source regions of this dust event. Lidar-derived vertical dust profiles in Beijing, Seoul, and Tokyo indicated dust aerosols were uplifted to an altitude of 1.5–3.5 km, whereas simulations by the Weather Research and Forecasting with Chemistry (WRFChem) model indicated 20.4 and 5.3 Tg of aeolian dust being deposited respectively across continental Asia and the North Pacific Ocean. According to forward trajectory analysis by the FLEXible PARTicle dispersion (FLEXPART) model, the East Asian dust plume moved across the North Pacific within a week. Dust concentrations decreased from the East Asian continent across the Pacific Ocean from a magnitude of 103 to 10−5 μg m−3, while dust deposition intensity ranged from 104 to 10−1 mg m−2. This dust event was unusual due to its impact on continental China, the Korean Peninsula, Japan, and the North Pacific Ocean. Asian dust storms such as those observed in early May 2017 may lead to wider climate forcing on a global scale.

Desertification and Blown Sand Disaster in China

Approximately 331 million ha, one-third of China’s total land, is prone to desertification processes, leading to natural disasters and economic losses. In this study, the situation, tendency, their influences and their risk governance of desertification and blown sand disaster in China were examined using satellite images, field photographs, field data and a literature review. The desiccated areas in Lop Nor and the lower Heihe River fluvial plain covered about 50,000 km and 40,000 km, respectively. In Ejina, about 100 species of vegetation became extinct. The rate of wind erosion in China was between 1,000 tons/km/year and 2,000 tons/km/year. There were 12 sand deserts and sandy lands, occupying a total of 710,000 km. Salinized soils occurred across 99.1 million ha. The two main sand and dust storm-prone areas in China were the Tarim Basin and its surroundings, and the Alxa Plateau and its surroundings. From 1981 to 2007, the annual average frequency of sand and dust storms varied from 1 d to 37 d with a general increase from southeast to northwest. Since 1978, China has implemented a number of ecological construction projects that have reduced desertification from 1999 to 2004 and from 2005 to 2009, and the number of dust and sand storm days from 9.3 d between 1954 and 1959 to 4.4 d between 2000 and 2007. The results could improve understanding of desertification and blown sand disasters in China and provide valuable experiences for global desertification control.