Search

In order to fully understand the inorganic water-soluble ions and their sources in the atmospheric fine particles PM2.5 in Beijing after coal-to-gas conversion, 41 PM2.5 samples were continuously collected in Haidian District of Beijing during the winter heating period in 2017.The concentrations of 10 kinds of water-soluble ions(Na+, NH4+, K+, Ca2+, Mg2+, F-, Cl-, NO2-, NO3-, SO42-)were analyzed by ion chromatography.The results show that the daily average mass concentration of PM2.5 in Beijing during the sampling period is (94.28±52.49) μg/m3.Compared with the winter of 2016, the average daily PM2.5 concentration in Beijing in 2017 decreased by 29 μg/m3, with a decrease of 28.2%, and the number of pollution days decreased significantly.During the pollution period, NO3-, SO42-, and NH4+in the particulate matter were significantly higher than the clean period.The ratio of the concentration of ρ(NO3-)/ρ(SO42-) is greater than 1, and the contribution of the mobile source is relatively large, reflecting that the implementation of the "coal to gas" policy has contributed to the reduction of sulfate emissions from fixed sources such as coal.Time-of-flight secondary ion mass spectrometry(TOF-SIMS) was combined with mass high resolution mode and positive and negative ion imaging mode to characterize PM2.5.The results show that NH4+tends to exist in the form of molecular ammonium sulfate or ammonium hydrogen sulfate during the pollution period.

The disasters of encounter of extreme rainstorm and high tide level will aggravate the flood in coastal cities.In order to explore the impact of the encounter of rainstorm and tide on flood control and drainage in coastal cities,based on the annual maximum 1 day rainfall and its corresponding tide level data of Chiwan Station in Shenzhen from 1967 to 2018,the Copula function is used to construct a joint distribution model of annual maximum 1 day rainfall and its corresponding tide level,and the co-occurrence risk,the flood control risk,the condition risk and the combination risk of rain and tide in Shenzhen are calculated and analyzed.The results show that the risk of the encounter of rain and tide in Shenzhen is small,and the co-occurrence and combination risk probability of rainfall whose return period greater than 100 years and tidal level whose return period greater than 200 years are only 0.12% and 0.09%.The probability of the occurrence of rainfall or tide exceeding the standard magnitude is 1.09%,and its return period is less than 100 years.When the rainfall exceeds the standard magnitude,the probability of encountering an over-standard tide level is greater,with a probability of 12.33%.At the same time,with the increase of rainfall,the risk will also increase.Therefore,in the planning and design of flood and tide prevention and drainage in cities,the focus should be on attention and prevention.