Haze formation in China: Importance of secondary aerosol

Air pollution is the world＇s largest single environmental hazard that causes more than a few million premature deaths in 2012（World Health Organization,2014）,particularly in developing countries with rapid industrialization and urbanization.Rapid economic growth of China in the last three decades has resulted in serious air pollution problems on both local and regional scales.

Role of secondary aerosols in haze formation in summer in the Megacity Beijing

A field experiment from 18 August to 8 September 2006 in Beijing, China, was carried out. A hazy day was defined as visibility 〈 10 km and RH（relative humidity） 〈 90%. Four haze episodes, which accounted for ～ 60% of the time during the whole campaign, were characterized by increases of SNA（sulfate, nitrate, and ammonium） and SOA（secondary organic aerosol） concentrations. The average values with standard deviation of SO2-＋4, NO-3, NH4 and SOA were 49.8（± 31.6）, 31.4（±22.3）, 25.8（±16.6） and 8.9（±4.1） μg/m3, respectively, during the haze episodes, which were 4.3, 3.4, 4.1, and 1.7 times those in the non-haze days. The SO2-4,NO-3, NH＋4, and SOA accounted for 15.8%, 8.8%, 7.3%, and 6.0% of the total mass concentration of PM10 during the non-haze days. The respective contributions of SNA species to PM10 rose to about27.2%, 15.9%, and 13.9% during the haze days, while the contributions of SOA maintained the same level with a slight decrease to about 4.9%. The observed mass concentrations of SNA and SOA increased with the increase of PM10 mass concentration, however, the rate of increase of SNA was much faster than that of the SOA. The SOR（sulfur oxidation ratio） and NOR（nitrogen oxidation ratio） increased from non-haze days to hazy days, and increased with the increase of RH. High concentrations of aerosols and water vapor favored the conversion of SO2 to SO2-4and NO2 to NO-3, which accelerated the accumulation of the aerosols and resulted in the formation of haze in Beijing.

Spatio-temporal Characteristics of Atmospheric Pollution and Cause Analysis of Haze Events in Sichuan Basin,China

This study analyzed the spatio-temporal variability of air quality data for six standard air pollutants(Particulate Matter 2.5(PM2.5),Particulate Matter 10(PM10),SO2,NO2,CO,and O3)in the Sichuan Basin(SCB),China from 2015 to 2018 in relation to the formation of haze using conventional meteorological data(temperature,wind speed,and relative humidity),satellite data(fire point data,vertical profiles of aerosol subtypes,and aerosol optical depth),planetary boundary layer height,and backward trajectories.The results indicated that the spatio-temporal evolution of the air quality index(AQI)had notable seasonality for the pollution severity in descending order:winter,spring,summer,and autumn.Autumn and winter severe haze events occurred in November and January,respectively,and were caused by higher local pollution emissions under stagnant air conditions.Spring severe haze events occurred in May and were caused by dust from Northwest China and local regions.Severe summer haze events occurred in July and were caused by local burning.Therefore,the analyses showed that local burning,stagnant meteorological conditions,air mass transport and anthropogenic pollution emissions played a key role in haze in the SCB.This study provides scientific insights for fully analyzing heavy air pollution in SCB,China,and also provides a scientific basis for pollution research in regions of complex terrain as basins and mountains.

Characteristics and formation mechanism of regional haze episodes in the Pearl River Delta of China

To investigate the characteristics and the specific mechanism of continuous haze,comprehensive measurements were conducted from 15 October to 19 November in the Atmospheric Environment Monitoring Super-Station in Heshan of Guangdong province.Five haze episodes occurred in October and November 2014 in the Pearl River Delta（PRD）region. The meteorological parameters, gas data, chemical compositions, and optical parameters of the aerosols were obtained. Among these events, the second haze episode,with the highest concentration of PM2.5 of 187.51 μg/m^3, was the most severe. NO^3-was always higher than SO_4^（2-）, which indicated that motor vehicles played an important role in the haze, even though the oxidation rate from SO_2 to SO_4^（2-）was faster than that of NOXto NO_3^-. The difference between the hourly averages of Na＋and K＋during the haze episode and clean days was small, implying that straw combustion and sea salt had no significant effect on the occurrence of haze, and the backward trajectories of the air masses also conformed with this result. The air pollutants were difficult to disperse because of the significant decrease in the planetary boundary layer（PBL） height. Relative humidity played a crucial role in the formation of haze by leading to hygroscopic growth of the diameter of aerosols.

Sulfate formation and its key role in severe haze development over China

Subject Code:B07With the financial support by the National Natural Science Foundation of China and the Chinese Academy of Sciences,Prof.Wang Gehui(王格慧)at the State Key Laboratory of Loess and Quaternary,Institute of Earth Environment,Chinese Academy of Sciences,and the researchers from China,USA and other countries have revealed a key role of sulfate in the developing process of Chinese haze,which