Particulate matter(i.e.,PM_(1.0) and PM_(2.5)),considered as the key atmospheric pollutants,exerts negative effects on visibility,global climate,and human health by associated chemical compositions.However,our understanding of PM and its chemical compositions in Beijing under the current atmospheric environment is still not complete after witnessing marked alleviation during 2013–2017.Continuous measurements can be crucial for further air quality improvement by better characterizing PM pollution and chemical compositions in Beijing.Here,we conducted simultaneous measurements on PM in Beijing during 2018–2019.Results indicate that annualmean PM_(1.0) and PM_(2.5) concentrations were 35.49±18.61μg/m^(3) and 66.58±60.17μg/m^(3),showing a positive response to emission controls.The contribution of sulfate,nitrate,and ammonium(SNA)played an enhanced role with elevated PM loading and acted as the main contributors to pollution episodes.Discrepancies observed among chemical species between PM_(1.0) and PM_(2.5) in spring suggest that sand particles trend to accumulate in the range of 1–2.5μm.Pollution episodes occurred accompanied with southerly clusters and high formation of SNA by heterogeneous reactions in summer and winter,respectively.Results from positive matrix factorization(PMF)combined with potential source contribution function(PSCF)models showed that potential areas were seasonal dependent,secondary and vehicular sources became much more important compared with previous studies in Beijing.Our study presented a continuous investigation on PM and sources origins in Beijing,which provides a better understanding for further emission control as well as a reference for other cities in developing countries.
The mass concentration and major chemical components of fine particulate matter were measured before,during and after Beijing＇s massive parade commemorating 70th anniversary of the Chinese Victory in World War II on September 3,2015.Regional emission inventory,positive matrix factorization（PMF）,observations from space and backward air mass trajectories were jointly applied to identify the major pollution sources and their temporal and spatial variations.The contributions of emissions variations and the meteorological conditions related to the＂parade blue＂phenomenon in Beijing and its surrounding areas were investigated in detail.The main cause of the decreased PM（2.5）mass concentration was attributed to the absolute reduction in emissions of primary air pollutants.The chemical composition of PM（2.5）varied significantly before,during and after the parade.Fugitive dust particles were well controlled,the secondary formation of PM（2.5）was reduced along with the controlled gaseous precursors＇emissions from vehicles and industrial sources during the temporary intensified control period.During the parade period,the SO2and NO2column concentrations in Beijing and the surrounding areas decreased sharply,indicating that the coordinated reduction in primary emissions from the surrounding areas of Beijing played an important role in lowering the ambient concentration of SO2and NO2and accordingly lowered PM（2.5）and improved the regional air quality.A comparison of the temperature,humidity,and wind speed and direction during the same periods in 2014 and 2015 showed that the meteorological conditions positively influenced the achievement of＂parade blue＂.
