A rapid reaction occurs near the exhaust nozzle when vehicle emissions contact the air. Twenty diesel vehicles were studied using a new multipoint sampling system that is suitable for studying the exhaust plume near the exhaust nozzle. The variation characteristics of fine particle matter (PM2.5) and its components in diesel vehicle exhaust plumes were analyzed. The PM2.5 emissions gradually increased with increasing distance from the nozzle in the plume. Elemental carbon emissions remained basically unchanged, organic carbon and total carbon (TC) increased with increasing distance. The concentrations of SO42-, NO3- and NH4+ (SNA) directly emitted by the vehicles were very low but increased rapidly in the exhaust plume. The selective catalytic reduction (SCR) reduced 42.7% TC, 40% NO3- emissions, but increased 104% SO42- and 36% NH4+ emissions, respectively. In summary, the SCR reduced 29% primary PM2.5 emissions for the tested diesel vehicles. The NH4NO3 particle formation maybe more important in the plume, and there maybe other forms of formation of NH4+ (eg. NH4Cl). The generation of secondary organic carbon (SOC) plays a leading role in the generation of secondary PM2.5. The SCR enhanced the formation of SOC and SNA in the plume, but comprehensive analysis shows that the SCR more enhanced the SNA formation in the plume, which is mainly new particles formation process. The inconsistency between secondary organic aerosol (SOA) and primary organic aerosol definitions is one of the important reasons for the difference between SOA simulation and observation.

Emergency response mechanisms were activated throughout China during the COVID-19 outbreak. It is different from the temporary, partial, and limited pollution control measures taken to ensure the regional environmental quality during several important events such as the 2008 Beijing Olympic Games and the 2014 Asia-Pacific Economic Cooperation (APEC). During the COVID-19 epidemic period, extensive movement of people and almost all unnecessary industrial production (necessary industrial production refers to the production of food, epidemic prevention materials, etc.) have been severely restricted, so transportation and industrial production have been greatly reduced. This is a rare extreme emission reduction scenario that presents a unique opportunity for atmospheric research. In this study, based on hourly mass concentration data of NO2 and SO2 from atmospheric monitoring sites in the Beijing-Tianjin-Hebei (BTH) region during the COVID-19 epidemic period, the changes in transportation and industrial production in the region, data statistics, and spatial analysis were used to analyze the pollution changes and their causes. The results indicate that the NO2 and SO2 concentrations in the BTH region decreased significantly during the epidemic period. The spatial distribution pattern of NO2 pollution in the BTH region was \"high in the southeast and low in the northwest,\" and SO2 pollution in the BTH region was high in the southern and eastern parts of Hebei. The initiation of emergency response level 1 had an obvious effect on reducing NO2 and SO2 pollution in the region, while the impact of emergency response level 2 and below was limited. Compared with the single traffic control, the comprehensive control, similar to the emergency response, had a better effect on reducing NO2 pollution in the region. The control of major large cities in the region also had a certain effect on alleviating NO2 and SO2 pollution in the entire region. Moreover, for activities under short-term control, it is particularly important to guard against the \"retaliatory growth\" after the control is lifted. By reducing and controlling some polluting industries in industrial production, the degree of NO2 and SO2 pollution in the region can be effectively reduced. The manufacturing industry of chemical raw materials and the chemical products and non-metallic mineral products industry made a great contribution to the change in industrial source pollution emissions in the BTH region during the COVID-19 epidemic. Road traffic emissions remained an important source of NO2 emissions in the BTH region during this period. NO2 emission reduction can be effectively achieved by controlling road traffic and transportation.

The ultralow emission (ULE) retrofits for Chinese coal-fired power plants (CFPPs) are nearing completion. Large-scale and rapid retrofits have resulted in significant changes in the emission level and characteristics of particulate matter (PM). To investigate the variation characteristics of final three size fractions PM (PM2.5, PM10-2.5, PM>10) emissions, we conducted field tests at the outlets of wet flue gas desulfurization (WFGD) and wet electrostatic precipitator (WESP) by a pair of two-stage virtual impactors in eight representative ULE CFPPs. Our results indicate that, after WESP installations, the mass concentrations of final PM are significantly reduced and those of the final total ions and elements decrease as most individual chemical compositions are reduced. WESP presents an excellent removal performance for large particle sizes and high PM concentrations. SO42- is the major ionic component at both the outlets of WFGD and WESP, and its proportion in total ions is reduced to some extent through WESP. Furthermore, the average mass contents of SO42- and most elements in PM2.5 are significantly lower than those in PM10-2.5 and PM>10 whether at the WFGD-outlets or WESP-outlets. By comparison, chemical profiles of PM have substantially changed after ULE retrofits, and those after WFGD (e.g., sulfate, Zn, Pb, and Cu) have also changed relative to existing data. The end-tail emission factors (EFs) of PM2.5, PM10, and PMtotal under the typical ULE technical routes of WESP are calculated in time, and the corresponding EFs are in the range of 2.82-8.97, 15.7-27.6, and 38.6-61.7 g t-1, respectively. We believe the latest detailed PM EFs and the associated chemical profiles provided in this study are more representative of the current emission situations of Chinese CFPPs.

The distribution characteristics, sources and ecological risk of thallium (Tl) in the surface sediments of Yangtze Estuary and its adjacent sea were studied. Tl concentrations ranged from 0.369 to 1.197 μg g-1 with an average of 0.674 μg g-1, which was slightly higher than the corresponding background values. Tl concentrations were relatively high in sediments of the south bank of Chongming Island and the Hangzhou Bay mouth, and gradually decreased from inner shelf to outer seas. The variation trend of Tl concentrations was controlled by sediment characteristics, hydrodynamic conditions and sources together. The sediment flux of Tl in the study area was 428.6 t/yr. The Yangtze River, the Yellow River and atmospheric inputs of Tl accounted for 52.7%, 10.5%, and 0.15% of the total sediment flux, respectively. The result of potential ecological index indicated that Tl in surface sediments of the study area had no threat to the ecological environment.