[Pollution Characteristics and Factors Influencing the Reduction in Ambient PM2.5 in Beijing from 2018 to 2020].

Air quality data from 33 environment sites and five regional sites from 2018 to 2020, as well as meteorological data, were used to research PM2.5 variation,spatial and temporal change, diurnal variation, and heavy pollutions in Beijing. The annual average mass concentrations of PM2.5 in Beijing were 51, 42, and 38 µg·m-3, which showed great progress in air quality improvement. However, the PM2.5 concentration in 2020 was still 8.6% above the national limit value despite a 30.9% decline since 2017. The PM2.5 south-north gradient in Beijing remained throughout the three years, but this pattern showed a less significant trend. The highest monthly mean PM2.5 concentrations in Beijing tended to occur in January-March, with the lowest in August-September. NOx, CO, and PM2.5 concentrations were significantly higher in the heating season than in the non-heating season by 58.4%, 52.9%, and 27.5%, respectively. Diurnal variation showed that greater PM2.5 concentrations were observed at nighttime during the heating season and, conversely, at noontime during the non-heating season. Sixteen pollution episodes occurred in Beijing over the last three years, resulting in 25 heavy pollution days distributed in autumn-winter of 2018-2020. The regional heavy pollution characteristics of PM2.5 in Beijing were significant. Through analysis, a continuous pollution reduction was still the most important reason for the yearly decrease in PM2.5. The concentrations of organic matter, elemental carbon, and crustal matter in the PM2.5 in Beijing decreased by 43.3%, 53.2%, and 51.5% since 2017, respectively, and nitrate, sulfate, and ammonium decreased by 34.2%, 52.2%, and 43.7%.The results showed that the control effect of PM2.5 in Beijing was obvious.

Particle size distribution and polycyclic aromatic hydrocarbons emissions from agricultural crop residue burning.

Laboratory measurements were conducted to determine particle size distribution and polycyclic aromatic hydrocarbons (PAHs) emissions from the burning of rice, wheat, and corn straws, three major agricultural crop residues in China. Particle size distributions were determined by a wide-range particle spectrometer (WPS). PAHs in both the particulate and gaseous phases were simultaneously collected and analyzed by GC-MS. Particle number size distributions showed a prominent accumulation mode with peaks at 0.10, 0.15, and 0.15 µm for rice, wheat, and corn-burned aerosols, respectively. PAHs emission factors of rice, wheat, and corn straws were 5.26, 1.37, and 1.74 mg kg(-1), respectively. It was suggested that combustion with higher efficiency was characterized by smaller particle size and lower PAHs emission factors. The total PAHs emissions from the burning of three agricultural crop residues in China were estimated to be 1.09 Gg for the year 2004.

[Transmission of Coronavirus via Aerosols and Influence of Environmental Conditions on Its Transmission].

The COVID-19 pandemic has endangered human health and production since 2019. As an emerging disease caused by SARS-CoV-2, its potential transmissibility via aerosols has caused heated debate. This work summarizes the current research findings on virus aerosol generation, aerodynamic properties, and environmental influencing factors on their survivability in order to elucidate coronavirus transmission via aerosols. The occurrence and distinction of SARS-CoV-2, SARS-CoV-1, and MERS-CoV in real atmospheric environments are summarized. The deficiencies of existing research and directions for necessary future research on confirming the airborne transmission mechanism of coronavirus as well as the need for multidisciplinary research are discussed.

[Measuring the Condensable Particle Matter from a Stationary Source].

With the retrofitting of coal-fired power plants and steel plants for ultra-low-emission control, the concentration of filterable particles (FPM) from these sources is decreasing gradually. The condensable particle matter (CPM) draws more attention. The understanding of CPM emission concentration and chemical characteristics is still limited. There has been no standard determination method of CPM in China until now. In this study, three methods, including the dry impinger method (US EPA method 202), indirect dilution method, and direct dilution method, are discussed and compared in measuring CPM emissions from coal-fired power plants, coke-making plants and sintering plants. The results show that method 202 overestimates the emissions of CPM, due to the fact that the gaseous HCl or SO2 dissolves into condensable liquid and cannot be completely eliminated by N2 purging after sampling. Instead, CPM measured using the indirect dilution method better represents its real emission levels into the atmosphere.

[Well-to-Wheels Fossil Energy Consumption and CO2 Emissions of Hydrogen Fuel Cell Vehicles in China].

Hydrogen fuel cell vehicles (FCVs) have the advantage of high energy efficiency and zero tailpipe emissions. They have been progressively commercialized in recent years. Hydrogen production has diversified technological pathways, which vary greatly in terms of energy and environmental impacts. In this study, the life cycle assessment (LCA) method was applied to evaluate well-to-wheels (WTW) fossil energy consumption and carbon dioxide (CO2) emissions of FCVs using various hydrogen production pathways. The greenhouse gases, regulated emissions, and energy use in transportation (GREET) model, developed by the Argonne National Laboratory, was applied as the assessment tool, and a China-specific database was investigated and developed to evaluate typical hydrogen production pathways. Then, we compared the WTW fossil energy consumption and CO2 emissions of FCVs with those of gasoline vehicles (GVs), hybrid electric vehicles (HEVs), and battery electric vehicles (BEVs). The results indicated that renewable-energy-based electrolysis of water and biomass gasification are two prospective hydrogen production pathways with significant WTW energy and climate benefits which can help FCVs reduce fossil energy consumption and CO2 emissions by approximately 90% more than GVs. Among the current pathways with mass adoption, hydrogen production from coke oven gas (COG) has substantial energy and CO2 mitigation benefits, which enables FCVs to achieve a lower WTW fossil energy consumption than HEVs and lower WTW CO2 emissions than HEVs and BEVs. Considering the resource reserves and technological maturity in China, hydrogen production from COG and other industrial by-products is recommended for hydrogen energy and FCV development in the short term. In the medium and long terms, utilization of renewable energy to produce hydrogen should be promoted.

Approach of technical decision-making by element flow analysis and Monte-Carlo simulation of municipal solid waste stream.

This paper deals with the procedure and methodology which can be used to select the optimal treatment and disposal technology of municipal solid waste (MSW), and to provide practical and effective technical support to policy-making, on the basis of study on solid waste management status and development trend in China and abroad. Focusing on various treatment and disposal technologies and processes of MSW, this study established a Monte-Carlo mathematical model of cost minimization for MSW handling subjected to environmental constraints. A new method of element stream (such as C, H, O, N, S) analysis in combination with economic stream analysis of MSW was developed. By following the streams of different treatment processes consisting of various techniques from generation, separation, transfer, transport, treatment, recycling and disposal of the wastes, the element constitution as well as its economic distribution in terms of possibility functions was identified. Every technique step was evaluated economically. The Mont-Carlo method was then conducted for model calibration. Sensitivity analysis was also carried out to identify the most sensitive factors. Model calibration indicated that landfill with power generation of landfill gas was economically the optimal technology at the present stage under the condition of more than 58% of C, H, O, N, S going to landfill. Whether or not to generate electricity was the most sensitive factor. If landfilling cost increases, MSW separation treatment was recommended by screening first followed with incinerating partially and composting partially with residue landfilling. The possibility of incineration model selection as the optimal technology was affected by the city scale. For big cities and metropolitans with large MSW generation, possibility for constructing large-scale incineration facilities increases, whereas, for middle and small cities, the effectiveness of incinerating waste decreases.

[Evaluation and Development of a Weighing Chamber by Using Saturated MgCl2 Solution].

In recent years, China has suffered a lot from atmospheric particles. Many studies of particles are based on filters. As a result, the accuracy of filter weighing is of great importance. A weighing chamber (1.2 m×0.6 m×0.8 m) was developed and evaluated using saturated MgCl2 solution with a self-made flow control system to maintain constant relative humidity (RH). By evaluating the mass change of blank and aerosol-enriched filters after weighing in different RH, we selected RH of 30%-40% as the range for the proper constant RH. To reach a constant RH, 20 L·min-1 dry air was put through a RH-constant chamber with MgCl2 solution in it. Then, the RH-constant air was put continually into the weighing chamber. After the weighing chamber reached stable RH, the flow rate was adjusted to 5 L·min-1 to maintain the RH. Throughout a one-month test, the weighing chamber maintained 30.1%-34.0% RH while the outside RH changed a lot. We weighed 60 filters with this weighing chamber after equilibration for 24 hours. The standard deviation after three times' weighing was no more than 0.02 mg. compared to other methods, the RH-controlling method of this weighing chamber was simple, stable, easy to maintain, and cost effective.

[Impact of Gusty Northwesterly Winds on Biological Particles in Winter in Beijing].

Biological aerosol particles play a crucial role in cloud formation and succession of ecosystems and have a large impact on human health. However, the variations in the concentration, composition, and viability of biological particles remain unclear. This study, conducted in January 2013 and January 2015 in Beijing, explores the influence of meteorological conditions on the variations in the concentration and composition of biological particles. Concentrations of biological particles were measured by an online optical detector, waveband integrated bioaerosol sensor (WIBS-4A). The composition of bacterial communities within biological particles was measured by 16S rDNA sequencing. The results showed that the number concentration of biological particles ranged from 2 L-1 to 150 L-1 during winter. The wind could largely influence the concentration and composition of biological particles. During gusty northwesterly winds, when wind speed was above 4 m·s-1 and wind direction was from the northwest (~30°), the concentration increased by one order of magnitude, and the composition of bacterial communities sharply changed. After the passage of gusty winds, the composition gradually changed back to its prior state.

[Assessment of PM2.5 Pollution Mitigation due to Emission Reduction from Main Emission Sources in the Bejing-Tianjin-Hebei Region].

This study chose two months (January and July) in 2012 which represent winter and summer respectively, to assess the effects of fine particle(PM2.5) pollution elimination due to emission control from different sectors in the Bejing-Tianjin-Hebei region by using CMAQ/2D-VBS modeling system. The results showed that, industrial emissions contributed most to PM2.5 pollution in the Beijing-Tianjin-Hebei region, followed by domestic emissions, while the contribution of per ton emission reduced for industrial sectors subject to domestic sectors. The total contribution and contribution of per ton emission reduced for transportation and power plant were both at low level. Among industrial sectors, the iron, steel and metallurgical industry was the greatest contributor, followed by cement industry, industrial boiler, coking industry, lime and bricks industry and chemical industry. It was found that the contribution of each emission source had significant association with its primary PM2.5 emission level. The control of NOx emissions would promote the formation of PM2.5, and atmospheric vertical diffusion effect was weak during wintertime in the Beijing-Tianjin-Hebei region. As a result, emission control of various sectors was universally more effective for PM2.5 pollution mitigation in summer than in winter. Emission control in summer was significantly more effective for transportation, powerplant, cement industry, industrial boiler and lime and bricks industry. Due to considerable emissions in heating season, domestic emissions showed more contribution in winter. Agricultural sources showed greater contribution per emission reduction in winter by the reason of substantial emissions from straw open burning during this time. With respect to a certain reduction ratio of emission, future control strategies should pay more attention to industrial emissions, especially to the primary PM2.5 emissions. In details, priorities should be given to NOx and SO2 emission control for iron, steel and metallurgical industry, NOx emission control for cement industry and SO2 and NMVOC emission control for coking industry. Besides, domestic emission control should also be taken into consideration, and it will be more effective in winter.

[Characteristics of Speciated Atmospheric Mercury in Chongming Island, Shanghai].

Continuous monitoring of gaseous elemental mercury (GEM), reactive gaseous mercury (RGM) and particulate mercury (PBM) was conducted in the Dongtan wetland park in Chongming Island, Shanghai from March 2014 to February 2015. The average concentrations of GEM, RGM, and PBM were (2.75±1.13) ng·m-3, (13.39±15.95) pg·m-3, and (21.89±40.42) pg·m-3, respectively, higher than the background concentrations of Northern Hemisphere. The atmospheric mercury showed obvious seasonal variations, with the highest seasonal average GEM concentration in summer (3.65 ng·m-3), which was mainly influenced by natural sources, while lower GEM concentrations appeared in autumn and winter influenced mainly by anthropogenic sources. The concentration of RGM was highest in spring and lowest in winter, mainly influenced by the wind direction, while PBM showed higher concentrations in autumn and winter, when heavy fine particulate pollution episodes occurred frequently. The concentrations of GEM and PBM were generally elevated in nighttime and lower in daytime caused by the mixing condition of the air masses. Most of the high RGM concentration values occurred in the afternoon of all seasons due to the higher atmospheric oxidation. The concentrations of GEM and PBM were higher in the west wind due to the emission from anthropogenic sources in Shanghai, Jiangsu, etc. The RGM concentration in southeast wind was obviously higher than those in other wind directions. The RGM was mainly from the anthropogenic sources, and the smaller wind in the southeast direction was against the dispersion of RGM.