[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.

[Characteristics of Condensable Particulate Matter in Ultra-low Emission Coal-Fired Power Plants].

The condensable particle matter (CPM) from coal-fired power plants has attracted significant attention for its potential influence on air quality. The knowledge of CPM emissions from coal-fired power plants is limited. In this study, CPM was collected at the inlet and outlet of wet flue gas desulfurization (WFGD) and the outlet of wet electrostatic precipitator (WESP) using in-direct dilution method. Both mass concentration and water-soluble ions of CPM were analyzed after sampling. The gas precursors were measured at the same time. We showed that gas precursors such as HCl, HNO3, SO3, and NH3 significantly contributed to CPM from coal-fired power plants. As the temperature of flue gas decreased, these gas precursors were observed to form CPM. The major components of CPM were water-soluble ions such as SO42-, Cl-, NO3-, and NH4+. WFGD and WESP could reduce the CPM gas precursors. Therefore, CPM concentrations after WFGD and WESP of the five tested coal-fired power plants were reduced by 27% and 45%, respectively. In addition, the condensation of SO3 increased SO42- concentration but reduced Cl- and NO3- contents. Finally, SO42- was found to be the major water-soluble ion of CPM.

[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.

[Effect of a Wet Flue Gas Desulphurization System on the Emission of PM2.5 from Coal-Fired Power Plants].

Wet flue gas desulphurization (WFGD) is wildly used to control SO2 emission from coal-fired power plants. The influence of WFGD on particulate matter (PM) emission has recently drawn significant public attentions in China. In this study, PM2.5 was collected at both the inlet and outlet from three WFGD units, including a single scrubber lime-stone-gypsum FGD unit, a cascade scrubber lime-stone-gypsum FGD unit, and a seawater FGD unit. PM2.5 mass concentrations and their chemical compositions were analyzed. A method to calculate the addition and removal ratios is proposed according to the concertation of PM2.5 components, such as Ti, Pb, Cr, and V. The results indicate that the removal ratio was similar between the three WFGD units (77.1% on average). However, the addition ratio varied significantly. The performance of the cascade scrubber lime-stone-gypsum FGD unit was best, with a lower addition ratio of 8.6%, which is attributed to the weaker evaporation of desulphurization slurry droplets in their second tower under the low temperature of the flue gas. The addition ratio of the seawater FGD unit was also low (23.9%) because of its low concentration of solids in the seawater. The addition ratio of the single scrubber lime-stone-gypsum FGD system was highest, with a value of 162.3%, which was probably due to the low efficiency of the de-mister.

[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.

[Physiochemical Properties and Sources of Atmospheric Particulate Matter During Pollution Monitoring in Nanning, China].

Distribution characteristics, chemical constituents, and sources of particulate matter were measured using a scanning mobility particle sizer and single particle aerosol mass spectrometer during pollution monitoring that occurred between December 5th and December 11th, 2016, in Nanning. Results showed that particulate matter (PM) sized between 20 nm-10 µm were concentrated in the 23 to 395 nm range, with a peak of 100 nm. Three new particle types were generated during the course of this monitoring. These new 30 nm particles came into existence between 14:00 to 18:00, and grew to a size of between 40 nm and 110 nm between 20:00 to 06:00 the next day. The generation of the all three new particles was affected by motor vehicle exhaust emissions. Many secondary particles were also produced during this period of pollution. The source of the fine particulate matter was mainly from the burning of biomass, dust, and the combustion of coal. In addition, a long-distance transmission also contributed to the particles from biomass burning.

[Development and Performance Evaluation of a Supermicron Particle Generation System for Aerosol Instrument Calibration].

Accurate calibration of aerosol measurement instruments is critical for ensuring the data quality when sampling ambient particulate matter (PM) or those from emission sources. A system for calibrating these instruments was set up, which included an ultrasonic device to generate polydisperse supermicron particles, a chamber, and an aerodynamic particle spectrometer to measure particle size distribution. We verified its performance in stably generated testing aerosol with good spatial uniformity, controlled size distributions and concentrations. The testing aerosol generated had a lognormal distribution. A PM10 and PM2.5 two-stage virtual impactor was calibrated using this online method. Collection efficiencies of PM10 and PM2.5 stages calibrated by an off-line method using monodisperse particles were also used for comparison. The results from two different methods were consistent with each other. Though the off-line method has been widely used to calibrate PM samplers, it suffers from long experimental duration (2-3 days for calibrating one sampler). In contrast, the online method allows for a rapid calibration (less than half a day for calibrating one sampler).

[Application of a Two-stage Virtual Impactor in Measuring of PM10 and PM2.5 Emissions from Stationary Sources].

Recently, the Ministry of Environmental Protection of China started the development of emission inventories in fifteen Chinese cities. It includes the esmission of PM10 and PM2.5 from stationary sources. However, there is no national standard method in China for stationary source PM10 and PM2.5 sampling. In this study, a two-stage virtual impactor was developed for sampling PM10 and PM2.5 from stationary sources. Its performance was evaluated for four types of sataionary sources, i.e., coal-fired power plant, waste incineration, circulating fluid bed, and converter steelmaking. These four tested emission sources were equipped with high efficiency PM control devices. PM2.5 mass concentrations measured in the chimneys of these emission sources were (0.93±0.03), (3.3±0.65), (0.59±0.04), and (0.15±0.04) mg·m-3, respectively, while the PM10 mass concentrations were (1.13±0.11), (6.9±0.86), (1.12±0.16), and (0.43±0.15) mg·m-3, respectively.

[Number Concentration and Size Distribution of Particles Emitted by Light-duty Gasoline Vehicles].

In this study, three GDI (gasoline direct injection) and one PFI (port fuel injection) light-duty gasoline vehicles were characterized for their particle emission (number concentration and size distributions). Two condensation particle counters (CPC) with different activation efficiencies (50% cut off diameter) were used. It was found that the number concentration of particles emitted by GDI gasoline vehicle was approximately one order of magnitude higher than that from PFI gasoline vehicle. High emission of particles occurred within the first 200 s of cold start. The number concentration of particles emitted from GDI vehicle was largely influenced by the vehicle working condition, while that of PFI vehicle was relatively stable despite of varying working conditions. The size distributions of particles emitted from GDI and PFI vehicles had both nucleation mode and accumulation mode. The peak diameter of nucleation mode particles was in the range of 20-27 nm, while that of accumulation mode particle was in the range of 80-95 nm. The number concentrations measured by the UCPC (50% cut off diameter of 2.5 nm) were 35% (GDI) and 50.4% (PFI), respectively, higher than those measured by the CPC (50% cut off diameter of 23 nm) used by the regulation.

[Characterizing Beijing's Airborne Bacterial Communities in PM2.5 and PM1 Samples During Haze Pollution Episodes Using 16S rRNA Gene Analysis Method].

During 8th-14th Jan., 2013, severe particulate matter (PM) pollution episodes happened in Beijing. These air pollution events lead to high risks for public health. In addition to various PM chemical compositions, biological components in the air may also impose threaten. Little is known about airborne microbial community in such severe air pollution conditions. PM2.5 and PM10 samples were collected during that 7-day pollution period. The 16S rRNA gene V3 amplification and the MiSeq sequencing were performed for analyzing these samples. It is found that there is no significant difference at phylum level for PM2.5 bacterial communities during that 7-day pollution period both at phylum and at genus level. At genus level, Arthrobacter and Frankia are the major airborne microbes presented in Beijing winter.samples. At genus level, there are 39 common genera (combined by first 50 genera bacterial of the two analysis) between the 16S rRNA gene analysis and those are found by Metagenomic analysis on the same PM samples. Frankia and Paracoccus are relatively more abundant in 16S rRNA gene data, while Kocuria and Geodermatophilus are relatively more abundant in Meta-data. PM10 bacterial communities are similar to those of PM2.5 with some noticeable differences, i.e., at phylum level, more Firmicutes and less Actinobacteria present in PM10 samples than in PM2.5 samples, while at genus level, more Clostridium presents in PM10 samples. The findings in Beijing were compared with three 16S rRNA gene studies in other countries. Although the sampling locations and times are different from each other, compositions of bacterial community are similar for those sampled at the ground atmosphere. Airborne microbial communities near the ground surface are different from those sampled in the upper troposphere.

[Characteristics of Water-Soluble Inorganic Ions in PM2.5 Emitted from Coal-Fired Power Plants].

To characterize the primary PM2.5 emission from coal-fired power plants in China, and to quantitatively evaluate the effects of flue gas denitrification and desulfurization on PM2.5 emission, a pulverized coal fired (PC) power plant and a circulating fluidized bed (CFB) plant were selected for measuring the mass concentration and water-soluble ion composition of PM2.5 in flue gas. The results showed that the mass concentration of PM2.5 generated from the CFB was much higher than that from the PC, while the mass concentrations of PM2.5 emitted from these two plants were very similar, because the CFB was equipped with an electrostatic-bag precipitator (EBP) with higher PM2.5 removal efficiency than the common electrostatic precipitator (ESP). Although the total concentration of water-soluble ions in PM2.5 generated from the PC was lower than that from the CFB, the total concentration of water-soluble ions in PM2.5 emitted from the PC was much higher than that from the CFB, which implied that PM2.5 emission from the PC was greatly affected by the flue gas treatment installations. For example, the flue gas denitrification system produced H2SO4 mist, part of which reacted with the excessive NH3 in the flue gas to form NH4HSO4 in PM2.5 and to increase the acidity of PM2.5. In addition, the escaping of desulfurization solution during the flue gas desulfurization process could also introduce NH4+ and SO2- into PM2.5. Therefore, although the main water-soluble ions in PM2.5 generated from both of the plants were Ca2+ and SO(4)2-, the major cation was changed to NH4+ when emitted from PC.

[Characteristics of water soluble inorganic ions in fine particles emitted from coal-fired power plants].

Currently, China suffers from serious pollution of fine particulate matter (PM2.5). Coal-fired power plant is one of the most important sources of PM2.5 in the atmosphere. To achieve the national goals of total emission reductions of sulfur dioxide (SO2) and nitrogen oxides (NO(x)) during the 11th and 12th Five-Year Plan, most of coal-fired power plants in China have installed or will install flue gas desulfurization (FGD) and flue gas denitrification (DNO(x)) systems. As a result, the secondary PM2.5, generated from gaseous pollutants in the atmosphere, would be decreased. However, the physical and chemical characteristics of PM2.5 in flue gas would be affected, and the emission of primary PM2.5 might be increased. This paper summarized the size distributions of PM2.5 and its water soluble ions emitted from coal-fired power plants, and highlighted the effects of FGD and DNO(x) on PM2.5 emission, especially on water soluble ions (such as SO4(2-), Ca2+ and NH4+) in PM2.5. Under the current condition of serious PM2.5 pollution and wide application of FGD and DNO(x), quantitative study on the effects of FGD and DNO(x) installation on emission characteristics of PM2.5 from coal-fired power plants is of great necessity.

[Sampling methods for PM2.5 from stationary sources: a review].

The new China national ambient air quality standard has been published in 2012 and will be implemented in 2016. To meet the requirements in this new standard, monitoring and controlling PM2,,5 emission from stationary sources are very important. However, so far there is no national standard method on sampling PM2.5 from stationary sources. Different sampling methods for PM2.5 from stationary sources and relevant international standards were reviewed in this study. It includes the methods for PM2.5 sampling in flue gas and the methods for PM2.5 sampling after dilution. Both advantages and disadvantages of these sampling methods were discussed. For environmental management, the method for PM2.5 sampling in flue gas such as impactor and virtual impactor was suggested as a standard to determine filterable PM2.5. To evaluate environmental and health effects of PM2.5 from stationary sources, standard dilution method for sampling of total PM2.5 should be established.

[Development of a two stage virtual impactor for stationary source PM10 and PM2.5 sampling].

China does not have a national standard method for stationary source PM10 and PM2.5 sampling. Current commercial PM10/PM2.5 samplers have some limitations when used in China. In this study, we developed a two stage virtual impactor for sampling PM10/PM2.5 from stationary source. Its performance was evaluated using laboratory generated aerosol. Its collection efficiency curve satisfies the requirement of ISO 7708:1995 for PM10/PM2.5 samplers. The diameter of this cylindrical virtual impactor is 74 mm, smaller than the diameter of the sampling port in most stationary sources in China. Both filter papers and filter thimbles can be used with this impactor which makes it suitable for both low and high dust concentration sampling. The ratio of the minor flowrate to the total flowrate influences the cutoff size (D50) of the virtual impactor. Reducing this ratio will lead to an increase in D50. The distance from the bottom of the accelerating nozzle to the top of the collecting nozzle should be greater than 1.5-2.0 times the diameter of the accelerating nozzle.

[Design and evaluation of an aerosol nanoparticle generation system].

Aerosol nanoparticle generation is a key step in calibrating aerosol instruments, examining nanoparticle properties, and investigating aerosol formation mechanism in photochemical smog systems. An aerosol nanoparticle generation system (including an atomizer and a diffusion dryer) was developed and evaluated in this study. Aqueous solution of NaCl and isopropanol solution of DOS are used to generate solid and liquid aerosols, and the size distribution is measured by a scanning mobility particle spectrometer (SMPS). With the concentration of 0.01-0.50 g x L(-1) and the carrying gas flow rate of 1.64-3.67 L x min(-1), generated aerosols have the geometric mean diameter of 25-51 nm and the total number concentration of 10(6)-10(7) cm(-3). The stability of the generation system was demonstrated. During the three-hours consecutive operation, the variations of the geometric mean diameter and the total number concentration are less than 6% and 12%, respectively.

[Estimate the mercury emissions from non-coal sources in China].

Based on the activity level and emission factors, we estimated the provincial mercury emissions from non-coal sources during the period of 1995 -2003 in China. In the year of 2003, non-coal mercury emissions in China reached 393 tonnes, which was 137 tonnes more than the emissions from coal combustion. Approximately 84 % of the non-coal mercury emissions came from nonferrous metals smelting. The zinc production, lead production, copper production and gold production contributed respectively 51%, 18%, 4% and 11% of total non-coal mercury emissions. The shares of elemental mercury (Hg0), oxidized mercury (Hg2+ ) and particulate mercury (HgP) were 77 % , 18 % and 5 % , respectively. The mercury emissions from non-coal sources in provinces including Hunan, Henan and Yunnan exceeded 30 t x a(-1). The emission intensity of Shanghai, Hunan, Henan and Liaoning exceeded 100 g x (km(2)xa)(-1). Main emission sources in these provinces are nonferrous metals smelting and household waste burning. Mercury emissions from non-coal sources in China increased averagely 9 percent from 1995 to 2003, and the household waste burning increased extremely fast, with an average increase rate of 42 percent.

[Development of mercury emission inventory from coal combustion in China].

Mercury emission inventory by province from coal combustion in China was developed by combining fuel consumption, mercury content in fuel and emission factors after combustion in this study. The study is intended to provide an understanding of mercury transformation, transportation and deposition in atmosphere, as well as propose measures to control mercury pollution in China. Mercury emission sources were classified into 65 categories by economic sectors, fuel types, boiler types and pollution control technologies. For two different data sets of mercury content in coal the total amounts of mercury released into atmosphere in 2000 in China were estimated at about 161.6 tons and 219.5 tons, respectively. The biggest three source sectors were industry, power plants, and residential use, contributing 46%, 35% and 14% of total mercury emissions, respectively. The shares of elemental mercury (Hg0), oxidized mercury (Hg2+ ) and particulate mercury (Hgp) were 16% , 61% and 23% , respectively. The spatial distribution of mercury emissions from coal combustion in China is not uniform. Henan, Shanxi, Hebei, Liaoning and Jiangsu contributed large amounts of mercury emissions, exceeding 10t x a(- 1).