[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.

[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.

[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.

[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).

[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.

[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.

[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.

[Characteristics of total gaseous mercury concentrations at a rural site of Yangtze Delta, China].

The ambient concentrations of total gaseous mercury (TGM) in Chongming Island, Shanghai, were continuously observed using the Tekran 2537B mercury analyzer from 15th September to 17th December, 2009. The average concentration of TGM during our observation is (2.50 +/- 1.50) ng x m(-3), much higher than the background TGM of north hemisphere. The TGM concentration increased from September to December. During September to December, the concentration peaks appear during 08:00-10:00 am and the daytime TGM concentration approximately equaled that in the night. The TGM in Chongming significantly correlated with concentrations of CO, which indicates that TGM most likely comes from the coal combustion of power plants and industrial boilers. The back trajectory analysis demonstrates the atmospheric mercury in Chongming Island mainly comes from inland China, especially Jiangsu province and Shandong province which locate in the northwest of Chongming. The mercury concentrations are lower in September and October since the airflow is mainly from the eastern ocean. In November and December, the atmospheric mercury content is much higher because the northwest wind brings the pollutants from the western industrial areas.

[Spatial distribution characteristics of NMHCs during winter haze in Beijing].

NMHCs and NOx samples were simultaneously collected and analyzed in six urban and suburban representative sampling sites (Sihuan, Tian'anmen, Pinguoyuan, Fatou, Beijing Airport and Miyun) during a typical haze period in winter 2005, Beijing. The concentrations of NMHCs during the sampling period in descending order were: Sihuan (1101.29 microg x m(-3)) > Fatou (692.40 microg x m(-3)) >Tian'anmen (653.28 microg x m(-3)) >Pinguoyuan (370.27 microg x m(-3)) > Beijing Airport (350.36 microg x m(-3)) > Miyun (199.97 microg x m(-3)). Atmospheric benzene pollution in Beijing was rather serious. The ratio of NMHCs/NOx ranged from 2.1 to 6.3, indicating that the peak ozone concentrations in urban Beijing were controlled by VOCs during the sampling period. Analysis of propylene equivalent concentration and ozone formation potential showed that the NMHCs reactivity descended in the order of Sihuan > Fatou > Tian'anmen > Pinguoyuan > Beijing Airport > Miyun. B/T values (0.52 to 0.76) indicated that besides motor vehicle emission, coal combustion and other emission sources were also the sources of NHMCs in Beijing in winter. The spatial variations of isoprene in Beijing indicated that the contribution of anthropogenic sources to isoprene increased and the emissions by biogenic sources decreased in winter. The spatial variations of propane and butane indicated that LPG emissions existed in the urban region of Beijing.

[Particle number size distribution near a major road with different traffic conditions].

The profiles of number concentration of ambient particles at a roadside site in Beijing were studied with different traffic conditions. A Scanning Mobility Particle Sizer (SMPS) was utilized to measure the number concentrations of fine and ultrafine (10-100 nm) particles in August 2008 and August 2009, which represented the normal and Olympic traffic conditions, respectively. Size distributions of particle number concentration were identified and their temporal variations were also discussed. Results indicated that with normal traffic pattern, the total number concentration of ultrafine and 10-478 nm particles were (1.15 +/- 0.49) x 10(4) cm(-3) and (1.61 +/- 0.57) x 10(4) cm(-3), respectively. While the concentrations were decreased to (0.55 +/- 0.14) x 10(4) cm(-3) and (1.21 +/- 0.24) x 10(4) cm(-3), respectively, with special traffic condition during the Beijing Olympic Games. Largest reduction of 52.2% was observed for ultrafine particles among all size ranges. With normal traffic condition, bimodal distribution was found with two peak values in number concentrations around 22.5 nm and 113.0 nm. During the Olympic period, nucleation mode particles were significantly reduced due to a series of temporal control measures on motor vehicles such as the removal of yellow-labeled vehicles from the roads and travel restrictions based on odd-even license plate numbers. As a result, the peak in particle number concentration at 22.5 nm disappeared. The temporal variation indicated that significantly higher ultrafine particle number concentrations occurred around 00 : 00-04 : 00, 11 : 00-13 : 00 and 17 : 00-20 : 00 with normal traffic situation, which primarily attributed to the contributions of diesel exhaust at night, secondary formation at noon and traffic jam in the evening, respectively. However during the Olympic period, the temporal variation pattern changed significantly. The gap in the number concentrations of ultrafine particle between these three time periods and other time periods were narrowed, which should be attributed to the reduction of traffic flow as well as the increase of fleet speed during the Olympics.

Mechanism of monolignol biotransformation by Rhus laccases in water-miscible organic solutions.

Several important monolignols such as coniferyl alcohol were catalyzed using Rhus laccase (RL) from Rhus vernicifera in a water/acetone solution. The enzymatic mechanism is discussed in detail. Sites 6, ß, and phenolic oxygen were the main active sites of phenylpropanoid compounds, which were first oxidized by the enzyme and then radicalized. RL was also responsible for lignin biosynthesis, especially in the early stage.

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.