Assessment of the Biospheric Contribution to Surface Atmospheric CO_2 Concentrations over East Asia with a Regional Chemical Transport Model

A regional chemical transport model,RAMS-CMAQ,was employed to assess the impacts of biosphere-atmosphere CO2 exchange on seasonal variations in atmospheric CO2 concentrations over East Asia.Simulated CO2 concentrations were compared with observations at 12 surface stations and the comparison showed they were generally in good agreement.Both observations and simulations suggested that surface CO2 over East Asia features a summertime trough due to biospheric absorption,while in some urban areas surface CO2 has a distinct summer peak,which could be attributed to the strong impact from anthropogenic emissions.Analysis of the model results indicated that biospheric fluxes and fossil-fuel emissions are comparably important in shaping spatial distributions of CO2 near the surface over East Asia.Biospheric flux plays an important role in the prevailing spatial pattern of CO2 enhancement and reduction on the synoptic scale due to the strong seasonality of biospheric CO2 flux.The elevation of CO2 levels by the biosphere during winter was found to be larger than 5 ppm in North China and Southeast China,and during summertime a significant depletion （≥ 7 ppm） occurred in most areas,except for the Indo-China Peninsula where positive bioflux values were found.

Vertical distributions of tropospheric SO_(2) based on MAX-DOAS observations: Investigating the impacts of regional transport at different heights in the boundary layer

Information on the vertical distribution of air pollutants is essential for understanding their spatiotemporal evolution underlying urban atmospheric environment. This paper presents the SO_(2) profiles based on ground-based Multi-Axis Differential Optical Absorption Spectroscopy(MAX-DOAS) measurements from March 2018 to February 2019 in Hefei, East China. SO_(2) decrease rapidly with increasing heights in the warm season, while lifted layers were observed in the cold season, indicating accumulation or long-range transport of SO_(2) in different seasons might occur at different heights. The diurnal variations of SO_(2) were roughly consistent for all four seasons, exhibiting the minimum at noon and higher values in the morning and late afternoon. Lifted layers of SO_(2) were observed in the morning for fall and winter, implying the accumulation or transport of SO_(2) in the morning mainly occurred at the top of the boundary layer. The bivariate polar plots showed that weighted SO_(2) concentrations in the lower altitude were weakly dependent on wind, but in the middle and upper altitudes, higher weighted SO_(2) concentrations were observed under conditions of middlehigh wind speed. Concentration weighted trajectory(CWT) analysis suggested that potential sources of SO_(2) in spring and summer were local and transported mainly occurred in the lower altitude from southern and eastern areas;while in fall and winter, SO_(2) concentrations were deeply affected by long-range transport from northwestern and northern polluted regions in the middle and upper altitudes. Our findings provide new insight into the impacts of regional transport at different heights in the boundary layer on SO_(2) pollution.

A Case Study of Typical Regional Pollution Transport in Fuzhou City

Based on data of PM2.5 hourly concentration and HYSPLIT model backward trajectory in coastal cities of Fujian Province during January 25 -26, 2014, a typical regional pollution process affecting Fujian from the north to the south and the east to the west on January 26 was investiga- ted. Taking Fuzhou as an example, based on weather situation on the ground and at high altitudes as well as corresponding meteorological data such as wind direction, wind velocity, and visibility, the changes of meteorological elements before, during and after the pollution were compared. Based on the V-3θ atmospheric vertical structure diagrams, the weather reasons for the generation, maintaining and dissipation of the pollution were discussed. The results indicated that the regional pollution was transported from the northeast to the southwest. The northeasterly air flow in front of the cold ridge strengthened and moved toward the east, so that the pollutant from the north affected Fujian form the north to the south and from the east to the west. As a result, there was a dramatic increase of pollutant concentration, rapid drop of visibility, and deterioration of air quality in the affected areas. The heavy pollution process featured high-speed transport and short-time generation. The air quality changed from good state to heavy pollution in just 3 -4 hours. The maximum of IAQIpM2.5 reached 280. The whole pollution process lasted for 14 hours. Solar radiation had been deeply affected by aerosol clouds, so that atmospheric stratification was extremely stable. Along with the eastward movement of cold high pressure into the sea, the dominant wind direction near the ground changed from the northeast to the east, so that the source of the pollutant was cut off , and air quality quickly turned well. The changes of atmospheric vertical structure indicated that the high inversion layer and clouds near 700 hPa kept lower air clean and blocked upper pollution transport. The later sudden increase of wind speed and strengthening of atmospheric mechanical turbu- lent destroyed inversion layer, so that the upper pollutants invaded air near the ground rapidly. During the period of high pollution, the isothermal layer （aerosol clouds） leaded to decrease of wind speed, and the atmosphere became more stable. The pollution ended until the wind field changed.

Effects of transport on aerosols over the eastern slope of the Tibetan Plateau:synergistic contribution of Southeast Asia and the Sichuan Basin

The aerosol optical properties and chemical components of PM2.1(particulate matter with a diameter of 2.1μm or less)were investigated at Mount Gongga on the eastern slope of the Tibetan Plateau from April 2012 to December 2014.The annual mean aerosol optical depth(AOD)was 0.35±0.23,and the?ngstr?m exponent was 1.0±0.38.The AOD exhibited higher values in summer and winter,but lower values in spring and autumn.Dividing the observational periods into dry and wet seasons,the authors found that the concentrations of K^+,elemental carbon,secondary inorganic aerosols,and primary and secondary organic carbon in the dry(wet)season were 0.29(0.21),0.88(0.60),7.4(4.5),7.5(5.1),and 3.9(12)μg m?3,respectively.Combined with trajectory analysis,the authors found that higher concentrations of K^+,elemental carbon,and primary organic carbon indicated the effects of biomass burning from Southeast Asia during the dry season.However,the oxidation of volatile organic compounds was the main source of aerosols during the wet season,which originated from the Sichuan Basin.

Modeling the circulation and sediment transport in the Beibu Gulf

Water circulation and sediment transport in the Beibu Gulf are important for its environmental protection and resource exploitation.By employing the Regional Ocean Modeling System（ROMS）,we studied the seasonal variation of circulation,sediment transport and long-term morphological evolution in the Beibu Gulf.The simulation results show that the circulation induced by tide and wind is cyclonic both in winter and summer in the gulf and that the wind-driven circulation is stronger in winter than that in summer.The sediment concentration is higher in the Qiongzhou Strait,west of the Hainan Island and the coast of Vietnam and the Leizhou Peninsula.The sediment is transported westwards in winter and eastwards in summer in the Qiongzhou Strait.The west entrance of the Qiongzhou Strait is dominated by westward transport all the year round.The sediment discharged by rivers is deposited near the river mouths.The simulated result demonstrates that the sediment transport is mainly controlled by tidal induced bottom resuspension in the Beibu Gulf.Four characteristics are summarized for the distribution patterns of erosion and deposition.（1） The erosion and deposition are insignificant in most area of the gulf.（2） Sediment deposition is more significant in the mouths of Qiongzhou Strait.（3） The erosion is observed in the seabed of Qiongzhou Strait.（4） Erosion and deposition occur alternatively in the west of Hainan Island.

Association of serotonin transporter gene polymorphisms and major depressive disorder in Chinese Han population

BACKGROUND： Serotonin transporter （5-HTT） polymorphisms comprise 5-HTT gene-linked polymorphism region （5-HTTLPR） and variable number of tandem repeats （VNTR）. Studies have revealed an association between 5-HTT polymorphism and major depressive disorder, which suggests that the ＂S＂ allele of 5-HTTLPR and Stin2.9 of 5-HTTVNTR are associated with major depressive disorder. However, there are a number of studies that do not support the 5-HTT polymorphism effect in major depressive disorder. OBJECTIVE： To study the relationship between 5-HTT gene polymorphism and major depressive disorder in Chinese Han population. DESIGN, TIME AND SETTING： Case-controlled study of 5-HTT gene polymorphism. The experiment was performed at the Central Laboratory, Third Affiliated Hospital of Sun Yat-sen University, China from March 2005 to January 2006. PARTICIPANTS： A total of 99 depressive patients of Chinese Han nationality were recruited for this study. All patients met DSM-IV diagnostic criteria for major depressive disorder and had a total score of Hamilton Depression Scale （24 items） ≥21 points. In addition, 101 healthy subjects, matched for age and gender, served as the control group. METHODS： Venous blood was collected from all subjects. 5-HTT genotypes and alleles were determined by polymerase chain reaction. Consistent with the Hardy-Weinberg equilibrium, the association between 5-HTT gene polymorphism and major depressive disorder were analyzed by Chi-square test. MAIN OUTCOME MEASURES： 5-HTTLPR and 5-HTTVNTR genotypes and allele frequencies were measured. RESULTS： No significant differences in 5-HTTLPR genotypes and allele frequencies were determined between patients and controls （P 〉 0.05）. However, significant differences in 5-HTTVNTR genotypes and allele frequencies were detected （P 〈 0.01 ）. The Stin2.10 allele and 10/10 genotype associated with major depressive disorder （OR = 2.61,7.7, P 〈 0.05; analysis of dose-response relationships Х^2 = 12.35, P 〈 0.01）. CONCLUSION： Results from the present study revealed no association between 5-HTTLPR and major depressive disorder. However, a significant association between 5-HTTVNTR and major depressive disorder existed in a population of Chinese Han. The presence of Stin2.10 and 10/10 genotypes increased the risk for major depressive disorder in a dose-dependent manner.

Association between serotonin transporter gene polymorphisms and non-lesional temporal lobe epilepsy in a Chinese Han population

Serotonin （5-hydroxytryptamine, 5-HT） influences the cortical and subcortical excitatory/inhibitory balance and participates in the pathophysiological processes of epilepsy. The serotonin transporter （5-HTT） is the most important factor in serotonin inactivation. We tested whether 5-HTT polymorphisms are involved in the pathogenesis of epilepsy in Chinese Han population. We did not find a significant difference in the frequencies of genotypes and alleles in the 5-HTT gene-linked poLymorphic region （5-H-I-FLPR） in patients with non-lesional temporal lobe epilepsy and normal controls （P〉 0.05）. Frequencies of the 5-H1-1- intron 2 variable number tandem repeat （5-HTTVNTR） 12/12 genotype and allele 12 were higher in the patients with non-lesional temporal lobe epilepsy than normal controls （P 〈 0.01）. The odds ratio of affecting non-lesional temporal lobe epilepsy was 1.435 （95% Cl, 1.096 1.880） in patients carrying allele 12 （P 〈 0.05）. Although the 5-HTTLPR may not be a genetic locus of non-lesional temporal lobe epilepsy in Chinese Hart population, allele 12 in the 5-HTTVNTR may correlate with non-lesional temporal lobe epilepsy. The Stin2.12 allele and 12/12 genotype could be predisposing to non-lesional temporal lobe epilepsy.

Ballistic Transport through a Strained Region on Monolayer Phosphorene

We investigate quanturn transport of carriers through a strained region on monolayer phosphorene theoretically. The electron tunneling is forbidden when the incident angle exceeds a critical value. The critical angles for electrons tunneling through a strain region for different strengths and directions of the strains are different. Owing to the anisotropic effective masses, the conductance shows a strong anisotropic behavior. By tuning the Fermi energy and strain, the channels can be transited from opaque to transparent, which provides us with an efiqcient way to control the transport of monolayer phosphorene-based microstruetures.

Ground-Based Hyperspectral Stereoscopic Remote Sensing Network: A Promising Strategy to Learn Coordinated Control of O_(3) and PM_(2.5) over China

With the coming of the“14th Five-Year Plan,”the coordinated control of particulate matter with an aerodynamic diameter no greater than 2.5 lm(PM_(2.5))and O_(3) has become a major issue of air pollution prevention and control in China.The stereoscopic monitoring of regional PM_(2.5) and O_(3) and their precursors is crucial to achieve coordinated control.However,current monitoring networks are currently inadequate for monitoring the vertical profiles of both PM_(2.5) and O_(3) simultaneously and support air quality control.The University of Science and Technology of China(USTC)has established a nationwide ground-based hyperspectral stereoscopic remote sensing network based on multi-axis differential optical absorption spectroscopy(MAX-DOAS)since 2015.This monitoring network provides a significant opportunity for the regional coordinated control of PM_(2.5) and O_(3) in China.One-year vertical profiles of aerosol,NO_(2) and HCHO monitored from four MAX-DOAS stations installed in four megacities(Beijing,Shanghai,Shenzhen,and Chongqing)were used to characterize their vertical distribution differences in four key regions,Jing–Jin–Ji(JJJ),Yangtze River Delta(YRD),Pearl River Delta(PRD),and Sichuan Basin(SB),respectively.The normalized and yearly averaged aerosol vertical profiles below 400 m in JJJ and PRD exhibit a box shape and a Gaussian shape,respectively,and both show exponential shapes in YRD and SB.The NO_(2) vertical profiles in four regions all exhibit exponential shapes because of vehicle emissions.The shape of the HCHO vertical profile in JJJ and PRD was Gaussian,whereas an exponential shape was shown in YRD and SB.Moreover,a regional transport event occurred at an altitude of 600–1000 m was monitored in the southwest–northeast pathway of the North China Plain(NCP)by five MAX-DOAS stations(Shijiazhuang(SJZ),Wangdu(WD),Nancheng(NC),Chinese Academy of Meteorological Sciences(CAMS),and University of Chinese Academy of Sciences(UCAS))belonging to the above network.The aerosol optical depths(AOD)in these five stations decreased in the order of SJZ>WD>NC>CAMS>UCAS.The short-distance regional transport of NO2 in the 700–900 m layer was monitored between WD and NC.As an important precursor of secondary aerosol,the peak of NO_(2) air mass in WD and NC all occurred 1 h earlier than that of aerosol.This was also observed for the short-distance regional transport of HCHO in the 700–900 m layer between NC and CAMS,which potentially affected the O_(3) concentration in Beijing.Finally,CAMS was selected as a typical site to determine the O_(3)–NO_(x)–volatile organic compounds(VOCs)sensitivities in vertical space.We found the production of O_(3) changed from predominantly VOCs-limited conditions to mainly mixed VOCs–NO_(x)-limited condition from the 0–100 m layer to the 200–300 m layer.In addition,the downward transport of O_(3) could contribute to the increase of ground surface O_(3) concentration.This ground-based hyperspectral stereoscopic remote sensing network provide a promising strategy to support management of PM_(2.5) and O_(3) and their precursors and conduct attribution of sources.

Analysis about the Characteristics and Formation Mechanism of a Serious Pollution Event in Beijing in October 2014

In this paper, atmospheric environmental background, weather conditions and formation mechanism of one typical air pollution episode in Beijing during October 6th -12th, 2014 were investigated by combining observed data with numerical model CAMx. Results showed that the occurrence of heavy air pollution resulted mainly from stable atmospheric conditions regionally or locally. Observed heavy pollution episodes were characterized by a stagnant atmospheric structure with average wind speed of 1.56 m/s, high humidity of 83.13%, large inversion strength of 3.42℃（3/100 m which were disadvantageous to the dispersal of air pollutants. The air pollution episode during October 8th -11th was the most serious with daily average PM2.5 concentration of 264 μg/ms in Beijing, and heavily polluted land area at Beijing, Tianjin and Hebei districts was about 2 × 10^5 km2. Model research showed that regional transmission contributions to the receptor sites in Beijing were between 61% -69% dudng 8th -11th, and regional transportation played a more important role in this serious air pollution episode. Key words Serious pollution incident; Formation mechanism; Regional transportation; Inversion layer; Beijing; PM2.5

Battery with Integrated Power Supply(BALIN)

The BALIN is a modern device,consisting of a battery with integrated battery charger,dedicated to powering the 24 V services of the carriages.In various Trenitalia rolling stock,used for the regional transport of travelers,there are old and obsolete battery charger devices and there are lead acid batteries that need frequent maintenance operations to be kept efficient.These components,due to their low reliability,are the source of serious disruptions to passenger transport,and the management of their maintenance involves high costs for Trenitalia.In order to solve these problems,Trenitalia has therefore decided to invest resources to develop a new system of integrated power supplies and batteries,therefore the BALIN has been developed.The main advantages of BALIN compared to the original components are the presence of a high energy efficiency battery charger designed to operate in a wide range of temperatures and the presence of sealed lead-acid batteries without maintenance with a life exceeding 6 years.The BALIN is able to disconnect its own batteries from the carriage electrical circuits.The BALIN battery charger also implements an intelligent battery management logic and thanks to the interface with the command and control signals present on the rolling stock,the batteries are isolated from the carriage electric load automatically when the train is off and the service it's over.Another important automatic feature of the BALIN is to protect its batteries from deep discharge,in fact the power supply from the batteries to the electric carriage loads is interrupted when the voltage reaches 21 V.The characteristics mentioned go towards the reduction of the charge/discharge cycles of batteries and contribute to increasing the reliability and durability of batteries throughout the entire life of the rolling stock.

Modeling study on the roles of the deposition and transport of PM_(2.5) in air quality changes over central-eastern China

The role of PM_(2.5)(particles with aerodynamic diameters≤_(2.5)μm)deposition in air quality changes over China remains unclear.By using the three-year(2013,2015,and 2017)simulation results of the WRF/CUACE v1.0 model from a previous work(Zhang et al.,2021),a non-linear relationship between the deposition of PM_(2.5)and anthropogenic emissions over central-eastern China in cold seasons as well as in different life stages of haze events was unraveled.PM_(2.5)deposition is spatially distributed differently from PM_(2.5)concentrations and anthropogenic emissions over China.The North China Plain(NCP)is typically characterized by higher anthropogenic emissions compared to southern China,such as the middlelow reaches of Yangtze River(MLYR),which includes parts of the Yangtze River Delta and the Midwest.However,PM_(2.5)deposition in the NCP is significantly lower than that in the MLYR region,suggesting that in addition to meteorology and emissions,lower deposition is another important factor in the increase in haze levels.Regional transport of pollution in central-eastern China acts as a moderator of pollution levels in different regions,for example by bringing pollution from the NCP to the MLYR region in cold seasons.It was found that in typical haze events the deposition flux of PM_(2.5)during the removal stages is substantially higher than that in accumulation stages,with most of the PM_(2.5)being transported southward and deposited to the MLYR and Sichuan Basin region,corresponding to a latitude range of about 24°N-31°N.

Numerical Simulation of CO_2 Concentrations in East Asia with RAMS-CMAQ

The regional air quality modeling system RAMS-CMAQ(Regional Atmospheric Modeling System and Models-3 Community Multi-scale Air Quality) was developed by incorporating a vegetation photosynthesis and respiration module(VPRM) and used to simulate temporal-spatial variations in atmospheric CO2 concentrations in East Asia,with prescribed surface CO2 fluxes(i.e.,fossil fuel emission,biomass burning,sea-air CO2 exchange,and terrestrial biosphere CO2 flux).Comparison of modeled CO2 mixing ratios with eight ground-based in-situ measurements demonstrated that the model was able to capture most observed CO2 temporal-spatial features.Simulated CO2 concentrations were generally in good agreement with observed concentrations.Results indicated that the accumulated impacts of anthropogenic emissions contributed more to increased CO2 concentrations in urban regions relative to remote locations.Moreover,RAMS-CMAQ analysis demonstrates that surface CO2 concentrations in East Asia are strongly influenced by terrestrial ecosystems.

A CNN-SVR model for NO_(2)profile prediction based on MAX-DOAS observations:The influence of Chinese New Year overlapping the 2020 COVID-19 lockdown on vertical distributions of tropospheric NO_(2)in Nanjing,China

In this study,a hybrid model,the convolutional neural network-support vector regression model,was adopted to achieve prediction of the NO_(2)profile in Nanjing from January 2019to March 2021.Given the sudden decline in NO_(2)in February 2020,the contribution of the Coronavirus Disease-19(COVID-19)lockdown,Chinese New Year(CNY),and meteorologi cal conditions to the reduction of NO_(2)was evaluated.NO_(2)vertical column densities(VCDs) from January to March 2020 decreased by 59.05%and 32.81%,relative to the same period in 2019 and 2021,respectively.During the period of 2020 COVID-19,the average NO_(2)VCDs were 50.50%and 29.96%lower than those during the pre-lockdown and post-lockdown pe riods,respectively.The NO_(2)volume mixing ratios(VMRs)during the 2020 COVID-19 lock down significantly decreased below 400 m.The NO_(2)VMRs under the different wind fields were significantly lower during the lockdown period than during the pre-lockdown period This phenomenon could be attributed to the 2020 COVID-19 lockdown.The NO_(2)VMRs be fore and after the CNY were significantly lower in 2020 than in 2019 and 2021 in the same period,which further proves that the decrease in NO_(2)in February 2020 was attributed to the COVID-19 lockdown.Pollution source analysis of an NO_(2)pollution episode during the lockdown period showed that the polluted air mass in the Beijing-Tianjin-Hebei was trans ported southwards under the action of the north wind,and the subsequent unfavorable meteorological conditions(local wind speed of<2.0 m/sec)resulted in the accumulation o pollutants.

Characteristics and sources of peroxyacetyl nitrate(PAN)in the rural North China Plain:Results from1-year continuous observations

Peroxyacetyl nitrate(PAN)is an important photochemical pollutant in the troposphere,whereas long-term measurements are scarce in rural areas in North China Plain(NCP),resulting in unclear seasonal variations and sources of PAN in rural NCP.In this study,we conducted a 1-year observation of PAN during 2021-2022 at the rural NCP site.The average concentrations of PAN were 1.10,0.75,0.65,and 0.88 ppbv in spring,summer,autumn,and winter,respectively,with a 1-year average of 0.81±0.60 ppbv.Calculations indicate that the loss of PAN through thermal decomposition in summer accounts for 43.2% of the total formed PAN,which is an important reason for the low concentration of PAN in summer.We speculate that since the correlation between PAN and O_(3) in winter is significantly lower than that in other seasons,the observed regional transport of PAN cannot be ignored in winter.Through budget analysis,regional transport accounted for 12.8% and 55.9% of the observed PAN on the spring and winter pollution days,respectively,which showed that regional transport played key roles during the photochemical pollution of the rural NCP in winter.The potential source contribution function revealed that the transported PAN mainly comes from southern Hebei in spring.In winter,the transported PAN was mainly from Langfang,Hengshui,and southern Beijing.Our findings may aid in understanding PAN variations in different seasons in rural areas and highlight the impact of regional transport on the PAN budget.

Understand the local and regional contributions on air pollution from the view of human health impacts

The source-receptor matrix of PM_(2.5)concentration from local and regional sources in the Beijing-Tianjin-Hebei(BTH)and surrounding provinces has been created in previous studies.However,because the spatial distribution of concentration does not necessarily match with that of the population,such concentration-based source-receptor matrix may not fully reflect the importance of pollutant control effectiveness in reducing the PM_(2.5)-related health impacts.To demonstrate that,we study the source-receptor matrix of the PM_(2.5)-related deaths instead,with inclusion of the spatial correlations between the concentrations and the population.The advanced source apportionment numerical model combined with the integrated exposure-response functions is used for BTH and surrounding regions in 2017.We observed that the relative contribution to PM_(2.5)-related deaths of local emissions was 0.75%to 20.77%larger than that of PM_(2.5)concentrations.Such results address the importance of local emissions control for reducing health impacts of PM_(2.5)particularly for local residents.Contribution of regional transport to PM_(2.5)-related deaths in rural area was 22%larger than that in urban area due to the spatial pattern of regional transport which was more related to the rural population.This resulted in an environmental inequality in the sense that people staying in rural area with access to less educational resources are subjected to higher impacts from regional transport as compared with their more resourceful and knowledgeable urban compatriots.An unexpected benefit from the multi-regional joint controls is suggested for its effectiveness in reducing the regional transport of PM_(2.5)pollution thus mitigating the associated environmental inequality.

Distribution and transport characteristics of fine particulate matter in beijing with mobile lidar measurements from 2015 to 2018

Accurately quantifying the concentration and transport flux of atmospheric fine particu-late matter(PM_(2.5))is vital when attempting to thoroughly identify the pollution formation mechanism.In this study,the mobile lidar measurements in Beijing on heavily polluted days in December from 2015 to 2018 are presented.The lidar was mounted on a vehicle,which could perform measurements along designated routes.On the basis of mobile lidar mea-surements along closed circuits of the 6th Ring Road around Beijing,the spatial distribution and transport flux of PM_(2.5) in Beijing were determined with information of wind field.In the spatial distribution,both the concentration and transport of PM_(2.5) were revealed to be more significant in the southern section of Beijing.The regional transport layer at heights<1.3 km plays an important role in pollution formation.The maximum transport flux reached 1600μg/(m^(2)*sec)on 11 December 2016.With the aerosol boundary layer height determined from the image edge detection(IED)method,the inter-annual variations of the aerosol boundary layer height(ABLH)were also analysed.The ABLH decreased from 0.73 to 0.46 km during the same heavy pollution period from 2015 to 2018.Increasingly adverse aerosol boundary layer(ABL)meteorological factors,including lower ABLH,light winds,temperature inversions,and accumulated moisture,have become necessary for pollution formation in Beijing.

Size-resolved aerosol water-soluble ions at a regional background station of Beijing, Tianjin, and Hebei, North China

The characteristics of water-soluble ions in size-resolved particulate matter were investigated usingion chromatography at Shangdianzi, a regional background station of Beijing, Tianjin, and Hebei. Seasonal total concentrations of ions （Na＋, Mg2＋, IC, Ca2＋, NH＋4, Cl-, SO2-4 and NO-3） were 75.5 ± 52.9 μg/m3 in spring, 26.5 ± 12.3 Bg/m3 in summer, 22.7 ± 20.4 μg/m3 in autumn, and 31.1 ± 23.9 μg/m3 in winter, respectively. The secondary ions （NO3, SO2-4 and NH＋4）, mainly associated with fine particles, accounted for 84.2% in spring, 82.1% in summer, 81.5% in autumn and 76.3% in winter of all ions. Strong correlations were found between NH＋4 and SO2-4 （r = 0.95, p 〈 0.01） as well as NH＋4 and NO-3 （r = 0.90, p 〈 0.01） in fine particles; while in coarse particles, correlations between Mg2＋ and NO-3 （r = 0.80, p 〈 0.01）, and Ca2＋ and NO2＋ （r = 0.85, p 〈 0.01） were found. The concentrations of Na＋, IC, Mg2＋, Ca2＋, NH＋4, Cl-, NO3, and SC2-4 were 2.02, 0.81, 0.36, 1.65, 9.58, 4.01, 18.9, and 18.4 μg/m3 in particulate matter from southeast-derived air masses, which were typically 1.58-3.37 times higher than in northwest trajectories. Thus, concentrations of water-soluble ions at this background station were heavily influenced by regional transport of serious pollution derived from biomass burning, coal combustion, industrial and vehicle exhaust emissions from Beijing, Tianjin, and Hebei.

Modelling the effect of local and regional emissions on PM_(2.5) concentrations in Wuhan, China during the COVID-19 lockdown

PM_(2.5) concentrations in Wuhan,China decreased by 36.0%between the period prior to the COVID-19 pandemic(1–23 January,2020)and the COVID-lockdown period(24 January to 29 February,2020).However,decreases in PM_(2.5) concentration due to regional PM_(2.5) transport driven by meteorological changes,and the relationship between the PM_(2.5) source and receptor,are poorly understood.Therefore,this study assessed how changes in meteorology,local emissions,and regional transport from external source emissions contributed to the decrease in Wuhan's PM_(2.5) concentration,using FLEXPART-WRF and WRF-Chem modelling experiments.The results showed that meteorological changes in central China explain up to 22.2%of the total decrease in PM_(2.5) concentrations in Wuhan,while the remaining 77.8%was due to air pollutant emissions reduction.Reduction in air pollutant emissions depended on both local and external sources,which contributed alomst equally to the reduction in PM_(2.5) concentrations(38.7%and 39.1%of the total reduction,respectively).The key emissions source areas affecting PM_(2.5) in Wuhan during the COVID-lockdown were identified by the FLEXPART-WRF modeling,revealing that regional-joint control measures in key areas accounted for 89.3%of the decrease in PM_(2.5) concentrations in Wuhan.The results show that regional-joint control can be enhanced by identifying key areas of emissions reduction from the source–receptor relationship of regional PM_(2.5) transport driven by meteorology under the background of East Asian monsoon climate change.

Accounting for CO2 Variability over East Asia with a Regional Joint Inversion System and Its Preliminary Evaluation

A regional surface carbon dioxide （C02） flux inversion system, the Tan-Tracker-Region, was developed by incor- porating an assimilation scheme into the Community Multiscale Air Quality （CMAQ） regional chemical transport model to resolve fine-scale CO2 variability over East Asia. The proper orthogonal decomposition-based ensemble four-dimensional variational data assimilation approach （POD-4DVar） is the core algorithm for the joint assimilation framework, and simultaneous assimilations of CO2 concentrations and surface CO2 fluxes are applied to help reduce the uncertainty in initial CO2 concentrations. A persistence dynamical model was developed to describe the evolu- tion of the surface CO2 fluxes and help avoid the ＂signal-to-noise＂ problem; thus, CO2 fluxes could be estimated as a whole at the model grid scale, with better use of observation information. The performance of the regional inversion system was evaluated through a group of single-observation-based observing system simulation experiments （OSSEs）. The results of the experiments suggest that a reliable performance of Tan-Tracker-Region is dependent on certain assimilation parameter choices, for example, an optimized window length of approximately 3 h, an ensemble size of approximately 100, and a covariance localization radius of approximately 320 km. This is probably due to the strong diurnal variation and spatial heterogeneity in the fine-scale CMAQ simulation, which could affect the perform- ance of the regional inversion system. In addition, because all observations can be artificially obtained in OSSEs, the performance of Tan-Tracker-Region was further evaluated through different densities of the artificial observation net- work in different CO2 flux situations. The results indicate that more observation sites would be useful to systematic- ally improve the estimation of CO2 concentration and flux in large areas over the model domain. The work presented here forms a foundation for future research in which a thorough estimation of CO2 flux variability over East Asia could be performed with the regional inversion system.