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Black carbon (BC) plays an important role in air quality, public health, and climate, but its long-term variations in emissions and health effects have been insufficiently understood for China. Here, we present the spatiotemporal evolution of BC emissions and the associated premature mortality in China during 2000–2020 based on an integrated framework combining satellite observations from the Ozone Monitoring Instrument (OMI), an extreme gradient boosting (XGBoost) algorithm, a “top-down” inversion approach, and an exposure–response model. We found that the “bottom-up” approach most likely underestimated BC emissions, particularly in less developed western and remote areas. Pollution controls were estimated to reduce the annual BC emissions by 26 % during 2010–2020, reversing the 8 % growth during 2000–2010. BC emissions in the main coal-producing provinces declined by 2010 but rebounded afterwards. By contrast, provinces with higher economic and urbanization levels experienced emission growth (0.05–0.10 Mg km−2 yr−1) by 2010 and declined greatly (0.07–0.23 Mg km−2 yr−1) during 2010–2020. The national annual BC-associated premature mortality ranged between 733 910 (95 % confidence interval: 676 790–800 250) and 937 980 cases (864 510–1 023 400) for different years. The changing BC emissions contributed to an increase of 78 590 cases (72 520–85 600) during 2000–2005 and a decrease of 133 360 cases (123 150–145 180) during 2010–2015. Strategies differentiated by region are needed for further reducing BC emissions and their health and climate impacts.

The vertical distribution of black carbon (BC), as well as its mixing state, is of great concern due to BC's strong regional climatic and environmental effects. In this study, vertical measurements were conducted through a moveable container based on a meteorological tower in the Beijing urban area during June and July. A total of 112 vertical profiles (0–240 m), including the concentrations of BC, O3, NOx and the optical properties of aerosols, were obtained. Based on BC concentration, the vertical profiles could be classified into four categories: uniform, gradual decrease, sharp decrease and sudden increase. The uniform type indicates strong vertical mixing with similar pollutant concentrations along the vertical direction. The gradual and sharp decrease types indicate stable vertical conditions with higher pollutant concentrations on the ground and lower concentrations at higher altitudes. Due to the strong radiation in summer, the vertical profiles exhibited a clear diurnal variation in which ∼ 80 % of profiles were uniform during the daytime and ∼ 40 %–90 % of profiles were of the gradual and sharp decrease types at night. O3 is an exception, and its concentration generally increases with height, even under strong vertical mixing conditions. The size distribution of the BC core varied slightly along the vertical direction, and the coating thickness, denoted by the diameter ratio between the BC-containing particle and BC core (Dp/Dc), of BC increased with height under stable conditions. Although the coating thickness could increase the absorption ability with an average absorption enhancement of 1.25 at 23:00 LT (local time: UTC+8), the vertical difference of Dp/Dc (2 %) was much lower than that of BC concentration (∼ 35 %). The vertical variation in absorption ability was mainly caused by the variation in BC concentration. In addition, O3 and Dp/Dc occasionally increased during 06:00–08:00 but remained stable during 08:00–10:00. Vertical mixing and transportation from upper heights, such as the residual layer, could significantly influence the pollutant properties on the surface during early mornings. This study exhibits a continuous vertical picture of BC and its mixing state in urban areas, which would be helpful for understanding BC's regional environmental effect.

Abstract Introduction Gram-negative resistance is a well-acknowledged public health threat. Surveillance data can be used to monitor resistance trends and identify strategies to mitigate their threat. The objective of this study was to assess antibiotic resistance trends in Gram-negative bacteria. Methods The first cultures of Pseudomonas aeruginosa, Citrobacter, Escherichia coli, Enterobacter, Klebsiella, Morganella morganii, Proteus mirabilis, and Serratia marcescens per hospitalized patient per month collected from 125 Veterans Affairs Medical Centers (VAMCs) between 2011 to 2020 were included. Time trends of resistance phenotypes (carbapenem, fluoroquinolone, extended-spectrum cephalosporin, multi-drug, and difficult-to-treat) were analyzed with Joinpoint regression to estimate average annual percent changes (AAPC) with 95% confidence intervals and p values. A 2020 antibiogram of reported antibiotic percent susceptibilities was also created to evaluate resistance rates at the beginning of the COVID-19 pandemic. Results Among 40 antimicrobial resistance phenotype trends assessed in 494,593 Gram-negative isolates, there were no noted increases; significant decreases were observed in 87.5% (n = 35), including in all P. aeruginosa, Citrobacter, Klebsiella, M. morganii, and S. marcescens phenotypes (p

Although many considerable efforts have been done to reveal the driving factors on haze aggravation, however, the roles of aerosol liquid water (ALW) in secondary inorganic aerosol (SIA) formation were mainly focused on the condition of aerosol liquid water content (ALWC) < 100 µg m−3. Based on the in situ high-resolution field observations, this work studied the decisive roles and the shifting of secondary inorganic aerosol formation mechanisms during haze aggravation, revealing the different roles of ALWC on a broader scale (∼500 µg m−3) in nitrate and sulfate formation induced by aqueous chemistry in the ammonia-rich atmosphere. The results showed that chemical domains of perturbation gas limiting the generation of secondary particulate matter presented obvious shifts from a HNO3-sensitive to a HNO3- and NH3-co-sensitive regime with the haze aggravation, indicating the powerful driving effects of ammonia in the ammonia-rich atmosphere. When ALWC < 75 µg m−3, the sulfate generation was preferentially triggered by the high ammonia utilization and then accelerated by nitrogen oxide oxidation from clean to moderate pollution stages, characterized by nitrogen oxidation ratio (NOR) < 0.3, sulfur oxidation ratio (SOR) < 0.4, ammonia transition ratio (NTR) < 0.7 and the moral ratio of NO3-/SO42-=2:1. When ALWC > 75 µg m−3, the aqueous-phase chemistry reaction of SO2 and NH3 in ALW became the prerequisite for SIA formation driven by Henry's law in the ammonia-rich atmosphere during heavy and serious stages, characterized by high SOR (0.5–0.9), NOR (0.3–0.5) and NTR (>0.7), as well as the high moral ratio of NO3-/SO42-=1:1. A positive feedback of sulfate on nitrate production was also observed in this work due to the shift in ammonia partitioning induced by the ALWC variation during haze aggravation. It implies the target controlling of haze should not simply focus on SO2 and NO2, but more attention should be paid to gaseous precursors (e.g., SO2, NO2, NH3) and aerosol chemical constitution during different haze stages.

Real-world effectiveness studies of remdesivir in hospitalized patients with COVID-19 conducted to date have produced conflicting findings which may be due, in part, to treatment heterogeneity within standard of care comparison groups. Our objective was to evaluate the comparative effectiveness and safety of remdesivir in a cohort of patients all treated with corticosteroids. We conducted a retrospective cohort study in the National Veterans Affairs Healthcare System. We included hospitalized patients (>18 years old) with positive COVID-19 PCR tests and COVID-19 diagnosis codes, and corticosteroid treatment within 2 days of admission, from 1 May 2020 to 30 November 2021. Time-to-event outcomes included time to inpatient mortality (primary), discharge, mortality after discharge, readmission, and acute kidney injury and bacterial infection after treatment initiation. Propensity score (PS)-adjusted, PS-matched, and inverse probability of treatment weighted (IPTW) Cox proportional hazards regression models controlled for study timeframe, supplemental oxygen, vaccination status, and other important confounders. We observed significantly lower inpatient mortality, 90-day post-discharge mortality, 30-day post-discharge readmission, and significantly longer hospital stays in the remdesivir group (n = 14,509) compared with the non-remdesivir group (n = 4365). Higher rates of bacterial infections were observed in the remdesivir group. Acute kidney injury was lower in subgroup analyses restricting the study population to index dates in 2021, on supplemental oxygen, and fully vaccinated, and higher in those without baseline supplemental oxygen. When comparing the effectiveness and safety of remdesivir plus corticosteroids to a homogenous comparison group, all also treated with corticosteroids, mortality and readmission were significantly lower in the remdesivir group. Longer length of stay corresponds with duration of remdesivir treatment and may impact the risk of developing infections during the hospitalization, which requires further study.

This study reconstructed the flow field of a symmetrical variable inlet guide vane in a centrifugal compressor through the passive control method of vane slots. Based on the high-fidelity numerical simulation model verified by experiments, the influence of different slot forms on the flow field was investigated, and the passive control mechanism was revealed. The results demonstrated that the vane slot method can effectively suppress the suction surface separation and broaden the range of low-loss incidence angles. Overall, the 50_30 slotted vane achieves the best flow field control, with a 65.6% reduction in the total pressure loss coefficient and a 2.3° reduction in the deviation angle, respectively, at a 25° incidence angle. The linear characteristics of the pre-swirl grade variation curve with variable inlet guide vane incidence angles are also improved. Furthermore, changing the slot outlet angle has the most significant influence on the aerodynamic performance as it changes the throat width of the location, thereby affecting the flow rate and momentum of the jet. Finally, the impact of the velocity varies in the first self-similarity region on the slotted vane. The results indicate that, in contrast to the baseline vane, the suppression effect of the slot jet on the flow separation improves with the inlet velocity, whereas the deviation angle of the slotted vane declines with the inlet velocity. Meanwhile, the higher the incoming flow velocity, the better the slotted jet can inhibition of flow separation.

The variability of the mixing state of refractory black carbon aerosol (rBC) and the corresponding complicated light absorption capacity imposes great uncertainty for its climate forcing assessment. In this study, field observations using a single-particle soot photometer (SP2) were conducted to investigate the mixing state of rBC under different meteorological conditions at a rural site on the North China Plain. The results showed that the hourly mass concentration of rBC during the observation periods was 2.6±1.5 µg m−3 on average, with a moderate increase (3.1±0.9) during fog episodes. The mass-equivalent size distribution of rBC exhibited an approximately lognormal distribution with a mass median diameter (MMD) of 213 nm. We found that the count median diameter (CMD) of rBC particles during snowfall episodes was larger than that before snowfall, and the number of rBC particles with Dc nm were reduced by 28.4 % after snow. This may indicate that rBC-containing particles with small core sizes (Dc) were much more effectively removed by snow with light snow intensity (0.23 mm h−1). Based on the Mie scattering theory simulation, the relative and absolute coating thicknesses of rBC-containing particles were estimated to be ∼1.6 and ∼52 nm for the rBC core with a mass-equivalent diameter (Dc) of 170 to 190 nm, respectively, which indicates that most of the rBC-containing particles were thinly coated. Furthermore, a moderate light absorption enhancement (Eabs=1.3) and relatively low absorption cross section (MAC = 5.5 m2 g−1) at 880 nm were observed at the Gucheng (GC) site in winter compared with other typical rural sites. The relationship between the microphysical properties of rBC and meteorological conditions was also studied. Relatively warm and high-RH environments (RH>50 %, -4∘C

To investigate the impacts of multiscale circulations on the planetary boundary layer (PBL), we have carried out the PBL thermodynamic structure field experiment with a Doppler wind profile lidar, a microwave radiometer, and a ceilometer from January 2018 to December 2019 in Beijing. We found that the direct regulatory effect of synoptic circulation worked through transporting and accumulating pollutants in front of mountains in the daytime, while the indirect effect of multiscale circulations worked through coupling mechanisms in the nighttime. The horizontal coupling of different-direction winds produced a severe pollution convergent zone. The vertical coupling of upper environmental winds and lower regional breezes regulated the mixing and diffusion of pollutants by generating dynamic wind shear and advective temperature inversion. We also found that the dominating synoptic circulations led to great differences in PBL thermodynamic structure and pollution. The cyclonic circulation resulted in a typical multilayer PBL characterized by high vertical shear (600 m), temperature inversion (900 m), and an inhomogeneous stratification. Meanwhile, strong regional breezes pushed the pollution convergent zone to the south of Beijing. The southwesterly circulation resulted in a mono-layer PBL characterized by low vertical shear (400 m) and inversion (200 m). The westerly circulation led to a hybrid-structure PBL, and the advective inversion was generated by the vertical shear of zonal winds. Strong environmental winds of southwesterly and westerly circulations pushed the severe-pollution zone to the front of mountains. There was no distinct PBL structure under the anticyclone circulation. The study systematically revealed the appreciable effects of synoptic and regional circulations on PBL structure and air quality, which enriched the prediction theory of atmospheric pollution in the complex terrain.

Recently, there has been increasing interest in the relation between particulate matter (PM) pollution and atmospheric-boundary-layer (ABL) structure. This study aimed to qualitatively assess the interaction between PM and ABL structure in essence and further quantitatively estimate aerosol radiative forcing (ARF) effects on the ABL structure. Multi-period comparative analysis indicated that the key to determining whether haze outbreak or dissipation occurs is whether the ABL structure satisfies the relevant conditions. However, the ABL structure change was in turn highly related to the PM level and ARF. |SFC−ATM| (SFC and ATM are the ARFs at the surface and interior of the atmospheric column, respectively) is the absolute difference between ground and atmosphere layer ARFs, and the |SFC−ATM| change is linearly related to the PM concentrations. However, the influence of ARF on the boundary layer structure is nonlinear. With increasing |SFC−ATM|, the turbulence kinetic energy (TKE) level exponentially decreased, which was notable in the lower layers or ABL, but disappeared at high altitudes or above the ABL. Moreover, the ARF effects threshold on the ABL structure was determined for the first time, namely once |SFC−ATM| exceeded ∼55 W m−2, the ABL structure tends to quickly stabilize and thereafter change little with increasing ARF. The threshold of the ARF effects on the boundary layer structure could provide useful information for relevant atmospheric-environment improvement measures and policies, such as formulating phased air pollution control objectives.

Under a high atmospheric oxidization capacity, the synergistic effect of the physicochemical processes in the atmospheric boundary layer (ABL) caused summer haze pollution in Beijing. The southern and southwestern areas, generally 60–300 km away from Beijing, were seriously polluted in contrast to Beijing, which remained clean. Southerly winds moving faster than 20–30 km h−1 since the early morning primarily caused haze pollution initiation. The PM2.5 (particulate matter with a dynamic equivalent diameter smaller than 2.5 µm) level increased to 75 µg m−3 over several hours during the daytime, which was simultaneously affected by the ABL structure. Additionally, the O3 concentration was quite high during the daytime (250 µg m−3), corresponding to a high atmospheric oxidation capacity. Much sulfate and nitrate were produced through active atmospheric chemical processes, with sulfur oxidation ratios (SORs) up to ∼0.76 and nitrogen oxidation ratios (NORs) increasing from 0.09 to 0.26, which further facilitated particulate matter (PM) level enhancement. However, the increase in sulfate was mainly linked to southerly transport. At midnight, the PM2.5 concentration sharply increased from 75 to 150 µg m−3 over 4 h and remained at its highest level until the next morning. Under an extremely stable ABL structure, secondary aerosol formation dominated by nitrate was quite intense, driving the haze pollution outbreak. The PM levels in the southern and southeastern areas of Beijing were significantly lower than those in Beijing at this time, even below air quality standards; thus, the contribution of pollution transport had almost disappeared. With the formation of a nocturnal stable boundary layer (NSBL) at an altitude ranging from 0–0.3 km, the extremely low turbulence kinetic energy (TKE) ranging from 0 to 0.05 m2 s−2 inhibited the spread of particles and moisture, ultimately resulting in elevated near-surface PM2.5 and relative humidity (∼90 %) levels. Due to the very high humidity and ambient oxidization capacity, NOR rapidly increased from 0.26 to 0.60, and heterogeneous hydrolysis reactions at the moist particle surface were very notable. The nitrate concentration steeply increased from 11.6 to 57.8 µg m−3, while the sulfate and organics concentrations slightly increased by 6.1 and 3.1 µg m−3, respectively. With clean and strong winds passing through Beijing, the stable ABL dissipated with the potential temperature gradient becoming negative and the ABL height (ABLH) increasing to ∼2.5 km. The high turbulence activity with a TKE ranging from 3 to 5 m2 s−2 notably promoted pollution diffusion. The self-cleaning capacity of the atmosphere is commonly responsible for air pollution dispersion. However, reducing the atmospheric oxidization capacity, through strengthening collaborative control of nitrogen oxide (NOx) and volatile organic compounds (VOCs), as well as continuously deepening regional joint air pollution control, is urgent.

Severe wintertime PM2.5 pollution in Beijing has been receiving increasing worldwide attention, yet the decadal variations remain relatively unexplored. Combining field measurements and model simulations, we quantified the relative influences of anthropogenic emissions and meteorological conditions on PM2.5 concentrations in Beijing over the winters of 2002–2016. Between the winters of 2011 and 2016, stringent emission control measures resulted in a 21 % decrease in mean mass concentrations of PM2.5 in Beijing, with 7 fewer haze days per winter on average. Given the overestimation of PM2.5 by the model, the effectiveness of stringent emission control measures might have been slightly overstated. With fixed emissions, meteorological conditions over the study period would have led to an increase in haze in Beijing, but the strict emission control measures have suppressed the unfavorable influences of the recent climate. The unfavorable meteorological conditions are attributed to the weakening of the East Asia winter monsoon associated particularly with an increase in pressure associated with the Aleutian Low.

Although much effort has been put into studying air pollution, our knowledge of the mechanisms of frequently occurring intense haze episodes in China is still limited. In this study, using 3 years of measurements of air pollutants at three different height levels on a 325 m Beijing meteorology tower, we found that a positive aerosol–boundary layer feedback mechanism existed at three vertical observation heights during intense haze polluted periods within the mixing layer. This feedback was characterized by a higher loading of PM2.5 with a shallower mixing layer. Modelling results indicated that the presence of PM2.5 within the boundary layer led to reduced surface temperature, relative humidity and mixing layer height during an intensive haze episode. Measurements showed that the aerosol–boundary layer feedback was related to the decrease in solar radiation, turbulent kinetic energy and thereby suppression of the mixing layer. The feedback mechanism can explain the rapid formation of intense haze episodes to some extent, and we suggest that the detailed feedback mechanism warrants further investigation from both model simulations and field observations.

Radish is representative root vegetable; its edible parts are directly in contact with Cd-contaminated fields. Two radish cultivars (H4 and L19) with different resistance to Cd were selected to compare their growth, photosynthesis, and antioxidant systems. Our results revealed that H4 was more sensitive to Cd pollution than L19; a significant decrease in the biomass of H4 was observed at higher Cd concentrations. With increasing Cd concentrations, the net photosynthetic rate, effective quantum yield of PSII photochemistry, electron transport rate through PSII, and photochemical quenching were all lowered, however, reductions were more obvious in H4 compared to L19. Further, both peroxidase and catalase activities of L19 were remarkably higher than those of H4. Smaller reductions in ascorbic acid and no obvious changes in glutathione were observed in the leaves of H4. These results suggest that the differences in Cd tolerance could be attributed to the distinct photosynthetic parameters and differences in antioxidant system between L19 and H4.

As major chemical components of airborne fine particulate matter (PM2.5), organic carbon (OC) and elemental carbon (EC) have vital impacts on air quality, climate change, and human health. Because OC and EC are closely associated with fuel combustion, it is helpful for the scientific community and policymakers assessing the efficacy of air pollution control measures to study the impact of control measures and regional transport on OC and EC levels. In this study, hourly mass concentrations of OC and EC associated with PM2.5 were semi-continuously measured from March 2013 to February 2018. The results showed that annual mean OC and EC concentrations declined from 14.0 to 7.7 µg m−3 and from 4.0 to 2.6 µg m−3, respectively, from March 2013 to February 2018. In combination with the data of OC and EC in previous studies, an obvious decreasing trend in OC and EC concentrations was found, which was caused by clean energy policies and effective air pollution control measures. However, no obvious change in the ratios of OC and EC to the PM2.5 mass (on average, 0.164 and 0.049, respectively) was recorded, suggesting that inorganic ions still contributed a lot to PM2.5. Based on the seasonal variations in OC and EC, it appeared that higher OC and EC concentrations were still observed in the winter months, with the exception of winter of 2017–2018. Traffic policies executed in Beijing resulted in nighttime peaks of OC and EC, caused by heavy-duty vehicles and heavy-duty diesel vehicles being permitted to operate from 00:00 to 06:00 (China standard time, UTC+8, for all times throughout the paper). In addition, the fact that there was no traffic restriction in weekends led to higher concentrations on weekends compared to weekdays. Significant correlations between OC and EC were observed throughout the study period, suggesting that OC and EC originated from common emission sources, such as exhaust of vehicles and fuel combustion. OC and EC levels increased with enhanced SO2, CO, and NOx concentrations while the O3 and OC levels were enhanced simultaneously when O3 concentrations were higher than 50 µg m−3. Non-parametric wind regression analysis was performed to examine the sources of OC and EC in the Beijing area. It was found that there were distinct hot spots in the northeast wind sector at wind speeds of approximately 0–6 km h−1, as well as diffuse signals in the southwestern wind sectors. Source areas further away from Beijing were assessed by potential source contribution function (PSCF) analysis. A high-potential source area was precisely pinpointed, which was located in the northwestern and southern areas of Beijing in 2017 instead of solely in the southern areas of Beijing in 2013. This work shows that improvement of the air quality in Beijing benefits from strict control measures; however, joint prevention and control of regional air pollution in the regions is needed for further improving the air quality. The results provide a reference for controlling air pollution caused by rapid economic development in developing countries.

The detailed formation mechanism of an increased number of haze events in China is still not very clear. Here, we found that reduced surface visibility from 1980 to 2010 and an increase in satellite-derived columnar concentrations of inorganic precursors from 2002 to 2012 are connected with each other. Typically, higher inorganic mass fractions lead to increased aerosol water uptake and light-scattering ability in elevated relative humidity. Satellite observation of aerosol precursors of NO2 and SO2 showed increased concentrations during the study period. Our in situ measurement of aerosol chemical composition in Beijing also confirmed increased contribution of inorganic aerosol fraction as a function of the increased particle pollution level. Our investigations demonstrate that the increased inorganic fraction in the aerosol particles is a key component in the frequently occurring haze days during the study period, and particularly the reduction of nitrate, sulfate and their precursor gases would contribute towards better visibility in China.

We have previously identified substantial antibiotic treatment heterogeneity, even among organism-specific and site-specific infections with treatment guidelines. Therefore, we sought to quantify the extent of treatment heterogeneity among patients hospitalized with P. aeruginosa pneumonia in the national Veterans Affairs Healthcare System from Jan-2015 to Apr-2018. Daily antibiotic exposures were mapped from three days prior to culture collection until discharge. Heterogeneity was defined as unique patterns of antibiotic treatment (drug and duration) not shared by any other patient. Our study included 5300 patients, of whom 87.5% had unique patterns of antibiotic drug and duration. Among patients receiving any initial antibiotic/s with a change to at least one anti-pseudomonal antibiotic (n = 3530, 66.6%) heterogeneity was 97.2%, while heterogeneity was 91.5% in those changing from any initial antibiotic/s to only anti-pseudomonal antibiotics (n = 576, 10.9%). When assessing heterogeneity of anti-pseudomonal antibiotic classes, irrespective of other antibiotic/s received (n = 4542, 85.7%), 50.5% had unique patterns of antibiotic class and duration, with median time to first change of three days, and a median of two changes. Real-world evidence is needed to inform the development of treatment pathways and antibiotic stewardship initiatives based on clinical outcome data, which is currently lacking in the presence of such treatment heterogeneity.

Pseudomonas aeruginosa infections are challenging to treat due to multi-drug resistance (MDR) and the complexity of the patients affected by these serious infections. As new antibiotic therapies come on the market, limited data exist about the effectiveness of such treatments in clinical practice. In this comparative effectiveness study of ceftolozane/tazobactam versus aminoglycoside- or polymyxin-based therapies among hospitalized patients with positive MDR P. aeruginosa cultures, we identified 57 patients treated with ceftolozane/tazobactam compared with 155 patients treated with aminoglycoside- or polymyxin-based regimens. Patients treated with ceftolozane/tazobactam were younger (mean age 67.5 vs. 71.1, p = 0.03) and had a higher comorbidity burden prior to hospitalization (median Charlson 5 vs. 3, p = 0.01) as well as higher rates of spinal cord injury (38.6% vs. 21.9%, p = 0.02) and P. aeruginosa-positive bone/joint cultures (12.3% vs. 0.7%, p < 0.0001). Inpatient mortality was significantly lower in the ceftolozane/tazobactam group compared with aminoglycosides or polymyxins (15.8% vs. 27.7%, adjusted odds ratio 0.39, 95% confidence interval 0.16–0.93). There were no significant differences observed for the other outcomes assessed. In hospitalized patients with MDR P. aeruginosa, inpatient mortality was 61% lower among patients treated with ceftolozane/tazobactam compared to those treated with aminoglycoside- or polymyxin-based regimens.

The Campaign on Atmospheric Aerosol Research network of China (CARE-China) is a long-term project for the study of the spatio-temporal distributions of physical aerosol characteristics as well as the chemical components and optical properties of aerosols over China. This study presents the first long-term data sets from this project, including 3 years of observations of online PM2.5 mass concentrations (2012–2014) and 1 year of observations of PM2.5 compositions (2012–2013) from the CARE-China network. The average PM2.5 concentration at 20 urban sites is 73.2 µg m−3 (16.8–126.9 µg m−3), which was 3 times higher than the average value from the 12 background sites (11.2–46.5 µg m−3). The PM2.5 concentrations are generally higher in east-central China than in the other parts of the country due to their relatively large particulate matter (PM) emissions and the unfavourable meteorological conditions for pollution dispersion. A distinct seasonal variability in PM2.5 is observed, with highs in the winter and lows during the summer at urban sites. Inconsistent seasonal trends were observed at the background sites. Bimodal and unimodal diurnal variation patterns were identified at both urban and background sites. The chemical compositions of PM2.5 were analysed at six paired urban and background sites located within the most polluted urban agglomerations – North China Plain (NCP), Yangtze River delta (YRD), Pearl River delta (PRD), North-east China region (NECR), South-west China region (SWCR) – and the cleanest region of China – the Tibetan Autonomous Region (TAR). The major PM2.5 constituents across all the urban sites are organic matter (OM, 26.0 %), SO42− (17.7 %), mineral dust (11.8 %), NO3− (9.8 %), NH4+ (6.6 %), elemental carbon (EC) (6.0 %), Cl− (1.2 %) at 45 % RH and unaccounted matter (20.7 %). Similar chemical compositions of PM2.5 were observed at background sites but were associated with higher fractions of OM (33.2 %) and lower fractions of NO3− (8.6 %) and EC (4.1 %). Significant variations of the chemical species were observed among the sites. At the urban sites, the OM ranged from 12.6 µg m−3 (Lhasa) to 23.3 µg m−3 (Shenyang), the SO42− ranged from 0.8 µg m−3 (Lhasa) to 19.7 µg m−3 (Chongqing), the NO3− ranged from 0.5 µg m−3 (Lhasa) to 11.9 µg m−3 (Shanghai) and the EC ranged from 1.4 µg m−3 (Lhasa) to 7.1 µg m−3 (Guangzhou). The PM2.5 chemical species at the background sites exhibited larger spatial heterogeneities than those at urban sites, suggesting different contributions from regional anthropogenic or natural emissions and from long-range transport to background areas. Notable seasonal variations of PM2.5-polluted days were observed, especially for the megacities in east-central China, resulting in frequent heavy pollution episodes occurring during the winter. The evolution of the PM2.5 chemical compositions on polluted days was consistent for the urban and nearby background sites, where the sum of sulfate, nitrate and ammonia typically constituted much higher fractions (31–57 %) of PM2.5 mass, suggesting fine-particle pollution in the most polluted areas of China assumes a regional tendency, and the importance of addressing the emission reduction of secondary aerosol precursors including SO2 and NOx. Furthermore, distinct differences in the evolution of [NO3−]∕[SO42−] ratio and OC∕EC ratio on polluted days imply that mobile sources and stationary (coal combustion) sources are likely more important in Guangzhou and Shenyang, respectively, whereas in Beijing it is mobile emission and residential sources. As for Chongqing, the higher oxidation capacity than the other three cities suggested it should pay more attention to the emission reduction of secondary aerosol precursors. This analysis reveals the spatial and seasonal variabilities of the urban and background aerosol concentrations on a national scale and provides insights into their sources, processes and lifetimes.

Continental atmospheric relative humidity (RH) is a key climate parameter. Combined with atmospheric temperature, it allows us to estimate the concentration of atmospheric water vapor, which is one of the main components of the global water cycle and the most important gas contributing to the natural greenhouse effect. However, there is a lack of proxies suitable for reconstructing, in a quantitative way, past changes of continental atmospheric humidity. This reduces the possibility of making model–data comparisons necessary for the implementation of climate models. Over the past 10 years, analytical developments have enabled a few laboratories to reach sufficient precision for measuring the triple oxygen isotopes, expressed by the 17O-excess (17O-excess = ln (δ17O + 1) – 0.528 × ln (δ18O + 1)), in water, water vapor and minerals. The 17O-excess represents an alternative to deuterium-excess for investigating relative humidity conditions that prevail during water evaporation. Phytoliths are micrometric amorphous silica particles that form continuously in living plants. Phytolith morphological assemblages from soils and sediments are commonly used as past vegetation and hydrous stress indicators. In the present study, we examine whether changes in atmospheric RH imprint the 17O-excess of phytoliths in a measurable way and whether this imprint offers a potential for reconstructing past RH. For that purpose, we first monitored the 17O-excess evolution of soil water, grass leaf water and grass phytoliths in response to changes in RH (from 40 to 100 %) in a growth chamber experiment where transpiration reached a steady state. Decreasing RH from 80 to 40 % decreases the 17O-excess of phytoliths by 4.1 per meg/% as a result of kinetic fractionation of the leaf water subject to evaporation. In order to model with accuracy the triple oxygen isotope fractionation in play in plant water and in phytoliths we recommend direct and continuous measurements of the triple isotope composition of water vapor. Then, we measured the 17O-excess of 57 phytolith assemblages collected from top soils along a RH and vegetation transect in inter-tropical West and Central Africa. Although scattered, the 17O-excess of phytoliths decreases with RH by 3.4 per meg/%. The similarity of the trends observed in the growth chamber and nature supports that RH is an important control of 17O-excess of phytoliths in the natural environment. However, other parameters such as changes in the triple isotope composition of the soil water or phytolith origin in the plant may come into play. Assessment of these parameters through additional growth chambers experiments and field campaigns will bring us closer to an accurate proxy of changes in relative humidity.

Topic 3 of the Model Inter-Comparison Study for Asia (MICS-Asia) Phase III examines how online coupled air quality models perform in simulating high aerosol pollution in the North China Plain region during wintertime haze events and evaluates the importance of aerosol radiative and microphysical feedbacks. A comprehensive overview of the MICS-Asia III Topic 3 study design, including descriptions of participating models and model inputs, the experimental designs, and results of model evaluation, are presented. Six modeling groups from China, Korea and the United States submitted results from seven applications of online coupled chemistry–meteorology models. Results are compared to meteorology and air quality measurements, including data from the Campaign on Atmospheric Aerosol Research Network of China (CARE-China) and the Acid Deposition Monitoring Network in East Asia (EANET). The correlation coefficients between the multi-model ensemble mean and the CARE-China observed near-surface air pollutants range from 0.51 to 0.94 (0.51 for ozone and 0.94 for PM2.5) for January 2010. However, large discrepancies exist between simulated aerosol chemical compositions from different models. The coefficient of variation (SD divided by the mean) can reach above 1.3 for sulfate in Beijing and above 1.6 for nitrate and organic aerosols in coastal regions, indicating that these compositions are less consistent from different models. During clean periods, simulated aerosol optical depths (AODs) from different models are similar, but peak values differ during severe haze events, which can be explained by the differences in simulated inorganic aerosol concentrations and the hygroscopic growth efficiency (affected by varied relative humidity). These differences in composition and AOD suggest that future models can be improved by including new heterogeneous or aqueous pathways for sulfate and nitrate formation under hazy conditions, a secondary organic aerosol (SOA) formation chemical mechanism with new volatile organic compound (VOCs) precursors, yield data and approaches, and a more detailed evaluation of the dependence of aerosol optical properties on size distribution and mixing state. It was also found that using the ensemble mean of the models produced the best prediction skill. While this has been shown for other conditions (for example, the prediction of high-ozone events in the US (McKeen et al., 2005)), this is to our knowledge the first time it has been shown for heavy haze events.

To investigate the spatiotemporal variability of the mixing layer height (MLH) on the North China Plain (NCP), multi-site and long-term observations of the MLH with ceilometers at three inland stations (Beijing, BJ; Shijiazhuang, SJZ; Tianjin, TJ) and one coastal site (Qinhuangdao) were conducted from 16 October 2013 to 15 July 2015. The MLH of the inland stations in the NCP were highest in summer and lowest in winter, while the MLH on the coastal area of Bohai was lowest in summer and highest in spring. As a typical site in southern Hebei, the annual mean of the MLH at SJZ was 464 ± 183 m, which was 15.0 and 21.9 % lower than that at the BJ (594 ± 183 m) and TJ (546 ± 197 m) stations, respectively. Investigation of the shear term and buoyancy term in the NCP revealed that these two parameters in southern Hebei were 2.8 times lower and 1.5 times higher than that in northern NCP within 0–1200 m in winter, respectively, leading to a 1.9-fold higher frequency of the gradient Richardson number > 1 in southern Hebei compared to the northern NCP. Furthermore, combined with aerosol optical depth and PM2.5 observations, we found that the pollutant column concentration contrast (1.2 times) between these two areas was far less than the near-ground PM2.5 concentration contrast (1.5 times). Through analysis of the ventilation coefficient in the NCP, the near-ground heavy pollution in southern Hebei mainly resulted from the lower MLH and wind speed. Therefore, due to the importance of unfavorable weather conditions, heavily polluting enterprises should be relocated and strong emission reduction measures should be introduced to improve the air quality in southern Hebei.

Mineral dust aerosols (MDs) not only influence the climate by scattering and absorbing solar radiation but also modify cloud properties and change the ecosystem. From 3 April to 16 May 2014, a ground-based mobile laboratory was deployed to measure the optical and microphysical properties of MDs near dust source regions in Wuwei, Zhangye, and Dunhuang (in chronological order) along the Hexi Corridor over northwestern China. Throughout this dust campaign, the hourly averaged (±standard deviation) aerosol scattering coefficients (σsp, 550 nm) of the particulates with aerodynamic diameters less than 2.5 µm (PM2.5) at these three sites were sequentially 101.5 ± 36.8, 182.2 ± 433.1, and 54.0 ± 32.0 Mm−1. Correspondingly, the absorption coefficients (σap, 637 nm) were 9.7 ± 6.1, 6.0 ± 4.6, and 2.3 ± 0.9 Mm−1; single-scattering albedos (ω, 637 nm) were 0.902 ± 0.025, 0.931 ± 0.037, and 0.949 ± 0.020; and scattering Ångström exponents (Åsp, 450–700 nm) of PM2.5 were 1.28 ± 0.27, 0.77 ± 0.51, and 0.52 ± 0.31. During a severe dust storm in Zhangye (i.e., from 23 to 25 April), the highest values of σsp2.5 ( ∼ 5074 Mm−1), backscattering coefficient (σbsp2.5, ∼ 522 Mm−1), and ω637 ( ∼ 0.993) and the lowest values of backscattering fraction (b2.5, ∼ 0.101) at 550 nm and Åsp2.5 ( ∼ −0.046) at 450–700 nm, with peak values of aerosol number size distribution (appearing at the particle diameter range of 1–3 µm), exhibited that the atmospheric aerosols were dominated by coarse-mode dust aerosols. It is hypothesized that the relatively higher values of mass scattering efficiency during floating dust episodes in Wuwei and Zhangye are attributed to the anthropogenic soil dust produced by agricultural cultivations.

To investigate the atmospheric aerosols of the Himalayas and Tibetan Plateau (HTP), an observation network was established within the region's various ecosystems, including at the Ngari, Qomolangma (QOMS), Nam Co, and Southeastern Tibetan (SET) stations. In this paper we illustrate aerosol mass loadings by integrating in situ measurements with satellite and ground-based remote sensing datasets for the 2011–2013 period, on both local and large scales. Mass concentrations of these surface atmospheric aerosols were relatively low and varied with land cover, showing a general tendency of Ngari and QOMS (barren sites) > Nam Co (grassland site) > SET (forest site). Daily averages of online PM2.5 (particulates with aerodynamic diameters below 2.5 µm) at these sites were sequentially 18.2 ± 8.9, 14.5 ± 7.4, 11.9 ± 4.9 and 11.7 ± 4.7 µg m−3. Correspondingly, the ratios of PM2.5 to total suspended particles (TSP) were 27.4 ± 6.65, 22.3 ± 10.9, 37.3 ± 11.1 and 54.4 ± 6.72 %. Bimodal mass distributions of size-segregated particles were found at all sites, with a relatively small peak in accumulation mode and a more notable peak in coarse mode. Diurnal variations in fine-aerosol masses generally displayed a bi-peak pattern at the QOMS, Nam Co and SET stations and a single-peak pattern at the Ngari station, controlled by the effects of local geomorphology, mountain-valley breeze circulation and aerosol emissions. Dust aerosol content in PM2.1 samples gave fractions of 26 % at the Ngari station and 29 % at the QOMS station, or ∼ 2–3 times that of reported results at human-influenced sites. Furthermore, observed evidence confirmed the existence of the aerodynamic conditions necessary for the uplift of fine particles from a barren land surface. Combining surface aerosol data and atmospheric-column aerosol optical properties, the TSP mass and aerosol optical depth (AOD) of the Multi-angle Imaging Spectroradiometer (MISR) generally decreased as land cover changed from barren to forest, in inverse relation to the PM2.5 ratios. The seasonality of aerosol mass parameters was land-cover dependent. Over forest and grassland areas, TSP mass, PM2.5 mass, MISR-AOD and fine-mode AOD were higher in spring and summer, followed by relatively lower values in autumn and winter. At the barren site (the QOMS station), there were inconsistent seasonal patterns between surface TSP mass (PM2.5 mass) and atmospheric column AOD (fine-mode AOD). Our findings implicate that HTP aerosol masses (especially their regional characteristics and fine-particle emissions) need to be treated sensitively in relation to assessments of their climatic effect and potential role as cloud condensation nuclei and ice nuclei.

This study investigates a cross-variable ozone data assimilation (DA) method based on an ensemble Kalman filter (EnKF) that has been used in the companion study to improve ozone forecasts over Beijing and surrounding areas. The main purpose is to delve into the impacts of the cross-variable adjustment of nitrogen oxide (NOx) emissions on the nitrogen dioxide (NO2) forecasts over this region during the 2008 Beijing Olympic Games. A mixed effect on the NO2 forecasts was observed through application of the cross-variable assimilation approach in the real-data assimilation (RDA) experiments. The method improved the NO2 forecasts over almost half of the urban sites with reductions of the root mean square errors (RMSEs) by 15–36 % in contrast to big increases of the RMSEs over other urban stations by 56–239 %. Over the urban stations with negative DA impacts, improvement of the NO2 forecasts (with 7 % reduction of the RMSEs) was noticed at night and in the morning versus significant deterioration during daytime (with 190 % increase of the RMSEs), suggesting that the negative data assimilation impacts mainly occurred during daytime. Ideal-data assimilation (IDA) experiments with a box model and the same cross-variable assimilation method confirmed the mixed effects found in the RDA experiments. In the same way, NOx emission estimation was improved at night and in the morning even under large biases in the prior emission, while it deteriorated during daytime (except for the case of minor errors in the prior emission). The mixed effects observed in the cross-variable data assimilation, i.e., positive data assimilation impacts on NO2 forecasts over some urban sites, negative data assimilation impacts over the other urban sites, and weak data assimilation impacts over suburban sites, highlighted the limitations of the EnKF under strong nonlinear relationships between chemical variables. Under strong nonlinearity between daytime ozone concentrations and NOx emissions uncertainties (with large biases in the a priori emission), the EnKF may come up with inefficient or wrong adjustments to NOx emissions. The present findings reveal that bias correction is essential for the application of the EnKF in dealing with the data assimilation problem over strong nonlinear system.

The mixing layer is an important meteorological factor that affects air pollution. In this study, the atmospheric mixing layer height (MLH) was observed in Beijing from July 2009 to December 2012 using a ceilometer. By comparison with radiosonde data, we found that the ceilometer underestimates the MLH under conditions of neutral stratification caused by strong winds, whereas it overestimates the MLH when sand-dust is crossing. Using meteorological, PM2.5, and PM10 observational data, we screened the observed MLH automatically; the ceilometer observations were fairly consistent with the radiosondes, with a correlation coefficient greater than 0.9. Further analysis indicated that the MLH is low in autumn and winter and high in spring and summer in Beijing. There is a significant correlation between the sensible heat flux and MLH, and the diurnal cycle of the MLH in summer is also affected by the circulation of mountainous plain winds. Using visibility as an index to classify the degree of air pollution, we found that the variation in the sensible heat and buoyancy term in turbulent kinetic energy (TKE) is insignificant when visibility decreases from 10 to 5 km, but the reduction of shear term in TKE is near 70 %. When visibility decreases from 5 to 1 km, the variation of the shear term in TKE is insignificant, but the decrease in the sensible heat and buoyancy term in TKE is approximately 60 %. Although the correlation between the daily variation of the MLH and visibility is very poor, the correlation between them is significantly enhanced when the relative humidity increases beyond 80 %. This indicates that humidity-related physicochemical processes is the primary source of atmospheric particles under heavy pollution and that the dissipation of atmospheric particles mainly depends on the MLH. The presented results of the atmospheric mixing layer provide useful empirical information for improving meteorological and atmospheric chemistry models and the forecasting and warning of air pollution.

The online coupled Weather Research and Forecasting-Chemistry (WRF-Chem) model was applied to simulate a haze event that happened in January 2010 in the North China Plain (NCP), and was validated against various types of measurements. The evaluations indicate that WRF-Chem provides reliable simulations for the 2010 haze event in the NCP. This haze event was mainly caused by high emissions of air pollutants in the NCP and stable weather conditions in winter. Secondary inorganic aerosols also played an important role and cloud chemistry had important contributions. Air pollutants outside Beijing contributed about 64.5 % to the PM2.5 levels in Beijing during this haze event, and most of them are from south Hebei, Tianjin city, Shandong and Henan provinces. In addition, aerosol feedback has important impacts on surface temperature, relative humidity (RH) and wind speeds, and these meteorological variables affect aerosol distribution and formation in turn. In Shijiazhuang, Planetary Boundary Layer (PBL) decreased about 278.2 m and PM2.5 increased more than 20 µg m−3 due to aerosol feedback. It was also shown that black carbon (BC) absorption has significant impacts on meteorology and air quality changes, indicating more attention should be paid to BC from both air pollution control and climate change perspectives.

The implementation of emission reductions during the 2014 Asia-Pacific Economic Cooperation (APEC) summit provides a valuable opportunity to study air pollution in Beijing. From 15 October to 30 November 2014, the height of the atmospheric mixing layer and the vertical attenuated backscattering coefficient profiles were observed online using a~lidar ceilometer. Compared with fine particulate matter (PM2.5) and aerosol optical depth (AOD) data, the attenuated backscattering coefficients measured by the lidar ceilometer were strongly correlated with the PM2.5 concentration and AOD (correlation coefficients of 0.89 and 0.86, respectively). This result demonstrated the reliability of the vertical distribution of particles measured by the lidar ceilometer. By classifying different degrees of air pollution based on visibility, we found that during the transition period of air pollution, which was affected by transport of southerly flows in the mixing layer, the attenuated backscattering coefficient from 0 to 1500 m was enhanced by approximately 1.4 Mm−1 sr−1 (140 %). During the polluted period, the attenuated backscattering coefficient from 0 to 300 m suddenly increased, and the coefficient near the surface peaked (approximately 14 Mm−1 sr−1); however, the attenuated backscattering coefficient from 300 to 900 m decreased gradually, and the average value from 0 to 1500 m decreased by 0.5 Mm−1sr−1 (20 %). The height of the mixing layer gradually decreased, and the ratio of CO / SO2 gradually increased, which indicate that the polluted period was dominated by local contribution. Due to the emission reductions during APEC (DAPEC), the concentration of PM2.5 decreased by 59.2 and 58.9 % and visibility improved by 70.2 and 56.0 % compared to before (BAPEC) and after APEC (AAPEC), respectively. The contribution of regional transport in DAPEC decreased by approximately 36 and 25 %, and the local contribution decreased by approximately 48 and 54 % compared to BAPEC and AAPEC, respectively. The most effective method of controlling air pollution in the Beijing area is to reduce regional emissions during the transition period and reduce local emissions during the polluted period.

Beijing is a megacity situated in the rapidly developing Beijing-Tianjin-Hebei region of northern China. In this study, we analyze data on ozone and nitrogen oxide levels obtained at six urban sites in Beijing between the months of July and September. Our goal is to investigate average trends and interpretations over the 2001–2006 period. Average concentrations of NOx (NOx=NO+NO2), O3, and Ox (Ox=O3+NO2) were 49.2±5.9 ppbv, 26.6±2.8 ppbv, and 60.3±1.9 ppbv, respectively. NOx concentrations decreased linearly at a rate of 3.9±0.5 ppbv/yr after 2002, while ozone concentrations increased at a rate of 1.1±0.5 ppbv/yr during 2001–2006, and Ox concentrations remained nearly constant. The reduction of NOx emissions and elevated non-methane hydrocarbon (NMHCs) emissions may have contributed to the increased O3 concentrations in Beijing. When the contributions from Beijing's urban and surrounding areas were disaggregated via trajectory cluster analysis, daily maximum and average Ox concentrations attributable to Beijing's local emissions increased linearly at rates of 1.3±0.6 ppbv/yr and 0.8±0.6 ppbv/yr, while the Ox concentrations attributable to regional areas decreased linearly at rates of 0.6±0.3 ppbv/yr and 0.5±0.3 ppbv/yr, respectively. The decrease in Ox concentrations of the surrounding areas was found to counteract increasing Beijing urban Ox production, leading to nearly constant Ox concentrations in the Beijing region over the study period. Our results may be helpful for redefining government strategies to control the photochemical formation of air pollutants in the Beijing region. Our conclusions have relevance for developing megacities worldwide.

This paper proposes a network system reliability analysis method based on service. The significance of the network services becomes increasingly prominent in many fields like communication and aviation industry. More and more services depend on network transmission. Thus, the dependability and the reliability of network system are paid more and more attention. The reliability of network is related to several factors, such as hardware equipment, software services, human factors and so on. Most previous papers pay more attention on the hardware equipment factors than the others. The reliability of network is measured by if the equipment is normal running. Sometimes the hardware equipment is in normal operation, but some users may think that the network service is unavailable due to the network congestion, software errors or man-made mistakes which have no effect on the calculation of the reliability. There is a gap between the state of service execution in terms of reliability and what the network reliability data suggests. This paper attempts to propose a network service reliability analysis method based on service to bridge the gap. The paper satisfies these needs in the following ways:(1) we analyses various factors affecting reliability of the network system; (2) we establish the reliability block diagram of service operating process and calculate the reliability of the equipment by the diagram (3) we analyze a case utilizing the model in (2). This method will not overestimate the availability of network system. It enhances the previous study by utilizing the analysis based on service. With this method the gap between the service experience of users in term of reliability and the result reliability of the method will be bridged.