In this paper, we give a classification of real rank zero C*-algebras that can be expressed as inductive limits of a sequence of a subclass of Elliott-Thomsen algebras
C
.
The objective of this study is to quantify the relation of aerosol chemical compositions and optical properties, and to assess the impact of relative humidity (RH) on atmospheric visibility and ...aerosol direct radiative forcing (ADRF). Mass concentration and size distribution of aerosol chemical compositions as well as aerosol optical properties were concurrently measured at Guangzhou urban site during the PRD (Pearl River Delta) campaign from 1 to 31 July, 2006. Gaseous pollutant NO2 and meteorological parameter were simultaneously monitored. Compared with its dry condition, atmospheric ambient extinction coefficient σext(RH) averagely increased about 51% and atmospheric visibility deceased about 35%, among which RH played an important role on the optical properties of water soluble inorganic salts. (NH4)2SO4 is the most important component responsible for visibility degradation at Guangzhou. In addition, the asymmetry factor g increased from 0.64 to 0.74 with the up-scatter fraction β decreasing from 0.24 to 0.19 when RH increasing from 40% to 90%. At 80% RH, the ADRF increased about 280% compared to that at dry condition and it averagely increased about 100% during the campaign under ambient conditions. It can be inferred that aerosol water content is a key factor and could not be ignored in assessing the role of aerosols in visibility impairment and radiative forcing, especially in the regions with high RH.
► We quantify the relation of aerosol chemical compositions and optical properties. ► We assess the impact of relative humidity on atmospheric visibility and aerosol direct radiative forcing. ► We investigate the influence of relative humidity on aerosol asymmetry factor and up-scatter fraction.
A field experiment from 18 August to 8 September 2006 in Beijing, China, was carried out. A hazy day was defined as visibility 〈 10 km and RH（relative humidity） 〈 90%. Four haze episodes, which ...accounted for ～ 60% of the time during the whole campaign, were characterized by increases of SNA（sulfate, nitrate, and ammonium） and SOA（secondary organic aerosol） concentrations. The average values with standard deviation of SO2-＋4, NO-3, NH4 and SOA were 49.8（± 31.6）, 31.4（±22.3）, 25.8（±16.6） and 8.9（±4.1） μg/m3, respectively, during the haze episodes, which were 4.3, 3.4, 4.1, and 1.7 times those in the non-haze days. The SO2-4,NO-3, NH＋4, and SOA accounted for 15.8%, 8.8%, 7.3%, and 6.0% of the total mass concentration of PM10 during the non-haze days. The respective contributions of SNA species to PM10 rose to about27.2%, 15.9%, and 13.9% during the haze days, while the contributions of SOA maintained the same level with a slight decrease to about 4.9%. The observed mass concentrations of SNA and SOA increased with the increase of PM10 mass concentration, however, the rate of increase of SNA was much faster than that of the SOA. The SOR（sulfur oxidation ratio） and NOR（nitrogen oxidation ratio） increased from non-haze days to hazy days, and increased with the increase of RH. High concentrations of aerosols and water vapor favored the conversion of SO2 to SO2-4and NO2 to NO-3, which accelerated the accumulation of the aerosols and resulted in the formation of haze in Beijing.
In recent years, a new mode of transportation, referred to as “shared commuter buses,” has been introduced, which can considerably reduce the dependence of office workers on private cars and relieve ...urban traffic congestion, but is not widely used owing to efficiency issues. Improving the efficiency of shared commuter buses was set as a goal, and in this study, several research objects were selected to optimize the driving routes of shared commuter buses. The problem of stop location is combined with dynamic route optimization; the “shortest walking distance” model is established to select the most appropriate location for stops. The vehicle routing problem model and “key point updating strategy” are employed to plan routes with real-time traffic information. Finally, we conduct an empirical study to validate our conclusions. The results show that both the model and algorithm are reliable and effective; thus, travel efficiency can be effectively improved and traffic jams can be alleviated.
Significant increases of heavy precipitation and decreases of light precipitation have been reported over widespread regions of the globe. Global warming and effects of anthropogenic aerosols have ...both been proposed as possible causes of these changes. We examine data from urban and rural meteorological stations in eastern China （1955-2011） and compare them with Global Precipitation Climatology Project （GPCP） data （1979-2007） and reanalysis data in various latitude zones to study changes in precipitation extremes. Significant decreases in light precipitation and increases in heavy precipitation are found at both rural and urban stations, as well as low latitudes over the ocean, while total precipitation shows little change. Characteristics of these changes and changes in the equatorial zone and other latitudes suggest that global warming rather than aerosol effects is the primary cause of the changes. In eastern China, increases of annual total dry days （28 days） and ） 10 consecutive dry days （36%） are due to the decrease in light precipitation days, thereby establishing a causal link among global warming, changes in precipitation extremes, and higher meteorological risk of floods and droughts. Further, results derived from the GPCP data and reanalysis data suggest that the causal link exists over widespread regions of the globe.
Nitryl chloride (ClNO2) is a dominant source of chlorine radical in polluted environment, and can significantly affect the atmospheric oxidative chemistry. However, the abundance of ClNO2 and its ...exact role are not fully understood under different environmental conditions. During the summer of 2014, we deployed a chemical ionization mass spectrometer to measure ClNO2 and dinitrogen pentoxide (N2O5) at a rural site in the polluted North China Plain. Elevated mixing ratios of ClNO2 (> 350 pptv) were observed at most of the nights with low levels of N2O5 (< 200 pptv). The highest ClNO2 mixing ratio of 2070 pptv (1 min average) was observed in a plume from a megacity (Tianjin), and was characterized with a faster N2O5 heterogeneous loss rate and ClNO2 production rate compared to average conditions. The abundant ClNO2 concentration kept increasing even after sunrise, and reached a peak 4 h later. Such highly sustained ClNO2 peaks after sunrise are discrepant from the previously observed typical diurnal pattern. Meteorological and chemical analysis shows that the sustained ClNO2 morning peaks are caused by significant ClNO2 production in the residual layer at night followed by downward mixing after breakup of the nocturnal inversion layer in the morning. We estimated that ∼ 1.7–4.0 ppbv of ClNO2 would exist in the residual layer in order to maintain the observed morning ClNO2 peaks at the surface site. Observation-based box model analysis show that photolysis of ClNO2 produced chlorine radical with a rate up to 1.12 ppbv h−1, accounting for 10–30 % of primary ROx production in the morning hours. The perturbation in total radical production leads to an increase of integrated daytime net ozone production by 3 % (4.3 ppbv) on average, and with a larger increase of 13 % (11 ppbv) in megacity outflow that was characterized with higher ClNO2 and a relatively lower oxygenated hydrocarbon (OVOC) to non-methane hydrocarbon (NMHC) ratio.
•178 nitrate modeling studies in China published during 2007–2021 were reviewed.•Model performance on nitrate and possible reasons for model-observation biases were summarized.•The contribution of ...N2O5 heterogeneous chemistry to nitrate varies from 21.0% to 51.6% among studies.•Decreased SO2 emission, enhanced AOC, and weakened deposition account for increasing PM2.5 nitrate fraction.•Multiple-pollutant control strategies involving NH3, NOx, and VOCs are needed to mitigate nitrate pollution.
Particulate nitrate (pNO3) is now becoming the principal component of PM2.5 during severe winter haze episodes in many cities of China. To gain a comprehensive understanding of the key factors controlling pNO3 formation and driving its trends, we reviewed the recent pNO3 modeling studies which mainly focused on the formation mechanism and recent trends of pNO3 as well as its responses to emission controls in China. The results indicate that although recent chemical transport models (CTMs) can reasonably capture the spatial–temporal variations of pNO3, model-observation biases still exist due to large uncertainties in the parameterization of dinitrogen pentoxide (N2O5) uptake and ammonia (NH3) emissions, insufficient heterogeneous reaction mechanism, and the predicted low sulfate concentrations in current CTMs. The heterogeneous hydrolysis of N2O5 dominates nocturnal pNO3 formation, however, the contribution to total pNO3 varies among studies, ranging from 21.0% to 51.6%. Moreover, the continuously increasing PM2.5 pNO3 fraction in recent years is mainly due to the decreased sulfur dioxide emissions, the enhanced atmospheric oxidation capacity (AOC), and the weakened nitrate deposition. Reducing NH3 emissions is found to be the most effective control strategy for mitigating pNO3 pollution in China. This review suggests that more field measurements are needed to constrain the parameterization of heterogeneous N2O5 and nitrogen dioxide (NO2) uptake. Future studies are also needed to quantify the relationships of pNO3 to AOC, O3, NOx, and volatile organic compounds (VOCs) in different regions of China under different meteorological conditions. Research on multiple-pollutant control strategies involving NH3, NOX, and VOCs is required to mitigate pNO3 pollution, especially during severe winter haze events.
As has been the case in North America and western Europe,
the SO2 emissions have substantially reduced in the North China Plain (NCP) in
recent years. Differential rates of reduction in SO2 and NOx
...concentrations result in the frequent occurrence of particulate matter pollution dominated by nitrate
(pNO3-) over the NCP. In this
study, we observed a polluted episode with the particulate nitrate mass
fraction in nonrefractory PM1 (NR-PM1) being up to 44 % during
wintertime in Beijing. Based on this typical pNO3--dominated haze
event, the linkage between aerosol water uptake and pNO3-
enhancement, further impacting on visibility degradation, has been
investigated based on field observations and theoretical calculations.
During haze development, as ambient relative humidity (RH) increased from
∼10 % to 70 %, the aerosol particle liquid water
increased from ∼1 µg m−3 at the beginning to
∼75 µg m−3 in the fully developed haze period. The
aerosol liquid water further increased the aerosol surface area and volume,
enhancing the condensational loss of N2O5 over particles. From the
beginning to the fully developed haze, the condensational loss of
N2O5 increased by a factor of 20 when only considering aerosol
surface area and volume of dry particles, while increasing by a factor of 25 when
considering extra surface area and volume due to water uptake. Furthermore,
aerosol liquid water favored the thermodynamic equilibrium of HNO3 in
the particle phase under the supersaturated HNO3 and NH3 in the
atmosphere. All the above results demonstrated that pNO3- is
enhanced by aerosol water uptake with elevated ambient RH during haze
development, in turn facilitating the aerosol take-up of water due to the
hygroscopicity of particulate nitrate salt. Such mutual promotion between
aerosol particle liquid water and particulate nitrate enhancement can
rapidly degrade air quality and halve visibility within 1 d. Reduction
of nitrogen-containing gaseous precursors, e.g., by control of traffic
emissions, is essential in mitigating severe haze events in the NCP.
Particulate matter (PM) toxicity has mostly been investigated through in vitro exposure or tracheal infusion in animal models. However, given the complexity of ambient conditions, most animal studies ...do not mimic real-life PM exposure. In this work, we established a novel integrated exposure model to study the dynamic inflammatory response and defense strategies in ambient PM-exposed mice. Three groups of male C57BL/6 mice were kept in three chambers with pre-exposure to filtered air (FA), unfiltered air (UFA), or the air with a low PM concentration (PM
≤ 75 μg/m
) (LPM), respectively, for 37 days. Then all three groups of mice were exposed to haze challenge for 3 days, followed by exposure in filtered air for 7 days to allow recovery. Our results suggest that following a haze challenge, the defense strategies of mice of filtered air (FA) and low PM (LPM) groups comprised a form of "counterattack", whereas the response of the unfiltered air (UFA) group could be viewed as a "silence". While the latter strategy protected the lung tissues of mice from acute inflammatory damage, it also foreshadowed the development of chronic inflammatory diseases. These findings contribute to explaining previously documented PM-associated pathogenic mechanisms.
Steel fiber reinforced concrete (SFRC) is one of the fastest growing and most widely used fiber concrete as engineering structural material. Considering the importance of steel fiber concrete in ...tunneling applications, this paper reviews and discusses the damage mechanism of concrete and the crack arresting effect of steel fiber, and further investigates the application of SFRC in tunneling based on the reinforcement theory of SFRC. It was obvious that (1) steel fiber can not only delay the cracking damage of concrete, but also improve the deformation capacity of concrete, SFRC has excellent impact resistance and high tensile strength; (2) all the reinforcement theories can be considered to be developed on the basis of composite mechanics theory and fiber spacing theory by comprehensive improvement, but still need to further explore the reinforcement theory reflecting; (3) the combination of steel reinforcement and steel fiber will reduce the use of tunnel reinforcement, which is proven to be a better choice, because the content of steel fibers in SFRC has a certain degree of unevenness, so steel fibers can not completely replace the application of steel; and (4) SFRC applied to the node part of the tunnel structure is more effective, but the relevant research is less, in addition, steel fiber concrete tunnel node seismic resistance will be an important direction for future research. The relevant research in this paper can provide reference for the practical application of SFRC in tunnel engineering and other research directions.
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