Influence Factor Analysis on Strength of Lime-Fly Ash Loess

Lime-fly ash loess is composed of fly ash, lime and loess. It is a new material in subgrade backfill. Main factors to influence the strength of lime-fly ash loess are age, amount of fly ash and lime, ratio of fly ash to lime (1:K), and moisture content. In order to observe the effect of each factor influencing the strength of lime-fly ash loess and find out the relationship between each other, this paper adopted orthogonal test design to conduct unconfined compression tests. The result shows that 90d strength can be considered to calculate the strength of lime-fly ash loess in practice. And the most important factor to influence the 90d strength of lime-fly ash loess is the amount of fly ash and lime, the second is moisture content, and then is the ratio of fly ash to lime (1:K). These achievements are significant to the design and application of lime-fly ash loess in subgrade construction of loess areas.

Impacts of meteorology and precursor emission change on O_(3) variation in Tianjin, China from 2015 to 2021

Deterioration of surface ozone (O_(3)) pollution in Northern China over the past few years received much attention.For many cities,it is still under debate whether the trend of surface O_(3)variation is driven by meteorology or the change in precursors emissions.In this work,a time series decomposition method (Seasonal-Trend decomposition procedure based on Loess (STL)) and random forest (RF) algorithm were utilized to quantify the meteorological impacts on the recorded O_(3)trend and identify the key meteorological factors affecting O_(3)pollution in Tianjin,the biggest coastal port city in Northern China.After “removing” the meteorological fluctuations from the observed O_(3)time series,we found that variation of O_(3)in Tianjin was largely driven by the changes in precursors emissions.The meteorology was unfavorable for O_(3)pollution in period of 2015-2016,and turned out to be favorable during 2017-2021.Specifically,meteorology contributed 9.3μg/m^(3)O_(3)(13%) in 2019,together with the increase in precursors emissions,making 2019 to be the worst year of O_(3)pollution since 2015.Since then,the favorable effects of meteorology on O_(3)pollution tended to be weaker.Temperature was the most important factor affecting O_(3)level,followed by air humidity in O_(3)pollution season.In the midday of summer days,O_(3)pollution frequently exceeded the standard level (>160μg/m^(3)) at a combined condition with relative humidity in 40%-50%and temperature>31℃.Both the temperature and the dryness of the atmosphere need to be subtly considered for summer O_(3)forecasting.

Quantifying the impacts of emissions and meteorology on the interannual variations of air pollutants in major Chinese cities from 2015 to 2021

Air pollutant concentration is a function of emission rates and meteorology.To accurately evaluate the effect of control measures,the meteorological covariate must be corrected from the observations.This study quantified the impacts of emission abatement and meteorological condition on the interannual variations of SO_(2),NO_(2),CO,O_(3),PM_(10) and PM_(2.5) concentrations in 31 major Chinese cities using an optimized machine learning-based meteorological normalization technique.Overall,the annual average concentrations of SO_(2),NO_(2),CO,PM_(10)and PM_(2.5)were reduced by 86%,51%,99%,86% and 88%from 2015 to 2020,respectively,in the studied cities,attributable to their emission reductions.However,the concentration of O_(3) was found with no significant decrease with the reduction of precursors.Emission abatement notably improved air quality between 2015 and 2018.Such a decline in emissions tended to progressively slow down since 2018.Overall,the meteorological conditions in 2016–2017 and 2018–2019 were unfavorable for a better air quality,while it became favorable in 2020–2021.Specifically,emission abatement in 2021 further lowered the concentrations of SO_(2),NO_(2),CO,and PM_(2.5),while the emission of PM_(10) increased.And changes in precursors emissions worsened O_(3) air quality.To meet the demand of improving air quality,more aggressive abatement measures need to be formulated to synergistically reduce NOx,volatile organic compounds,and coarse particles.

Vertical characteristics and source identification of PM_(10) in Tianjin

Ambient PM 10 （particulate matter with a diameter less than 10μm） concentrations were measured on a 255 meter tower in Tianjin,China.The samples were collected at four vertical levels （10,40,120 and 220 m）.Vertical characteristics for PM 10 samples were studied.The results showed that the concentrations of PM 10 and constituent species had a negative correlation with the sampling height.The highest concentrations of PM 10 and species were obtained at the 10 m level,and the lowest concentrations were measured at the 220 m level.For the fractions of species to total mass,SO 4 2- and NO 3- had higher values （fraction） at greater height;while Ca had a higher fraction at lower height.Possible source categories for the PM 10 ambient dataset were identified by the principal component analysis method.The possible source categories included crustal dust,vehicles,cement dust,and incineration as well as secondary sulfate and nitrate sources.Analysis of meteorological factors on PM 10 concentrations indicated that wind speed and inversion may be the main factors contributing to different concentrations of PM 10 at different heights.

Size distribution and chemical characteristics of particles from crop residue open burning in North China

Crop residue open burning is an important emission source of ambient particles in China.This study analyzed the particle emission characteristics of crop residue open burning through combustion experiments with a novel open combustion simulation device using three typical crop straws in north China(corn,wheat,and rice).Particle samples size ranging from 0.006–9.890μm were collected by an Electrical Low Pressure Impactor plus,a high size-resolution instrument capable of dividing particles into 14 size stages.The size distributions of organic carbon(OC),elemental carbon(EC),water-soluble ions,and elements were analyzed,and source chemical profiles were constructed for PM0.1,PM1,PM2.5,and PM10.The number concentration of particles was concentrated in the Aiken nuclei mode(0.006–0.054μm),accounting for 75%of the total number,whereas the mass concentration was concentrated in the accumulation mode(0.054–0.949μm),accounting for 85.43%of the mass loading.OC,EC,Cl−,and K(include total K and water-soluble K)were the major chemical components of the particles,whose mass percentage distributions differed from those of other components.These fivemain components exhibited a bell-shaped size distribution in the 0.006–9.890μm range,whereas the other components exhibited a U-shaped distribution.Among the chemical profiles for PM0.1–PM10,OC was the most important component at 10–30%,followed by EC at 2%–8%.The proportions of K^(+),Cl^(−),and K varied substantially in different experimental groups,ranging from 0–15%,and K+and Cl−were significantly correlated(r=0.878,α=0.000).

Impact of meteorological condition changes on air quality and particulate chemical composition during the COVID-19 lockdown

Stringent quarantine measures during the Coronavirus Disease 2019(COVID-19)lockdown period(January 23,2020 to March 15,2020)have resulted in a distinct decrease in anthropogenic source emissions in North China Plain compared to the paralleled period of 2019.Particularly,22.7%decrease in NO_(2)and 3.0%increase of O_(3)was observed in Tianjin,nonlinear relationship between O_(3)generation and NO_(2)implied that synergetic control of NOx and VOCs is needed.Deteriorating meteorological condition during the COVID-19 lockdown obscured the actual PM2.5 reduction.Fireworks transport in 2020 Spring Festival(SF)triggered regional haze pollution.PM2.5 during the COVID-19 lockdown only reduced by 5.6%in Tianjin.Here we used the dispersion coefficient to normalize the measured PM2.5(DN-PM2.5),aiming to eliminate the adverse meteorological impact and roughly estimate the actual PM2.5 reduction,which reduced by 17.7%during the COVID-19 lockdown.In terms of PM2.5 chemical composition,significant NO_(3)−increase was observed during the COVID-19 lockdown.However,as a tracer of atmospheric oxidation capacity,odd oxygen(Ox=NO_(2)+O_(3))was observed to reduce during the COVID-19 lockdown,whereas relative humidity(RH),specific humidity and aerosol liquid water content(ALWC)were observed with noticeable enhancement.Nitrogen oxidation rate(NOR)was observed to increase at higher specific humidity and ALWC,especially in the haze episode occurred during 2020SF,high air humidity and obvious nitrate generation was observed.Anomalously enhanced air humidity may response for the nitrate increase during the COVID-19 lockdown period.

Insight into the critical factors determining the particle number concentrations during summer at a megacity in China

To identify the critical factors impacting the number concentration of particles with the aerodynamic diameters less than 2.5 μm(PNC_(2.5)), the continuous measurement of PNC_(2.5),chemical components in PM_(2.5), gaseous pollutants and meteorological conditions were conducted at an urban site in Tianjin in June 2015. Results indicated that the average PNC_(2.5) was 2839 ± 2430 d N/dlog Dp 1/cm^3 during the campaign. Compared to other meteorological parameters, the relative humidity(RH) had the strongest relationship with PNC_(2.5), with a Pearson's correlation coefficient of 0.53, and RH larger than 30% influenced strongly PNC_(2.5).The important influence of secondary reactions on PNC_(2.5) was inferred due to higher correlation coefficients between PNC_(2.5) and SO_4^(2-), NO_3^-, NH_4^+(r = 0.78–0.89; p < 0.01) and between PNC_(2.5) and ratios that represent the conversion of nitrogen and sulfur oxides to particulate matter(r = 0.42–0.49; p < 0.01). Under specific RH conditions, there were even stronger correlations between PNC_(2.5) and NO_3^-, SO_4^(2-), NH_4^+, while those between PNC_(2.5) and EC, OC were relatively weak, especially when RH exceeded 50%. Principal component analysis(PCA) and Pearson's correlation analysis indicated that secondary sources, vehicle emission and coal combustion might be major contributors to PNC_(2.5). Backward trajectory and potential source contribution function(PSCF) analysis suggested that the transport of air masses originated from these regions around Tianjin(Liaoning, Hebei, Shandong and Jiangsu) influenced critically PNC_(2.5). The north of Jiangsu, the west of Shandong, and the east of Hebei were distinguished as major potential source-areas of PNC_(2.5) by PSCF model.

Long-term trends in fog and boundary layer characteristics in Tianjin,China

Long-term trends in fog episodes, vertical variations of atmospheric boundary structure, and air pollutant concentrations during two different heavy fog events in the Tianjin area were analyzed. The total amount of fog has increased since 1980 due to the stability of the boundary layer and an increase of pollutant emissions. The variation in the characteristics of the boundary layer and air pollutant concentrations were significantly different between the two fog processes （fog I and fog ll）. The onset of fog I was accompanied by a temperature inversion in the low atmosphere, and the average kinetic energy showed a clear diurnal trend and vertical variation, which increased with height. The dissipation of fog I was mainly due to turbulence. However, the atmospheric stratification was not stable in the lower layer before the onset of fog If. The diurnal and vertical changes in kinetic energy were very small, in which turbulent momentum at each measurement height tended to be zero. In the dissipation process of fogⅡ, wind speed increased significantly. Surface PM2.s concentrations decreased, but the ratio of PMzs to PM10 increased from 0.66 to 0.82 until fog I dissipated. However, the concentration of PMzs did not decrease at the early stage of fog Ⅱ, but the ratio of PM2.5 to PM10 PM2.5JPM10 decreased to 0.21 when fog Ⅱ dissipated. This study showed that there was a clear difference in the evolution of pollutant concentration for different pollutants and in different developing stages during the fog events. PM2.5 concentration accumulated faster than those of SO2 and NOx, and the PM2.5 cumulative rate was greater in the mid-term of the fog process.

Differential Geochemical Features of Clinopyroxene from the Floodplain Sediments in Yangtze and Hanjiang Rivers and Its Implication for Detrital Source Identification

The evolution history of the Yangtze River attracted increasing attention in recent years. Comparison of the properties of the floodplain sediments between the upper and lower reaches of the Three Gorges is of significance to identify the material detrital sources for the Yangtze River Basin. Clinopyroxene （Cpx） is the typical mineral widely distributed in the sediments of the Yangtze River Ba- sin. Cpx was extracted from the fine sediments with the grain size ranging from 0.063 to 0.125 mm in the upper and lower reaches of the Three Gorges. The sediments, from which the Cpx was extracted, were taken from the floodplains of the catchments of both the Yangtze River and the Hanjiang River, as well as from the surface of the Zhoulao Core drilled in the center of the Jianghan Basin where the two rivers flow through. Geochemistry of these Cpx was investigated, concerning the contents of major elements measured by electron probe microanalysis （EPMA） and the contents of trace elements analyzed by laser ablation inductively coupled plasma-mass spectrometry （LA-ICP-MS）. The Cpx in the Yangtze River contains titaniferous augite which is sourced from the Panzhihua-Xichang region in South Sichuan Province, whereas the Cpx in the Hanjiang River is mainly from the surroundings without any titanif- erous augite. The REE analysis infers that the titaniferous augite is the diagnostic mineral of the upper Yangtze River, and thus could be used as a tracer mineral to identify the detrital sources for the sedi- ments formed during the evolution of the Yangtze River. The Cpx from the surface sediments of the Jianghan Plain （Zhoulao Core） shows comparable geochemical nature with that of the Yangtze River, but is different in geochemistry from that of the Hanjiang River, implying that the modern sediments in the Jianghan Plain are mainly sourced from the upper Yangtze River.