Long-term Temporal Variability Research Articles

ON THE ASSESSMENT OF EXPOSURE FROM LTE 800-MHZ DOWNLINK FREQUENCY BAND THROUGH THE TIME-AVERAGED AND INTEGRAL-BASED MEASURE.

Exposure assessment should consider the stochastic nature of the emitted signals. Therefore, the long-term temporal variability of E-field strength, obtained by band selective measurements for long-term evolution in a real mobile network environment, is considered in this paper. Intensive measurements were carried out 24h a day for 2 weeks at an indoor location in the urban area. The repeatability of the measurement results was achieved through descriptive statistics of the 24-h instantaneous, time-averaged and integral-based values. More specifically, we addressed the uncertainties on the temporal variability of the instantaneous exposure levels and the effects of duration of averaging and time-integrating on it. To this aim, a huge amount of signal levels (120960 samples) was collected during the measurement campaign by considering three operators in the 800 MHz downlink band. Results have shown how some factors, such as the time interval in which the measurements are taken, can significantly affect the measurement results and their repeatability. Furthermore, in some cases, such effects become comparable to, or even larger than typical measurement uncertainty. By applying both the 24-h time-averaged and integral-based measure, the variability of daily exposure levels could be reduced to values lower than the measurement uncertainty (i.e. lower than±20% of the mean week value obtained with either measure). Based on such results, an indicator depending on the exposure duration should better quantify the far-field exposure in each location.

Measurement of intraocular temperature in glaucoma: week-day and seasonal fluctuations

PurposeTo evaluate long-term intraocular temperature (IOT) variations in eyes with primary open-angle glaucoma (POAG) using an intraocular telemetric sensor.MethodsThis prospective, open-label, multicentre observational study analysed the IOT variations in 22...

Temperature response and thermal performance analysis of a super-long flexible thermosyphon for shallow geothermal utilization: Field test and numerical simulation

• Super-long flexible thermosyphon (SFTS) fabricated by metal corrugated pipe, 32m in length. • Field tests of SFTS for shallow geothermal utilization. • Start-up and steady-state thermal performance of SFTS. • CFD simulation of long-term underground temperature variation near SFTS. • A method to avoid the heat transfer problem due to super-high liquid column of working fluid in super-long thermosyphon. A super-long flexible thermosyphon (SFTS) fabricated by the corrugated pipe, with a total length up to 32m, was field-tested in a drilling, in order to evaluate its potential for use in shallow geothermal utilization. The seasonable dependence of local underground temperature and air temperature, the corresponding temperature response of SFTS, and the its heat transfer characterists were investigated. The underground temperature recovery characteristics under the operation of uni-directional heat extraction were also conducted by a combination analysis of field tests and CFD simulation. The temperature response characteristics of SFTS in start-up of field tests show that the SFTS could operate effectively as the vaporization of working fluid occurs all over the whole evaporator. This indicates that employing a corrugated pipe prevents the formation of a super-high liquid pool at evaporator, which would inhibit the boiling of working fluid at the bottom. The maximum heat transfer power of SFTS obtained in field tests of this work is approximately 305W under the conditions with the inlet temperature of cooling water controlled at 5.5°C and the flow rate at 1500mL/min. The analysis of steady-state heat transfer results reveal that the underground temperature plays the most important role in the overall thermal performance of SFTS, followed by the flow rate and the temperature of cooling water. The long-term uni-directional heat extraction of SFTS from underground for heating is feasible and however the heat extraction rate is recommended to be maintained below 30W/m at the drilling site aiming to make sure a good sustainability. This work reports field tests of a super-long flexible thermosyphon in geothermal utilization for the first time.

Formation of murtoos by repeated flooding of ribbed bedforms along subglacial meltwater corridors

Fluctuations in meltwater discharge below modern glaciers and ice sheets due to diurnal, seasonal and long-term temperature variations are modulated by complex interactions between subglacial drainage, basal processes and bedform development. The bed of palaeo-ice sheets contains a variety of bedforms recording these modulations and provides an open window into the subglacial environment. Through the morphometric analysis of natural and experimental bedforms, respectively mapped along Scandinavian meltwater corridors and produced in a physical model simulating transitory subglacial water flow, we observe a morphological and genetic bedform continuum corresponding to the progressive transformation of ribbed bedforms into murtoos. Two alternating drainage configurations, related to repeated subglacial flooding events, are involved in this transformation: (i) significant meltwater discharge, high hydraulic connectivity and ice-bed decoupling during flooding events lead to hydraulic alteration of ribbed bedforms by erosion, sediment deposition and channel incision, while (ii) limited meltwater flow, low hydraulic connectivity and ice-bed recoupling that follow flooding events lead to their deformational reshaping into murtoos. The degree of transformation of ribbed bedforms into murtoos can be quantified by combining two dimensionless morphometric parameters (circularity and sinuosity) and provides a convenient proxy to constrain magnitudes, durations and/or frequencies of subglacial floods in palaeo-meltwater corridors.

Impact of Temperature Changes on Groundwater Levels in Nzoia River Basin, Kenya

Climate change poses uncertainties to the supply and management of water resources under the observed increase in surface temperatures all over Africa. The aim of this study is to assess the impact of temperature changes on groundwater levels in Nzoia River Basin. Temperature and groundwater level variability and trends has been analyzed using the parametric test of Linear regression and the non-parametric Mann-Kendall statistical test. Temperature data was obtained from the Kenya meteorological department (KMD) whereas groundwater level data was collected from Water resources management agency (WRMA). Linear regression of the annual groundwater levels in Nzoia River Basin between 2011 and 2017 revealed a decreasing trend ranging from -0.49 ft/year (Kitale Golf Club) to -0.03 ft/year (Kakamega Tande School). Mann-Kendall statistical test also showed decreasing groundwater levels for all observation wells with the results for Kitale Golf Club and Mois Bridge Quarry observation wells being statistically significant, whereas those for Kapsabet Boys High School, Kakamega Mwikalikha School, Kakamega Tande School and Busia Town Prison were statistically insignificant at 5% significance level. The highest decline in groundwater levels was observed in the upper catchment of the basin.There are significant increases in annual tempratures for Kitale and Kakamega stations in the period 1979 - 2014. Kitale showed annual maximum temprature rising at 0.0006260C/year; annual minimum temperature rising at 0.0011630C/year and the annual mean temprature rising at 0.0008940C/year. Kakamega had annual maximum temprature rising at 0.0007710C/year; annual minimum tempratures rising at 0.0004710C/year and the annual mean tempratures rising at 0.0006230C/year. Eldoret showed falling maximum temprature at - 0.002020C/year; rising minimum temperature at 0.0008130C/year and falling mean temperatures at - 0.001420C/year. The results for Kitale and Eldoret stations showed statistically significant trends whereas those for Kakamega station had a statistically insignificant trend. In Nzoia River Basin, Kitale and Eldoret, annual minimum tempratures are rising faster than the maximum whereas in Kakamega it’s the annual maximum tempratures that are rising faster than the minimum. Kitale and Kakamega stations showed rising annual mean temperatures whereas Eldoret showed falling annual mean tempratures. As one would expect, temperatures in Nzoia River Basin are expected to be rising; however, the case of falling temperatures recorded at Eldoret international airport might occur because this region of Rift valley has highly protected natural resources and a high forest cover is available all the year round. Another possible explanation to this could be the changing cloudness around Eldoret station. Kitale and Kakamega showed annual mean tempratures rising at about 0.10C per century and Eldoret showed mean temperatures falling at about -1.40C per century. The findings for Kitale and Kakamega stations compare well with IPCC Third Assessment Report estimated global warming rate of 0.60C during the twentieth century and other studies from the African continent and East African region.The decreasing trend in groundwater levels in the basin appears to be linked to climate change. Increases in temperature have an impact on the hydrologic cycle because they enhance evaporation of accessible surface water and vegetation transpiration. As a result, these changes have an impact on precipitation volumes, timings, and intensity rates, as well as indirect effects on water flux and storage in surface and subsurface reservoirs. While changes in important long-term climatic factors such as air temperature, precipitation, and evapotranspiration directly affect surface water supplies, the interaction between changing climate variables and groundwater is more intricate and little understood. For efficient and long-term groundwater resource management, understanding long-term temperature variability and trends, as well as the corresponding reaction of groundwater levels, is critical. Despite the fact that groundwater level records are only available for a short period of time, they include essential information that may be utilized to establish strategies for managing the basin's limited groundwater resources.

Importance of long-term ground-loop temperature variation in performance optimization of Ground Source Heat Pump system

In a recent article published in this journal, a series of design optimization was executed for a ground source heat pump system. The optimization was conducted based on a COPall index, which considers both the hydraulic loss on the buried pipe network, as well as the soil thermal balance over a one-year period. In that article, it was concluded that a borehole spacing of 4 m is the optimal value. In this short communication, the comprehensive COPall index is re-evaluated with the same system setup with both the TRNSYS and OpenGeoSys-TESPy software, but over a 20-year period. The results show that the borehole heat exchanger array with a spacing of 4 m will suffer severe heat accumulation over a 20-year operation. This causes the soil temperature to rise by 5.68 °C, along with a decrease of COPall from 4.59 to 4.18. Due to the smaller increase of ground-loop temperature and lower electricity consumption from heat pumps, a larger spacing of 6 m will bring better COPall value over the long term, and thus should be recommended. The extended numerical study in this work suggests that when evaluating the performance of a ground source heat pump system, different time duration will lead to different results. Therefore, the variation of long-term ground-loop temperature needs to be quantitatively evaluated in advance, and the system optimization is recommended to be conducted over the entire life cycle of the system.

Into the wild-a field study on the evolutionary and ecological importance of thermal plasticity in ectotherms across temperate and tropical regions.

Understanding how environmental factors affect the thermal tolerance of species is crucial for predicting the impact of thermal stress on species abundance and distribution. To date, species' responses to thermal stress are typically assessed on laboratory-reared individuals and using coarse, low-resolution, climate data that may not reflect microhabitat dynamics at a relevant scale. Here, we examine the daily temporal variation in heat tolerance in a range of species in their natural environments across temperate and tropical Australia. Individuals were collected in their habitats throughout the day and tested for heat tolerance immediately thereafter, while local microclimates were recorded at the collection sites. We found high levels of plasticity in heat tolerance across all the tested species. Both short- and long-term variability of temperature and humidity affected plastic adjustments of heat tolerance within and across days, but with species differences. Our results reveal that plastic changes in heat tolerance occur rapidly at a daily scale and that environmental factors on a relatively short timescale are important drivers of the observed variation in thermal tolerance. Ignoring such fine-scale physiological processes in distribution models might obscure conclusions about species' range shifts with global climate change. This article is part of the theme issue 'Species' ranges in the face of changing environments (part 1)'.

Long-Term Temperature Variability and Risk of Dyslipidemia Among Middle-Aged and Elderly Adults: A Prospective Cohort Study - China, 2011-2018.

What is already known about this topic?Long-term temperature variability (TV) has been examined to be associated with cardiovascular disease (CVD). TV-related dyslipidemia helps us understand the mechanism of how climate change affects CVD.What is added by this report?Based on the China Health and Retirement Longitudinal Study (CHARLS) from 2011 to 2018, this study estimated the long-term effect of TV on dyslipidemia in middle-aged and elderly adults.What are the implications for public health practice?This study suggested that long-term TV may increase the risk of dyslipidemia. With the threat of climate change, these findings have great significance for making policies and adaptive strategies to reduce relevant risk of CVD.

Time Series Trend Analysis of Rainfall and Temperature over Kolkata and Surrounding Region

Study of long term variability of temperature and rainfall in the context of climate change is of much importance particularly in the region where rainfed agriculture is predominant. Long term trends of temperature and rainfall have been investigated over Kolkata, India, a tropical region using gridded monthly precipitation and temperature data obtained from Global Precipitation and Climate Centre (GPCC V7) with 0.5° X 0.5° resolution for the period 1901 to 2014. Precipitation concentration index, coefficient of variation, rainfall anomaly have been calculated and Palmer drought severity index data have been analyzed. Furthermore, Mann-Kendall test and sen’s slope estimator have been used to detect time series trend. Annual temperature and rainfall have been increased with a rate of 0.0082°C/ year and 0.03 mm/ year respectively. Statistically significant increasing trend has been observed for most of the months for temperature and rainfall. Winter and monsoon period shows highest and lowest inter-annual variability respectively. Rainfall with high precipitation concentration index (16-20) has been observed for the period 1951-1975 and 1976-2000. It has been observed that the number of years with dry conditions have been increased. However, the intensity of dryness is very near to zero. The information from this study will be helpful for the farmers to plan for resilient farming.

Control of Developmental Speed in Zebrafish Embryos Using Different Incubation Temperatures.

The zebrafish is a valuable model organism that is widely used in studies of vertebrate development. In the laboratory, zebrafish embryonic development is normally carried out at 28.5°C. In this study, we sought to determine whether it was possible to modify the speed of embryonic development through the use of short- and long-term variations in incubation temperature. After incubation at 20°C-32°C, most early-stage embryos survived to the epiboly stage, whereas more than half of the embryos died at <20°C or >32°C. The rate of development differed between embryos incubated at the lowest (18°C) and highest (34°C) temperatures: a difference of 60 min was observed at the 2-cell stage and 290 min at the 1k-cell stage. When blastulae that had developed at 28°C were transferred to a temperature lower than 18°C for one or more hours, they developed normally after being returned to the original 28°C. Analyses using green fluorescent protein-buckyball mRNA and in situ hybridization against vasa mRNA showed that primordial germ cells increase under low-temperature culture; this response may be of use for studies involving heterochronic germ cell transplantation. Our study shows that embryonic developmental speed can be slowed, which will be of value for performing time-consuming, complicated, and delicate microsurgical operations.

Вариация температуры воздуха холодного периода на Кольском полуострове как фактор изменения ледового режима

The paper considers the long-term spatial and temporal air temperature variability on the Kola Peninsula according to 26 hydro-meteorological stations and the ice regime of rivers according to 13 hydrological stations for 1950—2018 (base period 1950—1980, and control period 1981—2018). The cold season of the year on the Kola Peninsula lasts from October to the first decade of May, the average temperature for the season is –6.2°C. The average increase in air temperature during the cold season was 1.1 °C.

High-resolution marine data and transient simulations support orbital forcing of ENSO amplitude since the mid-Holocene

Lack of constraint on spatial and long-term temporal variability of the El Niño southern Oscillation (ENSO) and its sensitivity to external forcing limit our ability to evaluate climate models and ENSO future projections. Current knowledge of Holocene ENSO variability derived from paleoclimate reconstructions does not separate the role of insolation forcing from internal climate variability. Using an updated synthesis of coral and bivalve monthly resolved records, we build composite records of seasonality and interannual variability in four regions of the tropical Pacific: Eastern Pacific (EP), Central Pacific (CP), Western Pacific (WP) and South West Pacific (SWP). An analysis of the uncertainties due to the sampling of chaotic multidecadal to centennial variability by short records allows for an objective comparison with transient simulations (mid-Holocene to present) performed using four different Earth System models. Sea surface temperature and pseudo-δ18O are used in model-data comparisons to assess the potential influence of hydroclimate change on records. We confirm the significance of the Holocene ENSO minimum (HEM) 3-6ka compared to low frequency unforced modulation of ENSO, with a reduction of ENSO variance of ∼50 % in EP and ∼80 % in CP. The approach suggests that the increasing trend of ENSO since 6ka can be attributed to insolation, while models underestimate ENSO sensitivity to orbital forcing by a factor of 4.7 compared to data, even when accounting for the large multidecadal variability. Precession-induced change in seasonal temperature range is positively linked to ENSO variance in EP and to a lesser extent in other regions, in both models and observations. Our regional approach yields insights into the past spatial expression of ENSO across the tropical Pacific. In the SWP, today under the influence of the South Pacific Convergence Zone (SPCZ), interannual variability was increased by ∼200 % during the HEM, indicating that SPCZ variability is independent from ENSO on millennial time scales.

Field Test and Numerical Simulation on the Long-Term Thermal Response of PHC Energy Pile in Layered Foundation.

Investigation on the long-term thermal response of precast high-strength concrete (PHC) energy pile is relatively rare. This paper combines field experiments and numerical simulations to investigate the long-term thermal properties of a PHC energy pile in a layered foundation. The major findings obtained from the experimental and numerical studies are as follows: First, the thermophysical ground properties gradually produce an influence on the long-term temperature variation. For the soil layers with relatively higher thermal conductivity, the ground temperature near to the energy pile presents a slowly increasing trend, and the ground temperature response at a longer distance from the center of the PHC pile appears to be delayed. Second, the short- and long-term thermal performance of the PHC energy pile can be enhanced by increasing the thermal conductivity of backfill soil. When the thermal conductivities of backfill soil in the PHC pile increase from 1 to 4 W/(m K), the heat exchange amounts of energy pile can be enhanced by approximately 30%, 79%, 105%, and 122% at 1 day and 20%, 47%, 59%, and 66% at 90 days compared with the backfill water used in the site. However, the influence of specific heat capacity of the backfill soil in the PHC pile on the short-term or long-term thermal response can be ignored. Furthermore, the variation of the initial ground temperature is also an important factor to affect the short-and-long-term heat transfer capacity and ground temperature variation. Finally, the thermal conductivity of the ground has a significant effect on the long-term thermal response compared with the short-term condition, and the heat exchange rates rise by about 5% and 9% at 1 day and 21% and 37% at 90 days as the thermal conductivities of the ground increase by 0.5 and 1 W/(m K), respectively.

ТЕНДЕНЦИИ ИЗМЕНЧИВОСТИ ХИМИЧЕСКОГО СОСТАВА И СТЕПЕНИ ЗАГРЯЗНЕННОСТИ ВОДЫ РЕКИ КУБАНЬ

Introduction. The paper explores the long-term spatial and temporal variability of the chemical composition and water quality in the Kuban River. Methods. To study the variability of the chemical composition of river water, we analyzed data from systematic observations over the concentrations of major ions, biogenic and organic substances, petroleum products and heavy metals from 2010 to 2017. To describe the variability of water quality, we used such indicators as water quality class, water pollution level, and characteristic pollutants. Results. It is shown that the spatial change in the chemical composition is uneven — a number of components in the water have low concentrations in the upper reaches, increasing in the lower part of the river. Others are characterized by high concentrations in the middle reaches, followed by a decrease towards the mouth. Over time, the change in the concentrations of chlorides, sulfates, organic substances and petroleum products increases. As for the content of nitrates, a slight decrease was detected in its variability. For the remaining chemicals, there were no clear trends. We established that in most cases the water in the Kuban River can be classified as polluted and very polluted (water quality class 3). We also found that the nature of river water pollution regarding a number of components is stable. Conclusion. In modern conditions of sharp climate changes and anthropogenic impact, the identified features of the chemical composition and trends in water quality variability of the Kuban River are of great practical importance and can be used in the development of environmentally sound recommendations for improving water quality and the state of water ecosystems in the river basin.

Temporal variability in volatile organic compound concentrations in sanitary sewers at remediation sites

In recent years, there has been a growing recognition of the importance of sewers as preferential pathways for vapor intrusion. This pathway involves volatile organic compound (VOC)-impacted vapor migration through the interior of pipes or conduits towards the potential receptor. A number of research initiatives have been undertaken to improve the understanding of this pathway which, in turn, supports development of sampling methods to evaluate whether it is a concern at a given site. One aspect of the conceptual model that is important to understanding the potential risk of sewer vapor intrusion is the degree to which VOC concentrations vary over time. This paper presents results of field sampling conducted in Texas, Utah, and California to explore temporal variability of chlorinated VOC concentrations in sewer vapor over different timescales. These results, along with results from other studies, suggest that wide ranges of VOC concentrations can occur at given sampling locations. However, long-term temporal variability (months to years) is much higher than short-term variability (days). The timescale over which the variations occur has implications on sampling methods and frequency. The results suggest that multiple grab samples collected over a longer time period, such as on a quarterly basis, are more appropriate for characterizing the long-term average sewer vapor concentrations than single time-integrated samples collected over a period of hours to days. Because time-integrated samples can often be logistically more difficult to collect, an understanding of the timescale of variability may help practitioners balance field logistics considerations with data adequacy when characterizing VOC concentrations in sewers.

LONG-TERM TEMPERATURE VARIABILITY AND THE INCIDENCE OF CARDIOVASCULAR DISEASES: A LARGE, REPRESENTATIVE COHORT STUDY IN CHINA

Objective: In the context of global climate change, far less is known about the impact of long-term temperature variability (TV), especially in developing countries. The current study was aimed to estimate the effect of long-term TV on cardiovascular disease in China. Design and method: The current study enrolled 23,721 individuals with mean age of 56.15 years in China from 2012–2016 and followed up during 2017 and 2019. TV was defined as the standard deviation of daily temperatures during survey years. The Cox regression was used to estimate the multivariable-adjusted hazard ratio (HR) between TV and cardiovascular diseases (CVD). Results: During the follow-up time, we ascertained 836 cases of incident of CVD. A significant positive trend was observed between CVD risk and increasing levels of TV comparing to the lowest tertile with an HR = 1.343 (95% CI: 1.133–1.591) for the medium tertile and an OR = 1.717(95% CI: 1.347–2.189) for the highest tertile (ptrend &lt; 0.001). The HR per 1°C increase in TV was 1.062 (95% CI:1.014–1.112) for CVD. We also estimated that exposure to high TV would lost 2.11 years disease-free years for population aged 35 to 65 years, and was attributable to 2.93 million CVD cases (or 12.14% cases) in China. Conclusions: Long-term TV was associated with higher risk of incident CVD. Our findings will be valuable for future efforts assessing health risks related to the climate change and developing related policies to reduce TV related adverse health effect.

Short- and long-term variations in groundwater temperature caused by changes in vegetation cover

Several comparative studies of the earth's surface provide evidence that vegetation and other bio-physical processes at the earth's surface can directly affect the atmospheric boundary layer, leading to changes in temperature and precipitation patterns. In this study, we demonstrate how vegetation cover can be responsible for the subsurface temperature variation as well as how this temperature variation can be related to past events. A linear decrease of 0.0407 K/year was estimated, and a decrease of 2 mK was observed in subsurface temperature when the surface temperature exceeded 9 oC. This diurnal temperature variation occurs during the phenological growing season of the vegetation. The transient temperature shows an annual cycle at a depth of 40 m. Model calculation applying a linear decrease in surface temperature of 2 K as a boundary condition was simulated. Comparing the results with the trend it is realistic to assume that when an apparent thermal diffusivity of 1.8*10-6 m²/s is applied an event starting between 10 and 20 years ago is responsible for the detected decrease in temperature. However, with this thermal diffusivity the conductive annual temperature variation reaches an amplitude of 1.1 mK instead of the measured 5.4 mK at 40 m. In conclusion, beside the vegetation causing additional convective heat transport triggered by the annual surface temperature, the influence of reduced solar incoming heat radiation reaching the ground caused by the increased shadowing effect of vegetation cover might be responsible for a continuous decrease in local temperature of 2 K being active approximately 20 years after plantation.

Long-term temperature field of steel-box girder of a long-span bridge: Measurement and simulation

The temperature field of a long-span bridge is variant with an underlying statistical property due to the periodically time-varying solar radiation and the unceasing structural heat exchange with surrounding environment. A comprehensive understanding of the long-term temperature field of a steel-box girder is essential for the design and maintenance of cable-supported bridges. However, it is challenging to obtain the long-term temperature variations because of the complex geometric configuration of the main girder and the complicated heat transfer process. In this context, this paper presents a strategy to overcome this problem by simulating the long-term temperature field of a steel-box girder based on limited monitored data. In the simulation, the long-term temperature field is treated as a stochastic process with prescribed spectral and probabilistic properties. By analyzing the monitored temperature data on Sutong Bridge, the models of power spectral density (PSD), coherence function, and high-order moments are developed. A noteworthy feature captured in measurements is that the temperature is non-Gaussian with considerable kurtosis and skewness. Hence, the temperature field simulation is converted to the simulation of multivariate non-Gaussian stochastic processes. Based on the spectral representation method accompanied with Hermite transformation, the temperature field of the steel-box girder of Sutong Bridge is simulated with a two-year duration considering the non-Gaussianity. Verifications of the simulated field are made through comparisons with the developed spectral and probabilistic models. It is shown that the simulations match well with the measured temperature characteristics, specifically including the time histories and their PSD, PDF, and coherence functions. The good agreement indicates the effectiveness of the simulated long-term temperature field.

Long-term temperature variability and the incidence of cardiovascular diseases: A large, representative cohort study in China.

In the context of global climate change, far less is known about the impact of long-term temperature variability (TV), especially in developing countries. The current study aimed to estimate the effect of long-term TV on the incidence of cardiovascular disease (CVD) in China. A total of 23,721 individuals with a mean age of 56.15 years were enrolled at baseline from 2012 to 2016 and followed up during 2017-2019. TV was defined as the standard deviation of daily temperatures during survey years and was categorized into tertiles (lowest≤ 8.78°C, middle=8.78-10.07°C, highest≥10.07°C). The Cox proportional hazards regression was used to estimate the multivariable-adjusted hazard ratio (HR) between TV and CVD. During the median follow-up of 4.65 years, we ascertained 836 cases of incident CVD. For per 1°C increase in TV, there was a 6% increase of CVD (HR=1.06 [95% confidence interval (CI): 1.01-1.11]). A significant positive trend was observed between CVD risk and increasing levels of TV compared to the lowest tertile [HR=1.34 (95% CI: 1.13-1.59) for the medium tertile, HR=1.72 (95% CI: 1.35-2.19) for the highest tertile, Ptrend<0.001]. Exposure to high TV would lose 2.11 disease-free years for the population aged 35-65 years and 66 CVD cases (or 7.95% cases) could been attributable to TV higher than 8.11°C in the current study. The current findings suggested that long-term TV was associated with a higher risk of CVD incidence, it is needed to reduce the TV-related adverse health effect.

Long-term exposure to ambient PM2.5 and stroke mortality among urban residents in northern China

Evidence is still limited for the role of long-term PM2.5 exposure in cerebrovascular diseases among residents in high pollution regions. The study is aimed to investigate the long-term effects of PM2.5 exposure on stroke mortality, and further explore the effect modification of temperature variation on the PM2.5-mortality association in northern China. Based on a cohort data with an average follow-up of 9.8 years among 38,435 urban adults, high-resolution estimates of PM2.5 derived from a satellite-based model were assigned to each participant. A Cox regression model with time-varying exposures and strata of geographic regions was employed to assess the risks of stroke mortality associated with PM2.5, after adjusting for individual risk factors. The cross-product term of PM2.5 exposure and annual temperature range was further added into the regression model to test whether the long-term temperature variation would modify the association of PM2.5 with stroke mortality. Among the study participants, the annual mean level of PM2.5 concentration was 66.3 μg/m3 ranging from 39.0 μg/m3 to 100.6 μg/m3. For each 10 μg/m3 increment in PM2.5, the hazard ratio (HR) was 1.31 (95% CI: 1.04–1.65) for stroke mortality after multivariable adjustment. In addition, the HRs of PM2.5 decreased gradually as the increase of annual temperature range with the HRs of 1.95 (95% CI: 1.36–2.81), 1.53 (95% CI: 1.06–2.22), and 1.11 (95% CI: 0.75–1.63) in the low, middle, and high group of annual temperature range, respectively. The findings provided further evidence of long-term PM2.5 exposure on stroke mortality in high-exposure settings such as northern China, and also highlighted the view that assessing the adverse health effects of air pollution might not ignore the role of temperature variations in the context of climate change.