Low Ambient Temperature Research Articles

Effect of ambient temperature and density on the transition of hot temperature combustion to low temperature combustion of commercial diesel and waste plastic diesel in an optical access machine

Alternative diesel production from mixed waste plastic pyrolysis is an effective method for the management of waste plastic and its related costs. The low temperature combustion (LTC) of diesel enables the reduction of nitrogen oxides and soot simultaneously. However, because of the high quantity of unburned hydrocarbon (UHC) and carbon monoxide (CO) emissions, LTC has a low combustion efficiency. This paper investigated the combined effect of low ambient temperature and high density (LATHD) on the transition from hot temperature combustion (HTC) to LTC by using commercial diesel (CD) and waste plastic diesel (WPD) without exhaust gas recirculation (EGR) and low cetane fuels. The results showed that NOx and soot concentrations were decreased and integral heat release was increased. For a given unit heat release, the NOx emissions of CD and WPD decreased 60% and 38%, respectively, by decreasing the ambient temperature from 1050 K to 750 K. Furthermore, integral heat release is a more influential parameter on NOx than heat release rate. After that, soot concentrations of CD and WPD were significantly decreased by 85% and 81% with a reduction in ambient temperature from 1050 K to 750 K. At the same ambient temperature, the NOx and soot concentrations of WPD were higher than that of CD for all cases. With the same ignition delay, however, the NOx and soot concentrations of WPD/high cetane fuel decreased dramatically compared to CD. This information will be useful for determining compression ratio and combustion phasing when considering engine designs.

Energetic and exergetic analysis of a transcritical CO2 air-source heat pump water heating system in the cold region

To analyze the energetic and exergetic performance of the transcritical CO2 air-source heat pump water heating system in the cold region, the numerical model and simulation algorithm are set up and verified with the experiments. Under the low ambient temperature (−15 °C to 0 °C) and water inlet temperature (9 °C), the performance evaluation of the system is investigated using the developed numerical model at different compressor frequency (75, 80 and 85 Hz). The results show that Qgc, COP and ηex decrease by 14.47%, 12.78% and 20.83% respectively as the ambient temperature decreases from 0 °C to −15 °C. The CO2 outlet state of the gas cooler and corresponding slope of isotherms have significant effects on COP and ηex. The COPopt and ηex,opt exist in the system but at different compressor discharge pressures. With the compressor frequency increasing from 75 Hz to 85 Hz, the increase in Qgc is at the cost of a decrease in COP, and COPopt decreases by 5.31%. The effect of the compressor frequency on ηex is different as the compressor discharge pressure elevates. Thus, a suitable operating condition, considering different needs, should be selected in the system operation.

Experimental study on improving cold start performance of diesel engines at extremely low ambient temperatures with diethyl ether

How to achieve a fast and reliable cold start of diesel engines at extremely low temperatures is a significant and longstanding problem. In this study, a precise amount of diethyl ether was premixed in the intake to facilitate the starting at extremely low ambient temperatures down to −40 °C. The study investigated the effects of diesel fuel injection strategies, diethyl ether concentration, and ambient temperature on the cold-start performance. Additionally, an analysis was conducted on energy consumption and heat loss during the cold start period. The test engine could start quickly and steadily when diethyl ether was premixed in the intake. This was achieved by optimizing the diesel injection quantity to 60% of the original quantity and retarding the injection timing from 6 oCA BTDC to 2 oCA BTDC. The engine exhibited reliable starting at −40 °C when 2.0% v/v diethyl ether was premixed. However, excessive direct injection of diesel had an adverse effect on fuel ignition at such extremely low temperatures. Moreover, the electricity consumption was much lower with diethyl ether premixed in the intake than that with an electric intake heater, greatly reducing the requirements for starting batteries during the cold start under extremely low-temperature conditions.

Optical Study on Spray and Two-Stage Ignition Characteristics for Diesel Spray Under Low Ambient Temperature and Density Conditions

Optical Study on Spray and Two-Stage Ignition Characteristics for Diesel Spray Under Low Ambient Temperature and Density Conditions

Plasma-catalytic pyrolysis of polypropylene for hydrogen and carbon nanotubes: Understanding the influence of plasma on volatiles

Plasma-catalytic pyrolysis was developed for upgrading polypropylene (PP) pyrolysis volatiles to co-produce carbon nanotubes (CNTs) and hydrogen. To uncover the role of plasma on the plastic catalytic pyrolysis process, the pyrolysis of polypropylene (PP) over Fe/γ-Al2O3 was carried out in a two-stage pyrolysis system with a coaxial dielectric barrier discharge (DBD) plasma reactor. The results showed that the plastic pyrolysis volatiles were further cleaved and activated with plasma, resulting in more active carbon species for the growth of CNTs. Compared to conventional catalytic pyrolysis, plasma addition shifted the initial formation temperature of CNTs to a lower ambient temperature by ∼100 °C, and significantly promoted the conversion of liquid and gaseous products to CNTs and hydrogen, with higher carbon and hydrogen yields of ∼322 mg/gplastic and 30 mmol/gplastic, respectively. In addition, the degree of graphitization of the CNTs in the presence of the plasma was significantly enhanced with less defectivity. The influence of catalytic temperature variation caused by plasma on CNTs growth was also discussed from the perspective of volatile evolution. This work highlights the potential of plasma-catalytic pyrolysis for the production of hydrogen and high-value carbon materials from plastic waste.

Fatigue Assessment of Cable-Girder Anchorage Zone in a Low Ambient Temperature Environment Based on Extended Finite Element Method

The fatigue safety of cable-girder anchorage structures in cable-stayed bridges under long-term service has attracted much attention. For bridges located in seasonally cold regions, the effect of low-temperature environments should be considered when evaluating fatigue performance. Using the Heilongjiang Bridge in China as a case study, a room-temperature fatigue test with a numerical simulation that considers the low-temperature effect on both load effect and fatigue resistance was proposed. A fatigue test with increased testing load amplitude was performed on a 1:3.75 ratio specimen. After 3.2 million loading cycles and using an acoustic emission technique, no fatigue crack was observed in the anchorage structure. The extended finite element method was then adopted to analyze the anchorage zone’s fatigue crack initiation position and propagation path. Finally, based on the fatigue characteristics of bridge steel, the fatigue resistance to the crack propagation of the vulnerable area was evaluated under three different service conditions. The results show that the fatigue performance of the anchorage zone at low temperatures is sufficient. Moreover, this paper provides a more widely applicable and cost-effective approach for the fatigue evaluation of steel bridges.

Photothermal-Driven Polymer for a Smart Window with Adaptive Solar Modulation.

Although the thermochromic smart windows with adjustable sunlight transmittance to achieve energy savings are gradually improving, they are still difficult to use, limited by their unreasonable thermal response temperature, slow switching time, and poor durability. Here, we demonstrate a dual-function hybrid thermoresponsive smart window device (CPH) by trapping the phase-change polyHEA-HDA polymer (HEA = hydroxyethyl acrylate, HDA = hexadecyl acrylate) and polydopamine@CsxWO3 (PDA@CWO) core-shell nanoparticles within glasses. The introduced PDA@CWO nanoparticles substantially increase the energy transformation efficiency of solar energy to heat due to their outstanding photothermal conversion. When the temperature increases above the phase-transition temperature of polyHEA-HDA polymer, the copolymer components in the composite material undergo a reversible crystalline-amorphous transition, which enables the transformation of the whole smart window from transparency to opaque in a low ambient temperature. The light transmittance in the solar range can be dynamically modulated between 54.8 and 22.9% with a low ambient temperature while maintaining acceptable visible light transparency and effective UV shielding. A model house testing proves an indoor temperature cooling of 7.1 °C. This study offers a new approach to designing an energy-saving smart window system with multifunctionality.

Adaptive Properties of <i>Arthrobacter agilis</i> Strain wb28 Isolated from Wheat Bran

Abstract—The article presents the results of a study of some adaptive properties of a bacterial isolate from wheat bran, identified by the 16S rRNA gene as an Arthrobacter agilis strain. According to the literature data, A. agilis does not belong to the dominant bacterial species of wheat microbial associations and activates growth at low ambient temperatures. The studied A. agilis strain showed poor growth in a microbial consortium when an aqueous suspension of wheat bran, partially fermented at 28 ± 1°C by the native microbiota, was plated on a dense MPA medium and produced the pigment after three weeks of storage at 4 ± 1°C. Moderate growth of bacteria without increased pigmentation was observed during its subsequent transfer after low-temperature storage on agar media containing carbohydrates and nitrogen compounds, mineral salts, and vitamins that were more easily utilized than native bran. The growth of colonies upon plating on such media increased in the series: thermally fermented wheat bran → HMF agar → LB (without salt). It was revealed that the A. agilis strain, which was not typical of the wheat bran microflora, under the influence of osmotic and/or temperature shock (in response to a sharp change in the NaCl concentration and/or a difference in ambient temperatures) produced pigments both in agar and liquid cultures. According to the results of spectral analysis, the pigment was assigned to carotenoids and tentatively identified as bacterioruberin. Quantitative evaluation showed that, under stress conditions during submerged cultivation, the studied strain A. agilis wb28 was able to synthesize the pigment at the level of 52.8 mg/L (17.2 mg/g biomass).

Towards nationwide implementation of 40% biodiesel blend fuel in Indonesia: a comprehensive road test and laboratory evaluation

This research focused on evaluating the technical viability of using biodiesel with a blending ratio of 40% v/v, which is expected to be implemented soon in Indonesia. Two kinds of biodiesel blends were prepared, a blend of 60% diesel fuel and 40% biodiesel (B40) and a blend of 60% diesel fuel, 30% biodiesel, and 10% hydrogenated vegetable oil (HVO) (B30D10). The fuels were tested on EuroII vehicles without any engine modifications through a 50,000 km endurance road test. Laboratory tests were also performed at certain traveled distances to evaluate various engine parameters, including power, fuel economy, exhaust emissions, and used engine oil properties. Engine components were inspected upon the completion of the road test. Cold-start ability was also examined to confirm the suitability of the investigated biofuels at low-temperature operating conditions in Indonesia. The road test results showed that vehicles fuelled with B40 and B30D10 could reach a distance of 50,000 km without encountering any technical issues. The laboratory evaluation during the road test indicated that B30D10 had a higher power and fuel economy than B40, with a maximum difference of 2%. Furthermore, B30D10 emitted lower CO, HC, and PM emissions than B40 throughout the distance traveled, with maximum differences of 11.4%, 14.7%, and 22.6%, respectively, but led to 15% higher NOx. Engine component inspection and used engine oil analysis confirmed the fulfillment of the manufacturer's recommendations for both B40 and B30D10. Finally, B40 and B30D10 were suitable for operating at low ambient temperatures in Indonesia, confirming them as practical options to be implemented in the nationwide 40% biodiesel blend fuel.

Technical and economic assessment of a hybrid heat pump system as an energy retrofit measure in a residential building

Air to water electric heat pumps are one technological solution to achieve energy defossilisation goals for heating of residential building stock. Nevertheless, they may not necessarily be the only solution for all residential building stock. A case in point is where extensive fabric refurbishment is impracticable or where electric heat pumps are installed where low ambient temperatures prevail and/or high water delivery temperatures must be utilised. For such instances, hybrid (gas and electric) heat pumps offer an alternative option by facilitating fuel source switching between electricity and gas, when ambient temperatures are low or high water supply temperatures are required. In the current study, the effectiveness of an air-to-water electric heat pump and hybrid heat pump are examined for different building retrofit scenarios for a residential dwelling located in Ireland. This is achieved by means of a sensitivity study of a validated building simulation model, incorporating both heat pump systems, subject to different building retrofit scenarios. Relative to a conventional oil-fired boiler, for a deep building retrofit scenario, the hybrid and electric heat pumps achieve primary energy savings of 73% and 70%, respectively. For a minimal building retrofit scenario, the respective primary energy savings are 57% and 52%. For the deep retrofit scenario, compared to the baseline building with no retrofit measures, the carbon footprint reductions were found to be (8.5 gCO2e/m2/year or 44%) for the hybrid heat pump, (10.31 gCO2e/m2/year or 45%) for the electric heat pump, and (17-21 gCO2e/m2/year or 43-53%) for oil or gas boiler systems. Finally, the deployment of either an electric heat pump or hybrid heat pump for deep building fabric retrofit achieves approximately half heating system capital cost return within 20 years.

Development of Binder for Fast-Charging for Li-Ion Battery

In the recent years, fast-charging is a battery technology that continues to be in demand for portable devices, electric vehicles and grid storage. Especially, fast charging capability has become one of the key features targeted by battery and EV industries. However, charging at high rates has been shown to accelerate degradation, causing both the capacity and power capability of batteries to deteriorate. In addition, the efficiency of fast charging depends on the materials and current in the battery, but also ambient temperature is emerging as an important issue. When the ambient temperature decreases, there is a decrease in performance and battery stability problems. This is the reason that the diffusion of Li-ion is slower in the electrodes and the electrolyte at low temperatures due to sluggish kinetics of interaction. Therefore, it is recommended to use low charging speed and voltage at low ambient temperature. In order to increase the fast charging efficiency, the material and battery design must be well designed, and among them, by improving the ionic conductivity of the binder, the resistance of the entire battery is lowered and the fast charging efficiency is improved. In addition, the resistance of material change at low temperature and its effect on fast-charging were also examined.

Macroscopic and Microscopic Characteristics of a GDI Spray Under Various Thermodynamic Conditions

Article Macroscopic and Microscopic Characteristics of a GDI Spray Under Various Thermodynamic Conditions Jian Li 1, Lulu Li 1, Rujie Xiao 1, Yuanfei Liang 1, Shuyi Qiu 2, and Xuesong Li 2,* 1 SAIC GM Wuling Automobile Co., Ltd., 18 Hexi Rd, Liunan District, Liuzhou 545001, China 2 School of Mechanical Engineering, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China * Correspondence: xuesonl@sjtu.edu.cn Received: 12 June 2023 Accepted: 9 August 2023 Published: 28 August 2023 Abstract: Gasoline direct injection (GDI) is the most common and advanced fuel supply strategy for gasoline engines. The fuel atomization quality and fuel/air mix degree determine the subsequent combustion efficiency and emissions. However, the engine works in complex conditions which have numerous thermodynamic boundary conditions, and the characteristics of fuel atomization also change accordingly. It is necessary to clarify the influence of various thermodynamic conditions on the GDI spray. In this work, three different types of optics diagnostic methods were utilized to capture the macroscopic and microscopic characteristics of a commercial GDI injector spray under various thermodynamic boundary conditions. Specifically, Mie-scattering photography was employed to get the macroscopic parameters; planar Mie-scattering photography was utilized to get the spray pattern; phase Doppler interferometry (PDI) was used to get the microscopic characteristic, i.e., the droplet size distributions. It is found from this study that higher injection pressure, lower ambient pressure, and lower ambient temperature would lead to longer penetration and larger plume width. Lower ambient pressure and higher ambient temperature would cause a smaller spray pattern. Higher injection pressure, lower ambient pressure, and higher ambient temperature would result in smaller droplet sizes.

Fluid-rock interaction modeling to constrain Au enrichment: Implication for the giant Jiaodong Au mineralization, eastern North China Craton

The devolatilization model of the metasomatized lithospheric mantle without pre-enriched gold has been proposed to account for the giant gold mineralization. An excellent example is the world-class Jiaodong gold province with >5000 tonnes Au resources in the eastern North China Craton. The auriferous fluid transport and gold enrichment during wallrock alterations are two vital processes to determine the giant gold mineralization formation in this province. However, the effects of the fluid-rock interaction with alterations on the auriferous fluid transport and gold enrichment still keep poor understanding, which leads the above model to be imperfect. The giant Jiaojia goldfield in this province recorded a wallrock alteration evolution from K-feldspar alteration to pyrite-sericite-quartz alteration, and some parts of the latter can become gold orebodies when the gold grade is >1 ppm. This study conducts thermodynamic fluid-rock interaction modeling to reveal auriferous fluid transport and coupled relationship between gold enrichment and alteration mineral assemblage based on the alteration-mineralization and ore fluid characteristics of the goldfield. The modeling of fluid-rock interaction with cooling indicates the transformation of Au-Cl complexes to Au-S complexes combined with the total sulfur concentration decrease by pyrite precipitation when cooling from ∼460 °C can trigger the dispersive gold precipitation, which should hinder the gold long-range transport to lower ambient temperature. The high oxygen fugacity at >400 °C can enhance Au-Cl complexes stability, and the low pH can maintain high total sulfur concentration in the auriferous fluid, both of which facilitate the long-range gold transport to a lower-temperature environment. The auriferous fluid would acquire higher pH by the buffering of feldspars or sericite, which was beneficial for the high-efficiency precipitations of pyrite and gold. The ankerite-siderite assemblage without pyrophyllite in the pyrite-sericite-quartz alteration zone indicates that a cumulative fluid to rock mass ratio (f/r) of 3.8–4.8 should be needed for the transformation from K-feldspar alteration to pyrite-sericite-quartz alteration according to the fluid-rock interaction modeling at 300 °C and 2000 bar. In the case of auriferous fluids with ≤200 ppb Au concentration, the single fluid-rock interaction can only elevate the gold grade to ≤0.69–0.87 ppm in the pyrite-sericite-quartz alteration zone at f/r 3.8–4.8. Therefore, the fracture-induced fluid flow coupled with fluid-rock interaction is proposed to the prerequisite to elevate the gold grade to >1 ppm in the pyrite-sericite-quartz alteration zone. The metasomatized lithospheric mantle volume for the required ore fluid and Au in the Jiaodong province is estimated according to the modeling results and alteration-mineralization characteristics, which provides a link between the mantle without abnormal Au enrichment and the alteration-mineralization processes.

Complex temperature dependence of vehicular emissions: Evidence from a global meta-analysis

The significant impact of low ambient temperature, which was less regulated, on vehicle exhaust emissions had garnered considerable attention. This study investigated the impact of ambient temperature on exhaust emissions based on the global meta-analysis. The estimated sizes (mean difference, MDt) of 11 exhaust pollutants were quantified with 1795 observations at low ambient temperatures (LATs, −18 °C to −7 °C) versus warm ambient temperatures (WATs, 20 °C–30 °C). The results indicated a strong and positive effect of LATs on vehicular emissions, with the average ratio of vehicular emission factors at LATs to those at WATs (EFLAT/EFWAT) ranging from 1.14 to 3.84. Oil-based subgroup analysis indicated a quite large MDt [NOx] of diesel engines (12.42–15.10 mg km−1·k−1). Particulate emissions were 0.22–1.41 mg km−1·k−1 enhanced during cold-start tests at LATs. The application of particulate filters on motor vehicles greatly reduced the impact of ambient temperature on tailpipe particulate emissions, at the expense of induced NOx emissions. During the Federal Test Procedure (FTP-75), exhaust emissions showed higher temperature dependence compared to the averaged levels (1.31–39.31 times). Locally weighted regression was used to determine exhaust temperature profiles, revealing that gasoline vehicles emitted more particulates at LATs, while diesel vehicles showed the opposite trend. Given the widespread use of motor vehicles worldwide, future motor vehicle emission standards should include tighter limits on exhaust emissions at LATs.

Field investigation of thermal comfort with face masks in outdoor spaces in South China: A case study

After the outbreak of coronavirus disease 2019 (COVID-19), individuals have paid significant attention to protecting themselves indoors and outdoors by wearing masks. However, wearing masks can affect the exchange of heat and moisture between the body and the environment, which in turn affects the thermal comfort of the body and causes discomfort, leading people to wear them in an unscientific and standardized manner, affecting people's healthy lives. Thus, to analyze its effects on thermal comfort, outdoor parameter measurements and field surveys were conducted at Guangzhou University to investigate the thermal comfort of pedestrians wearing masks outdoors. In this study, the physiological equivalent temperature (PET) was chosen for thermal comfort evaluation. Based on the field survey, the neutral PET and preferred PET of the subjects with and without masks were determined. The results indicated that the neutral temperature of people wearing masks are slightly lower than that of people without masks, and people with masks need a lower ambient temperature to feel comfortable. Out of the total, wearing masks raised the heat sensation in the face more and caused discomfort to the face. In addition, the suitability of PET for the people with masks was initially evaluated.

Comprehensive performance analysis of cold storage Rankine Carnot batteries: Energy, exergy, economic, and environmental perspectives

Rankine Carnot batteries have demonstrated promise as a viable solution for electricity storage due to their high energy density at low temperatures. A specific variant of these batteries, known as the Cold Storage Rankine Carnot Battery (CSRCB), utilizes a vapor compression refrigeration (VCR) unit to store cold energy at sub-ambient temperatures. In this paper, three different configurations of CSRCB are constructed: the Basic CSRCB (B-CSRCB), CSRCB with a recuperator in VCR (R-CSRCB), and CSRCB with a recuperator in VCR and a preheater in ORC (RP-CSRCB). The system is analyzed from four perspectives: energy, exergy, economic, and environmental (4E). The impact of key parameters, such as heat source temperature, ambient temperature, and pinch point temperature, on the system's performance is evaluated. The results indicate that the RP-CSCBR configuration outperforms others in terms of energy, exergy, and economic analysis. The evaporator in ORC-subsystem is the component with the largest exergy loss. When the three configurations of CSRCB achieve the maximum exergy efficiency under different conditions, the ORC-subsystem evaporator accounts for 41.9 %, 41.9 % and 17.6 % of the exergy loss of B-CSRCB, R-CSRCB and RP-CSRCB, respectively. The lowest levelized cost of storage (LCOS) can be obtained when the system is operating at high heat source temperature, low ambient temperature and small pinch temperature difference. The environment assessment results show that the changes of the key parameters of the system have different effects on the annual emission reduction (AER) and total equivalent warming impact (TEWI) of CSRCB with different configurations.

Thermodynamic analyses and performance improvement on a novel cascade-coupling-heating heat pump system for high efficiency hot water production

In the background of global warming and reducing carbon emission, air-source heat pump water heater is used as an energy efficient technology to improve the efficiency of building hot water production, which may account for 21–41% of building energy cost. However, there are still space for the energy efficiency improvement of heat pump water heater, as there is large temperature difference between water and refrigerant, which may limit the energy performance (especially at low ambient temperature) but receives little attention. Therefore, a novel cascade-coupling-heating heat pump system with less water-refrigerant temperature different is proposed in this paper, where part of the heat is first provided at the low-temperature stage, reducing the heat load at the high-temperature stage and the high-temperature stage compressor power, and increasing system energy efficiency. To study the system, a theoretical model was established and verified through experiments. Experimental and theoretical results show that: in the ambient temperature range of 243.15 K ∼ 323.15 K, the average and maximum improvement in the coefficient of performance of the new system reach 34.8% and 107.7%, respectively, comparing with cascade heat pump; and in the ambient temperature range of 248.15 K ∼ 323.15 K, when comparing with single-stage heat pump, the new system reveals average and maximum improvement in the coefficient of performance as high as 25.8% and 55.6%, respectively. This study provide a promising potential technology for efficiency water heating, and lay the basis for further study and application of the new system.

Short-term effects of air pollution and weather changes on the occurrence of acute aortic dissection in a cold region.

Air pollution and severe weather conditions can adversely affect cardiovascular disease emergencies. Nevertheless, it remains unclear whether air pollutants and low ambient temperature can trigger the occurrence of acute aortic dissection (AAD) in cold regions. We applied a retrospective analysis to assess the short-term effects of air pollution and ambient temperature on the occurrence of AAD in Harbin, China. A total of 564 AAD patients were enrolled from a major hospital in Harbin between January 1, 2017, and February 5, 2021. Weather condition data and air pollutant concentrations, including fine particulate matter smaller than 10 μm (PM10) and 2.5 μm in diameter (PM2.5), nitrogen dioxide (NO2), sulfur dioxide (SO2), carbon monoxide (CO), and ozone (O3), were collected every day. Conditional logistic regressions and correlation analysis were applied to analyze the relationship of environmental and atmospheric parameters with AAD occurrence at lags of 0 to 7 days. Specifically, we appraised the air quality index, CO, NO2, SO2, O3, PM10, PM2.5, temperature, dew point temperature, atmospheric pressure, and cloud amount. A total of 1,496 days at risk were assessed, of which 564 patients developed AAD. Specifically, AAD did not occur on 1,043 (69.72%) days, while 1 or more cases occurred on 453 (30.28%) days. Several pollution and weather predictors for AAD were confirmed by multilevel modeling. The air quality index (p = 0.0012), cloud amount (p = 0.0001), and concentrations of PM2.5 (p = 0.0004), PM10 (p = 0.0013), NO2 (p = 0.0007) and O3 (p = 0.0001) predicted AAD as early as 7 days before the incident (lag of 7 days) in the study period. However, only concentrations of the air pollutants NO2 (p = 0.0468) and O3 (p = 0.011) predicted the occurrence of AAD after the COVID-19 outbreak. Similar predictive effects were observed for temperature, dew point temperature, and atmospheric pressure (all p < 0.05) on all days. The risk of AAD is closely related to air pollution and weather characteristics in Harbin. While causation was not determined, the impact of air pollutants on the risk of AAD was reduced after the COVID-19 outbreak.

The impact of low ambient temperature on cardiovascular health

Abstract Extreme weather events and climate change have witnessed a substantial increase in recent years, leading to heightened concerns. The rise in abnormal ambient temperatures, both in intensity and frequency, directly and indirectly impacts cardiovascular health. While the impact of high ambient temperatures on cardiovascular response is a common concern in the context of global warming, the significance of low temperatures cannot be overlooked. The challenges posed by low temperatures contribute to increased cardiovascular morbidity and mortality, posing a significant threat to global public health. This review aims to provide an overview of the relationship between low ambient temperature and cardiovascular health, encompassing the burden of cardiovascular outcomes and underlying mechanisms. Additionally, the review explores strategies for cold adaptation and cardioprotection. We posit that to optimize cold adaptation strategies, future research should delve deeper into the underlying mechanisms of cardiovascular health in response to low ambient temperature exposure.

The mediation of the placenta on the association between maternal ambient temperature exposure and birth weight

Studies have indicated that exposure to low and high temperatures during pregnancy negatively affects fetal development. The placenta plays vital functions in fetal development and could also be impacted by suboptimal temperatures. However, whether the placenta mediates the association between suboptimal temperature and birth weight is unknown. Our study aims to evaluate the association between ambient temperature and birth weight as well as the mediation effect of the placenta. A prospective birth cohort study was conducted during 2017–2020 in Guangzhou, China (n = 3349 participants). We defined extreme temperature exposure during the whole pregnancy by using different thresholds, including low temperatures (< 25th, < 15th, < 10th, < 5th percentiles), and high temperatures (> 75th, > 85th, > 90th, > 95th percentiles). Three different approaches (generalized linear model, inverse probability weighting, and doubly robust model) were applied to estimate the effects of low/high temperatures on birth weight and placental indicators, including placental weight, placental volume, and placental–to–birth weight ratio (PFR), respectively. We observed that both low and high ambient temperatures during the whole pregnancy were associated with lower birth weight and negative changes in placental indicators. The estimated lower mean birth weight ranged from −158 g (95 % CI: −192 g, −123 g) to −363 g (95 % CI: −424 g, −301 g) for low temperatures and from −97 g (95 % CI: −135 g, −59 g) to −664 g (95 % CI: −742 g, −585 g) for high temperatures. In mediation analyses, placental weight mediated 28.79 % to 40.47 % and 48.22 % to 54.38 % of the association of low and high temperatures with birth weight, respectively. The findings suggest that placental weight may mediate the association between ambient temperature exposure and birth weight.