Air Temperature Research Articles

Evaluating the spatiotemporal patterns of drought characteristics in a semi‐arid region of Limpopo Province, South Africa

Drought is a complex phenomenon resulting from below-average rainfall and is characterized by frequency, duration, and severity, occurring at a regional scale with dire consequences, especially in semiarid environments. This study used the Reconnaissance Drought Index (RDI) to assess drought severity in two district municipalities in Limpopo Province. Rainfall and air temperature data from 12 stations covering 1970–2020 were obtained from the Agricultural Research Council. The calculation of RDI relies on the monthly accumulation ratio of total rainfall to potential evapotranspiration (PET). For this study, PET was estimated using the Hargreaves and Samani temperature-based approach. The RDI results showed a high spatial–temporal variation in drought characteristics over the study area. All stations experienced extreme drought conditions in different years, with the maximum drought severity (-3.40) occurring from 2002–2003 in the western parts of the study area, indicating extreme drought. Furthermore, the results revealed continuous drought conditions over various periods, including severe droughts between 1995 and 1998 and between 2014 and 2016, with the severity varying between mild and moderate drought conditions. The results reveal notable but nonuniform drought patterns as the climate evolves, with potential implications for water availability and livelihoods. The study's findings underscore the significance of adopting multidimensional approaches to drought assessment that encompass meteorological and hydrological factors to inform strategies for adaptive water management and policy formulation in the face of a changing climate.

Minimally processed yam beam roots fortified with probiotics and phenolic compound from green coffee microencapsulated

Yam beam (Pachyrhizus erosus L.) root, commonly known as jicama, is widely consumed by health-conscious individuals due to its low caloric content. However, its nutritional value is relatively low, despite containing some. To enhance these nutritional properties, jicama can be supplemented with probiotics and antioxidant compounds. In this study, the jicama pieces were coated with an edible layer containing microencapsulated Lactobacillus acidophilus, Bifidobacterium spp. and phenolic compounds derived from green coffee, which were microencapsulated using a double spray drying technique. The probiotics and phenolic compounds were dried using double spray drying with chitosan at 120 and 140 °C. The results showed that the inlet air temperature did not have a statistically significant effect (p ≥ 0.05) on the encapsulation efficiency of probiotics, chlorogenic acid and caffeine content, or antioxidant activity expressed as IC50 value (110 - 116 µg/mL). After 6 d of storage at 4 °C, the jicama supplemented with the microcapsules containing Lactobacillus acidophilus and Bifidobacterium spp. exhibited a reduction in microbial viability by 1 and 2 log CFU/g, respectively. However, the addition of microcapsules allowed a higher concentration of phenolic compounds than the control group. Minimally processed jicama containing microcapsules with probiotics and phenolic compounds could be a functional food, and the reported procedure could be applied for industrial purposes.

Correlation dimension for temperature and other micrometeorological variables in different ground cover from six biomes of the Amazon basin

Correlation dimension () for embedding dimensions, varying between 3 to 11, were estimated for a 1- or 2-month time series of air temperature and other micrometeorological variables, such as energy fluxes, solar radiation and concentration, in six ecosystems in Amazon and the central region of Brazil. Dc remained within the 1.5 - 3.0 range, for variables locally coupled to ecosystems, and outside the range for variables not locally coupled, such as precipitation and wind velocity. Results indicate that the feature of the variables does not have an important stochastic component. There is a small amount of data available concerning estimates of correlation dimension () of micrometeorological variables. The measurement of for several variables from six Brazilian biomes indicates that this parameter is sensitive to environmental conditions as the rainfall. The obtained results also indicates that the natural processes in the ecosystems remain in a non-chaotic regime. In certain circumstances, as in conditions of high humidity, natural ecosystems may stay inside a limit which is close but lower than chaos. Moreover, an important stochastic component was not observed.

Cardiovascular morbidity risk attributable to thermal stress: analysis of emergency ambulance dispatch data from Shenzhen, China

BackgroundClimate change has raised scientific interest in examining the associations of weather conditions with adverse health effects, while most studies determined human thermal stress using ambient air temperature rather than the thermophysiological index.ObjectivesTo evaluate the association between emergency ambulance dispatches (EADs) related to cardiovascular causes and heat/cold stress in Shenzhen, a city in southern China, with the aim of providing new insights for local policymakers.MethodsA time series analysis using ambulance dispatch data of cardiovascular diseases in Shenzhen, China (2013–2019) was conducted. A quasi-Poisson nonlinear distributed lag model was applied to explore the relationship between emergency ambulance dispatches (EADs) due to cardiovascular causes and thermal stress (determined by Universal Thermal Climate Index, UTCI). Attributable fractions were estimated to identify which UTCI ranges have a greater health impact.ResultsThe relationship between UTCI and EADs due to cardiovascular diseases exhibits a reverse J-shaped curve. The effects of cold stress were immediate and long-lasting, whereas the effects of heat stress were non-significant. Compared with the optimal equivalent temperature (71st percentile of UTCI, 29.22 °C), the relative risks for cumulative (0–21 days) exposures to cold stress (1st percentile, − 0.13 °C; 5th percentile, 7.68 °C) were 1.55 (95%CI:1.28,1.88) and 1.44 (95%CI:1.22,1.69), respectively. Thermal (cold and heat) stress was responsible for 10.81% (95%eCI: 5.67%,15.43%) of EADs for cardiovascular diseases, with 9.46% (95%eCI: 3.98%,14.40%) attributed to moderate cold stress (2.5th ~ 71st percentile). Greater susceptibility to cold stress was observed for males and the elderly. Heat stress showed harmful effects in the warm season.ConclusionsOur results demonstrated that cold exposure elevates the risk of EADs for cardiovascular causes in Shenzhen, and moderate cold stress cause the highest burden of ambulance dispatches. Health authorities should consider effective adaptation strategies and interventions responding to cold stress to reduce the morbidity of cardiovascular diseases.

Brain-derived neurotrophic factor in older adults exposed to simulated indoor overheating.

Brain-derived neurotrophic factor (BDNF) is a neuroprotective growth factor that increases in young adults during short, intense bouts of passive heat stress. However, this may not reflect the response in heat-vulnerable populations exposed to air temperatures more consistent with indoor overheating during hot weather and heatwaves, especially as the BDNF response to acute stressors may diminish with increasing age.We therefore evaluated the ambient and body temperature-dependent responses of BDNF inolder adults during daylong passive heating. Sixteenolder adults (6 females; aged 66-78years) completed 8-h exposure to four randomized ambient conditions simulating those experienced indoors during hot weather and heatwaves in continental climates: 22°C (air-conditioning; control), 26°C (health-agency-recommended indoor temperature limit), 31°C, and 36°C (non-airconditioned home); all 45% relative humidity. To further investigate upstream mechanisms of BDNF regulation during thermal strain, we also explored associations between BDNF and circulating heat shock protein 70 (HSP70; taken as an indicator of the heat shock response). Circulating BDNF was elevated by ~ 28% (1139 [95%CI: 166, 2112] pg/mL) at end-exposure in the 36°C compared to the 22°C control condition (P = 0.026; 26°C-and 31°C-22°C differences: P ≥ 0.090), increasing 90 [22, 158] pg/mL per 1°C rise in ambient temperature (linear trend: P = 0.011). BDNF was also positively correlated with mean body temperatures (P = 0.013), which increased 0.12 [0.10, 0.13]°C per 1°C rise in ambient temperature (P < 0.001). By contrast, serum HSP70 did not change across conditions (P ≥ 0.156), nor was it associated with BDNF (P = 0.376). Our findings demonstrate a progressive increase in circulating BDNF during indoor overheating in older adults.

Drivers of summer Arctic sea-ice extent at interannual time scale in CMIP6 large ensembles revealed by information flow

Arctic sea-ice extent has strongly decreased since the beginning of satellite observations in the late 1970s. While several drivers are known to be implicated, their respective contribution is not fully understood. Here, we apply the Liang-Kleeman information flow method to five different large ensembles from the Coupled Model Intercomparison Project Phase 6 (CMIP6) over the 1970-2060 period to investigate the extent to which fluctuations in winter sea-ice volume, air temperature and ocean heat transport drive changes in subsequent summer Arctic sea-ice extent. This allows us to go beyond classical correlation analyses. Results show that air temperature is the most important controlling factor of summer sea-ice extent at interannual time scale, and that winter sea-ice volume and Atlantic Ocean heat transport play a secondary role. If we replace air temperature by net shortwave and downward longwave radiations, we find that the sum of influences from both radiations is almost similar to the air temperature influence, with the longwave radiation being dominant in driving changes in summer sea-ice extent. Finally, we find that the influence of air temperature is more prominent during periods of large sea-ice reduction and that this temperature influence has overall increased since 1970.

Changing climate intensifies downstream eutrophication by enhancing nitrogen availability from tropical forests

The contribution of diffuse nutrient exports from forests to downstream water bodies is significant owing to their extensive spatial distribution across watersheds. However, the intricacies of coupling mechanism between diffuse nutrient exports and meteorological factors driving downstream eutrophication remain poorly understood. Multiple methods involving field sampling, laboratory analysis, and model simulation were utilized to investigate the impact of diffuse nutrient exports from tropical forests on chlorophyll a concentration dynamic in the downstream reservoir. A strong positive correlation was observed between air temperature and chlorophyll a concentration, indicating the direct influence of climatic factors on microalgal biomass. The significant positive linear relationship was also observed between diffuse nitrate exports and chlorophyll a concentration, with a regression coefficient of 0.36 (P < 0.001), underscoring the role of nitrogen inputs in stimulating microalgal growth. The interplay between diffuse nitrate exports and meteorological factors was shown to regulate chlorophyll a concentration fluctuation. Additionally, the structural equation model revealed that increasing temperature and decreasing precipitation could elevate chlorophyll a concentration by enhancing nitrogen availability. Monte Carlo simulation results further revealed that temperature and precipitation were the most influential factors affecting chlorophyll a concentration during dry and rainy seasons, with sensitivity values of 0.94 and − 0.76, respectively. Notably, the eutrophication status was projected to deteriorate from light to moderate under diminishing precipitation conditions. These findings underscore the urgency of addressing eutrophication risks in reservoirs surrounded by tropical forests and the implementation of effective nitrate mitigation strategies is imperative, which offers theoretical guidance for the management of eutrophic water restoration within tropical rainforest regions under changing climate conditions.

A micro-scale look into pedestrian thermophysiological comfort in an urban environment

Different spatial scales enable the analysis of thermophysiological conditions of pedestrians in an urban environment. A higher resolution hotspot analysis was conceived using GIS technology in some areas of Lisbon with different morphological conditions. Eleven hotspots were found across six study areas, located in high to moderate urban density conditions and in different types of urban spaces. So, six hotspots were found in avenues (high urban density conditions), three in streets, and two in general open spaces (moderate urban density conditions). These spaces are characterized by being busy areas with high anthropogenic influence, with high-absorbing and reflective materials, and with very poor green infrastructure. Environmental conditions, namely, radiation, mean radiant temperature, and air temperature, were the main cause of hotspot existence, and the main propellers for UTCI intensification. The urban density variable was also found to be important, especially in avenues and open spaces. In these areas, the adjusted component for environmental and urban density conditions can increase 0.60 to 1.35 °C in open spaces and 0.30 to 0.60 °C in avenues, each time there is a one-unit increase in the component. Trees, either in the street or in parks, have generally been found to decrease the UTCI.

Quantifying human thermal adaptation for indoor environments through field surveys and climate chamber experiments

ABSTRACT Thermal comfort boundaries established through climate chamber experiments are often found to significantly vary in real-world conditions based on the potential for thermal adaptation. In this context, this research aims to quantify the extent of thermal adaptation using a personalized ventilation system. We hypothesize that a personalized ventilation system can enhance thermal adaptation compared to real-world settings with limited opportunity for thermal adaptation. The study is based on thermal comfort surveys in mixed-mode open-plan office spaces of a humid subtropical region (Cwa), and a controlled climate chamber with a provision for personalized ventilation. We obtained 5629 subjective thermal responses through longitudinal field surveys accompanied by environmental measurements. In a climate chamber, 16 acclimatized volunteers were subjected to 140 different set-points with air temperature (Ta), relative humidity (RH), and air velocity (Va) variations yielding 19,200 subjective responses. A thermo-neutral temperature (Tn) of 26.5°C with an acceptability band of ±5.9°C was obtained through the field surveys. The Tn obtained from climate chamber surveys varied from 28.0°C to 29.3°C with an acceptability band of ±3.6°C depending on the ventilation rate. An empirical relationship between thermal sensation vote (TSV) and multiple environmental variables (Calidity) suggests 2°C higher Tn for Caliditychamber, Thermal adaptation correction factor of 2.1°C for warm-dry indoor environment and 1°C for warm-humid indoor environment were deduced through comparative analysis.

Monitoring of volcanic precursors using satellite data: the case of Taftan volcano in Iran

Abstract In recent weeks, there have been reports of gas emanations from the crater of the dormant Taftan volcano in Iran. In this study, due to the limitations of ground stations and the advantages of satellite remote sensing, it has been tried to detect possible anomalies using the plasma data measured by Swarm (A, B and C) and GPS (Global Positioning System) satellites around the location of the mentioned volcano. Also, lithospheric and atmospheric data including OLR (Outgoing Longwave Radiation), water vapor, ozone, relative humidity, surface and air temperature, AOD (Aerosol Optical Depth), sulfur dioxide (SO2) and nitrogen dioxide (NO2) using the Giovanni website in a period of about 5 months, were downloaded and analyzed. Using the median and interquartile method, possible anomalies were detected in the pre-processed time series of the desired parameters. To justify some of the non-volcanic anomalies, synoptic data including precipitation and temperature were prepared from the nearest ground station. By rejecting the possibility that some detected anomalies are related to volcanic activities, hypotheses were presented for other proposed anomalies. As a result of this research, the capabilities of Swarm satellites and GPS-TEC (Total Electron Content) are emphasized in studies related to the prediction, detection and tracking of volcanic activities and it is shown that by comparative comparison with other lithospheric and atmospheric precursors, uncertainty in eruption prediction can be reduced.

Experimental and numerical research on the thermal performance of a vertical earth-to-air heat exchanger system

The Earth-to-Air Heat Exchanger (EAHE) system is an efficient and clean geothermal application technology that can be used for pre-cooling in summer and heating in winter. This paper proposes a novel Vertical Earth-to-Air Heat Exchanger (VEAHE) system that uses baffles to divide the vertical duct into two ventilation tunnels with a hollow area at the bottom for air circulation. This system occupies a small land area and has a relatively high geothermal energy utilization efficiency. This study evaluates the thermal performance of the system through experimental tests under various operating conditions. Additionally, a numerical model of the system was established to explore the influence of baffles length, thickness, and duct depth on its thermal performance. The experimental results show that the 2.5-meter deep VEAHE system achieves an average air pre-cooling temperature reduction of 5.42 °C, with a maximum temperature reduction of up to 7.58 °C. Below the 1.2-meter mark of the system, the cooling capacity of the descending pipe is 1.52 times that of the ascending pipe. The simulation showed a Maximum Absolute Relative Error (MARE) of 3.15 % compared to the experimental results. As the length and thickness of the baffles, duct length, and soil thermal conductivity increase, the average outlet air temperature gradually decreases, while the system's heat exchange capacity significantly improves, in contrast to the duct diameter. Among the influencing factors, the duct length has the greatest impact on the system. Under the recommended configuration, the system's maximum pre-cooling potential is 915.90 W, with the outlet air temperature ranging from 12.05 °C to 14.79 °C.

Construction of a comprehensive meteorological risk index for wheat Fusarium head blight prediction based on more than a half-century of monitoring data.

Fusarium head blight (FHB) represents a critical threat to wheat production globally, not only reducing yields but also contaminating crops with harmful mycotoxins. This study aimed to elucidate new spatiotemporal patterns of FHB incidence and to develop a comprehensive meteorological risk index to enhance scientific prevention and control of the disease. Through the analysis of annual and decadal variations from 1965 to 2023, the study assessed FHB trends across four agricultural regions (I, II, III, and IV) in Jiangsu Province, located in the middle and lower reaches of the Yangtze River-a hotspot for FHB in China. Key findings include: Since 1965, Regions I and III consistently exhibited higher FHB incidence rates compared to Regions II and IV. Post-2000, there was a notable increase in years with high incidence rates, with Region III overtaking Region I as the region with the highest incidence. Since 2010, occurrences of FHB reaching the most severe grade (Grade 5) have surpassed those in previous decades across all regions. The study also revealed a stronger correlation between meteorological factors (cumulative precipitation, number of days with rainfall ≥ 0.1 mm, total rainy days with ≥ 2 and ≥3 consecutive days of rain, total rainy days with both average daily air temperature ≥ 15 °C and daily rainfall ≥ 0.1 mm, days with average daily relative humidity ≥ 85%, cumulative sunshine hours, and cumulative cloudy days) and the FHB incidence rates during the heading-flowering-grain filling period in Regions I, II, and III, compared to the heading-flowering period alone. This indicates that optimal temperature and high humidity during the grain filling stage significantly contribute to the final FHB incidence rates. Despite the less apparent correlation between temperature changes and disease rates, the significant warming trend observed since 2000 has likely fostered conditions conducive to the proliferation of FHB. The comprehensive meteorological risk index, constructed to incorporate key meteorological factors during the heading-flowering-filling period, showed a strong correlation with actual disease incidences. The index demonstrated fitting accuracy rates of 84.7% for Region I, 72.9% for Region II, 83.1% for Region III, and 90.9% for Region IV, underscoring its effectiveness in predicting FHB occurrences. This tool offers both convenience and practicality, providing valuable insights for strategically managing FHB risks based on local weather conditions.

Assessing the Cooling Potential of Vegetation in a Central European Rural Landscape: A Local Study

This study investigates the cooling potential of vegetation in rural landscapes of the Czech Republic to mitigate heat-related issues. Using remote sensing, the Cooling Capacity Index (CCI) is assessed to measure green spaces’ ability to lower air temperatures using evapotranspiration and shading. Landsat 8/9 and meteorological data are utilised, with CCI calculated based on vegetation cover, albedo, and evapotranspiration. Our results demonstrate significant variations in cooling capacity across different land use types. Forests exhibited the highest cooling potential, while urban areas, characterised by heat-absorbing materials, displayed the least. We analysed temporal and spatial variations in cooling capacity using various visualisation tools and validated the results against the InVEST software (v3.14.0). This study highlights the effectiveness of remote sensing in quantifying ecosystem functions, particularly the cooling services provided by vegetation. Our findings emphasise the crucial role of vegetation in mitigating urban heat islands and addressing climate change. This research provides valuable insights for developing climate change adaptation strategies in rural landscapes.

Assessment of the influence of climatic factors on the state of terrestrial ecosystems in the Northwestern region of Russia

The article analyzes the change of climatic conditions in the Northwest of Russia, including the characteristics of dangerous hydrometeorological events (cold and heat waves, strong winds, extreme rainfall, snowfall, ice-frost deposits, hail) and slow climatic changes (increase in the number of days with the transition of air temperature through 0°С, coastal abrasion) in connection with their negative impact on terrestrial ecosystems. It was found that the influence of meteorological and climatic factors on terrestrial ecosystems is most pronounced in the northern part of the studied region, especially on the coast of the Barents Sea. Towards the south, the values of all indicators gradually decrease, and their structure changes. In the northern part of the study area (Murmansk and Arkhangelsk oblasts, the Nenets Autonomous Okrug), phenomena associated with strong winds and intensive ice-frost deposition, which contribute to the formation of an ice crust on the Earth’s surface, prevail. As one moves away from the coast, severe frost is observed more often (Komi Republic). In the center and south of the region, heavy rainfall, severe frost, and intense heat are the most frequent, resulting in a high fire hazard. The study carried out the ranking of the subjects of the Northwestern Federal District according to the degree of intensity of this process. Comprehensive assessments of the negative impact of changing climatic conditions on terrestrial ecosystems can be used to make decisions on the development of a strategy for environmental security of the regions of the Russian Federation.

Performance assessment of a high-efficiency indirect dew-point evaporative cooler through three-dimensional modeling

The escalating demand for eco-friendly air cooling, driven by concerns over global warming, necessitates sustainable alternatives to air conditioners. Dew-point evaporative coolers offer a green alternative yet face challenges due to high flow resistances caused by the U-turn of the working air. Recently, we have developed a new compact counterflow dew-point cooler that eliminates the U-turn of the working air, mitigating flow resistance. In this paper, a precise three-dimensional simulation, based on fluid dynamics, heat transfer and mass transportation, is developed to assess the cooler's performance. The validation against experiments shows maximum 8 % deviation in input pressure and 3 % in product air temperature. The simulation provides insights into the cooler's operation, efficiency, and performance, which are not easily obtained experimentally. Optimal cooling coefficients of performance occurs at working ratios of 0.5–0.6. Notably, while metallic channel separator excels at higher flow rates, plastic ones like high-density polyethylene and polycarbonate match performance at lower rates. Furthermore, the cooler performs better in hotter, drier climates. In locales like Xian and New Delhi, the cooler is suitable for standalone use, while in regions like Dubai, Texas, Singapore, Beijing, and Monterrey, it can be coupled with air conditioners to enhance the ventilation and energy efficiency.

MATHEMATICAL MODELLING OF DRYING PROCESS

The aim of this study is to experimentally investigate the drying kinetics of common basil using a solar drying unit. The tests consist in studying the effect of constant and variable drying air temperature on the drying kinetics. In this empirical approach, we aim to determine and compare drying characteristic curves under conditions where the drying air temperature is constant or variable. Subsequently, correlations describing the drying rate will be developed, these will be used at a later stage to size and model the solar dryer. Few numerical models have been used in the literature to explain the drying kinetics of common basil, in fact, given the complexity of the transport mechanisms and the diversity of products, a single model cannot represent all situations. This justifies an experimental study in the laboratory to determine the drying kinetics of a particular product.

Waterborne novolac epoxy‐based thermal resistant and fire‐retardant thermal insulation coatings

AbstractWaterborne novolac epoxy based thermal resistant and fire‐retardant thermal insulation coatings were developed in this work. Novolac (phenolic) epoxy emulsion (PEE) was prepared by the phase inversion method based on formulation optimization by orthogonal array testing. The prepared emulsions have similar particle size, viscosity, and stability to commercial bisphenol a glycidyl ether epoxy emulsion (PZ). DSC results showed that the varnish film based on PEE had a higher glass transition temperature and initial thermal decomposition temperature compared with PZ cured by the same curing agent. Waterborne thermal insulation coating with PEE and PZ as binders and hollow glass microspheres (HGMs) as thermal insulation fillers were studied. The results indicated that the thermal conductivity of the coating decreased with an increase in HGMs content. Specifically, the thermal conductivity of the PEE coating containing 20 wt% HGMs is as low as 0.093 W/(m·K). It reduces the exterior temperature of the hot tank from approximately 200 °C to approximately 106 °C. Furthermore, the HGMs/PEE waterborne thermal insulation coating exhibits good thermal stability and flame retardance.

Thermal preference and pleasantness of a students’ population in a coastal urban area during summer

In thermal comfort research, two main domains are identified: objective and subjective. This study focusses on the latter, examining various aspects of preference, sensation, and pleasantness. It also clearly distinguishes each concept and sets the groundwork for their standardised use in urban planning and urban climate studies. Additionally, this study emphasises the often-overlooked geographical perspective, aiming to address previous gaps in this research area. Environmental conditions were found to be the main determinants influencing pedestrians' thermal sensation, preference, and pleasure. Key factors include air temperature, solar radiation, and wind speed, which exhibit strong correlations with pleasure responses. Additionally, urban density, clothing type and colour, shading, sex, and weather type significantly impact thermal sensation and reported pleasantness. It was observed that people who overdressed for the season, wore dark or warmer clothes, experienced air temperature and solar radiation more intensely. Similarly, those in high-density urban areas, without shade, or when weak continental wind conditions were observed, reported stronger thermal sensations. Women generally sensed air temperature and solar radiation as more intense compared to men. These factors influence thermal pleasantness, varying in importance, spatial distribution, and statistical relationship. Higher wind speeds, particularly from an Atlantic direction, were found to enhance thermal pleasantness by balancing conditions and reducing thermal sensation votes for air temperature and solar radiation. Green areas also increased thermal pleasantness by lowering air temperature and solar radiation sensations and promoting a sense of happiness among pedestrians.

The Effects of Air Quality and the Impact of Climate Conditions on the First COVID-19 Wave in Wuhan and Four European Metropolitan Regions

This paper investigates the impact of air quality and climate variability during the first wave of COVID-19 associated with accelerated transmission and lethality in Wuhan in China and four European metropolises (Milan, Madrid, London, and Bucharest). For the period 1 January–15 June 2020, including the COVID-19 pre-lockdown, lockdown, and beyond periods, this study used a synergy of in situ and derived satellite time-series data analyses, investigating the daily average inhalable gaseous pollutants ozone (O3), nitrogen dioxide (NO2), and particulate matter in two size fractions (PM2.5 and PM10) together with the Air Quality Index (AQI), total Aerosol Optical Depth (AOD) at 550 nm, and climate variables (air temperature at 2 m height, relative humidity, wind speed, and Planetary Boundary Layer height). Applied statistical methods and cross-correlation tests involving multiple datasets of the main air pollutants (inhalable PM2.5 and PM10 and NO2), AQI, and aerosol loading AOD revealed a direct positive correlation with the spread and severity of COVID-19. Like in other cities worldwide, during the first-wave COVID-19 lockdown, due to the implemented restrictions on human-related emissions, there was a significant decrease in most air pollutant concentrations (PM2.5, PM10, and NO2), AQI, and AOD but a high increase in ground-level O3 in all selected metropolises. Also, this study found negative correlations of daily new COVID-19 cases (DNCs) with surface ozone level, air temperature at 2 m height, Planetary Boundary PBL heights, and wind speed intensity and positive correlations with relative humidity. The findings highlight the differential impacts of pandemic lockdowns on air quality in the investigated metropolises.

Atmospheric Transport of Semivolatile Organic Contaminants across an Urban-Alpine Boundary.

Current understanding of atmospheric transport of semivolatile organic contaminants (SVOCs) in alpine areas is limited due to complex meteorology and topography. Salt Lake City, Utah borders protected wilderness areas in the Wasatch Mountains, exhibiting a useful model system in which an urban source of SVOCs, including polyaromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs), is located directly adjacent to an alpine sink. Our objective was to investigate the impacts of topographical features on the transport and deposition of SVOCs across an urban-alpine boundary. To do so, we measured PAHs and PCBs in soils along a transect starting at the urban-mountain interface and extending into an alpine wilderness, crossing several prominent ridgelines. Concentrations of PAHs and PCBs in soils were heavily influenced by soil organic carbon content, air temperature, and proximity to the urban boundary. However, the role of source proximity was only revealed after normalizing concentrations in soil to organic carbon content and air temperature. Further, we present evidence of SVOC emission/deposition cycles driven by diurnal alpine winds that do not extend past topographical features. Our results illustrate the roles of multiple competing processes on SVOC transport in alpine systems and their importance at an urban-alpine boundary.