Limited Ventilation Research Articles

Thermal characteristics of ghosting flame in coal mine dead-end roadway pool fires affected by fire locations

As an important phenomenon in the evolution of fire, the ghosting flame exhibits dynamic and irregular behavior in environments with limited ventilation. By ghosting flame, we mean the phenomenon where the flame separates from the fuel surface under certain conditions. This study investigates the combustion characteristics of the ghosting flame in pool fires within a coal mine dead-end roadway by small-scale experiments. Results indicate that the ghosting flame appears more readily and earlier when the fire source is closer to the heading face or when the oil pan size is larger. Additionally, the fire source's location significantly influences the type of ghosting flame observed. When the fire source is near the heading face, the flame predominantly exhibits horizontal-type ghosting flame; however, when the fire source is at the entrance of the roadway, only the edge-type ghosting flame occurs. Furthermore, dead-end roadway fires easily transition to ventilation-controlled conditions, leading to a continuous increase in the mass loss rate. The occurrence of a ghosting flame does not result in a sudden change in the mass loss rate. Moreover, the transient oxygen volume fraction when the ghosting flame occurs is related to the ghosting flame type and is also affected by ventilation conditions, fuel types, roadway structure, and the location of measurement points. Importantly, the root cause for the occurrence of the ghosting flame lies in the pressure differential generated by the temperature disparity between the two sides of the fire source.

Assessment of the Ergonomic Exposures for Home Healthcare Workers in the United Kingdom

Home healthcare has been identified amongst the most hazardous industries in healthcare. Many of the tasks being conducted by home healthcare workers are associated with significant demands including physical demands such as mobility and repositioning activities as well as psychological demands which is attributed by dealing with a complex environment whilst administering medical and life saving care to patients, and social demands that encompasses dealing with dying and grieving patients. With the homes in United Kingdom having potentially unique exposures due to the healthcare system and design of the homes such as multi-floors, smaller condensed rooms, and limited ventilation, the purpose of this study was to investigate the exposures for home healthcare workers in the United Kingdom. Ergonomic hazards were observed through various tasks such as repositioning in bed (34.8%), transfer from bed to chair (30.4%), transfer from bed to chair (26.1%), and transfer from chair to chair (26.1%) and particularly for nursing aides. Lifting hoists were only used 13 times (19%) and predominantly by nursing aides (12 of 13, 92%). A slip sheet or slide board was used 7 times (10.1%), all being nursing aides using them.

Field Investigation on the Thermal Environment and Comfort of People Exercising in a Fitness Center

A favorable thermal environment in fitness centers is important to attract more members and is beneficial to the health of exercising people. The purpose of this study was to research the actual thermal environment of a typical fitness center in different seasons and the thermal requirement of exercising people. A field investigation covering winter, spring, and summer was conducted. The environmental parameters were measured. Subjective questionnaires involving individual information, clothing insulation, thermal sensation, etc., were collected. Participants’ heart rates were tested to estimate their metabolic rate (MR). A total of 740 valid questionnaires were collected. The results showed that a scissors gap existed between the predictive mean vote (PMV) and the thermal sensation vote (TSV) for the exercising people. For the higher MR group, there was a separation between the TSV and thermal preference vote, e.g., most participants would not prefer to cooler or warmer thermal environment when they felt hot or cold. The CO2 concentration changed greatly among seasons and the distribution in the fitness center was not uniform. With mechanical ventilation, the CO2 concentration in summer was the lowest. In other seasons it became much higher due to limited natural ventilation. However, subjective response to indoor air quality showed no significant difference among seasons. The participants felt more satisfied to the overall thermal environment in the transition season. The results can be referenced in the thermal environment management in fitness centers during seasonal changes.

PENINGKATAN KUALITAS HUNIAN PADA PERMUKIMAN PADAT DI RW 02, KELURAHAN KRENDANG, JAKARTA BARAT

The settlement in RW 02, Krendang sub-district, Tambora district, West Jakarta, is a dense and unorganized urban settlement resulting from an unplanned incremental growth process. Apart from poor environmental sanitation conditions, this settlement has a low quality of residential space with very limited natural lighting and ventilation due to the closeness of the buildings and the lack of open space. This settlement is the location for implementing a community service program which aims to help the West Jakarta government deal with the city's slum problem by involving community participation to improve the quality of residential space. The initial program in 2023 aims to open people's minds about the importance of healthy residential spaces, and to make this happen can be done using simple, low-cost methods. In the next stage, sustainable programs will be continued until a model of healthy, low-cost housing is realized in this settlement. A series of community service activities have been carried out with the culmination of counseling activities for social treatment to build collective insight and awareness among residents. The counseling took place at the community hall, attended by RW administrators as well as RT representatives and community leaders within RW 02. The counselor team used pictures of simulation designs for the renovation of multi-purpose buildings and pre-school children's education in RW 02 as counseling aids. Based on pre-test and post-test data through filling out questionnaires by participants, it shows a significant increase in collective awareness regarding the program objectives.

Assessment of the urban pollution island intensity in Rome (Italy) from in-situ PM measurements

The Urban Pollution Island (UPI), describing the temporal and spatial distribution of pollutants’ concentration attributed to the presence of urban features and activities, is one of the major problems affecting urban areas and has become more severe with rapid urbanization. To correctly evaluate the UPI Intensity (UPII), i.e., the difference in pollution concentration between the urban agglomeration and its rural surroundings, it is crucial to carefully select rural and, above all, urban reference stations, as local factors such as orography, location of the air quality monitoring stations, and street orientation can significantly impact UPII values. In this work, the UPII in Rome (Italy) is determined using daily-averaged concentrations of PM10 and PM2.5 collected by in-situ stations over the period 2018–2023. Three different methods for the assessment of UPII are tested and compared by varying the sub-set of selected urban stations, according to their environmental classification. The approach proposed will have significant implications on the management of urban environment and on the tailored design of urban air quality improvement strategies.Results show slight differences in the monthly-averaged concentrations of both PM10 and PM2.5 between the “urban traffic” and “urban background” stations, suggesting that the proximity of the emission sources to the monitoring stations moderately influences the concentrations, potentially due to limited ventilation within street canyons, which can inhibit mixing processes. The annual variation of UPII reveals that PM10 is more sensitive to the selection of the stations particularly during winter, when the differences between the three assessment methods reach 100%. Our findings also indicate that, in the case of Rome, using the largest number of stations available in the urban area could enhance the UPII evaluation, taking into consideration the urban structure and the specific characteristics of local emission sources. The results presented here, although related to a single city, demonstrate that the selection of urban stations for the evaluation of UPII is not straightforward and requires further investigation.

Enhancing Energy Conservation, Visual and Thermal Comfort in Small Houses of Karachi

The significance of housing in developing cities cannot be overstated, as individuals strive to acquire and own physical assets throughout their lives, even in the case of small plots as modest as 80 square yards. In urban areas such as Karachi, smaller houses ranging from 80 to 240 square yards mostly are predominantly constructed by contractors or by owners themselves. This is to avoid additional fees charged by architects who may tailor the design to suit the context and specific requirements. Consequently, these houses tend to exhibit a similar layout, maximizing the utilization of allowable space as stipulated by the bylaws. However, this approach often leads to limited natural ventilation and daylighting, resulting in increased energy consumption for thermal and visual comfort. Hence, the current research underscores the urgency of addressing the prevailing lack of natural ventilation and daylighting in these houses. To address these concerns, it presents a comprehensive framework of passive strategies aimed at enhancing the thermal and visual comfort of occupants. Firstly, an archival study was conducted, encompassing a comprehensive literature review, which served as a foundation to understand the subject matter. Secondly, a comparative study was undertaken to examine conventional small house typical plans prevalent in Karachi. This study was followed by the formulation of proposals for improved planning. Various secondary resources were utilized to support the comparative analysis of two typical house plans in Karachi, in conjunction with the proposed passive strategies. Through the application of these strategies, occupants can benefit from improved comfort, reduced energy consumption, and heightened well-being.

Employing PCM vests to improve the thermal comfort for staff wearing mascot costumes in summer

Due to the high thermal resistance, limited ventilation efficiency, and substantial weight of mascot costumes, staffs wearing mascot costumes in summer are subjected to significant thermal stress, resulting in physiological strain and posing a grave threat to their health. To improve the thermal comfort of staff wearing mascot costumes, this study employed a phase change material (PCM) vest with a phase-change temperature of 26 °C as a cooling measure. The 32 participants were recruited and randomly divided into two groups to analyze the effect of the PCM vest. The results showed that, participants wearing mascot costumes along with an additional PCM vest underneath (MC-PCM) experienced a decrease in oral temperature by 0.06 °C and mean skin temperature by 0.63 °C, compared to those wearing common mascot costumes (CMC). However, there was an increase in body-mass loss relative to initial weight by 0.045 % and heart rate by 5.08 bpm. Wearing the additional PCM vest can improve humidity sensation and thermal sensation, In addition, the average thermal comfort voting score of participants wearing MC-PCM was 0.24 lower than that of participants wearing CMC. It was showed that employing a PCM vest reduced heat stress evidently in staff wearing mascot costumes in high-temperature environments and improved their thermal comfort.

Experimental and Theoretical Investigation of Longitudinal Temperature Attenuation and Smoke Movement in Urban Utility Tunnel Fires

The urban utility tunnel is an indispensable part of modern engineering construction. However, the fire risk cannot be ignored due to the narrow space and limited ventilation of the utility tunnel. A study of smoke filling is performed in a 1/8-scaled utility tunnel (25 m × 0.5 m × 0.45 m). Five heat release rates (5, 10, 15, 20 and 25 kW) and four positions of fire sources are used for tests. The initial position of the one-dimensional smoke movement of strong plume is determined. Based on the traditional model, the longitudinal temperature attenuation model of tunnel smoke is established with consideration of radiation and convection heat losses. The theoretical value of the longitudinal temperature rise of smoke is in good agreement with the experimental value. A one-dimensional spreading velocity model is established that coincides well with the experimental value, and the relative error is less than 20%. The spreading velocity of smoke is increased by the heat release rate. The velocity of the smoke spreading at the near end is smaller than that at the center, due to the long spreading route. The current conclusions disclosed in this study provide important guidance for the ventilation design of utility tunnels for fire smoke scenarios.

DEVELOPMENT OF ULTRASTRUCTURAL CHANGES IN DIAPHRAGM MUSCLE FIBERS DURING PARTIAL TRACHEAL STENOSIS IN YOUNG SEXUALLY IMMATURE RATS

Introduction. The study of congenital pathology of the respiratory tract in children is of great importance for theoretical and clinical pediatric otolaryngology. Currently, in the scientific literature there are single works concerning the study of the pathogenesis and clinic of laryngomalacia. First of all, this concerns the effect of acute and chronic hypoxia on the muscles of the respiratory system, in particular, the diaphragm. The aim of thіs work is to reveal the effect of hypoxia on the development of pronounced structural and functional changes in the diaphragm muscles of sexually immature animals when modeling partial tracheal occlusion. Materials and methods. Surgical partial occlusion of the trachea was performed on in sexually immature Wistar rats; we applied electron microscopy, morphometric and statistical research methods.
 Results. The obtained data demonstrated that the muscle fibers of the diaphragm are characterized by significant structural, functional and metabolic resistance to the development of acute or chronic hypoxia due to limited lung ventilation in rats. The density of muscle fibers did not change in any of the used terms of the experiment (7 and 21 days). On the 7th day of hypoxic exposure, a change in the state of the matrix of mitochondria of muscle fibers was observed, which was accompanied by partial ultrastructural rearrangements of the organization of these organelles. At the same time, no significant changes were observed during histological studies. Electrongrams demonstrated the ultrastructural damages were mainly limited to focal reduction of myofibrils and an increase in the mitochondria's diameter and found as especially pronounced on day 21 (a state of chronic hypoxia) on the muscular component of the respiratory system in rats. These changes are accompanied by the development of dystrophic disorders in the diaphragm myofibrils. On day 21 changes in the transendothelial transport of substance molecules were also detected. This was based on establishing the fact of a significant reduction in the number of pinocytosis vesicles in the cytoplasm of endothelial cells of diaphragm hemocapillaries in animals with partial tracheal occlusion. Disruption of the structural organization of actomyosin complexes was revealed in muscle fibers due to pathological changes in the mitochondria of myofibrils. It should be noted the development of destruction or complete loss of an important ultrastructural component of muscle fibers, Z-lines. These changes were completely absent on the 7th day following the influence of partial tracheal occlusion and the development of acute hypoxia. Moreover, on day 21, partial lysis of a significant amount of myofilaments of muscle fibers was observed. In addition, the development of the process of fiber swelling was detected against the background of which the above-mentioned ultrastructural destruction of the muscular component in the diaphragm was observed. These changes indicate the need for earlier treatment of laryngomalacia in children. The delay in surgical intervention leads to the development of severe or irreversible structural changes not only in the respiratory organs, but also in their muscular system.
 Conclusion. The muscular elements of the diaphragm have the pronounced and significant resistance to the state of hypoxia under conditions of limited ventilation of the respiratory tract. Ultrastructural and morphometric data, found on the 21st day after the modeling of partial tracheal stenosis, are not only of a compensatory and adaptive in nature, but also signs of pronounced disorders in the muscle fibers of the central part of the diaphragm in test animals.

Comparative Analysis of Thermal Comfort in Residential Buildings: A Study of the impact of Urban Density, Height, and Layout Patterns in the Context of Dhaka

The thermal environment of residential spaces significantly influences residents’ physical and emotional well-being, affecting daily activities and overall quality of life. With a growing global emphasis on sustainability, energy efficiency, and healthy living understanding how architectural and urban elements impact thermal comfort becomes crucial. This study focuses on Dhaka, Situated in a tropical monsoon climate, this context presents unique challenges for ensuring thermal comfort within structures. The research conducts a comparative analysis of two residential structures with different layout configurations but similar orientations, situated in diverse urban settings with varying levels of density, exposure and openings. Investigating the influence of urban density, adequate openings, shading within the plan layout, and vertical positioning of structures on residents’ thermal comfort, the study employs extensive field data collection, observation, questionnaire survey and simulation. The findings indicate that high-density residential areas offer advantages such as reduced direct heat intake and loss, yet may encounter challenges including limited natural ventilation and increased heat absorption, resulting in elevated indoor temperatures. Conversely, low-density areas with open spaces benefit from enhanced natural ventilation and reduced heat accumulation, leading to improved thermal comfort, particularly in hot and humid conditions. This paper underscores the significance of considering architectural and urban aspects in residential buildings in Dhaka’s context to ensure the thermal comfort and well-being of residents. By addressing these factors, designers and urban planners can contribute to creating healthier and more sustainable living environments amidst changing climatic conditions.

Innovative Photovoltaic Cooling System

With the ever-increasing adoption of solar energy and the lack of space for PV installations, targeting maximum photovoltaic operational efficiencies has become essential. One of the key challenges faced by PV installations in warm climates is thermal management, which is caused by increasing temperatures due to PV conversion inefficiencies and limited ventilation possibilities in certain installations. Despite prior art, further improvement is still needed to provide a novel system that can offer more efficient and controllable temperature decrease of photovoltaic modules in both land and offshore installations. The present invention, termed IPCoSy, satisfies the aforementioned needs in the art by providing a novel system for cooling a solar panel assembly, including at least one photovoltaic module having a plurality of solar cells generating electrical power and a PV junction box attached to the back of the photovoltaic module. A part of this invention discloses a new type of PV module that is a modification of standard commercial modules. This new PV module incorporates a water chamber at the back of a solar cell assembly to regulate operational temperatures. Another part of this invention presents an after-market cooling system that can be fitted to existing standard PV modules to add the cooling effect. This part of the invention presents solid and flexible water tanks that can be fitted directly into a gap at the back of standard PV modules. Moreover, this invention presents details on parts that distinguish this cooling system from prior art, such as an internal stream spreader to obtain better fluid dynamics and external fittings that allow the PV module to be installed at any tilt angle without jeopardising the cooling effect. Finally, this invention discloses different application areas of this cooling system, such as residential and industrial water heating, reverse osmosis plants and offshore photovoltaic installations, showcasing the product's versatility, adaptability and large market suitability.

Indoor environmental quality in an Apulian kindergarten

Indoor environmental quality (IEQ) in school buildings is crucial for the health and well-being of students, educators, and staff. Poor air quality and inadequate thermal conditions compromise students’ comfort and can lead to potential long-term health issues. Since children’s comfort differs from adults’, it is important to consider surveys on IEQ in school buildings. For this reason, this paper focuses on air quality and thermal comfort in kindergartens in Italy. An IEQ monitoring campaign was conducted within a kindergarten, with data used for thermal comfort and IAQ analyses, including CO2 levels generated by occupants and thermal discomforting hours. The simulations of carbon dioxide levels showed that the amount of CO2 accumulated in the classrooms exceeds the threshold recommended by ASHRAE guidelines. During the winter seasons, CO2 levels are significantly higher than those accumulated in summer due to the limited ventilation practiced during the colder months. Moreover, thermal comfort analyses indicate that the summer season can be problematic due to overheating: 42% of the occupied hours during the monitoring period exceeded the temperature threshold, causing thermal discomfort for the occupants. The winter thermal comfort analyses demonstrated that heating systems are essential to maintain temperatures within comfort thresholds.

Standardization of indoor radon measurements based on rational criterion for conformity assessment

Significant temporal variations in radon are observed in any buildings, including unoccupied buildings with limited ventilation. This fact causes serious difficulties in radiation monitoring to assess the compliance of premises with the requirements of the normative, which limits the annual average level of radon in buildings. Therefore, neither at the national nor at the international level has yet been solved the problem of standardizing the indoor radon measurement if the test duration is less than a year. An analysis of approaches to radon measurement, including an assessment of the effectiveness of regulation, shows very significant differences between practices established in different countries. For example, in Russia, rapid (no more than 20 min) measurements are mainly used and mitigation measures to protect existing buildings from radon are practically not carried out. In European countries, mainly long-term (at least two months) measurements are used, while mitigation measures are still relatively rare, with the exception of the UK and Sweden. In the USA, short-term (2–7 days) measurements are widely used, which are not only carried out, but also paid for by residents themselves, including mitigation measures. However, despite the established approaches to indoor radon monitoring in Russia and the USA, there is a persistent distrust among specialists in the results of shortterm and, especially, rapid measurements. In this regard, a compromise approach is proposed to standardize radon measurements based on a rational criterion by applying fundamental ISO/IEC concepts such as “measurement uncertainty” and “conformity assessment”. The rational criterion for conformity assessment allows using measurements of different durations, providing a given reliability when making a decision. It also proposes a rationale for optimizing indoor radon monitoring through the participation of not only professional inspectors, but also the population itself due to the possibility of introducing simple methods and inexpensive radon devices within the rational criterion.

Modelling the transmission and control of airborne infectious disease in healthcare settings

The transmission of airborne infectious diseases, such as tuberculosis (TB) and coronavirus disease 2019 (COVID-19), among healthcare workers (HCW) in healthcare settings (HCS), remains a public health concern. TB and COVID-19 transmission mostly occur in congregated and confined areas with limited ventilation per person through respiratory droplets from infectious individuals.

Experimental and numerical investigation on effects of air compressibility on dynamic performance of the damaged ship

This paper presents a detailed test procedure, including the test facilities, the design of the ship model and the releasing mechanism of the damaged opening. The aim is to analyze the effects of air compressibility on the flooding process and motion responses of the damaged ship. To assist in the explanation of the test results, necessary numerical simulations are performed. Through carrying out series of model tests, it was found that the limited ventilation level not only delays the flooding process but also affects the dynamic responses of the damaged ship. In addition, the test results verify the assumption of 10% full ventilation publihsed by the International Maritime Organization (IMO) while analyzing the applicability of this assumption to the single flooding compartment. The results also show that ensuring a proper ventilation level in the flooding compartments can mitigate gas-liquid interactions and thus improve the dynamic response of the damaged ship. Based on the research results in this paper, an 8% ventilation ratio can be preliminarily used as a reference standard for similarventilation designs. Finally, the obtained experimental data in this paper can be used as a benchmark for future reliability analysis of the numerical methods.

Experimental study on combustion characteristics of pool fires in a sealed environment

The results of a series of bench-scale pool fire experiments to explore the burning characteristics under a sealed environment are presented in this work.Although the oxygen fraction in the space gradually decreases by burning consumingin comparison to open conditions, the transient heat release rate can still be calculated using the PER approach using the in-situ measured oxygen fraction. The dimensionless flame height can still be calculated using the McCaffrey's model for open conditions, but a greater coefficient should be used because the flame burns in a ‘hunger’ mode when the oxygen fraction is low. The current non-sealed fire model for centerline temperature rise of pool fires is unsuitable for the sealed environment: the centerline temperature rise decreases more quickly than that predicted by Nasr's model developed for cases with a limited ventilation in the middle and later stages of the fire. A new engineering model has been developed in this study by curve fitting sealed fire test results. Pagni's law can still be suitable to describe the relationship between the frequency of flame oscillation and the diameter of a pool fire in a sealed environment, but the modified coefficients are required.

The combustion of torrefied biomass in commercial-scale domestic boilers

The use of solid renewable fuels in domestic-scale boilers, DSB is especially common in places where the distribution of other renewable energy sources is strongly limited (mountain and foothill regions). High moisture content and limited ventilation have a destructive impact on wood pellets' stability. Torrefaction of biomass is recognized as a possible way to enhance the wood pellets’ hardness under wet conditions. It was found that the maximal water uptake for torrefied biomass after its water immersion was only 18.7 wt%. In this work, the combustion performance and emission of main pollutants during the combustion of thermally–treated biomass are analyzed using two types of boilers: coal-fired 25 kWth (retort burner) and biomass-fired 10 kWth (pellets burner). The best results were obtained during the combustion of torrefied biomass in a 10 kWth DSB, i.e. emission of CO 218 g/GJ, SO2 2.5 g/GJ, NOx 111 g/GJ, and particulates 10.5 g/GJ, boiler efficiency of 90.23%. The combustion of torrefied biomass met the requirement of a 5th-class boiler according to the PN-EN 303-5 standard. Thermally–treated biomass can be used as a substitute fuel in DSB. Nevertheless, the boiler construction can be improved to obtain lower emissions of CO.

Experiments on Microclimatically adapt a courtyard to climate change

Climate change impacts biodiversity, the use of public spaces, as well as building energy demand, and health in Mediterranean cities. The courtyard is a common typology of private/public open space in the area, which, according to previous research, is substantially affected by climate change. The main reasons are to be found in limited ventilation and the significant amount of radiation received by upper surfaces. A preliminary microclimate, simulation-based evaluation of mitigation strategies to adapt and capitalize on climate changes is here performed through the assessment of a series of analyses using reference year 2020 and 2080. The study addresses a representative courtyard, San Sepolcro cloister (Parma, Italy). One mitigation strategy is explored, limiting direct solar radiation. The shading system, which reduces solar radiation, arises from a process of morphogenesis based on solar parameters and exploits a strategy with vertical structures typical of some cacti, following the biomimicry approach of imitating natural strategies. In this case, the imitation regards both form and function, as well as the generative process. The research was conducted through parametric and generative design in Rhino-Grasshopper and environmental analysis in ENVI-Met. The Universal Thermal Climate Index (UTCI) was the reference index for the assessment of thermal comfort. The shading system allows for improving thermal comfort, through protection from the sun’s rays and the non-obstruction of the vertical ventilation of the courtyard.

Limited ventilation of the central Baltic Sea due to elevated oxygen consumption

The Baltic Sea is known as the world’s largest marine system suffering from accelerating, man-made hypoxia. Notably, despite the nutrient load reduction policy adopted in the 1980s, the oxygen conditions of the Baltic Sea’s deep waters are still worsening. This study disentangles oxygen and hydrogen sulfide sources and sinks using the results from the 3-dimensional coupled MOM-ERGOM numerical model and investigates ventilation of the deep central Baltic Sea by the 29 biggest oxygen inflows from 1948 to 2018 utilizing the element tagging technic. Everywhere across the central Baltic Sea, except in the Bornholm Basin, a shift in oxygen consumption from sediments to water column and a significant positive trend in hydrogen sulfide content were observed. The most notable changes happened in the northern and western Gotland basins. Mineralization of organic matter, both in the water column and sediments, was identified as the primary driver of the observed changes. A significant negative trend in the lifetime of inflowing oxygen was found everywhere in the central Baltic Sea. It leads to the reduced efficiency of natural ventilation of the central Baltic Sea via the saltwater inflows, especially in the northern and western Gotland basins.

Evaluation of Photostationary and Non-Photostationary Operational Models for [formula omitted] Pollution in a Street Canyon

To predict pollutant concentration in urban areas, it is crucial to take into account the chemical transformations of reactive pollutants in operational dispersion models. In this work, we derive and discuss two photostationary (with constant or varying transformation rates) and one non-photostationary chemical models for NO − NO2−O3 pollution in a street canyon. In the analytical derivation, we focus on the chemical and transport time scales to evaluate the applicability of the models in different urban contexts. We then assess their performance in predicting NO2, NO and O3 concentration at three locations within an urban district by comparing the model predictions with measurements acquired in a field campaign. The results are in line with analytical speculations and highlight in which street types non-photostationary models can bring substantial advantages. In courtyards with limited ventilation and without direct emissions, the performance of the photostationary model with meteorology-based transformation rates is satisfactory. On the other hand, the application of a non-photostationary model significantly improves the predictions in urban canyons with direct vehicular emissions. The applicability of the proposed models in operational tools at the city scale is finally discussed.