Urban Boundary Layer Research Articles

Nonlinear changes in urban heat island intensity, urban breeze intensity, and urban air pollutant concentration with roof albedo

This study systematically examines how the urban heat island (UHI) and urban breeze circulation (UBC) respond to an increase in roof albedo (αr) and its influence on urban air pollutant dispersion. For this, idealized ensemble simulations are performed using the Weather Research and Forecasting (WRF) model. The increase in αr from 0.20 to 0.65 decreases the UHI intensity, UBC intensity, and urban planetary boundary layer (PBL) height in the daytime (from 1200 to 1700 LST) by 47%, 36%, and 6%, respectively. As both UBC intensity and urban PBL height decrease, the daytime urban near-surface passive tracer concentration increases by 115%. The daytime UHI intensity, UBC intensity, and urban tracer concentration nonlinearly change with αr: For 0.10 ≤ αr < 0.80, the rates of changes in the UHI intensity, UBC intensity, and urban tracer concentration with αr overall increase as αr increases. For αr ≥ 0.80, the daytime roof surface temperature is notably lower than the daytime urban near-surface air temperature, the UHI intensity, UBC intensity, and urban tracer concentration very slightly changing with αr. This study provides insights into the associations between changes in roof surface temperature and roof surface energy fluxes with αr and those in UHI intensity.

Impact of land use land cover changes on urban temperature in Jakarta: insights from an urban boundary layer climate model

Urbanization is one of the important drivers of increasing local temperatures. As cities and urban areas evolve, extensive land use and land cover (LULC) changes alter the physical characteristics of surface materials. This modification results in reduced evapotranspiration rates, ultimately contributing to higher surface and air temperatures. This study investigated the impact of urbanization on urban temperature in Jakarta. Urban temperature was simulated for a 20-year time period (1995–2014) by the urban boundary layer climate model UrbClim, using LULC data for both 1995 and 2014. Temperature changes were analysed by assessing the temperature anomaly across different LULC change classes divided into four main classes namely no built-up changes (BB), no green spaces changes (GG), built-up to green spaces (BG), and green spaces to built-up (GB). The study revealed that the conversion of green spaces to built-up areas (GB) had the most significant impact on the increase in air temperature. This was indicated by the mean values of the temperature anomaly of GB of about 0.24°C followed by GG, BB, and BG with the mean values of the temperature anomaly of about 0.20°C, 0.19°C, 0.17°C, respectively. The different temperature anomalies of the LULC change classes indicate that green spaces have an important role in maintaining local climate. Hence, it is important for local government to effectively manage the composition, the quantity, as well as the distribution of green spaces within a city. By looking at temperature anomalies of LULC change classes, the present study provides an alternative approach to many existing methods that provide general information about temperature changes, without specifically analyzing the effects of LULC transformations.

Evaluating Reduced-Order Urban Wind Models for Simulating Flight Dynamics of Advanced Aerial Mobility Aircraft

Advanced Aerial Mobility (AAM) platforms are poised to begin high-density operations in urban areas nationwide. This new category of aviation platforms spans a broad range of sizes, from small package delivery drones to passenger-carrying vehicles. Unlike traditional aircraft, AAM vehicles operate within the urban boundary layer, where large structures, such as buildings, interrupt the flow. This study examines the response of a package delivery drone, a general aviation aircraft, and a passenger-carrying urban air mobility aircraft through an urban wind field generated using Large Eddy Simulations (LES). Since it is burdensome to simulate flight dynamics in real-time using the full-order solution, reduced-order wind models are created. Comparing trajectories for each aircraft platform using full-order or reduced-order solutions reveals little difference; reduced-order wind representations appear sufficient to replicate trajectories as long as the spatiotemporal wind field is represented. However, examining control usage statistics and time histories creates a stark difference between the wind fields, especially for the lower wing-loading package delivery drone where control saturation was encountered. The control saturation occurrences were inconsistent across the full-order and reduced-order winds, advising caution when using reduced-order models for lightly wing-loaded aircraft. The results presented demonstrate the effectiveness of using a simulation environment to evaluate reduced-order models by directly comparing their trajectories and control activity metrics with the full-order model. This evaluation provides designers valuable insights for making informed decisions for disturbance rejection systems. Additionally, the results indicate that using Reynolds-averaged Navier–Stokes (RANS) solutions to represent urban wind fields is inappropriate. It was observed that the mean wind field trajectories fall outside the 95% confidence intervals, a finding consistent with the authors’ previous research.

Statistical modeling of the effects of wind speed, air temperature and relative humidity on the concentration of carbon monoxide in the urban atmosphere

The high carbon monoxide content in the urban atmosphere is one of the most important indicators of poor air quality in megacities such as Moscow. This study is to evaluate the importance of wind speed, air temperature, and relative air humidity for predicting the concentrations of carbon monoxide for the day ahead using a simplified one-dimensional quasistationary statistical model. It is shown that the concentration of carbon monoxide in the Moscow atmosphere is determined by a combination of internal (previous days CO concentration) and external (meteorological conditions) factors. The variation of carbon monoxide concentration at one station differs from the variation at another station due to the differences in local conditions. Taking into account wind speed and air temperature increases the predictive value of the onedimensional quasi-stationary statistical model for most of the stations. In contrast to wind, relative air humidity decreases the predictive value of the model for most of the stations. This means that meteorological factors considered in this study could have different effects on predicting carbon monoxide concentration in the case of Moscow. The data from the Balchug weather station, located in the city center, offers a more accurate CO concentration forecast for most Moscow stations compared to the VDNKh weather station. For a more complete description of the influence of meteorological conditions on the predicted low concentration of gases, it is useful to take into account the model wind direction, surface air pressure, and the intensity of mixing in the urban boundary layer.

Impacts of building modifications on the turbulent flow and heat transfer in urban surface boundary layers

This study examines turbulent airflow and upward heat transport in real urban environments using a building-resolving large-eddy simulation model to understand the characteristics of turbulent airflow and upward heat transport when geometrical distributions of buildings are modified. The target areas were two real urban districts within Osaka City, Japan, having different morphological features. In the numerical experiments, the initial condition was set to a neutral condition in which temperature is uniformly distributed vertically, and buildings emitted heat at a constant rate. The results in the two districts indicated that the features of turbulence and heat transport distinctly differed with different building arrangement. Specifically, taller buildings significantly decelerated airflows and induced warming behind buildings. More high-rise buildings (which resulted in a larger building variability) in a district with a larger building density caused a large heat flux and warming at higher levels. The sensitivity experiments in which a density and height variability of buildings were modified showed that a building density at higher levels and a building height variability significantly influenced warming at upper levels. An increased building height variability weakened wind speed and disturbed horizontal heat advection, whereas a large building density caused numerous heat sources.

Similarity of the low-occurrence wind profiles within urban turbulent boundary layers of uniform and non-uniform height block arrays

Within urban boundary layers, the safety of pedestrians is markedly affected by wind speed, particularly in urban areas. The characteristics of turbulence above the canopy layers can lead to unpredictable changes in wind speed at the pedestrian level. Therefore, this study analyzes low-occurrence wind speed phenomena above canopy heights for uniform and nonuniform block configurations using wind tunnel experiments (WTE) to understand the background turbulence characteristics which the wind profile is generated by the boundary layer above the canopy. The urban canopy arrays were reproduced using solid blocks arranged in 30 rows in a streamwise direction with a packing density of 25 % at three different heights. An x-type hot-wire anemometer was used to measure the streamwise and vertical velocity components. The low-occurrence values were classified based on wind speed percentiles of 0.1 %, 1.0 %, 99.0 %, and 99.9 % wind speeds. The results demonstrated that above the canopy, there were minor influences of block height variations on the low occurrence factor. The peak factor demonstrated a comparable value between the uniform and nonuniform cases, regardless of the block arrangement. Statistical models based on the Weibull distribution and Gram–Charlier series demonstrating good agreement with the WTE data in predicting the low occurrence and peak factors. This study found that variations in block height have a minor influence on the low occurrence and peak factors within the turbulent boundary layers, implying that we can separate the effect of background turbulence from the local turbulent generation within the urban canopy layers.

Initiation and evolution of urban-induced precipitation under different background wind speeds: Roles of urban breeze circulation and cold pool

Urban-enhanced precipitation is often observed far downwind of cities, suggesting important roles of background wind. This study examines the impacts of background wind on the initiation and evolution of urban-induced precipitation through idealized ensemble large-eddy simulations with different initial background wind speeds of 0, 1, 2, 3, 4, and 5 m s−1. Without background wind, a strong urban breeze circulation (UBC) initiates a relatively large number of cumulus clouds in the urban area, which exhibit greater cloud top heights than those in the rural area. The early-initiated clouds do not produce precipitation but moisten the middle troposphere, assisting later-initiated clouds to develop into deep convective clouds and produce concentrated precipitation in the urban area. As the background wind speed increases, the UBC weakens. Also, the high-humidity area generated by early-initiated clouds is continuously advected away from the urban area. Consequently, the precipitation initiation is delayed as the background wind speed increases. Precipitating clouds are advected downwind and generate a cold pool, and updrafts are repeatedly produced at the downwind boundary of the cold pool. The downwind-advected clouds are fed by the newly produced updrafts, being a long-lived organized precipitation system that produces a considerable amount of precipitation in the downwind area. This feeding effect is most prominent for a moderate background wind (3 m s−1), causing the precipitation amount and duration to be maximized. For stronger background winds, precipitation is initiated by the mechanical lifting of the warm air of the urban boundary layer over the cool rural boundary layer around sunset.

Occurrence of tyre-derived particles in size-segregated aerosol in the urban area of Venice

Benzothiazoles (BTHs), commonly used in various industrial applications, have emerged as significant contaminants due to their widespread usage and potential adverse effects on ecosystems and human health. The aim of this study is to quantify and, for the first time, to characterize the particle size distribution of eight BTHs across twelve fractions of atmospheric aerosol representative of the urban boundary layer. Samples were collected from August to October 2023 in the urban area of Venice, located in the Po Valley, known for its poor air quality. Instrumental analysis was achieved via an UHPLC system coupled with a triple quadrupole mass spectrometer.All target compounds were present in the samples analyzed and most of them tended to distribute mainly in the fine fraction of aerosol (<1.8 μm). An exception is given by BTH-SO3H, which presents a bimodal distribution with maxima centered in the coarse fraction; this may imply a different source compared to other BTHs. BTH-SH is the most abundant benzothiazole derivative, suggesting tyre debris as the main source since it is the main compound used in vulcanizing accelerators in rubber manufacture. Given its mutagenic properties, its high relative abundance could be of concern for human health. Resultsof this work provide valuable insights into the distribution of BTHs in urban aerosols, laying the groundwork for future research aimed at better understanding their sources and environmental pathways, fate and impacts.

Investigating the influence of stepped roofs on wind dynamics using large eddy simulation

This study investigates airflow and turbulence within varying roof configurations in urban boundary layers by using the parallelized large-eddy simulation model (PALM). Key findings reveal stark contrasts in airflow between stepped and flat roof arrangements, with the former presenting dual counter-rotating vortices and enhanced vertical motion in one street, while the latter exhibited a primary vortex and several secondary vortices. Additionally, normalized turbulence kinetic energy (TKE) was markedly lower in flat roof configurations, with stepped roofs fostering more significant turbulence and small-scale turbulent motion. This variability intensified with decreasing step height and quantity. Vertical profiles further disclosed considerable velocity disturbances and larger Reynolds numbers in one street of stepped roofs, affirming the roof’s influence on turbulence generation and transport. Dispersive stress also displayed differing characteristics in various canyons. Turbulent momentum transport through eddies significantly differs between the windward and leeward streets of flat and stepped roofs. Further exploration into density stratification effects and scalar transport in stepped roofs would enhance practical implications.

Onsite measurements of pedestrian-level wind and preliminary assessment of effects of turbulence characteristics on human body convective heat transfer

Wind is an important factor affecting outdoor thermal comfort in urban environment, but its turbulence characteristics at the pedestrian level and effects on convective heat transfer (hc) from a human body remain poorly understood. Previous studies were only conducted in wind tunnels with low turbulence intensity, small turbulence integral length scale, and fixed prevailing wind direction. To address this knowledge gap, this field study was conceived to monitor the pedestrian level wind in actual outdoor settings and to measure the hc of a thermal manikin at the same time. The results show that both longitudinal and lateral turbulence intensity significantly enhance whole body hc. It remains to be examined whether the small-scale wind direction variation can be included in the lateral turbulence intensity or vice versa. The integral length scale found at the two sites were larger than a typical manikin dimension, and the whole body hc peaked when these two scales were comparable. As the first major field study to quantify convection heat loss of a thermal manikin exposed to real-life urban boundary layer wind, it is demonstrated crucial to consider realistic turbulence characteristics in the field when evaluating hc over a human body for urban microclimate design.

Numerical Studies on the Influence of Building Morphology on Urban Canopy Wind Speed

AbstractBuildings increase the urban surface roughness and reduce near‐surface wind speeds in the urban canopy due to the drag effect. Urban heat storage and other effects cause urban warming as well, which decreases the urban boundary layer stability and enhances the turbulence exchange between upper and lower layer. As upper momentum is transported downward, the wind speed of urban canopy increases. Quantitative descriptions of these mechanisms are still lacking currently. This paper presents high‐resolution numerical simulation results of a mega city, Shanghai, China from 2016 to 2020 using the building effect parameterization in WRF (WRF‐BEP) with urban morphological parameters. The dynamic and thermal effects of building morphology on urban canopy wind speed were separated and their quantitative expression functions were given. The results indicate that the influence of building morphology on urban canopy wind speed is mainly dynamic resulting in a wind speed attenuation of approximately 50% and nearly constant. The thermal effect of building morphology on urban canopy wind speed increases with the urban heat island intensity, and the thermal effect could increase urban canopy wind speed by about 30% under the condition of strong urban heat island. The relative contributions of the dynamic and thermal effects of building morphology to urban canopy wind speed change with the wind speed. As wind speed increases, the contribution of the thermal effect of building morphology to urban canopy wind speed gradually decreases. This paper provides a quantitative relationship between the urban canopy wind speed variation and urban morphology, as well as urban heat island intensity.

Urban boundary‐layer flows in complex terrain: Dynamic interactions during a hot and dry summer season in Phoenix, Arizona

AbstractAnthropogenic modification of natural landscapes to urban environments impacts land–atmosphere interactions in the boundary layer. Ample research has demonstrated the effect of such landscape transitions on development of the urban heat island (UHI), but considerably less attention has been given to impacts on regional wind flow. Here, we use a set of high‐resolution (1 km grid spacing) regional climate modeling simulations with the Weather Research and Forecasting model coupled to a multilayer urban canopy scheme to investigate the dynamical interaction between the urban boundary layer of the Phoenix metro (United States) area and the thermal circulation of the complex terrain it resides within. We conduct paired simulations for the extremely hot and dry summer of 2020, using a contemporary urban representation and a pre‐settlement landscape representation to examine the effect of the built environment on local to regional‐scale wind flow. Analysis of our simulation results shows that, during the summer of 2020, (a) the thermo‐topographical circulation dominates over both urban and rural areas for a majority of the diurnal cycle; (b) the built environment obstructs wind flow in the inertial sublayer during the late afternoon and the nighttime, whereas more intense daytime urban sensible heat flux dampens the urban‐roughness‐induced drag effect through a deeper urban boundary layer and vigorous mixing; (c) the Phoenix metro UHI does not result in a well‐developed and clearly discernible induced circulation as observed in other urban areas and described in the scientific literature; (d) shortly before dawn, the local UHI is able to affect the local thermo‐topographical circulation through flow intensity modulation that results in an ~10 km eastward shift of the center of mass convergence. Our results highlight the need for future research—both observational and simulation based—into urbanizing regions where multiscale flows are dominant.

On the Kinematics of Sea-Land Breeze and the Local Development of Convective Storms in the Metropolitan Area of Rio de Janeiro

This work presents an analysis of the kinematic properties of the wind flow in the Metropolitan Area of Rio de Janeiro in the State of Rio de Janeiro, Brazil, using meteorological data from the aerodromes Santos Dumont, Galeão and Campo dos Afonsos, located in the city of Rio de Janeiro. The calculation of these kinematic quantities is based on the 'Linear Vector Point Function' (LVPF) method. The results indicate the main role of the circulation of the sea-land breeze, the effects of topography (by blockages, channeling and differential heating) and the urban breeze associated with the development of the Urban Boundary Layer in the local formation of convective rainstorms in the Metropolitan Area of Rio de Janeiro.

Challenges in Simulating Prevailing Fog Types Over Urban Region of Delhi

AbstractAccurately predicting fog is challenging due to interplay of myriad processes in its formation and high spatiotemporal variability. This study compares the performance of the Weather Research and Forecasting model with control (CNTL‐WRF) and assimilated fine‐grid (HRLDAS‐WRF) soil fields in the Ingo‐Gangetic Plain (IGP) over a 2‐years winter period (2019–2020 and 2020–2021). Results show HRLDAS‐WRF enhances accuracy in representing surface fog's heterogeneity and lifecycle across the IGP, demonstrating a spatial skill improvement of approximately 18% with a Fraction Skill Score of 0.44, compared to CNTL‐WRF's (0.36). Employing fog classification algorithm identifies 25 dense fog episodes (Vis &lt; 500 m) over Delhi's urban boundary layer, including 14 radiation (RAD), 5 cloud‐base lowering (CBL), 3 advection + radiation (ADV + RAD), and 3 evaporation (EVA) episodes. CNTL‐WRF predicts 20 episodes but misses five due to a dry bias in the initial moisture conditions. However, HRLDAS‐WRF demonstrates limited vertical fog growth in various occurrences, highlighting the crucial role of fine‐gridded soil states for enhanced land‐surface feedback. Detailed analysis shows a 40% reduction in mean onset error for RAD fog occurrences in HRLDAS‐WRF when compared to CNTL‐WRF. In CBL fog episodes, both models exhibit significant radiative cooling and inversion before fog onset, leading to inaccurate predictions as RAD fog. Similarly, forecasting the abrupt development of ADV + RAD fog episodes is challenging as models struggle to replicate moisture intrusion over radiatively cooled surfaces in windy conditions. Predicting EVA fog, forms within an hour after sunrise, remains difficult due to the current model parameterization that rapidly dissipates fog soon after sunrise.

On the Applicability of Ground-Based Microwave Radiometers for Urban Boundary Layer Research.

Significant knowledge gaps exist in our understanding of urban boundary layer processes, particularly the hygrothermal state. The earth system community has successfully used microwave radiometers for several decades. However, the applicability in complex urban environments has never been adequately tested. Here, observations from a microwave radiometer are compared to radiosonde readings in a densely urbanized site in Houston, Texas. The site was influenced by both an urban heat island and the sea breeze phenomenon. The analysis showed significant disagreement between the virtual potential temperature predicted by the microwave radiometer and the radiosonde for all periods within the boundary layer. However, the values were reasonably comparable above the boundary layer. The microwave radiometer incorrectly predicted an inversion layer instead of a mixed layer during convective periods. The microwave radiometer measurements deviated from the radiosonde measurements throughout the lower troposphere for the relative humidity.

RPAS operations in urban airflow: Efficient modelling of representative wind speed variations along a flight path through a flow field with changing turbulence characteristics

For remotely piloted aircraft systems (RPAS) operating in the urban environment, the flight path will most likely pass through the turbulent airflow of building wakes. To attenuate or reject instabilities caused by the turbulent airflow, control systems strategies are being developed in preparation for increased demand on the smaller urban air mobility vehicles. In this paper, results from urban airflow measurements of four 1:300 scaled Canadian city model flow fields are examined to provide detailed understanding of flow characteristics that can be found in typical Canadian cities. The results show common patterns for the range of inner city wind speed and turbulence intensity but that within the urban boundary layer (UBL) the variation of flow characteristics does not have a gradient with respect to altitude and that flow characteristics are highly variable along representative flight paths. For the purpose of simulation of RPAS response to the complex urban airflow, methods for using real urban flows data as inputs to simulations is presented. Demonstration of an Advancing Fourier Series (AFS) method, using the measured city data, shows successful preservation of the spatial- and temporal-correlations for reconstruction of a flow time series offering a novel, efficient and flexible approach for implementation of a time-based simulation of RPAS response in complex flow environments such as the urban environment.

Across-wind response characteristics of tall-square towers in urban flow: An experimental study focused on the aeroelastic effects

To fully use the land resource in the urban regions of metropolises, high-rise buildings of large aspect ratio maybe preferred for the new constructions. To systematically investigate the across-wind responses of these quite slender structures, the urban boundary layer flow of high turbulence intensity was simulated in the wind tunnel, and aeroelastic tests realized by the pivot model setup were carried out for the square cross section towers of various heights resulting in large aspect ratios (λ = 12, 16, 20). No appreciable aeroelastic behaviors have been observed for the λ = 12 tower even for a very low damping ratio (0.57%). This is in line with the many previous studies for the tall-square tower with an aspect ratio not higher than 10, likely due to the very high turbulence intensity in the urban terrain, mitigating the occurrence of possible aeroelastic behaviors. In contrast, the λ = 16 and (especially) the λ = 20 towers exhibit strong oscillations known as the across-wind galloping, evidenced by the monotonic increase in the amplitude–velocity curve and the clear characteristics of simple-harmonic oscillations. Moreover, it is observed that for a certain range of low damping ratios, these large oscillations were initiated at the same wind speed very close to the vortex-resonance wind speed. The interaction mechanism between vortex induced vibration and galloping is thus supposed responsible for this observation (even in urban flow). Finally, peak across-wind responses at various damping ratios were provided as well, serving as a useful reference for the future design of similar tall-square towers.

Observational Evidence of the Vertical Exchange of Ozone within the Urban Planetary Boundary Layer in Shanghai, China

The vertical mass exchange of ozone (O3) plays an important role in determining surface O3 air quality, the understanding of which, however, is greatly limited by the lack of continuous measurements in the vertical direction. Here, we characterize O3 variations at a high-altitude monitoring site at the top of Shanghai Tower (SHT) and discuss the potential impacts of the vertical exchange of air pollutants on O3 air quality within the urban planetary boundary layer (PBL) based on continuous measurements during 2017–2018. During the daytime, two distinct patterns of vertical O3 gradient are detected. In summer, the daytime O3 formation at SHT is observed to be more limited by nitrogen oxides (NOx) than the surface, which, together with the efficient vertical mixings, results in higher O3 levels in the upper mixing layer. In cold months, the opposite vertical gradient is observed, which is associated with weak vertical exchange and NOx-saturated O3 formation. A nighttime O3 reservoir layer and consistent morning O3 entrainments are detected all year round. These results provide direct evidence of the vertical mixings within the urban PBL, underscoring the pressing need for improving vertical resolution in near-surface layers of air quality models.

Impact of urban land use on mean and heavy rainfall during the Indian summer monsoon

Abstract. Northern India has undergone intense urbanization since the middle of the 20th century. The impact of such drastic land-use change on the regional weather and climate remains to be assessed. In this work, we study the impact of the modification of land use – from vegetation to urban – on the Indian summer monsoon rainfall as well as on other meteorological variables. We use the regional Meso-scale Non-Hydrostatic (Meso-NH) model coupled with an urban module (the Town Energy Balance model) to perform monthlong sensitivity simulations centered around Kolkata, the most urbanized area in northeastern India. Paired simulations, one with and another without urban settings, have been performed to identify the impacts related to urbanization through both thermodynamic and kinetic effects. We find that the perturbation induced by urban land use enhances the mean rainfall over the model domain, principally by intensifying the convective activity through thermodynamic perturbation, leading to a 14.4 % increase in the monthly mean rainfall. The urban area also induces a 15.0 % rainfall increase during two modeled periods of heavy precipitation caused by low-pressure systems. In addition, the modeling results demonstrate that the urban area not only generally acts as a rainfall enhancer, particularly during nighttime, but also induces the generation of a specific storm in one modeled case that would not have formed in the absence of the urban area. The initiation of this storm over the city was primarily due to the urban terrain's disturbance of the near-surface wind flow, leading to a surge in dynamically produced turbulent kinetic energy (TKE). The thermal production of TKE over the nighttime urban boundary layer, on the other hand, serves as a contributing factor to the storm formation.

An open-path observatory for greenhouse gases based on near-infrared Fourier transform spectroscopy

Abstract. Monitoring the atmospheric concentrations of the greenhouse gases (GHG) carbon dioxide (CO2) and methane (CH4) is a key ingredient for fostering our understanding of the mechanisms behind the sources and sinks of these gases and for verifying and quantitatively attributing their anthropogenic emissions. Here, we present the instrumental setup and performance evaluation of an open-path GHG observatory in the city of Heidelberg, Germany. The observatory measures path-averaged concentrations of CO2 and CH4 along a 1.55 km path in the urban boundary layer above the city. We combine these open-path data with local in situ measurements to evaluate the representativeness of these observation types on the kilometer scale. This representativeness is necessary to accurately quantify emissions, since atmospheric models tasked with this job typically operate on kilometer-scale horizontal grids. For the operational period between 8 February and 11 July 2023, we find a precision of 2.7 ppm (0.58 %) and 18 ppb (0.89 %) for the dry-air mole fractions of CO2 (xCO2) and CH4 (xCH4) in 5 min measurements, respectively. After bias correction, the open-path measurements show excellent agreement with the local in situ data under atmospheric background conditions. Both datasets show clear signals of traffic CO2 emissions in the diurnal xCO2 cycle. However, there are particular situations, such as under southeasterly wind conditions, in which the in situ and open-path data reveal distinct differences up to 20 ppm in xCO2, most likely related to their different sensitivity to local emission and transport patterns. Our setup is based on a Bruker IFS 125HR Fourier transform spectrometer, which offers a spacious and modular design providing ample opportunities for future refinements of the technique with respect to finer spectral resolution and wider spectral coverage to provide information on gases such as carbon monoxide and nitrogen dioxide.