Impact of urban canopy meteorological forcing on aerosol concentrations

Abstract. The regional climate model RegCM4 extended with the land surface model CLM4.5 was coupled to the chemistry transport model CAMx to analyze the impact of urban meteorological forcing on surface fine aerosol (PM2.5) concentrations for summer conditions over the 2001–2005 period, focusing on the area of Europe. Starting with the analysis of the meteorological modifications caused by urban canopy forcing, we found a significant increase in urban surface temperatures (up to 2–3 K), a decrease of specific humidity (by up to 0.4–0.6 gkg−1), a reduction of wind speed (up to −1 ms−1) and an enhancement of vertical turbulent diffusion coefficient (up to 60–70 m2s−1). These modifications translated into significant changes in surface aerosol concentrations that were calculated by a “cascading” experimental approach. First, none of the urban meteorological effects were considered. Then, the temperature effect was added, then the humidity and the wind, and finally, the enhanced turbulence was considered in the chemical runs. This facilitated the understanding of the underlying processes acting to modify urban aerosol concentrations. Moreover, we looked at the impact of the individual aerosol components as well. The urbanization-induced temperature changes resulted in a decrease of PM2.5 by −1.5 to −2 µg m−3, while decreased urban winds resulted in increases by 1–2 µg m−3. The enhanced turbulence over urban areas resulted in decreases of PM2.5 by −2 µg m−3. The combined effect of all individual impact depends on the competition between the partial impacts and can reach up to −3 µg m−3 for some cities, especially when the temperature impact was stronger in magnitude than the wind impact. The effect of changed humidity was found to be minor. The main contributor to the temperature impact is the modification of secondary inorganic aerosols, mainly nitrates, while the wind and turbulence impact is most pronounced in the case of primary aerosol (primary black and organic carbon and other fine particle matter). The overall as well as individual impacts on secondary organic aerosol are very small, with the increased turbulence acting as the main driver. The analysis of the vertical extent of the aerosol changes showed that the perturbations caused by urban canopy forcing, besides being large near the surface, have a secondary maximum for turbulence and wind impact over higher model levels, which is attributed to the vertical extent of the changes in turbulence over urban areas. The validation of model data with measurements showed good agreement, and we could detect a clear model improvement in some areas when including the urban canopy meteorological effects in our chemistry simulations.

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Impact of urban canopy meteorological forcing on aerosol concentrations

10.5194/acp-2018-415 ◽

2018 ◽

Author(s):

Peter Huszar ◽

Michal Belda ◽

Jan Karlický ◽

Tatsiana Bardachova ◽

Tomas Halenka ◽

...

Keyword(s):

Land Surface ◽

Urban Areas ◽

Urban Canopy ◽

Specific Humidity ◽

Surface Model ◽

Meteorological Forcing ◽

Turbulent Diffusion Coefficient ◽

Temperature Impact ◽

The Impact ◽

Meteorological Effects

Abstract. The regional climate model RegCM4 extended with the land-surface model CLM4.5 was coupled to the chemistry transport model CAMx to analyze the impact of urban meteorological forcing on the surface fine aerosol (PM2.5) concentrations for summer conditions over the 2001–2005 period focusing on the area of Europe. Starting with the analysis of the meteorological modifications caused by urban canopy forcing we found significant increases of urban surface temperatures (up to 2–3 K), decrease of specific humidity (by up to 0.4–0.6 g/kg) reduction of wind speed (up to −1 m/s) and enhancement of vertical turbulent diffusion coefficient (up to 60–70 m2/s). These modifications translated into significant changes in surface aerosol concentrations that were calculated by cascading experimental approach. First, none of the urban meteorological effects were considered. Than, the temperature effect was added, than the humidity, the wind and finally, the enhanced turbulence was considered in the chemical runs. This facilitated the understanding of the underlying processes acting to modify urban aerosol concentrations. Moreover, we looked at the impact of the individual aerosol components as well. The urban induced temperature changes resulted in decreases of PM2.5 by −1.5 to −2 μg/m3, while decreased urban winds resulted in increases by 1–2 μg/m3. The enhanced turbulence over urban areas results in decreases of PM2.5 by −2 μg/m3. The combined effect of all individual impact depends on the competition between the partial impacts and can reach up to −3 μg/m3 for some cities, especially were the temperature impact was stronger in magnitude than the wind impact. The effect of changed humidity was found to be minor. The main contributor to the temperature impact is the modification of secondary inorganic aerosols, mainly nitrates, while the wind and turbulence impact is most pronounced in case of primary aerosol (primary black and organic carbon and other fine particle matter). The overall as well as individual impacts on secondary organic aerosol is very small with the increased turbulence acting as the main driver. The analysis of the vertical extend of the aerosol changes showed that the perturbations caused by urban canopy forcing, besides being large near the surface, have a secondary maximum for turbulence and wind impact over higher model levels, which is attributed to the vertical extend of the changes in turbulence over urban areas. The validation of model data with measurements showed good agreement and we could detect a clear model improvement at some areas when including the urban canopy meteorological effects in our chemistry simulations.

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Impact of an improved WRF urban canopy model on diurnal air temperature simulation over northern Taiwan

Atmospheric Chemistry and Physics ◽

10.5194/acp-16-1809-2016 ◽

2016 ◽

Vol 16 (3) ◽

pp. 1809-1822 ◽

Cited By ~ 16

Author(s):

Chuan-Yao Lin ◽

Chiung-Jui Su ◽

Hiroyuki Kusaka ◽

Yuko Akimoto ◽

Yang-Fan Sheng ◽

...

Keyword(s):

Land Surface ◽

Urban Areas ◽

Urban Canopy ◽

Anthropogenic Heat ◽

Surface Model ◽

Urban Canopy Model ◽

Simulation Performance ◽

The Impact ◽

Canopy Model ◽

Northern Taiwan

Abstract. This study evaluates the impact of urbanization over northern Taiwan using the Weather Research and Forecasting (WRF) Model coupled with the Noah land-surface model and a modified urban canopy model (WRF–UCM2D). In the original UCM coupled to WRF (WRF–UCM), when the land use in the model grid is identified as "urban", the urban fraction value is fixed. Similarly, the UCM assumes the distribution of anthropogenic heat (AH) to be constant. This may not only lead to over- or underestimation of urban fraction and AH in urban and non-urban areas, but spatial variation also affects the model-estimated temperature. To overcome the abovementioned limitations and to improve the performance of the original UCM model, WRF–UCM is modified to consider the 2-D urban fraction and AH (WRF–UCM2D).The two models were found to have comparable temperature simulation performance for urban areas, but large differences in simulated results were observed for non-urban areas, especially at nighttime. WRF–UCM2D yielded a higher correlation coefficient (R2) than WRF–UCM (0.72 vs. 0.48, respectively), while bias and RMSE achieved by WRF–UCM2D were both significantly smaller than those attained by WRF–UCM (0.27 and 1.27 vs. 1.12 and 1.89, respectively). In other words, the improved model not only enhanced correlation but also reduced bias and RMSE for the nighttime data of non-urban areas. WRF–UCM2D performed much better than WRF–UCM at non-urban stations with a low urban fraction during nighttime. The improved simulation performance of WRF–UCM2D in non-urban areas is attributed to the energy exchange which enables efficient turbulence mixing at a low urban fraction. The result of this study has a crucial implication for assessing the impacts of urbanization on air quality and regional climate.

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Impact of urban emission on local and regional air-quality: investigating the role of the urban canopy meteorological forcing

10.5194/egusphere-egu21-1992 ◽

2021 ◽

Author(s):

Peter Huszar ◽

Jan Karlicky ◽

Jana Markova ◽

Tereza Novakova ◽

Marina Liaskoni ◽

...

Keyword(s):

Rural Areas ◽

Urban Areas ◽

Climate Models ◽

Regional Scale ◽

Urban Canopy ◽

Meteorological Forcing ◽

Island Effect ◽

Regional Air Quality ◽

Urban Emissions ◽

The Impact

Urban canopies impact the meteorological conditions in the planetary boundary layer (PBL) and above in many ways: apart from urban heat island effect, the urban breeze circulation can form. Further, the enhanced drag causes intensification of the turbulent diffusion leading to elevated PBL height and this drag, at the same time causes lower windspeeds. These changes together act as a 'meteorological forcing' for the chemical processes involing transport, diffusion and chemical transformation of urban pollutants in the urban canopy and over larger scales, therefor we use the term urban canopy meteorological forcing (UCMF). Using regional scale coupled chemistry-climate models over central Europe (involving models RegCM, CAMx and WRF-Chem),&#160; we investigate here how the UCMF influences the urban emissions and their dispersion into regional scales. The analysis covers key pollutants as O3, NO2 and PM2.5 and the 2015-2016 period. While urban emissions contribute by about 60-80% to the total NO2 and PM2.5 concentrations in cities, for ozone, they cause decrease in the urban cores and slight increase over sourrounding rural areas. More importantly, we found that if UCMF is considered, the impacts on all three pollutants are reduced, by about 20-30%. This is caused by the fact that vertical turbulence is greatly enhanced in urban areas leading to reduced fingerprint of the urban emissions (the case of NO2 and PM2.5) while in case of O3, reduction of the NO2 impact means smaller first-order titraltion therefor higher ozone concentrations - i.e. the ozone fingerprint of urban emissions is smaller. Our analysis showed that for evaluating the impact of urban emissions over regional scales, the meterological effects caused by the urban canopy have to be considered in modeling studies.

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Impact of an improved WRF-urban canopy model on diurnal air temperature simulation over northern Taiwan

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-15-28483-2015 ◽

2015 ◽

Vol 15 (20) ◽

pp. 28483-28516

Author(s):

C.-Y. Lin ◽

C.-J. Su ◽

H. Kusaka ◽

Y. Akimoto ◽

Y. F. Sheng ◽

...

Keyword(s):

Land Surface ◽

Urban Areas ◽

Urban Canopy ◽

Anthropogenic Heat ◽

Surface Model ◽

Urban Canopy Model ◽

Simulation Performance ◽

The Impact ◽

Canopy Model ◽

Northern Taiwan

Abstract. This study evaluated the impact of urbanization over northern Taiwan using the Weather Research and Forecasting (WRF) model coupled with the Noah land-surface model and a modified Urban Canopy Model (WRF-UCM2D). In the original UCM coupled in WRF (WRF-UCM), when the land use in the model grid net is identified as "urban", the urban fraction value is fixed. Similarly, the UCM assumes the distribution of anthropogenic heat (AH) to be constant. Such not only may lead to over- or underestimation, the temperature difference between urban and non-urban areas has also been neglected. To overcome the above-mentioned limitations and to improve the performance of the original UCM model, WRF-UCM is modified to consider the 2-D urban fraction and AH (WRF-UCM2D). The two models were found to have comparable simulation performance for urban areas but large differences in simulated results were observed for non-urban, especially at nighttime. WRF-UCM2D yielded a higher R2 than WRF-UCM (0.72 vs. 0.48, respectively), while bias and RMSE achieved by WRF-UCM2D were both significantly smaller than those attained by WRF-UCM (0.27 and 1.27 vs. 1.12 and 1.89, respectively). In other words, the improved model not only enhanced correlation but also reduced bias and RMSE for the nighttime data of non-urban areas. WRF-UCM2D performed much better than WRF-UCM at non-urban stations with low urban fraction during nighttime. The improved simulation performance of WRF-UCM2D at non-urban area is attributed to the energy exchange which enables efficient turbulence mixing at low urban fraction. The achievement of this study has a crucial implication for assessing the impacts of urbanization on air quality and regional climate.

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Modelling carbon sink of urban street trees and soil in Helsinki, Finland

10.5194/egusphere-egu2020-13833 ◽

2020 ◽

Author(s):

Minttu Havu ◽

Liisa Kulmala ◽

Anu Riikonen ◽

Leena Järvi

Keyword(s):

Carbon Dioxide ◽

Soil Moisture ◽

Carbon Cycle ◽

Soil Carbon ◽

Urban Areas ◽

Carbon Dioxide Flux ◽

Specific Humidity ◽

Soil Conditions ◽

Surface Model ◽

Flow Measurements

A high proportion of anthropogenic carbon dioxide emissions originate from urban areas, which has led cities to become interested in reducing their own emissions and determining how much carbon could be sequestered by their own vegetation and soil. The challenge with the latter is that our current knowledge on carbon storage is based on data and models from natural and forest ecosystems, whereas the response of vegetation and soil to environmental factors most probably is altered in urban green space where the soil conditions, water availability and temperature are highly variable. Therefore, ecosystem models are required to correctly account for urban vegetation and soil to understand and quantify the biogenic carbon cycle in urban areas. In this study, urban land surface model SUEWS (the Surface Urban Energy and Water Balance Scheme) and the soil carbon decomposition model Yasso15 are used to simulate urban carbon cycle on two streets in Helsinki, Finland for years 2003-2016. Curbside trees (Alnus glutinosa and Tilia x Vulgaris) were planted while the two test streets were constructed in 2002. Thereafter, carbon and water fluxes and pools with detailed street tree soil compositions were monitored in 2002-2014. SUEWS creates a local spatially variable temperature and specific humidity environment which is used in the model runs. The modelled evaporation is evaluated against sap flow measurements and modelled soil moisture against soil moisture observations. The Yasso15 model is evaluated against loss-on-ignition based soil carbon measurements as it has not been previously evaluated in urban soils. The modelled carbon dioxide flux combined with the changes in the soil carbon stock is used to estimate the carbon cycle of urban street trees and soils.

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Integration of Lidar Data into a Coupled Mesoscale–Land Surface Model: A Theoretical Assessment of Sensitivity of Urban–Coastal Mesoscale Circulations to Urban Canopy Parameters

Journal of Atmospheric and Oceanic Technology ◽

10.1175/2011jtecha1524.1 ◽

2012 ◽

Vol 29 (3) ◽

pp. 328-346 ◽

Cited By ~ 22

Author(s):

Michael Carter ◽

J. Marshall Shepherd ◽

Steve Burian ◽

Indu Jeyachandran

Keyword(s):

Urban Environment ◽

Land Surface ◽

Urban Canopy ◽

Vertical Motion ◽

Sea Breeze ◽

Surface Model ◽

Lidar Data ◽

Mesoscale Circulations ◽

The Impact ◽

Urban Weather

Abstract Urban–coastal circulations affect urban weather, dispersion and transport of pollutants and contaminants, and climate. Proper characterization and prediction of thermodynamic and dynamic processes in such environments are warranted. A new generation of observation and modeling systems is enabling unprecedented characterization of the three-dimensionality of the urban environment, including morphological parameters. Urban areas of Houston, Texas, are classified according to lidar-measured building heights and assigned typical urban land surface parameters appropriate to each classification. The lidar data were degraded from 1 m to the model resolution (1 km) with the goal of evaluating the impact of degraded resolution urban canopy parameters (UCPs) and three-dimensionality on the coastal–urban mesoscale circulations in comparison to typical two-dimensional urban slab approaches. The study revealed complex interactions between the sea breeze and urban heat island and offers a novel diagnostic tool, the bulk Richardson shear number, for identifying shallow mesoscale circulation. Using the Advanced Research Weather Research and Forecasting model (ARW-WRF) coupled to an atmosphere–land surface–urban canopy model, the authors simulated a theoretical sea-breeze day and confirmed that while coastal morphology can itself lead to complex sea-breeze front structures, including preferred areas of vertical motion, the urban environment can have an impact on the evolution of the sea-breeze mesoscale boundary. The inclusion of lidar-derived UCPs, even at degraded resolution, in the model’s land surface representation can lead to significant differences in patterns of skin surface temperature, convergence, and vertical motion, which have implications for many aspects of urban weather.

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The urban canopy meteorological forcing and its impact on ozone and PM2.5: role of the vertical turbulent transport

10.5194/acp-2019-486 ◽

2019 ◽

Author(s):

Peter Huszar ◽

Jan Karlický ◽

Jana Ďoubalová ◽

Kateřina Šindelářová ◽

Tereza Nováková ◽

...

Keyword(s):

Diffusion Coefficient ◽

Turbulent Transport ◽

Urban Canopy ◽

Eddy Diffusion ◽

Meteorological Forcing ◽

Eddy Diffusion Coefficient ◽

The Impact ◽

Vertical Eddy ◽

Vertical Eddy Diffusion

Abstract. Urban surfaces due to specific geometry and physical properties bring modified transport of momentum, moisture and heat between them and the air above and perturb the radiative, thermal and mechanical balance resulting in changed meteorological condition (e.g. the UHI – urban heat island phenomenon). From an air quality perspective, many studies argue that one of the most important changes is the increased turbulence enhancing vertical mixing of pollutants above cities, although increased temperatures and wind stilling play an important role too. Using the regional climate model RegCM4 coupled to chemistry transport model CAMx over central Europe we study how urban surfaces affect the vertical turbulent transport of selected pollutants through modifications of the vertical eddy diffusion coefficient (Kv). For the period of 2007–2011 and over central Europe numerous experiments are carried out in order to evaluate the impact of six different methods for Kv calculation on the surface concentrations as well as vertical profiles of ozone and PM2.5 over selected cities (Prague and Berlin). Three cascading domains are set up at 27 km, 9 km and 3 km resolutions, which further enables to analyze the sensitivity to model grid resolution. Numerous experiments are performed where urban surfaces are considered or replaced by rural ones in order to isolate the urban canopy meteorological forcing. Apart from the well pronounced and expected impact on temperature (increases up to 2 °C) and wind (decreases up to −2 m s−1) there is strong impact on vertical eddy diffusion in all of the six Kv methods. The Kv enhancement ranges from a few 0.5 up to 30 m2 s−1 at the surface and from 1 to 100 m2 s−1 at higher levels depending on the methods, while the turbulent kinetic energy (TKE) based methods produce the largest impact. The range of impact on the vertical eddy diffusion coefficient propagates to a range of ozone (O3) increase of 0.4 to 4 ppbv near the surface in both summer and winter, while at higher levels, decreases occur from a few −0.4 ppbv to as much as −2 ppbv. In case of PM2.5, enhanced vertical eddy diffusion leads to decrease of near surface concentrations ranging from almost zero to −1 μg m−3 in summer and to decreases from −0.5 to −2 μg m−3 in winter. Comparing these results to the total-impact, i.e. to the impact of all considered urban meteorological changes, we can conclude that much of the overall urban meteorological forcing is explained by acting of the enhanced vertical eddy diffusion, which counterweights the opposing effects of other components of this forcing (temperature, humidity and wind impact). The results further show that this conclusion holds regardless of the resolution chosen and in both the warm and cold part of the year. Our study demonstrates the dominant role of turbulent transport of pollutants above urban areas and stresses the need for further investigation how variation of urban land-use influence the pollutant transport from the urban canopy.

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Sensitivity of Simulated Urban–Atmosphere Interactions in Oklahoma City to Urban Parameterization

Journal of Applied Meteorology and Climatology ◽

10.1175/jamc-d-16-0223.1 ◽

2017 ◽

Vol 56 (5) ◽

pp. 1405-1430 ◽

Cited By ~ 2

Author(s):

Larissa J. Reames ◽

David J. Stensrud

Keyword(s):

Urban Areas ◽

Urban Canopy ◽

Oklahoma City ◽

Surface Model ◽

Urban Canopy Model ◽

Near Surface ◽

Modeling Studies ◽

Suburban Cities ◽

The City ◽

Canopy Model

AbstractThe world’s population is increasingly concentrated in large urban areas. Many observational and modeling studies have explored how these large, population-dense cities modify local and mesoscale atmospheric phenomena. These modeling studies often use an urban canopy model to parameterize urban surfaces. However, it is unclear whether this approach is appropriate for more suburban cities, such as those found in the Great Plains. Thus, the Weather Research and Forecasting Model was run for a week over Oklahoma City, Oklahoma, and results were compared with observations. Overall, four configurations were examined. Two simulations used the Noah LSM, one with all urban areas removed (CTRL), and the other with urban areas parameterized by a modified Noah land surface model with three urban categories (LSMMOD). Additional simulations utilized a single-layer urban canopy model (SLUCM) either with default urban fraction values (SLUCM1) or with urban fractions taken from the National Land Cover Database (SLUCM2). Results from the three urban runs compared favorably to high-density temperature observations of the urban heat island. The SLUCM1 run was the most realistic, although the urban fractions applied were the least representative of Oklahoma City. All urban runs also produced a drier and deeper planetary boundary layer over the city. The prediction of near-surface winds was most problematic, with the two SLUCM runs unable to correctly reproduce reduced wind speeds over the city. The modified Noah LSM provided best overall agreement with observations and represents a reasonable option for simulating the urban effects of more-suburban cities.

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Multi-layer coupling between SURFEX-TEB-V9.0 and Meso-NH-v5.3 for modelling the urban climate of high-rise cities

10.5194/gmd-2020-190 ◽

2020 ◽

Author(s):

Robert Schoetter ◽

Yu Ting Kwok ◽

Cécile de Munck ◽

Kevin Ka Lun Lau ◽

Wai Kin Wong ◽

...

Keyword(s):

Weather Prediction ◽

Grid Point ◽

Urban Canopy ◽

Atmospheric Model ◽

Surface Model ◽

Point Scale ◽

Near Surface ◽

High Rise ◽

Heat And Moisture ◽

The Impact

Abstract. Urban Canopy Models (UCMs) represent the exchange of momentum, heat, and moisture between cities and the atmosphere. Single-layer UCMs interact with the lowest atmospheric model level and are suited for low- to mid-rise cities whereas multi-layer UCMs interact with multiple levels and can also be employed for high-rise cities. The present study describes the multi-layer coupling between the UCM Town Energy Balance (TEB) included in the land surface model SURFEX and the mesoscale atmospheric model Meso-NH. This is a step towards better high-resolution weather prediction for urban areas in the future and studies quantifying the impact of climate change adaptation measures in high-rise cities. The effect of the buildings on the wind is considered using a drag force and a production term in the prognostic equation for turbulent kinetic energy. The heat and moisture fluxes from the walls and the roofs to the atmosphere are released at the model levels intersecting these urban facets. No variety of building height at grid point scale is considered to remain the consistency between the modification of the Meso-NH equations and the geometric assumptions of TEB. The multi-layer coupling is evaluated for the heterogeneous high-rise high-density city of Hong Kong. It leads to a strong improvement of model results for near-surface air temperature and relative humidity, which is due to better consideration of the process of horizontal advection in the urban canopy layer. For wind speed, model results are improved on average by the multi-layer coupling, but not for all stations. Future developments of the multi-layer SURFEX-TEB will focus on improving the calculation of radiative exchanges, which will allow a variety of building heights at grid point scale to be taken into account.

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The regional impact of urban emissions on air quality in Europe: the role of the urban canopy effects

10.5194/acp-2021-355 ◽

2021 ◽

Author(s):

Peter Huszar ◽

Jan Karlický ◽

Jana Marková ◽

Tereza Nováková ◽

Marina Liaskoni ◽

...

Keyword(s):

Air Quality ◽

Rural Areas ◽

Land Surface ◽

Urban Areas ◽

Regional Climate ◽

Regional Scale ◽

Urban Canopy ◽

Near Surface ◽

Urban Emissions ◽

The Impact

Abstract. Urban areas are hot-spots of intense emissions and they influence air-quality not only locally but on regional or even global scales. The impact of urban emissions over different scales depends on the dilution and chemical transformation of the urban plumes which are governed by the local and regional scale meteorological conditions. These are influenced by the presence of urbanized land-surface via the so called urban canopy meteorological forcing (UCMF). In this study, we investigate for selected central European cities (Berlin, Budapest, Munich, Prague, Vienna and Warsaw), how the urban emission impact (UEI) is modulated by the UCMF for present day climate conditions (2015–2016) using three regional climate-chemistry models: the regional climate models RegCM and WRF-Chem (its meteorological part), the chemistry transport model CAMx coupled to either RegCM and WRF and the “chemical” component of WRF-Chem. The UCMF was calculated by replacing the urbanized surface by rural one while the UEI was estimated by removing all anthropogenic emissions from the selected cities. We analyzed the urban emissions induced changes of near surface concentrations of NO2, O3 and PM2.5. We found increases of NO2 and PM2.5 concentrations over cities by 4–6 ppbv, and 4–6 μgm−3, respectively meaning that about 40–60 % and 20–40 % of urban concentrations of NO2 and PM2.5 are caused by local emissions and the rest is the result of emissions from surrounding rural areas. We showed that if UCMF is included, the UEI of these pollutants is about 40–60 % smaller, or in other words, the urban emission impact is overestimated if urban canopy effects are not taken into account. In case of ozone, models due to UEI usually predict decreases around −2 to −4 ppbv (about 10–20 %), which is again smaller if UCMF is considered (by about 60 %). We further showed that the impact on extreme (95th percentile) air-pollution is much stronger, as well as the modulation of UEI is larger for such situations. Finally, we evaluated the contribution of the urbanization induced modifications of vertical eddy-diffusion to the modulation of UEI, and found that it alone is able to explain the modelled decrease of the urban emission impact if the effects of UCMF are considered. In summary, our results showed that the meteorological changes resulting from urbanization have to be included in regional model studies if they intend to quantify the regional fingerprint of urban emissions. Ignoring these meteorological changes can lead to strong overestimation of UEI.

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Impact of urban canopy meteorological forcing on aerosol concentrations