The regional impact of urban emissions on air quality in Europe: the role of the urban canopy effects
TL;DR: In this paper, the authors investigated how the urban emission impact (UEI) is modulated by the urban canopy meteorological forcing (UCMF) for present-day climate conditions (2015-2016) for selected central European cities (Berlin, Budapest, Munich, Prague, Vienna and Warsaw).
Abstract: . Urban areas are hot spots of intense emissions, and they influence air quality not only locally but on a regional or even global scale. 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 two regional climate models, the regional climate models RegCM and Weather Research and Forecasting model coupled with Chemistry (WRF-Chem; its meteorological part), and two chemistry transport models, Comprehensive Air Quality Model with Extensions (CAMx) coupled to either RegCM and WRF and the “chemical” component of WRF-Chem. The UCMF was calculated by replacing the urbanized surface by a rural one, while the UEI was estimated by removing all anthropogenic emissions from the selected cities. We analyzed the urban-emission-induced changes in near-surface concentrations of NO2 , O3 and PM 2.5 . We found increases in NO2 and PM 2.5 concentrations over cities by 4–6 ppbv and 4–6 µg m−3 , respectively, meaning that about 40 %–60 % and 20 %–40 % of urban concentrations of NO2 and PM 2.5 are caused by local emissions, and the rest is the result of emissions from the 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 of 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, and the modulation of UEI is also 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 modeled decrease in 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 footprint of urban emissions. Ignoring these meteorological changes can lead to the strong overestimation of UEI.
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01 Dec 2016
TL;DR: In this paper, the authors used a climate model to investigate the effectiveness of various urban heat mitigation strategies: cool roofs, street vegetation, green roofs, and reflective pavement, and found that by adopting highly reflective roofs, almost all the cities in the United States and southern Canada are transformed into white oases.
Abstract: Abstract. Heat stress is one of the most severe climate threats to human society in a future warmer world. The situation is further exacerbated in urban areas by urban heat islands (UHIs). Because the majority of world's population is projected to live in cities, there is a pressing need to find effective solutions for the heat stress problem. We use a climate model to investigate the effectiveness of various urban heat mitigation strategies: cool roofs, street vegetation, green roofs, and reflective pavement. Our results show that by adopting highly reflective roofs, almost all the cities in the United States and southern Canada are transformed into white oases – cold islands caused by cool roofs at midday, with an average oasis effect of −3.4 K in the summer for the period 2071–2100, which offsets approximately 80 % of the greenhouse gas (GHG) warming projected for the same period under the RCP4.5 scenario. A UHI mitigation wedge consisting of cool roofs, street vegetation, and reflective pavement has the potential to eliminate the daytime UHI plus the GHG warming.
3 citations
TL;DR: For instance, this article found that female birds preferred the multimodal cues while males foraged more randomly with respect to which cue was present, while urban birds preferred olfactory cues while forest birds preferred visual cues.
Abstract: Animals interpret their environment by combining information from multiple senses. The relative usefulness of different senses may vary between species, habitats and sexes; yet, how multimodal stimuli are integrated and prioritized is unknown for most taxa. We experimentally assessed foraging preferences of great tits (Parus major) to test whether urban and forest individuals prioritize visual and olfactory cues differently during foraging. We trained 13 wild-caught birds to associate multimodal (colour + odour) cues with a food reward and assessed their foraging preferences in a cue-separation test. In this, the birds could choose between the multimodal training cue and its olfactory or visual components. Our results suggest that the birds did not perceive multimodal cues in an integrated way, as their response was not stronger than for unimodal cue components. Urban birds preferred olfactory cues, while forest birds preferred visual cues. Nevertheless, female birds preferred the multimodal cue, while males foraged more randomly with respect to which cue was present. These findings contribute to our understanding of the relative roles of vision and olfaction in bird foraging behaviour. Future work should focus on how habitat- and sex-specific sensory prioritization modifies bird foraging behaviour and foraging success in the context of urban adaptations across populations.
1 citations
TL;DR: Based on the WRF-CMAQ model, the LULC2017 and LULC2001 (LULC data in 2001) scenarios were simulated for January and July 2017, respectively, to assess the impact of LULC changes on meteorology and fine particulate matter (PM2.5) concentrations in Changchun as discussed by the authors .
TL;DR: In this paper , a regional-scale numerical model (regional climate models RegCM and WRF coupled to chemistry transport model CAMx) is presented for present-day conditions (2015-2016) focusing on a range of central European cities and quantify the individual and combined impact of four potential contributors.
Abstract: Abstract. Urbanization or rural–urban transformation (RUT) represents one of the most important anthropogenic modifications of land use. To account for the impact of such process on air quality, multiple aspects of how this transformation impacts the air have to be accounted for. Here we present a regional-scale numerical model (regional climate models RegCM and WRF coupled to chemistry transport model CAMx) study for present-day conditions (2015–2016) focusing on a range of central European cities and quantify the individual and combined impact of four potential contributors. Apart from the two most studied impacts, i.e., urban emissions and the urban canopy meteorological forcing (UCMF, i.e., the impact of modified meteorological conditions), we also focus on two less studied contributors to the RUT impact on air quality: the impact of modified dry deposition due to transformed land use and the impact of modified biogenic emissions due to urbanization-induced vegetation modifications and changes in meteorological conditions affecting these emissions. To quantify each of these RUT contributors, we performed a cascade of simulations with CAMx driven with both RegCM and WRF wherein each effect was added one by one while we focused on gas-phase key pollutants: nitrogen, sulfur dioxide (NO2 and SO2), and ozone (O3). The validation of the results using surface observations showed an acceptable match between the modeled and observed annual cycles of monthly pollutant concentrations for NO2 and O3, while some discrepancies in the shape of the annual cycle were identified for some of the cities for SO2, pointing to incorrect representation of the annual emission cycle in the emissions model used. The diurnal cycle of ozone was reasonably captured by the model. We showed with an ensemble of 19 central European cities that the strongest contributors to the impact of RUT on urban air quality are the urban emissions themselves, resulting in increased concentrations for nitrogen (by 5–7 ppbv on average) and sulfur dioxide (by about 0.5–1 ppbv) as well as decreases for ozone (by about 2 ppbv). The other strongest contributor is the urban canopy meteorological forcing, resulting in decreases in primary pollutants (by about 2 ppbv for NO2 and 0.2 ppbv for SO2) and increases in ozone (by about 2 ppbv). Our results showed that they have to be accounted for simultaneously as the impact of urban emissions without considering UCMF can lead to overestimation of the emission impact. Additionally, we quantified two weaker contributors: the effect of modified land use on dry deposition and the effect of modified biogenic emissions. Due to modified dry deposition, summer (winter) NO2 increases (decreases) by 0.05 (0.02) ppbv, while there is almost no average effect for SO2 in summer and a 0.04 ppbv decrease in winter is modeled. The impact on ozone is much stronger and reaches a 1.5 ppbv increase on average. Due to modified biogenic emissions, a negligible effect on SO2 and winter NO2 is modeled, while for summer NO2, an increase by about 0.01 ppbv is calculated. For ozone, we found a much larger decreases of 0.5–1 ppbv. In summary, when analyzing the overall impact of urbanization on air pollution for ozone, the four contributors have the same order of magnitude and none of them should be neglected. For NO2 and SO2, the contributions of land-use-induced modifications of dry deposition and modified biogenic emissions have a smaller effect by at least 1 order of magnitude, and the error will thus be small if they are neglected.
TL;DR: The deadline for submission of abstracts is 01 June 2022 as discussed by the authors and the call for abstracts https://iaucposter2022.com/submission-and-registration.
Abstract: The deadline for submission of abstracts is 01 June 2022. Remember that this low-fee conference is focused on our graduate and early career researchers and will feature daily keynotes, a multiple time-zone friendly format, and will provide significant points of difference from other virtual conferences. Remember also that this is a stepping-stone to our flagship ICUC-11 conference to be held face-to-face in 2023. Please enjoy this current Urban Climate News – David Pearlmutter and his dedicated team have once again provided a newsletter packed with useful and informative material on various urban projects, features of special interest and newsworthy reports. With my very best wishes to you in these turbulent times. I wish to begin this column by briefly reflecting on the tragic situation that continues to unfold in Ukraine as a result of the totally unjust war inflicted on that country. Our IAUC membership includes a number of colleagues from Ukraine and there have been several memorable IAUC activities in that country. I wish to express my concern for them and their relatives in these very difficult times; please feel free to reach out if there is anything that we can do to help you in these difficult circumstances. In a recent column I mentioned the increased focus on urban areas in the current deliberations of the IPCC. This is confirmed with the recent release (February 28 and April 4) of the reports from IPCC Working Groups (WGs) II and III. This is especially the case for the WG II report “Impacts, Adaptation and Vulnerability” where a substantial number of the headline statements in the Summary for Policymakers (SPM) explicitly mention the key vulnerabilities of cities and their important role in addressing issues of climate change. This is impressive justification for our work in the area. For example, some key statements drawn from the WGII SPM include that... “4.3 billion urban people, property and critical infrastructure are increasingly adversely affected by climate change (high confidence). Key impacts include heat stress and flooding, and cascading impacts through supply chains and resource flows, which damage the lives, health and livelihoods of urban residents and connected rural places (high confidence).” And in relation to adaptation...“Urban systems are critical adaptation spaces for advancing the health and well-being of the majority of the world’s population (high confidence). Adaptation of natural, physical and social infrastructure play a critical role in building climate resilient urban systems.” The statement ...“Increasing evidence shows that nature-based solutions in urban areas (e.g., shade trees, natural ecosystems, green roofs) can provide important livelihood options and health benefits and reduce poverty while also supporting mitigation and adaptation (high confidence)”... and the underlying material in the background report draws heavily on the work of our community. I am sure that our membership will find many ways of using material from the current assessment for promoting their work. The August 2022 IAUC Virtual Poster Conference Organising Committee has met several times since the beginning of the year and has developed an very exciting program. I am delighted to announce the opening of the website (iaucposter2022.com) and the call for abstracts https://iaucposter2022.com/submission-and-registration. From the IAUC President
References
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01 Jan 2006
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TL;DR: In this paper, a simple spectral cloud ensemble was proposed to provide realistic values of the thermal forcing by convection under various synoptic conditions, such as tropical penetrative convection, tradewind cumuli, and extratropical organized convection.
Abstract: Observational studies indicate that a mass flux approach may provide a realistic framework for cumulus parameterization in large-scale models, but this approach, through the introduction of a spectral cloud ensemble, leads normally to rather complex schemes. In this paper the question is addressed whether much simpler schemes can already provide realistic values of the thermal forcing by convection under various synoptic conditions. This is done through verifying such a scheme first on data from field experiments for periods of tropical penetrative convection (GATE, Marshall Islands), tradewind cumuli (ATEX, BOMEX) and extratropical organized convection (SESAME-79) and then in a NWP model. The scheme considers a population of clouds where the cloud ensemble is described by a one-dimensional bulk model as earlier applied by Yanai et al. in a diagnostic study of tropical convection. Cumulus scale downdrafts are included. Various types of convection are represented, i.e., penetrative convection in c...
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TL;DR: The WRF/Chem model is statistically better skilled in forecasting O3 than MM5/Chem, with no appreciable differences between models in terms of bias with the observations, and consistently exhibits better skill at forecasting the O3 precursors CO and NOy at all of the surface sites.
2,709 citations
"The regional impact of urban emissi..." refers background in this paper
...WRF-Chem is a regional weather and climate model including chemistry described in Grell et al. (2005)....
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TL;DR: In this paper, a revised approach to cloud microphysical processes in a commonly used bulk microphysics parameterization and the importance of correctly representing properties of cloud ice are discussed, and the impact of sedimentation of ice crystals is also investigated.
Abstract: A revised approach to cloud microphysical processes in a commonly used bulk microphysics parameterization and the importance of correctly representing properties of cloud ice are discussed. Several modifications are introduced to more realistically simulate some of the ice microphysical processes. In addition to the assumption that ice nuclei number concentration is a function of temperature, a new and separate assumption is developed in which ice crystal number concentration is a function of ice amount. Related changes in ice microphysics are introduced, and the impact of sedimentation of ice crystals is also investigated. In an idealized thunderstorm simulation, the distribution of simulated clouds and precipitation is sensitive to the assumptions in microphysical processes, whereas the impact of the sedimentation of cloud ice is small. Overall, the modifications introduced to microphysical processes play a role in significantly reducing cloud ice and increasing snow at colder temperatures and ...
2,277 citations
"The regional impact of urban emissi..." refers methods in this paper
...Boundary layer physics, cloud and rain microphysics and convection were treated by the Holtslag planetary boundary layer (PBL) parameterization (HOL; Holtslag et al., 1990), WSM5 5- class moisture scheme (Hong et al., 2004) and the Tiedtke scheme (Tiedtke et al., 1989)....
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