scholarly journals CO<sub>2</sub> dispersion modelling over Paris region within the CO<sub>2</sub>-MEGAPARIS project

2012 ◽  
Vol 12 (10) ◽  
pp. 28155-28193 ◽  
Author(s):  
C. Lac ◽  
R. P. Donnelly ◽  
V. Masson ◽  
S. Pal ◽  
S. Donier ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Temporal Variability ◽  
Urban Areas ◽  
Onset Time ◽  
Urban Canopy ◽  
Co2 Concentration ◽  
Horizontal Resolution ◽  
Spatial And Temporal Variability ◽  
Good Representation ◽  
Urban Sites

Abstract. Accurate simulation of the spatial and temporal variability of tracer mixing ratios over urban areas is challenging, but essential in order to utilize CO2 measurements in an atmospheric inverse framework to better estimate regional CO2 fluxes. This study investigates the ability of a high-resolution model to simulate meteorological and CO2 fields around Paris agglomeration, during the March field campaign of the CO2-MEGAPARIS project. The mesoscale atmospheric model Meso-NH, running at 2 km horizontal resolution, is coupled with the Town-Energy Balance (TEB) urban canopy scheme and with the Interactions between Soil, Biosphere and Atmosphere CO2-reactive (ISBA-A-gs) surface scheme, allowing a full interaction of CO2 between the surface and the atmosphere. Statistical scores show a good representation of the Urban Heat Island (UHI) and urban-rural contrasts. Boundary layer heights (BLH) at urban, sub-urban and rural sites are well captured, especially the onset time of the BLH increase and its growth rate in the morning, that are essential for tall tower CO2 observatories. Only nocturnal BLH at sub-urban sites are slightly underestimated a few nights, with a bias less than 50 m. At Eiffel tower, the observed spikes of CO2 maxima occur every morning exactly at the time at which the Atmospheric Boundary Layer (ABL) growth reaches the measurement height. The timing of the CO2 cycle is well captured by the model, with only small biases on CO2 concentrations, mainly linked to the misrepresentation of anthropogenic emissions, as the Eiffel site is at the heart of trafic emission sources. At sub-urban ground stations, CO2 measurements exhibit maxima at the beginning and at the end of each night, when the ABL is fully contracted, with a very strong spatio-temporal variability. The CO2 cycle at these sites is generally well reproduced by the model, even if some biases on the nocturnal maxima appear in the Paris plume parly due to small errors on the vertical transport, or in the vicinity of airports due to small errors on the horizontal transport (wind direction). A sensitivity test without urban parameterisation removes UHI and underpredicts nighttime BLH over urban and sub-urban sites, leading to large overestimation of nocturnal CO2 concentration at the sub-urban sites. The agreement of daytime and nighttime BLH and CO2 predictions of the reference simulation over Paris agglomeration demonstrates the potential of using the meso-scale system on urban and sub-urban area in the context of inverse modelling.

scholarly journals CO<sub>2</sub> dispersion modelling over Paris region within the CO<sub>2</sub>-MEGAPARIS project

2013 ◽  
Vol 13 (9) ◽  
pp. 4941-4961 ◽  
Author(s):  
C. Lac ◽  
R. P. Donnelly ◽  
V. Masson ◽  
S. Pal ◽  
S. Riette ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Temporal Variability ◽  
Urban Areas ◽  
Onset Time ◽  
Urban Canopy ◽  
Horizontal Resolution ◽  
Spatial And Temporal Variability ◽  
Good Representation ◽  
Mixing Ratios ◽  
Urban Rural

Abstract. Accurate simulation of the spatial and temporal variability of tracer mixing ratios over urban areas is a challenging and interesting task needed to be performed in order to utilise CO2 measurements in an atmospheric inverse framework and to better estimate regional CO2 fluxes. This study investigates the ability of a high-resolution model to simulate meteorological and CO2 fields around Paris agglomeration during the March field campaign of the CO2-MEGAPARIS project. The mesoscale atmospheric model Meso-NH, running at 2 km horizontal resolution, is coupled with the Town Energy Balance (TEB) urban canopy scheme and with the Interactions between Soil, Biosphere and Atmosphere CO2-reactive (ISBA-A-gs) surface scheme, allowing a full interaction of CO2 modelling between the surface and the atmosphere. Statistical scores show a good representation of the urban heat island (UHI) with stronger urban–rural contrasts on temperature at night than during the day by up to 7 °C. Boundary layer heights (BLH) have been evaluated on urban, suburban and rural sites during the campaign, and also on a suburban site over 1 yr. The diurnal cycles of the BLH are well captured, especially the onset time of the BLH increase and its growth rate in the morning, which are essential for tall tower CO2 observatories. The main discrepancy is a small negative bias over urban and suburban sites during nighttime (respectively 45 m and 5 m), leading to a few overestimations of nocturnal CO2 mixing ratios at suburban sites and a bias of +5 ppm. The diurnal CO2 cycle is generally well captured for all the sites. At the Eiffel tower, the observed spikes of CO2 maxima occur every morning exactly at the time at which the atmospheric boundary layer (ABL) growth reaches the measurement height. At suburban ground stations, CO2 measurements exhibit maxima at the beginning and at the end of each night, when the ABL is fully contracted, with a strong spatio-temporal variability. A sensitivity test without urban parameterisation removes the UHI and underpredicts nighttime BLH over urban and suburban sites, leading to large overestimation of nocturnal CO2 mixing ratio at the suburban sites (bias of +17 ppm). The agreement between observation and prediction for BLH and CO2 concentrations and urban–rural increments, both day and night, demonstrates the potential of using the urban mesoscale system in the context of inverse modelling

scholarly journals Intra–Community Scale Variability of Air Quality in the Center of a Megacity in South Korea: A High-Density Cost-Effective Sensor Network

2021 ◽  
Vol 11 (19) ◽  
pp. 9105
Author(s):  
Yongmi Park ◽  
Ho-Seon Park ◽  
Subin Han ◽  
Kyucheol Hwang ◽  
Seunghyun Lee ◽  
...  
Keyword(s):  
Air Quality ◽  
South Korea ◽  
Sensor Network ◽  
Temporal Variability ◽  
Urban Areas ◽  
Pearson Correlation ◽  
Urban Canopy ◽  
Air Pollutant ◽  
Sensor Nodes ◽  
Spatial And Temporal Variability

To investigate the spatial and temporal variability of air quality (CO, NO2, O3, and PM2.5) with a high spatial resolution in various adjacent micro-environments, 30 sets of sensor-nodes were deployed within an 800 × 800 m monitoring domain in the center of the largest megacity (Seoul) in South Korea. The sensor network was operated in summer and winter. The daily variation in air pollutant concentrations revealed a similar trend, with discernible concentration differences among monitoring sub-sites and a government-operated air quality monitoring station. These differences in pollutant levels (except PM2.5) among the sub-sites were pronounced in the daytime with high volumes of traffic. The coefficient of divergence and Pearson correlation coefficient showed that spatial and temporal variability was more significant in summer than winter. Ozone displayed the greatest spatial variability, with little temporal variability among the sub-sites and a negative correlation with NO2, implying that ozone concentrations were primarily determined by vehicular NOX emissions due to NO titration effects under the urban canopy. The PM2.5 concentration displayed homogeneous spatial and temporal distributions over the entire monitoring period, implying that PM2.5 monitoring with at least a 1 × 1 km resolution is sufficient to examine the spatial and temporal heterogeneity in urban areas.

scholarly journals Spatial and temporal variability of rainfall and their effects on hydrological response in urban areas – a review

2017 ◽  
Vol 21 (7) ◽  
pp. 3859-3878 ◽  
Author(s):  
Elena Cristiano ◽  
Marie-Claire ten Veldhuis ◽  
Nick van de Giesen
Keyword(s):  
Temporal Variability ◽  
Urban Areas ◽  
Rainfall Variability ◽  
Urban Environments ◽  
Hydrological Processes ◽  
Small Scale ◽  
Spatial And Temporal Variability ◽  
Hydrological Response ◽  
Weather Radars ◽  
New Instruments

Abstract. In urban areas, hydrological processes are characterized by high variability in space and time, making them sensitive to small-scale temporal and spatial rainfall variability. In the last decades new instruments, techniques, and methods have been developed to capture rainfall and hydrological processes at high resolution. Weather radars have been introduced to estimate high spatial and temporal rainfall variability. At the same time, new models have been proposed to reproduce hydrological response, based on small-scale representation of urban catchment spatial variability. Despite these efforts, interactions between rainfall variability, catchment heterogeneity, and hydrological response remain poorly understood. This paper presents a review of our current understanding of hydrological processes in urban environments as reported in the literature, focusing on their spatial and temporal variability aspects. We review recent findings on the effects of rainfall variability on hydrological response and identify gaps where knowledge needs to be further developed to improve our understanding of and capability to predict urban hydrological response.

scholarly journals Flow Variability in a North American Downtown Street Canyon

2007 ◽  
Vol 46 (6) ◽  
pp. 851-877 ◽  
Author(s):  
Petra Klein ◽  
James V. Clark
Keyword(s):  
Boundary Layer ◽  
Urban Areas ◽  
Street Canyon ◽  
Atmospheric Stability ◽  
Urban Canopy ◽  
Canopy Layer ◽  
Street Canyons ◽  
Sonic Anemometers ◽  
Roof Level ◽  
Street Canyon Flow

Abstract Previous field and laboratory studies have indicated that flow and turbulence inside urban areas and, in particular, in street canyons, is very complex and is associated with wakes and vortices developing near buildings. However, a number of open questions still exist, primarily with regard to which parameters determine the structure of street-canyon flow. The paper presents results from high-resolution wind measurements in a downtown urban street canyon in Oklahoma City, Oklahoma, that were conducted during the Joint Urban 2003 tracer experiment. Data collected with sonic anemometers on two towers installed on opposite sites of the street canyon, each with five different measurement levels, have been analyzed, and the variation of in-canyon flow and turbulence parameters with wind direction and atmospheric stability is discussed. It was found that the street-canyon flow is strongly channeled and its direction is determined by the along-canyon component of the above-roof-level winds. As a consequence, the direction of the street-level winds changes abruptly, and small variations of the upwind direction can significantly alter the in-canyon flow properties. Contrary to results from studies with idealized street canyons, the along-canyon flow components remained significant even for conditions with winds approaching the street at almost perpendicular angles. For such wind directions, a tendency toward development of street-canyon vortices with pronounced vertical motions have been found. However, the complex building geometries at the chosen measurement site enhance the complexity of the flow patterns, and situations with a classic street-canyon vortex rotating in the street could not be identified. In addition, the comprehensive dataset from the Joint Urban 2003 field campaign allowed detailed study of the influence of boundary layer stability on flow in the urban canopy layer. It has become clear that very different conclusions can be drawn with regard to these effects depending on the choice of reference values used in the analysis of the street-canyon data. Using winds from higher elevations in the atmospheric boundary layer (250 m) as reference data, one would conclude that atmospheric stability strongly influences in-canyon flow and, in particular, turbulence. However, only minor stability effects are still seen after normalization with wind speed values at average roof-level height (80 m). This choice allows one to conclude that the in-canyon flow is primarily driven by the boundary layer wind field at average roof level.

scholarly journals Spatial and temporal variability of ozone along the Colorado Front Range occurring over 2 days with contrasting wind flow

Elem Sci Anth ◽  
2021 ◽  
Vol 9 (1) ◽  
Author(s):  
Lisa S. Darby ◽  
Christoph J. Senff ◽  
Raul J. Alvarez II ◽  
Robert M. Banta ◽  
Laura Bianco ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Air Quality ◽  
Rocky Mountains ◽  
Urban Areas ◽  
High Elevation ◽  
Quality Data ◽  
Spatial And Temporal Variability ◽  
Front Range ◽  
Monitoring Networks ◽  
Wilderness Areas

Transport of pollution into pristine wilderness areas is of concern for both federal and state agencies. Assessing such transport in complex terrain is a challenge when relying solely on data from standard federal or state air quality monitoring networks because of the sparsity of network monitors beyond urban areas. During the Front Range air quality study, conducted in the summer of 2008 in the vicinity of Denver, CO, research-grade surface air quality data, vertical wind profiles and mixing heights obtained by radar wind profilers, and ozone profile data obtained by an airborne ozone differential absorption lidar augmented the local regulatory monitoring networks. Measurements from this study were taken on 2 successive days at the end of July 2008. On the first day, the prevailing winds were downslope westerly, advecting pollution to the east of the Front Range metropolitan areas. On this day, chemistry measurements at the mountain and foothills surface stations showed seasonal background ozone levels of approximately 55–68 ppbv (nmol mol–1 by volume). The next day, upslope winds prevailed, advecting pollution from the Plains into the Rocky Mountains and across the Continental Divide. Mountain stations measured ozone values greater than 90 ppbv, comparable to, or greater than, nearby urban measurements. The measurements show the progression of the ozone-enriched air into the mountains and tie the westward intrusion into high-elevation mountain sites to the growth of the afternoon boundary layer. Thus, under deep upslope flow conditions, ozone-enriched air can be advected into wilderness areas of the Rocky Mountains. Our findings highlight a process that is likely to be an important ozone transport mechanism in mountainous terrain adjacent to ozone source areas when the right circumstances come together, namely a deep layer of light winds toward a mountain barrier coincident with a deep regional boundary layer.

scholarly journals Energetics of Urban Canopies: A Meteorological Perspective

J ◽  
2021 ◽  
Vol 4 (4) ◽  
pp. 645-663
Author(s):  
Edson Marciotto ◽  
Marcos Vinicius Bueno de de Morais
Keyword(s):  
Boundary Layer ◽  
Urban Heat Island ◽  
Urban Areas ◽  
Numerical Models ◽  
Urban Canopy ◽  
Urban Heat Island Intensity ◽  
Heat Island ◽  
Local Flow ◽  
Urban Climatology ◽  
Urban Heat

The urban climatology consists not only of the urban canopy temperature but also of wind regime and boundary layer evolution among other secondary variables. The energetic input and response of urbanized areas is rather different to rural or forest areas. In this paper, we outline the physical characteristics of the urban canopy that make its energy balance depart from that of vegetated areas and change local climatology. Among the several canopy characteristics, we focus on the aspect ratio h/d and its effects. The literature and methods of retrieving meteorological quantities in urban areas are reviewed and a number of physical analyzes from conceptual or numerical models are presented. In particular, the existence of a maximum value for the urban heat island intensity is discussed comprehensively. Changes in the local flow and boundary layer evolution due to urbanization are also discussed. The presence of vegetation and water bodies in urban areas are reviewed. The main conclusions are as follows: for increasing h/d, the urban heat island intensity is likely to attain a peak around h/d≈4 and decrease for h/d>4; the temperature at the pedestrian level follows similar behavior; the urban boundary layer grows slowly, which in combination with low wind, can worsen pollution dispersion.

Sign in / Sign up

Export Citation Format

Share Document