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Trends of extreme-temperature episodes in cities are increasing (in frequency, magnitude and duration) due to regional climate change in interaction with urban effects. Urban morphologies and thermal properties of the materials used to build them are factors that influence spatial and temporal climate variability and are one of the main reasons for the climatic singularity of cities. This paper presents a methodology to evaluate the urban and peri-urban effect on extreme-temperature exposure in Barcelona (Spain), using the Local Climate Zone (LCZ) classification as a basis, which allows a comparison with other cities of the world characterised using this criterion. LCZs were introduced as input of the high-resolution UrbClim model (100 m spatial resolution) to create daily temperature (median and maximum) series for summer (JJA) during the period 1987 to 2016, pixel by pixel, in order to create a cartography of extremes. Using the relationship between mortality due to high temperatures and temperature distribution, the heat exposure of each LCZ was obtained. Methodological results of the paper show the improvement obtained when LCZs were mapped through a combination of two techniques (land cover–land use maps and the World Urban Database and Access Portal Tools – WUDAPT – method), and the paper proposes a methodology to obtain the exposure to high temperatures of different LCZs in urban and peri-urban areas. In the case of Barcelona, the distribution of temperatures for the 90th percentile (about 3–4 ∘ C above the average conditions) leads to an increase in the relative risk of mortality of 80 %. [ABSTRACT FROM AUTHOR]

Groundwater is a vital resource for the development of urban areas, where the problem focuses on the quantity and on the quality of this freshwater resource. Barcelona is a good example as because currently groundwater is used for irrigation of parks and gardens and street cleaning due to its poor quality as drinking water source. Among the pollutants found in groundwater, of special interest are contaminants of emerging concern (CEC), as they pose a high risk to the aquatic environment and human health. The behaviour, spatial distribution and processes that control them in the aquatic environment are still uncertain and most of them are unregulated. In this paper we study the inputs and processes controlling the hydrochemistry of Barcelona urban groundwater with special emphasis on the CEC. We selected 29 CEC that were detected at high concentrations of up to 1 µ g L -1 (e.g. gemfibrozil, benzotriazole, among others). Towards the higher zones we identify groundwater with relative low mineralization more proximate to the natural recharge composition, while towards the urban area the anthropic inputs are evident (e.g. nitrate concentrations range from 50 to 200 mg L -1). Near the Besòs river there is a clear contribution from this superficial water highly polluted, mostly from wastewater treatment plant (WWTP) discharges, and reducing conditions. The main contributor of CEC pollution in groundwater was the river-aquifer interaction (Besòs river), while towards the urban area it might come from sewage seepage and probably a minor input from urban runoff. The redox state of these waters seems to control the fate and occurrence of several of these CEC. The limitations of this study are restricted to a single sampling campaign, therefore these results should be corroborated with other sampling campaigns, including the seasonal variations, which would allow establishing more robust conclusions. [ABSTRACT FROM AUTHOR]

Trends of extreme temperature episodes in cities are increasing (in frequency, magnitude and duration) due to regional climate change in interaction with the urban effects. Urban morphologies and thermal properties of the materials used to build them are factors that influence the spatial and temporal climate variability and becomes one of the main reasons for the climatic singularity of cities. This paper presents a proposal to evaluate the urban and peri-urban effect on extreme temperatures exposure in Barcelona (Spain), using the Local Climate Zone (LCZ) framework as a base statement, that allows the comparison with other cities of the world characterized using this criterion. LCZs were introduced as input of the high resolution UrbClim model (100 m spatial resolution) to create the daily temperatures (median and maximum) series for summer (JJA) during the period 1987 to 2016, pixel by pixel, in order to create a cartography of extremes. Using the relationship between mortality due to high temperatures and the temperature distribution, the heat exposure of each LCZ was obtained. Methodological results of the paper show the improvement obtained when LCZs were mapped through a combination of two techniques (from Land Cover/Land Use maps and from WUDAPT method), as well as proposes a methodology to obtain the exposure to high temperatures of different LCZs on urban and peri-urban areas. In the case of Barcelona, the distribution of temperatures for the 90th percentile (about 3–4 °C compared to average conditions) leads to an increase in the relative risk of mortality of 80 %. [ABSTRACT FROM AUTHOR]

In orbit since late 2017, the Tropospheric Monitoring Instrument (TROPOMI) is offering new outstanding opportunities for better understanding the emission and fate of nitrogen dioxide (NO 2) pollution in the troposphere. In this study, we provide a comprehensive analysis of the spatio-temporal variability of TROPOMI NO 2 tropospheric columns (TrC-NO 2) over the Iberian Peninsula during 2018–2021, considering the recently developed Product Algorithm Laboratory (PAL) product. We complement our analysis with estimates of NO x anthropogenic and natural soil emissions. Closely related to cloud cover, the data availability of TROPOMI observations ranges from 30 %–45 % during April and November to 70 %–80 % during summertime, with strong variations between northern and southern Spain. Strongest TrC-NO 2 hotspots are located over Madrid and Barcelona, while TrC-NO 2 enhancements are also observed along international maritime routes close the strait of Gibraltar, and to a lesser extent along specific major highways. TROPOMI TrC-NO 2 appear reasonably well correlated with collocated surface NO 2 mixing ratios, with correlations around 0.7–0.8 depending on the averaging time. We investigate the changes of weekly and monthly variability of TROPOMI TrC-NO 2 depending on the urban cover fraction. Weekly profiles show a reduction of TrC-NO 2 during the weekend ranging from - 10 % to - 40 % from least to most urbanized areas, in reasonable agreement with surface NO 2. In the largest agglomerations like Madrid or Barcelona, this weekend effect peaks not in the city center but in specific suburban areas/cities, suggesting a larger relative contribution of commuting to total NO x anthropogenic emissions. The TROPOMI TrC-NO 2 monthly variability also strongly varies with the level of urbanization, with monthly differences relative to annual mean ranging from - 40 % in summer to + 60 % in winter in the most urbanized areas, and from - 10 % to + 20 % in the least urbanized areas. When focusing on agricultural areas, TROPOMI observations depict an enhancement in June–July that could come from natural soil NO emissions. Some specific analysis of surface NO 2 observations in Madrid show that the relatively sharp NO 2 minimum used to occur in August (drop of road transport during holidays) has now evolved into a much broader minimum partly de-coupled from the observed local road traffic counting; this change started in 2018, thus before the COVID-19 outbreak. Over 2019–2021, a reasonable consistency of the inter-annual variability of NO 2 is also found between both datasets. Our study illustrates the strong potential of TROPOMI TrC-NO 2 observations for complementing the existing surface NO 2 monitoring stations, especially in the poorly covered rural and maritime areas where NO x can play a key role, notably for the production of tropospheric O 3. [ABSTRACT FROM AUTHOR]

A powerful methodology, based on the multivariate curve resolution alternating least squares (MCR-ALS) method with quadrilinearity constraints, is proposed to handle complex and incomplete four-way atmospheric data sets, providing concise results that are easy to interpret. Changes in air quality by nitrogen dioxide (NO 2), ozone (O 3), and particulate matter (PM 10) in eight sampling stations located in the Barcelona metropolitan area and other parts of Catalonia during the COVID-19 lockdown period (2020) with respect to previous years (2018 and 2019), are investigated using such methodology. The MCR-ALS simultaneous analysis of the three contaminants among the eight stations and for the 3 years allows the evaluation of potential correlations among the pollutants, even when having missing data blocks. Correlated profiles are shown by NO 2 and PM 10 due to similar pollution sources (traffic and industry), evidencing a decrease in 2019 and 2020 due to traffic restriction policies and the COVID-19 lockdown period, especially noticeable in the most transited urban areas (i.e., Vall d'Hebron, Granollers and Gràcia). The O 3 evidences an opposed interannual trend, showing higher amounts in 2019 and 2020 with respect to 2018 due to the decreased titration effect, more significant in rural areas (Begur) and in the control site (Obserbatori Fabra). [ABSTRACT FROM AUTHOR]

The NO2 annual air quality limit value is systematically exceeded in many European cities. In this context, understanding human exposure, improving policy and planning, and providing forecasts requires the development of accurate air quality models at the urban (street level) scale. We describe CALIOPE-Urban, a system coupling CALIOPE – an operational mesoscale air quality forecast system based on the HERMES (emissions), WRF (meteorology) and CMAQ (chemistry) models – with the urban roadway dispersion model R-LINE. Our developments have focused on Barcelona city (Spain), but the methodology may be replicated for other cities in the future. WRF drives pollutant dispersion and CMAQ provides background concentrations to R-LINE. Key features of our system include the adaptation of R-LINE to street canyons, the use of a new methodology that considers upwind grid cells in CMAQ to avoid double counting traffic emissions, a new method to estimate local surface roughness within street canyons, and a vertical mixing parameterisation that considers urban geometry and atmospheric stability to calculate surface level background concentrations. We show that the latter is critical to correct the night-time overestimations in our system. Both CALIOPE and CALIOPE-Urban are evaluated using two sets of observations. The temporal variability is evaluated against measurements from five traffic sites and one urban background site for April–May 2013. While both systems show a fairly good agreement at the urban background site, CALIOPE-Urban shows a better agreement at traffic sites. The spatial variability is evaluated using 182 passive dosimeters that were distributed across Barcelona during 2 weeks for February–March 2017. In this case, the coupled system also shows a more realistic distribution than the mesoscale system, which systematically underpredicts NO2 close to traffic emission sources. Overall CALIOPE-Urban improves mesoscale model results, demonstrating that the combination of both scales provides a more realistic representation of NO2 spatio-temporal variability in Barcelona. [ABSTRACT FROM AUTHOR]

Continuous measurements of surface mixed layer (SML), decoupled residual/convective layer (DRCL) and aerosol backscatter coefficient were performed within the Barcelona (Spain) boundary layer from September to October 2010 (30 days) in the framework of the SAPUSS (Solving Aerosol Problems by Using Synergistic Strategies) field campaign. Two near-infrared ceilometers (Jenoptik CHM15K), vertically and horizontally probing (only vertical profiles are herein discussed), were deployed. Ceilometer-based DRCLs (1761±363m a.g.l.) averaged over the campaign duration were twice as high as the mean SML (904±273m a.g.l.). Both DRCL and SML showed a marked SML diurnal cycle. Ceilometer data were compared with potential temperature profiles measured by daily radiosounding (twice a day, midnight and midday) to interpret the boundary layer structure in the coastal urban area of Barcelona. The overall agreement (R² = 0.80) between the ceilometer-retrieved and radiosounding-based SML heights (h) revealed overestimation of the SML by the ceilometer (Δh =145±145 m). After separating the data in accordance with different atmospheric scenarios, the lowest SML (736±183 m) and DRCL (1573±428 m) were recorded during warm North African (NAF) advected air mass. By contrast, higher SML and DRCL were observed during stagnant Regional (REG) (911±234m and 1769±314 m, respectively) and cold Atlantic (ATL) (965±222m and 1878±290 m, respectively) air masses. In addition to being the lowest, the SML during the NAF scenario frequently showed a flat upper boundary throughout the day possibly because of the strong winds from the Mediterranean Sea limiting the midday SML convective growth. The mean backscatter coefficients were calculated at two selected heights representative of middle and top SML portions, i.e. ^500 = 0.59±0.45Mm-1 sr-1 and 800 = 0.87±0.68Mm-1 sr-1 at 500m and 800m a.g.l., respectively. The highest backscatter coefficients were observed during NAF (β500 = 0.77±0.57Mm-1 sr-1) when compared with ATL (β500 = 0.51±0.44Mm-1 sr-1) and REG (β500 = 0.64±0.39Mm-1 sr-1). The relationship between the vertical change in backscatter coefficient and atmospheric stability (∂θ/∂z) was investigated in the first 3000m a.g.l., aiming to study how the unstable, stable or neutral atmospheric conditions of the atmosphere alter the distribution of aerosol backscatter with height over Barcelona. A positive correlation between unstable conditions and enhanced backscatter and vice versa was found. [ABSTRACT FROM AUTHOR]