Found 2670 publications. Showing page 50 of 267:
Due to its comparatively high spatial resolution and its daily repeat frequency, the tropospheric nitrogen dioxide product provided by the TROPOspheric Monitoring Instrument (TROPOMI) onboard the Sentinel-5 Precursor platform has attracted significant attention for its potential for urban-scale monitoring of air quality. However, the exploitation of such data in, for example, operational assimilation of local-scale dispersion models is often complicated by substantial data gaps due to cloud cover or other retrieval limitations. These challenges are particularly prominent in high-latitude regions where significant cloud cover and high solar zenith angles are often prevalent. Using the example of Norway as a representative case for a high-latitude region, we here evaluate the spatiotemporal patterns in the availability of valid data from the operational TROPOMI tropospheric nitrogen dioxide (NO2) product over five urban areas (Oslo, Bergen, Trondheim, Stavanger, and Kristiansand) and a 2.5 year period from July 2018 through November 2020. Our results indicate that even for relatively clean environments such as small Norwegian cities, distinct spatial patterns of tropospheric NO2 are visible in long-term average datasets from TROPOMI. However, the availability of valid data on a daily level is limited by both cloud cover and solar zenith angle (during the winter months), causing the fraction of valid retrievals in each study site to vary from 20% to 50% on average. A temporal analysis shows that for our study sites and the selected period, the fraction of valid pixels in each domain shows a clear seasonal cycle reaching a maximum of 50% to 75% in the summer months and 0% to 20% in winter. The seasonal cycle in data availability shows the inverse behavior of NO2 pollution in Norway, which typically has its peak in the winter months. However, outside of the mid-winter period we find the TROPOMI NO2 product to provide sufficient data availability for detailed mapping and monitoring of NO2 pollution in the major urban areas in Norway and see potential for the use of the data in local-scale data assimilation and emission inversions applications.
2021
Implementing Citizen Science in Primary Schools: Engaging Young Children in Monitoring Air Pollution
Most European cities have air pollution levels that exceed the threshold for human health protection. Children are sensitive to air pollution and thus it is important to ensure they are not exposed to high concentrations of air pollutants. In order to make a positive change toward cleaner air, a joint effort is needed, involving all civil society actors. Schools and local communities have a decisive role, and can, for example, become engaged in citizen science initiatives and knowledge coproduction. In 2019, with the aim of raising awareness for air quality, NILU developed a citizen science toolbox to engage primary schools in monitoring air quality using a simple and affordable measuring method based on paper and petroleum jelly. This is a very visual method, where the students can clearly see differences from polluted and non-polluted places by looking at “how dirty” is the paper. In addition to the qualitative analysis, we have developed an air meter scale making possible for the students to obtain an indicative measurement of the air pollution level. The comparison between the paper and petroleum jelly method against reference PM10 data collected at two official air quality stations showed a good agreement. The method is a strong candidate for dust monitoring in citizen science projects, making participation possible and empowering people with simple tools at hand. The toolbox is targeted at primary schools and children aged 6–12 years, although it can easily be adapted to other age groups. The main objective of the toolbox is to involve young children who are usually not targeted in air quality citizen science activities, to develop research skills and critical thinking, as well as increase their awareness about the air they breathe. The toolbox is designed to engage students in hands-on activities, that challenge them to create hypotheses, design scientific experiments, draw conclusions and find creative solutions to the air pollution problem. The toolbox includes all the necessary material for the teachers, including guidance, background information and templates facilitating the incorporation in the school curricula. The toolbox was launched as part of the Oslo European Green Capital in March 2019 and was later included as part of the European Clean Air Day initiative coordinated by the European Citizen Science Association (ECSA) working group on air quality. A total of 30 schools and 60 4th grade classes (aged 8–9 years) participated in the Oslo campaign. The citizen science approach employed in the schools, combined the four key elements that promote knowledge integration: elicit ideas, add new ideas, distinguish among ideas and reflect and sort out ideas. Although the main goal of the study was to provide simple but robust tools for engaging young children in air quality monitoring, we also carried out ex-ante and ex-post evaluations in 12 of the participating classes using a 10-question multiple choice test to have an indication of the contribution of the activity to knowledge integration. The results show that there is an increase in the number of correct answers, as well as a reduction in the misconceptions after conducting the activity. These results indicate that applying a citizen science approach improved science instruction and helped knowledge integration by including students' views and taking advantage of the diverse ideas students generated. Citizen science gives learners an insight into the ways that scientists generate solutions for societal problems. But more important, citizen science provides a way to differ from the classic view of the learner as an absorber of information, by considering the social context of instruction and making the topic personally relevant.
2021
Measurements of total ozone column and effective cloud transmittance have been performed since 1995 at the three Norwegian sites Oslo/Kjeller, Andøya/Tromsø, and in Ny-Ålesund (Svalbard). These sites are a subset of nine stations included in the Norwegian UV monitoring network, which uses ground-based ultraviolet (GUV) multi-filter instruments and is operated by the Norwegian Radiation and Nuclear Safety Authority (DSA) and the Norwegian Institute for Air Research (NILU). The network includes unique data sets of high-time-resolution measurements that can be used for a broad range of atmospheric and biological exposure studies. Comparison of the 25-year records of GUV (global sky) total ozone measurements with Brewer direct sun (DS) measurements shows that the GUV instruments provide valuable supplements to the more standardized ground-based instruments. The GUV instruments can fill in missing data and extend the measuring season at sites with reduced staff and/or characterized by harsh environmental conditions, such as Ny-Ålesund. Also, a harmonized GUV can easily be moved to more remote/unmanned locations and provide independent total ozone column data sets. The GUV instrument in Ny-Ålesund captured well the exceptionally large Arctic ozone depletion in March/April 2020, whereas the GUV instrument in Oslo recorded a mini ozone hole in December 2019 with total ozone values below 200 DU. For all the three Norwegian stations there is a slight increase in total ozone from 1995 until today. Measurements of GUV effective cloud transmittance in Ny-Ålesund indicate that there has been a significant change in albedo during the past 25 years, most likely resulting from increased temperatures and Arctic ice melt in the area surrounding Svalbard.
2021
The influence of probe spacing and probe bias in a double Langmuir probe setup
Multi-needle Langmuir probes are mounted on satellites and sounding rockets for high-frequency characterization of plasma in the ionosphere. Mounted on a spacecraft, the recorded probe current often differs from expected results. In this paper, we perform a numerical study using a particle in cell model to see how the spacing between the individual probes used in a multi-needle setup influences the measured current. We also study how the applied probe bias voltage can contribute to deviations. In our study, we use realistic electron temperatures and electron densities for the relevant part of the ionosphere. However, the results should be generally applicable and valid for other space environments as well as for laboratory Langmuir probe applications. From our study, we can see that when the distance is short, less than two Debye lengths, the current is highly affected, and we can see deviations of more than 60% compared to a single probe setup.
2021
The Integrated Carbon Observation System in Europe
Since 1750, land use change and fossil fuel combustion has led to a 46 % increase in the atmospheric carbon dioxide (CO2) concentrations, causing global warming with substantial societal consequences. The Paris Agreement aims to limiting global temperature increases to well below 2°C above pre-industrial levels. Increasing levels of CO2 and other greenhouse gases (GHGs), such as methane (CH4) and nitrous oxide (N2O), in the atmosphere are the primary cause of climate change. Approximately half of the carbon emissions to the atmosphere is sequestered by ocean and land sinks, leading to ocean acidification but also slowing the rate of global warming. However, there are significant uncertainties in the future global warming scenarios due to uncertainties in the size, nature and stability of these sinks. Quantifying and monitoring the size and timing of natural sinks and the impact of climate change on ecosystems are important information to guide policy-makers’ decisions and strategies on reductions in emissions. Continuous, long-term observations are required to quantify GHG emissions, sinks, and their impacts on Earth systems. The Integrated Carbon Observation System (ICOS) was designed as the European in situ observation and information system to support science and society in their efforts to mitigate climate change. It provides standardized and open data currently from over 140 measurement stations across 12 European countries. The stations observe GHG concentrations in the atmosphere and carbon and GHG fluxes between the atmosphere, land surface and the oceans. This article describes how ICOS fulfills its mission to harmonize these observations, ensure the related long-term financial commitments, provide easy access to well-documented and reproducible high-quality data and related protocols and tools for scientific studies, and deliver information and GHG-related products to stakeholders in society and policy.
2021
Within the framework of the AeroCom (Aerosol Comparisons between Observations and Models) initiative, the state-of-the-art modelling of aerosol optical properties is assessed from 14 global models participating in the phase III control experiment (AP3). The models are similar to CMIP6/AerChemMIP Earth System Models (ESMs) and provide a robust multi-model ensemble. Inter-model spread of aerosol species lifetimes and emissions appears to be similar to that of mass extinction coefficients (MECs), suggesting that aerosol optical depth (AOD) uncertainties are associated with a broad spectrum of parameterised aerosol processes.
Total AOD is approximately the same as in AeroCom phase I (AP1) simulations. However, we find a 50 % decrease in the optical depth (OD) of black carbon (BC), attributable to a combination of decreased emissions and lifetimes. Relative contributions from sea salt (SS) and dust (DU) have shifted from being approximately equal in AP1 to SS contributing about 2∕3 of the natural AOD in AP3. This shift is linked with a decrease in DU mass burden, a lower DU MEC, and a slight decrease in DU lifetime, suggesting coarser DU particle sizes in AP3 compared to AP1.
Relative to observations, the AP3 ensemble median and most of the participating models underestimate all aerosol optical properties investigated, that is, total AOD as well as fine and coarse AOD (AODf, AODc), Ångström exponent (AE), dry surface scattering (SCdry), and absorption (ACdry) coefficients. Compared to AERONET, the models underestimate total AOD by ca. 21 % ± 20 % (as inferred from the ensemble median and interquartile range). Against satellite data, the ensemble AOD biases range from −37 % (MODIS-Terra) to −16 % (MERGED-FMI, a multi-satellite AOD product), which we explain by differences between individual satellites and AERONET measurements themselves. Correlation coefficients (R) between model and observation AOD records are generally high (R>0.75), suggesting that the models are capable of capturing spatio-temporal variations in AOD. We find a much larger underestimate in coarse AODc (∼ −45 % ± 25 %) than in fine AODf (∼ −15 % ± 25 %) with slightly increased inter-model spread compared to total AOD. These results indicate problems in the modelling of DU and SS. The AODc bias is likely due to missing DU over continental land masses (particularly over the United States, SE Asia, and S. America), while marine AERONET sites and the AATSR SU satellite data suggest more moderate oceanic biases in AODc.
Column AEs are underestimated by about 10 % ± 16 %. For situations in which measurements show AE > 2, models underestimate AERONET AE by ca. 35 %. In contrast, all models (but one) exhibit large overestimates in AE when coarse aerosol dominates (bias ca. +140 % if observed AE < 0.5). Simulated AE does not span the observed AE variability. These results indicate that models overestimate particle size (or underestimate the fine-mode fraction) for fine-dominated aerosol and underestimate size (or overestimate the fine-mode fraction) for coarse-dominated aerosol. This must have implications for lifetime, water uptake, scattering enhancement, and the aerosol radiative effect, which we can not quantify at this moment.
Comparison against Global Atmosphere Watch (GAW) in situ data results in mean bias and inter-model variations of −35 % ± 25 % and −20 % ± 18 % for SCdry and ACdry, respectively. The larger underestimate of SCdry than ACdry suggests the models will simulate an aerosol single scattering albedo that is too low. The larger underestimate of SCdry than ambient air AOD is consistent with recent findings that models overestimate scattering enhancement due to hygroscopic growth. The broadly consistent negative bias in AOD and surface scattering suggests an underestimate of aerosol radiative effects in current global aerosol models.
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2021
How Atmospheric Chemistry and Transport Drive Surface Variability of N2O and CFC-11
Nitrous oxide (N2O) is a long-lived greenhouse gas that affects atmospheric chemistry and climate. In this work, we use satellite measurements of N2O, ozone (O3), and temperature from the Aura Microwave Limb Sounder (MLS) instrument to calculate stratospheric loss of N2O, and thus its atmospheric lifetime. Using three chemistry transport models simulating the Aura period 2005–2017, we verify the stratospheric sink using MLS data and follow that loss signal down to the surface and compare with surface observations. Stratospheric loss has a strong seasonal cycle and is further modulated by the Quasi-Biennial Oscillation (QBO); these cycles are seen equally in both observations and the models. When filtered for interannual variability, the modeled surface signal is QBO-caused, and it reproduces the observed pattern, highlighting the potential role of the QBO in tropospheric chemistry and composition, as well as in model evaluation. The observed annual surface signal in the northern hemisphere matches well with the models run without emissions, indicating the annual cycle is driven mostly by stratosphere-troposphere exchange (STE) flux of N2O-depleted air and not surface N2O emissions. In the southern hemisphere (SH), all three models disagree and thus provide no guidance, except for indicating that modeling annual STE in the SH remains a major model uncertainty. Parallel model simulations of CFCl3, which has greater stratospheric loss that N2O and possibly surreptitious emissions, show that its interannual variations parallel those of N2O, and thus the observed N2O variability can identify the stratospheric component of the observed CFCl3 variability.
2021
Atmospheric nitrogen and sulfur deposition is an important effect of atmospheric pollution and may affect forest ecosystems positively, for example enhancing tree growth, or negatively, for example causing acidification, eutrophication, cation depletion in soil or nutritional imbalances in trees. To assess and design measures to reduce the negative impacts of deposition, a good estimate of the deposition amount is needed, either by direct measurement or by modeling. In order to evaluate the precision of both approaches and to identify possible improvements, we compared the deposition estimates obtained using an Eulerian model with the measurements performed by two large independent networks covering most of Europe. The results are in good agreement (bias <25%) for sulfate and nitrate open field deposition, while larger differences are more evident for ammonium deposition, likely due to the greater influence of local ammonia sources. Modeled sulfur total deposition compares well with throughfall deposition measured in forest plots, while the estimate of nitrogen deposition is affected by the tree canopy. The geographical distribution of pollutant deposition and of outlier sites where model and measurements show larger differences are discussed.
2021
2021
Low-risk removal of embedded surface soiling on delicate heritage objects can require novel alternatives to traditional cleaning systems. Edvard Munch’s monumental Aula paintings (1911–16) have a long history of exposure to atmospheric pollution and cleaning campaigns that have compromised the appearance and the condition of these important artworks. Soiling removal from porous and water-sensitive, unvarnished oil paintings continues to be a major conservation challenge. This paper presents the approach and results of research into the effect and efficiency of three novel systems used for soiling removal: soft particle blasting, CO2-snow blasting, and Nanorestore Gel® Dry and Peggy series hydrogels. Cleaning tests were performed on accelerated-aged and artificially soiled mock-ups consisting of unvarnished oil paint and chalk-glue grounds. Visual and analytical assessment (magnification using a light microscope and scanning electron microscope, as well as colour- and gloss measurement) was carried out before and after mock-up cleaning tests and the results were compared to those obtained using the dry polyurethane sponges employed in the most recent Aula surface cleaning campaign (2009–11). Although the results varied, the Nanorestore Gel® series proved promising with respect to improved soiling removal efficiency, and reduced pigment loss for the water-sensitive surfaces evaluated, compared to dry sponges.
2021