Browsing by Subject "aerosols"

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  • Huttunen, Jani (Finnish Meteorological Institute, 2017)
    Finnish Meteorological Institute Contributions 135
    Aerosols affect the climate both directly and indirectly. The direct effect comes from their influence on the radiation balance by scattering and absorption of solar radiation, while the indirect effect is based on the ways in which aerosols interact via clouds. Currently the total anthropogenic aerosol forcing includes one of the main uncertainties in the assessment of human induced climate change. The aerosol direct radiative effect (ADRE) can be simulated with either the radiative transfer modelling or estimated with solar radiation and aerosol amount measurements. Both approaches include significant uncertainties and this thesis focuses on the uncertainties on the measurement based estimation of ADRE and the uncertainties therein. The main scientific objectives of this thesis are to seek answers to the following four questions: 1) are the machine learning algorithms better than the a traditional lookup table (LUT) approach in estimating aerosol load (aerosol optical depth, AOD)?; 2) what is the role of water vapor (WVC) variability in the measurementbased regression method used to estimate the surface ADRE?; 3) how well do the radiative transfer codes, typically used in global aerosol models, agree?; 4) what is the impact of typically neglected diurnal aerosol variability in ADRE estimation? The results show that: 1) the machine learning algorithms are able to provide AOD more accurately than the LUT approach for conditions of varying aerosol optical properties, since in the LUT approach the aerosol model (e.g. single scattering albedo, asymmetry factor) needs to be fixed in advance. 2) It was found that covariability of AOD and WVC can have an influence in ADRE estimates, when using groundbased measurements of surface solar radiation and AOD. This has not been taken into account previously, but needs to be considered when these methods are applied. 3) The model intercomparison study, in which the models estimated the radiative fluxes for the same atmospheric states, revealed that there is relatively large diversity between models regarding the results from their radiative transfer modelling. 4) The main conclusion from the study focusing on the impact of systematic diurnal AOD cycles in aerosol direct radiative effect, was that even a notable diurnal change in AOD does not typically affect the 24h-average ADRE significantly.
  • Popp, Thomas; De Leeuw, Gerrit; Bingen, Christine; Bruehl, Christoph; Capelle, Virginie; Chedin, Alain; Clarisse, Lieven; Dubovik, Oleg; Grainger, Roy; Griesfeller, Jan; Heckel, Andreas; Kinne, Stefan; Klueser, Lars; Kosmale, Miriam; Kolmonen, Pekka; Lelli, Luca; Litvinov, Pavel; Mei, Linlu; North, Peter; Pinnock, Simon; Povey, Adam; Robert, Charles; Schulz, Michael; Sogacheva, Larisa; Stebel, Kerstin; Zweers, Deborah Stein; Thomas, Gareth; Tilstra, Lieuwe Gijsbert; Vandenbussche, Sophie; Veefkind, Pepijn; Vountas, Marco; Xue, Yong (2016)
    Producing a global and comprehensive description of atmospheric aerosols requires integration of ground-based, airborne, satellite and model datasets. Due to its complexity, aerosol monitoring requires the use of several data records with complementary information content. This paper describes the lessons learned while developing and qualifying algorithms to generate aerosol Climate Data Records (CDR) within the European Space Agency (ESA) Aerosol_cci project. An iterative algorithm development and evaluation cycle involving core users is applied. It begins with the application-specific refinement of user requirements, leading to algorithm development, dataset processing and independent validation followed by user evaluation. This cycle is demonstrated for a CDR of total Aerosol Optical Depth (AOD) from two subsequent dual-view radiometers. Specific aspects of its applicability to other aerosol algorithms are illustrated with four complementary aerosol datasets. An important element in the development of aerosol CDRs is the inclusion of several algorithms evaluating the same data to benefit from various solutions to the ill-determined retrieval problem. The iterative approach has produced a 17-year AOD CDR, a 10-year stratospheric extinction profile CDR and a 35-year Absorbing Aerosol Index record. Further evolution cycles have been initiated for complementary datasets to provide insight into aerosol properties (i.e., dust aerosol, aerosol absorption).
  • Kuhn, Thomas; Kupiainen, Kaarle; Miinalainen, Tuuli; Kokkola, Harri; Paunu, Ville-Veikko; Laakso, Anton; Tonttila, Juha; Van Dingenen, Rita; Kulovesi, Kati; Karvosenoja, Niko; Lehtonen, Kari E.J. (EGU, 2020)
    Atmospheric Chemistry and Physics 20 9 (2020)
    We use the ECHAM-HAMMOZ aerosol-climate model to assess the effects of black carbon (BC) mitigation measures on Arctic climate. To this end we constructed several mitigation scenarios that implement all currently existing legislation and then implement further reductions of BC in a successively increasing global area, starting from the eight member states of the Arctic Council, expanding to its active observer states, then to all observer states, and finally to the entire globe. These scenarios also account for the reduction of the co-emitted organic carbon (OC) and sulfate (SU). We find that, even though the additional BC emission reductions in the member states of the Arctic Council are small, the resulting reductions in Arctic BC mass burdens can be substantial, especially in the lower troposphere close to the surface. This in turn means that reducing BC emissions only in the Arctic Council member states can reduce BC deposition in the Arctic by about 30 % compared to the current legislation, which is about 60 % of what could be achieved if emissions were reduced globally. Emission reductions further south affect Arctic BC concentrations at higher altitudes and thus only have small additional effects on BC deposition in the Arctic. The direct radiative forcing scales fairly well with the total amount of BC emission reduction, independent of the location of the emission source, with a maximum direct radiative forcing in the Arctic of about −0.4 W m−2 for a global BC emission reduction. On the other hand, the Arctic effective radiative forcing due to the BC emission reductions, which accounts for aerosol–cloud interactions, is small compared to the direct aerosol radiative forcing. This happens because BC- and OC-containing particles can act as cloud condensation nuclei, which affects cloud reflectivity and lifetime and counteracts the direct radiative forcing of BC. Additionally, the effective radiative forcing is accompanied by very large uncertainties that originate from the strong natural variability of meteorology, cloud cover, and surface albedo in the Arctic. We further used the TM5-FASST model to assess the benefits of the aerosol emission reductions for human health. We found that a full implementation in all Arctic Council member and observer states could reduce the annual global number of premature deaths by 329 000 by the year 2030, which amounts to 9 % of the total global premature deaths due to particulate matter.
  • Leskinen, Ari (2008)
    Finnish Meteorological Institute Contributions
  • Prank, Marje (Finnish Meteorological Institute, 17-0)
    Finnish Meteorological Institute Contributions 128
    Atmospheric composition has strong influence on human health, ecosystems and also Earth's climate. Among the atmospheric constituents, particulate matter has been recognized as both a strong climate forcer and a significant risk factor for human health, although the health relevance of the specific aerosol characteristics, such as its chemical composition, is still debated. Clouds and aerosols also contribute the largest uncertainty to the radiative budget estimates for climate projections. Thus, reliable estimates of emissions and distributions of pollutants are necessary for assessing the future climate and air-quality related health effects. Chemistry-transport models (CTMs) are valuable tools for understanding the processes influencing the atmospheric composition. This thesis consists of a collection of developments and applications of the chemistry-transport model SILAM. SILAM's ability to reproduce the observed aerosol composition was evaluated and compared with three other commonly used CTM-s in Europe. Compared to the measurements, all models systematically underestimated dry PM10 and PM2.5 by 10-60%, depending on the model and the season of the year. For majority of the PM chemical components the relative underestimation was smaller than that, exceptions being the carbonaceous particles and mineral dust - species that suffer from relatively small amount of available oservational data. The study stressed the necessity for high-quality emissions from wild-land fires and wind-suspended dust, as well as the need for an explicit consideration of aerosol water content in model-measurement comparison. The average water content at laboratory conditions was estimated between 5 and 20% for PM2.5 and between 10 and 25% for PM10. SILAM predictions were used to assess the annual mortality attributable to short-term exposures to vegetation-fire originated PM2.5 in different regions in Europe. PM2.5 emitted from vegetation fires was found to be a relevant risk factor for public health in Europe, more than 1000 premature deaths per year were attributed to vegetation-fire released PM2.5. CTM predictions critically depend on emission data quality. An error was found in the EMEP anthropogenic emission inventory regarding the SOx and PM missions of metallurgy plants on the Kola Peninsula and SILAM was applied to estimate the accuracy of the proposed correction. Allergenic pollen is arguably the type of aerosol with most widely recognised effect to health. SILAM's ability to predict allergenic pollen was extended to include Ambrosia Artemisiifolia - an invasive weed spreading in Southern Europe, with extremely allergenic pollen capable of inducing rhinoconjuctivitis and asthma in the sensitive individuals even in very low concentrations. The model compares well with the pollen observations and predicts occasional exceedances of allergy relevant thresholds even in areas far from the plants' habitat. The variations of allergenicity in grass pollen were studied and mapped to the source areas by adjoint computations with SILAM. Due to the high year-to-year variability of the observed pollen potency between the studied years and the sparse observational network, no clear geographic pattern of pollen allergenicity was detected.
  • Stolzenburg, Dominik; Fischer, Lukas; Vogel, Alexander L.; Heinritzi, Martin; Schervish, Meredith; Simon, Mario; Wagner, Andrea C.; Dada, Lubna; Ahonen, Lauri R.; Amorim, Antonio; Baccarini, Andrea; Bauer, Paulus S.; Baumgartner, Bernhard; Bergen, Anton; Bianchi, Federico; Breitenlechner, Martin; Brilke, Sophia; Mazon, Stephany Buenrostro; Chen, Dexian; Dias, Antnio; Draper, Danielle C.; Duplissy, Jonathan; El Haddad, Imad; Finkenzeller, Henning; Frege, Carla; Fuchs, Claudia; Garmash, Olga; Gordon, Hamish; He, Xucheng; Helm, Johanna; Hofbauer, Victoria; Hoyle, Christopher R.; Kim, Changhyuk; Kirkby, Jasper; Kontkanen, Jenni; Kuerten, Andreas; Lampilahti, Janne; Lawler, Michael; Lehtipalo, Katrianne; Leiminger, Markus; Mai, Huajun; Mathot, Serge; Mentler, Bernhard; Molteni, Ugo; Nie, Wei; Nieminen, Tuomo; Nowak, John B.; Ojdanic, Andrea; Onnela, Antti; Passananti, Monica; Petäjä, Tuukka; Quélever, Lauriane L. J.; Rissanen, Matti P.; Sarnela, Nina; Schallhart, Simon; Tauber, Christian; Tome, Antonio; Wagner, Robert; Wang, Mingyi; Weitz, Lena; Wimmer, Daniela; Xiao, Mao; Yan, Chao; Ye, Penglin; Zha, Qiaozhi; Baltensperger, Urs; Curtius, Joachim; Dommen, Josef; Flagan, Richard C.; Kulmala, Markku; Smith, James N.; Worsnop, Douglas R.; Hansel, Armin; Donahue, Neil M.; Winkler, Paul M. (2018)
    Nucleation and growth of aerosol particles from atmospheric vapors constitutes a major source of global cloud condensation nuclei (CCN). The fraction of newly formed particles that reaches CCN sizes is highly sensitive to particle growth rates, especially for particle sizes <10 nm, where coagulation losses to larger aerosol particles are greatest. Recent results show that some oxidation products from biogenic volatile organic compounds are major contributors to particle formation and initial growth. However, whether oxidized organics contribute to particle growth over the broad span of tropospheric temperatures remains an open question, and quantitative mass balance for organic growth has yet to be demonstrated at any temperature. Here, in experiments performed under atmospheric conditions in the Cosmics Leaving Outdoor Droplets (CLOUD) chamber at the European Organization for Nuclear Research (CERN), we show that rapid growth of organic particles occurs over the range from -25 degrees C to 25 degrees C. The lower extent of autoxidation at reduced temperatures is compensated by the decreased volatility of all oxidized molecules. This is confirmed by particle-phase composition measurements, showing enhanced uptake of relatively less oxygenated products at cold temperatures. We can reproduce the measured growth rates using an aerosol growth model based entirely on the experimentally measured gas-phase spectra of oxidized organic molecules obtained from two complementary mass spectrometers. We show that the growth rates are sensitive to particle curvature, explaining widespread atmospheric observations that particle growth rates increase in the single-digit-nanometer size range. Our results demonstrate that organic vapors can contribute to particle growth over a wide range of tropospheric temperatures from molecular cluster sizes onward.
  • Mielonen, Tero; Hienola, Anca; Kuhn, Thomas; Merikanto, Joonas; Lipponen, Antti; Bergman, Tommi; Korhonen, Hannele; Kolmonen, Pekka; Sogacheva, Larisa; Ghent, Darren; Pitkanen, Mikko R. A.; Arola, Antti; de Leeuw, Gerrit; Kokkola, Harri (2018)
    Satellite data suggest that summertime aerosol optical depth (AOD) over the southeastern USA depends on the air/land surface temperature, but the magnitude of the radiative effects caused by this dependence remains unclear. To quantify these radiative effects, we utilized several remote sensing datasets and ECMWF reanalysis data for the years 2005-2011. In addition, the global aerosol-climate model ECHAM-HAMMOZ was used to identify the possible processes affecting aerosol loads and their dependence on temperature over the studied region. The satellite-based observations suggest that changes in the total summertime AOD in the southeastern USA are mainly governed by changes in anthropogenic emissions. In addition, summertime AOD exhibits a dependence on southerly wind speed and land surface temperature (LST). Transport of sea salt and Saharan dust is the likely reason for the wind speed dependence, whereas the temperature-dependent component is linked to temperature-induced changes in the emissions of biogenic volatile organic compounds (BVOCs) over forested regions. The remote sensing datasets indicate that the biogenic contribution increases AOD with increasing temperature by approximately (7 +/- 6) x 10(-3) K-1 over the southeastern USA. In the model simulations, the increase in summertime AOD due to temperature-enhanced BVOC emissions is of a similar magnitude, i.e., (4 +/- 1) x 10(-3) K-1. The largest source of BVOC emissions in this region is broadleaf trees, thus if the observed temperature dependence of AOD is caused by biogenic emissions the dependence should be the largest in the vicinity of forests. Consequently, the analysis of the remote sensing data shows that over mixed forests the biogenic contribution increases AOD by approximately (27 +/- 13) x 10(-3) K-1, which is over four times higher than the value for over the whole domain, while over other land cover types in the study region (woody savannas and cropland/natural mosaic) there is no clear temperature dependence. The corresponding clear-sky direct radiative effect (DRE) of the observation-based biogenic AOD is -0.33 +/- 0.29 W/m(2)/K for the whole domain and -1.3 +/- 0.7 W/m(2)/K over mixed forests only. The model estimate of the regional clear-sky DRE for biogenic aerosols is similar to the observational estimate for the whole domain: -0.29 +/- 0.09 W/m(2)/K. Furthermore, the model simulations showed that biogenic emissions have a significant effective radiative forcing (ERF) in this region: -1.0 +/- 0.5 W/m(2)/K.
  • Zhou, You (Helsingfors universitet, 2015)
    Long wave (LW) radiation in the Earth's atmosphere is defined as the radiation at wavelengths longer than 4 µm (infrared). The short wave (SW) radiation wavelengths are less than 4 µm (visible light, ultraviolet). SW radiation is usually from solar origin. The absorbed solar SW radiation is closely balanced by the outgoing LW radiation in the atmosphere. This radiation balance keeps the global average temperature stable. The main cause of the current global warming trend is human expansion of the 'greenhouse effect'. Atmospheric greenhouse gases absorb the thermal LW radiation from a planetary surface. The absorbed radiation is re-emitted to all directions. Some of the energy is transferred back to the surface and the lower atmosphere since part of the re-radiation is directed towards the surface, resulting in increased surface temperature. The local radiation balance is also affected by clouds and aerosols in the atmosphere since they too can absorb and scatter radiation. The effects of clouds and greenhouse gases on the global radiative balance and surface temperature are well known. The aerosols, however, are one of the greatest sources of uncertainty in the interpretation and projection of the climate change. Natural aerosols such as those due to large eruptions of volcanoes and wind-blown mineral dust are recognised as significant sources of climate forcing. In addition, there are several ways in which humans are altering atmospheric aerosols. These include industrial emissions to the lower atmosphere as well as emissions to as high as lower stratosphere by aircraft. In this thesis the effect of aerosols on LW radiation was studied based on narrowband LW calculations in a reference mid-latitude summer atmosphere with and without aerosols. Aerosols were added to the narrowband LW scheme based on their typical schematic observed spectral and vertical behaviour over European land areas. This was found to agree also with spectral aerosol data from the Lan Zhou University Semi-Arid Climate Observatory and Laboratory measurement stations in north-western China. A volcanic stratospheric aerosol load was found to induce local LW warming with a stronger column “greenhouse effect” than a doubled CO2 concentration. A heavy near-surface aerosol load was found to increase the downwelling LW radiation to the surface and to reduce the outgoing LW radiation, acting very much like a thin low cloud in increasing the LW greenhouse effect of the atmosphere. The short wave reflection of white aerosol has, however, stronger impact in general, but the aerosol LW greenhouse effect is non-negligible under heavy aerosol loads.
  • Nordling, Kalle (Ilmatieteen laitos - Finnish Meteorological Institute, 2021)
    Finnish Meteorological Institute Contributions 176
    Anthropogenic aerosols alter the climate by scattering and absorbing the incoming solar radiation and by modifying clouds’ optical properties, causing a global cooling or warming effect. Anthropogenic aerosols are partly co-emitted with anthropogenic greenhouse gases, and future climate mitigation actions lead to the decline of anthropogenic aerosols’ cooling effect. However, the exact cooling effect is still uncertain. Part of this uncertainty is related to the structural differences of current climate models. This work evaluates the present-day anthropogenic aerosol temperature and precipitation effect and factors affecting the model difference. The key objectives of this thesis were: 1) What are the climate effects of present-day anthropogenic aerosols?, 2) What mechanisms drive the model-to-model differences?, and 3) How do future reductions affect local and global climates? The global models ECHAM6 and NorESM1 were used to evaluate the present-day climate effects with theidentical anthropogenic aerosol scheme MACv2-SP. Results reveal that an identical anthropogenic aerosol description does not reduce the uncertainty related to anthropogenic aerosol climate effects, and the difference in the estimated difference is due to model dynamics and oceans. The key mechanism driving the difference in the models was evaluated using data from the Precipitation Driven Model Intercomparison Project (PRMIP). Similar mechanisms drive the model-to-model difference for greenhouse gases and aerosols, where the key drivers are the differences in water vapor, the vertical temperature structure of the atmosphere, and sea ice and snow cover changes. However, on a regional scale, the key drivers differ. Future anthropogenic aerosol effects were evaluated using new CMIP6 data. This work shows the importance of anthropogenic aerosols for current and future climate change. For amore accurate assessment of climate impacts of anthropogenic aerosols, one needs to also consider remote effects of the local aerosols. The Arctic regions are particularly sensitive to midlatitude aerosols, such as Asian aerosols, which are expected to decline in the next decades. To gain a more accurate estimation of anthropogenic aerosols, it is not sufficient to only focus on composition and geographical distribution of aerosols, as the dynamic response of climate is also important. On global temperature results did not indicate clear aerosols signal, however future temperature development over the Asian regions is modulated by the future Asian aerosol emissions.