2020, Laj, Paolo, Bigi, Alessandro, Rose, Clémence, Andrews, Elisabeth, Lund Myhre, Cathrine, Collaud Coen, Martine, Lin, Yong, Wiedensohler, Alfred, Schulz, Michael, Ogren, John A., Fiebig, Markus, Prenni, Anthony, Reisen, Fabienne, Romano, Salvatore, Sellegri, Karine, Sharma, Sangeeta, Schauer, Gerhard, Sheridan, Patrick, Sherman, James Patrick, Schütze, Maik, Schwerin, Andreas, Tuch, Thomas, Sohmer, Ralf, Sorribas, Mar, Steinbacher, Martin, Sun, Junying, Titos, Gloria, Toczko, Barbara, Tulet, Pierre, Tunved, Peter, Vakkari, Ville, Velarde, Fernando, Velasquez, Patricio, Villani, Paolo, Vratolis, Sterios, Wang, Sheng-Hsiang, Weinhold, Kay, Gliß, Jonas, Weller, Rolf, Yela, Margarita, Yus-Diez, Jesus, Zdimal, Vladimir, Zieger, Paul, Zikova, Nadezda, Mortier, Augustin, Pandolfi, Marco, Petäja, Tuukka, Kim, Sang-Woo, Aas, Wenche, Putaud, Jean-Philippe, Mayol-Bracero, Olga, Keywood, Melita, Labrador, Lorenzo, Aalto, Pasi, Ahlberg, Erik, Alados Arboledas, Lucas, Alastuey, Andrés, Andrade, Marcos, Artíñano, Begoña, Ausmeel, Stina, Arsov, Todor, Asmi, Eija, Backman, John, Baltensperger, Urs, Bastian, Susanne, Bath, Olaf, Beukes, Johan Paul, Brem, Benjamin T., Bukowiecki, Nicolas, Conil, Sébastien, Couret, Cedric, Day, Derek, Dayantolis, Wan, Degorska, Anna, Eleftheriadis, Konstantinos, Fetfatzis, Prodromos, Favez, Olivier, Flentje, Harald, Gini, Maria I., Gregorič, Asta, Gysel-Beer, Martin, Hallar, A. Gannet, Hand, Jenny, Hoffer, Andras, Hueglin, Christoph, Hooda, Rakesh K., Hyvärinen, Antti, Kalapov, Ivo, Kalivitis, Nikos, Kasper-Giebl, Anne, Kim, Jeong Eun, Kouvarakis, Giorgos, Kranjc, Irena, Krejci, Radovan, Kulmala, Markku, Labuschagne, Casper, Lee, Hae-Jung, Lihavainen, Heikki, Lin, Neng-Huei, Löschau, Gunter, Luoma, Krista, Marinoni, Angela, Martins Dos Santos, Sebastiao, Meinhardt, Frank, Merkel, Maik, Metzger, Jean-Marc, Mihalopoulos, Nikolaos, Nguyen, Nhat Anh, Ondracek, Jakub, Pérez, Noemi, Perrone, Maria Rita, Petit, Jean-Eudes, Picard, David, Pichon, Jean-Marc, Pont, Veronique, Prats, Natalia

Aerosol particles are essential constituents of the Earth's atmosphere, impacting the earth radiation balance directly by scattering and absorbing solar radiation, and indirectly by acting as cloud condensation nuclei. In contrast to most greenhouse gases, aerosol particles have short atmospheric residence times, resulting in a highly heterogeneous distribution in space and time. There is a clear need to document this variability at regional scale through observations involving, in particular, the in situ near-surface segment of the atmospheric observation system. This paper will provide the widest effort so far to document variability of climate-relevant in situ aerosol properties (namely wavelength dependent particle light scattering and absorption coefficients, particle number concentration and particle number size distribution) from all sites connected to the Global Atmosphere Watch network. High-quality data from almost 90 stations worldwide have been collected and controlled for quality and are reported for a reference year in 2017, providing a very extended and robust view of the variability of these variables worldwide. The range of variability observed worldwide for light scattering and absorption coefficients, single-scattering albedo, and particle number concentration are presented together with preliminary information on their long-term trends and comparison with model simulation for the different stations. The scope of the present paper is also to provide the necessary suite of information, including data provision procedures, quality control and analysis, data policy, and usage of the ground-based aerosol measurement network. It delivers to users of the World Data Centre on Aerosol, the required confidence in data products in the form of a fully characterized value chain, including uncertainty estimation and requirements for contributing to the global climate monitoring system.

2021, Evangeliou, Nikolaos, Platt, Stephen M., Eckhardt, Sabine, Lund Myhre, Cathrine, Laj, Paolo, Alados-Arboledas, Lucas, Backman, John, Brem, Benjamin T., Fiebig, Markus, Flentje, Harald, Marinoni, Angela, Pandolfi, Marco, Yus-Dìez, Jesus, Prats, Natalia, Putaud, Jean P., Sellegri, Karine, Sorribas, Mar, Eleftheriadis, Konstantinos, Vratolis, Stergios, Wiedensohler, Alfred, Stohl, Andreas

Following the emergence of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) responsible for COVID-19 in December 2019 in Wuhan (China) and its spread to the rest of the world, the World Health Organization declared a global pandemic in March 2020. Without effective treatment in the initial pandemic phase, social distancing and mandatory quarantines were introduced as the only available preventative measure. In contrast to the detrimental societal impacts, air quality improved in all countries in which strict lockdowns were applied, due to lower pollutant emissions. Here we investigate the effects of the COVID-19 lockdowns in Europe on ambient black carbon (BC), which affects climate and damages health, using in situ observations from 17 European stations in a Bayesian inversion framework. BC emissions declined by 23 kt in Europe (20 % in Italy, 40 % in Germany, 34 % in Spain, 22 % in France) during lockdowns compared to the same period in the previous 5 years, which is partially attributed to COVID-19 measures. BC temporal variation in the countries enduring the most drastic restrictions showed the most distinct lockdown impacts. Increased particle light absorption in the beginning of the lockdown, confirmed by assimilated satellite and remote sensing data, suggests residential combustion was the dominant BC source. Accordingly, in central and Eastern Europe, which experienced lower than average temperatures, BC was elevated compared to the previous 5 years. Nevertheless, an average decrease of 11 % was seen for the whole of Europe compared to the start of the lockdown period, with the highest peaks in France (42 %), Germany (21 %), UK (13 %), Spain (11 %) and Italy (8 %). Such a decrease was not seen in the previous years, which also confirms the impact of COVID-19 on the European emissions of BC.

2018, Pandolfi, Marco, Alados-Arboledas, Lucas, Alastuey, Andrés, Andrade, Marcos, Angelov, Christo, Artiñano, Begoña, Backman, John, Baltensperger, Urs, Bonasoni, Paolo, Bukowiecki, Nicolas, Collaud Coen, Martine, Conil, Sébastien, Coz, Esther, Crenn, Vincent, Dudoitis, Vadimas, Ealo, Marina, Eleftheriadis, Kostas, Favez, Olivier, Fetfatzis, Prodromos, Fiebig, Markus, Flentje, Harald, Ginot, Patrick, Gysel, Martin, Henzing, Bas, Hoffer, Andras, Holubova Smejkalova, Adela, Kalapov, Ivo, Kalivitis, Nikos, Kouvarakis, Giorgos, Kristensson, Adam, Kulmala, Markku, Lihavainen, Heikki, Lunder, Chris, Luoma, Krista, Lyamani, Hassan, Marinoni, Angela, Mihalopoulos, Nikos, Moerman, Marcel, Nicolas, José, O'Dowd, Colin, Petäjä, Tuukka, Petit, Jean-Eudes, Pichon, Jean Marc, Prokopciuk, Nina, Putaud, Jean-Philippe, Rodríguez, Sergio, Sciare, Jean, Sellegri, Karine, Swietlicki, Erik, Titos, Gloria, Tuch, Thomas, Tunved, Peter, Ulevicius, Vidmantas, Vaishya, Aditya, Vana, Milan, Virkkula, Aki, Vratolis, Stergios, Weingartner, Ernest, Wiedensohler, Alfred, Laj, Paolo

This paper presents the light-scattering properties of atmospheric aerosol particles measured over the past decade at 28 ACTRIS observatories, which are located mainly in Europe. The data include particle light scattering (σsp) and hemispheric backscattering (σbsp) coefficients, scattering Ångström exponent (SAE), backscatter fraction (BF) and asymmetry parameter (g). An increasing gradient of σsp is observed when moving from remote environments (arctic/mountain) to regional and to urban environments. At a regional level in Europe, σsp also increases when moving from Nordic and Baltic countries and from western Europe to central/eastern Europe, whereas no clear spatial gradient is observed for other station environments. The SAE does not show a clear gradient as a function of the placement of the station. However, a west-to-east-increasing gradient is observed for both regional and mountain placements, suggesting a lower fraction of fine-mode particle in western/south-western Europe compared to central and eastern Europe, where the fine-mode particles dominate the scattering. The g does not show any clear gradient by station placement or geographical location reflecting the complex relationship of this parameter with the physical properties of the aerosol particles. Both the station placement and the geographical location are important factors affecting the intraannual variability. At mountain sites, higher σsp and SAE values are measured in the summer due to the enhanced boundary layer influence and/or new particle-formation episodes. Conversely, the lower horizontal and vertical dispersion during winter leads to higher σsp values at all low-altitude sites in central and eastern Europe compared to summer. These sites also show SAE maxima in the summer (with corresponding g minima). At all sites, both SAE and g show a strong variation with aerosol particle loading. The lowest values of g are always observed together with low σsp values, indicating a larger contribution from particles in the smaller accumulation mode. During periods of high σsp values, the variation of g is less pronounced, whereas the SAE increases or decreases, suggesting changes mostly in the coarse aerosol particle mode rather than in the fine mode. Statistically significant decreasing trends of σsp are observed at 5 out of the 13 stations included in the trend analyses. The total reductions of σsp are consistent with those reported for PM2.5 and PM10 mass concentrations over similar periods across Europe.

2021, Cuesta-Mosquera, Andrea, Močnik, Griša, Drinovec, Luka, Müller, Thomas, Pfeifer, Sascha, Minguillón, María Cruz, Briel, Björn, Buckley, Paul, Dudoitis, Vadimas, Fernández-García, Javier, Fernández-Amado, María, Ferreira De Brito, Joel, Riffault, Veronique, Flentje, Harald, Heffernan, Eimear, Kalivitis, Nikolaos, Kalogridis, Athina-Cerise, Keernik, Hannes, Marmureanu, Luminita, Luoma, Krista, Marinoni, Angela, Pikridas, Michael, Schauer, Gerhard, Serfozo, Norbert, Servomaa, Henri, Titos, Gloria, Yus-Díez, Jesús, Zioła, Natalia, Wiedensohler, Alfred

Aerosolized black carbon is monitored worldwide to quantify its impact on air quality and climate. Given its importance, measurements of black carbon mass concentrations must be conducted with instruments operating in qualitychecked and ensured conditions to generate data which are reliable and comparable temporally and geographically. In this study, we report the results from the largest characterization and intercomparison of filter-based absorption photometers, the Aethalometer model AE33, belonging to several European monitoring networks. Under controlled laboratory conditions, a total of 23 instruments measured mass concentrations of black carbon from three wellcharacterized aerosol sources: synthetic soot, nigrosin particles, and ambient air from the urban background of Leipzig, Germany. The objective was to investigate the individual performance of the instruments and their comparability; we analyzed the response of the instruments to the different aerosol sources and the impact caused by the use of obsolete filter materials and the application of maintenance activities. Differences in the instrument-to-instrument variabilities from equivalent black carbon (eBC) concentrations reported at 880 nm were determined before maintenance activities (for soot measurements, average deviation from total least square regression was-2.0% and the range-16% to 7 %; for nigrosin measurements, average deviation was 0.4% and the range-15% to 17 %), and after they were carried out (for soot measurements, average deviation was-1.0% and the range-14% to 8 %; for nigrosin measurements, the average deviation was 0.5%and the range-12%to 15 %). The deviations are in most of the cases explained by the type of filter material employed by the instruments, the total particle load on the filter, and the flow calibration. The results of this intercomparison activity show that relatively small unit-to-unit variability of AE33-based particle light absorbing measurements is possible with wellmaintained instruments. It is crucial to follow the guidelines for maintenance activities and the use of the proper filter tape in the AE33 to ensure high quality and comparable black carbon (BC) measurements among international observational networks. © 2021 Author(s). This work is distributed under the Creative Commons Attribution 4.0 License.

2018, Bucci, Silvia, Cristofanelli, Paolo, Decesari, Stefano, Marinoni, Angela, Sandrini, Silvia, Größ, Johannes, Wiedensohler, Alfred, Di Marco, Chiara F., Nemitz, Eiko, Cairo, Francesco, Di Liberto, Luca, Fierli, Federico

Studying the vertical distribution of aerosol particle physical and chemical properties in the troposphere is essential to understand the relative importance of local emission processes vs. long-range transport for column-integrated aerosol properties (e.g. the aerosol optical depth, AOD, affecting regional climate) as well as for the aerosol burden and its impacts on air quality at the ground. The main objective of this paper is to investigate the transport of desert dust in the middle troposphere and its intrusion into the planetary boundary layer (PBL) over the Po Valley (Italy), a region considered one of the greatest European pollution hotspots for the frequency that particulate matter (PM) limit values are exceeded. Events of mineral aerosol uplift from local (soil) sources and phenomena of hygroscopic growth at the ground are also investigated, possibly affecting the PM concentration in the region as well. During the PEGASOS 2012 field campaign, an integrated observing-modelling system was set up based on near-surface measurements (particle concentration and chemistry), vertical profiling (backscatter coefficient profiles from lidar and radiosoundings) and Lagrangian air mass transport simulations by FLEXPART model. Measurements were taken at the San Pietro Capofiume supersite (44°39′ĝ€N, 11°37′ĝ€E; 11ĝ€mĝ€a.s.l.), located in a rural area relatively close to some major urban and industrial emissive areas in the Po Valley. Mt. Cimone (44°12′ĝ€N, 10°42′ĝ€E; 2165ĝ€mĝ€a.s.l.) WMO/GAW station observations are also included in the study to characterize regional-scale variability. Results show that, in the Po Valley, aerosol is detected mainly below 2000ĝ€mĝ€a.s.l. with a prevalent occurrence of non-depolarizing particles ( > 50ĝ€% throughout the campaign) and a vertical distribution modulated by the PBL daily evolution. Two intense events of mineral dust transport from northern Africa (19-21 and 29 June to 2 July) are observed, with layers advected mainly above 2000ĝ€m, but subsequently sinking and mixing in the PBL. As a consequence, a non-negligible occurrence of mineral dust is observed close to the ground ( ĝ1/4 7ĝ€% of occurrence during a 1-month campaign). The observations unambiguously show Saharan dust layers intruding the Po Valley mixing layer and directly affecting the aerosol concentrations near the surface. Finally, lidar observations also indicate strong variability in aerosol on shorter timescales (hourly). Firstly, these highlight events of hygroscopic growth of anthropogenic aerosol, visible as shallow layers of low depolarization near the ground. Such events are identified during early morning hours at high relative humidity (RH) conditions (RHĝ€ > 80ĝ€%). The process is observed concurrently with high PM1 nitrate concentration (up to 15ĝ€μgĝ€cmĝ'3) and hence mainly explicable by deliquescence of fine anthropogenic particles, and during mineral dust intrusion episodes, when water condensation on dust particles could instead represent the dominant contribution. Secondly, lidar images show frequent events (mean daily occurrence of ĝ1/4 ĝ€22ĝ€% during the whole campaign) of rapid uplift of mineral depolarizing particles in afternoon-evening hours up to 2000ĝ€mĝ€a.s.l. height. The origin of such particles cannot be directly related to long-range transport events, being instead likely linked to processes of soil particle resuspension from agricultural lands.

2016, Pfeifer, Sascha, Müller, Thomas, Weinhold, Kay, Zikova, Nadezda, dos Santos, Sebastiao Martins, Marinoni, Angela, Bischof, Oliver F., Kykal, Carsten, Ries, Ludwig, Meinhardt, Frank, Aalto, Pasi, Mihalopoulos, Nikolaos, Wiedensohler, Alfred

Aerodynamic particle size spectrometers are a well-established method to measure number size distributions of coarse mode particles in the atmosphere. Quality assurance is essential for atmospheric observational aerosol networks to obtain comparable results with known uncertainties. In a laboratory study within the framework of ACTRIS (Aerosols, Clouds, and Trace gases Research Infrastructure Network), 15 aerodynamic particle size spectrometers (APS model 3321, TSI Inc., St. Paul, MN, USA) were compared with a focus on flow rates, particle sizing, and the unit-to-unit variability of the particle number size distribution. Flow rate deviations were relatively small (within a few percent), while the sizing accuracy was found to be within 10 % compared to polystyrene latex (PSL) reference particles. The unit-to-unit variability in terms of the particle number size distribution during this study was within 10 % to 20 % for particles in the range of 0.9 up to 3 µm, which is acceptable for atmospheric measurements. For particles smaller than that, the variability increased up to 60 %, probably caused by differences in the counting efficiencies of individual units. Number size distribution data for particles smaller than 0.9 µm in aerodynamic diameter should only be used with caution. For particles larger than 3 µm, the unit-to-unit variability increased as well. A possible reason is an insufficient sizing accuracy in combination with a steeply sloping particle number size distribution and the increasing uncertainty due to decreasing counting. Particularly this uncertainty of the particle number size distribution must be considered if higher moments of the size distribution such as the particle volume or mass are calculated, which require the conversion of the aerodynamic diameter measured to a volume equivalent diameter. In order to perform a quantitative quality assurance, a traceable reference method for the particle number concentration in the size range 0.5–3 µm is needed.

2020, Collaud Coen, Martine, Andrews, Elisabeth, Alastuey, Andrés, Petkov Arsov, Todor, Backman, John, Brem, Benjamin T., Bukowiecki, Nicolas, Couret, Cédric, Eleftheriadis, Konstantinos, Flentje, Harald, Fiebig, Markus, Gysel-Beer, Martin, Hand, Jenny L., Hoffer, András, Hooda, Rakesh, Hueglin, Christoph, Joubert, Warren, Keywood, Melita, Eun Kim, Jeong, Kim, Sang-Woo, Labuschagne, Casper, Lin, Neng-Huei, Lin, Yong, Lund Myhre, Cathrine, Luoma, Krista, Lyamani, Hassan, Marinoni, Angela, Mayol-Bracero, Olga L., Mihalopoulos, Nikos, Pandolfi, Marco, Prats, Natalia, Prenni, Anthony J., Putaud, Jean-Philippe, Ries, Ludwig, Reisen, Fabienne, Sellegri, Karine, Sharma, Sangeeta, Sheridan, Patrick, Sherman, James Patrick, Sun, Junying, Titos, Gloria, Torres, Elvis, Tuch, Thomas, Weller, Rolf, Wiedensohler, Alfred, Zieger, Paul, Laj, Paolo

In order to assess the evolution of aerosol parameters affecting climate change, a long-term trend analysis of aerosol optical properties was performed on time series from 52 stations situated across five continents. The time series of measured scattering, backscattering and absorption coefficients as well as the derived single scattering albedo, backscattering fraction, scattering and absorption Ångström exponents covered at least 10 years and up to 40 years for some stations. The non-parametric seasonal Mann-Kendall (MK) statistical test associated with several pre-whitening methods and with Sen's slope was used as the main trend analysis method. Comparisons with general least mean square associated with autoregressive bootstrap (GLS/ARB) and with standard least mean square analysis (LMS) enabled confirmation of the detected MK statistically significant trends and the assessment of advantages and limitations of each method. Currently, scattering and backscattering coefficient trends are mostly decreasing in Europe and North America and are not statistically significant in Asia, while polar stations exhibit a mix of increasing and decreasing trends. A few increasing trends are also found at some stations in North America and Australia. Absorption coefficient time series also exhibit primarily decreasing trends. For single scattering albedo, 52 % of the sites exhibit statistically significant positive trends, mostly in Asia, eastern/northern Europe and the Arctic, 22 % of sites exhibit statistically significant negative trends, mostly in central Europe and central North America, while the remaining 26 % of sites have trends which are not statistically significant. In addition to evaluating trends for the overall time series, the evolution of the trends in sequential 10-year segments was also analyzed. For scattering and backscattering, statistically significant increasing 10-year trends are primarily found for earlier periods (10-year trends ending in 2010-2015) for polar stations and Mauna Loa. For most of the stations, the present-day statistically significant decreasing 10-year trends of the single scattering albedo were preceded by not statistically significant and statistically significant increasing 10-year trends. The effect of air pollution abatement policies in continental North America is very obvious in the 10-year trends of the scattering coefficient - there is a shift to statistically significant negative trends in 2009-2012 for all stations in the eastern and central USA. This long-term trend analysis of aerosol radiative properties with a broad spatial coverage provides insight into potential aerosol effects on climate changes. © 2020 Royal Society of Chemistry. All rights reserved.