Sources, spatio-temporal variation and co-variability of cloud condensation nuclei and black carbon

Abstract Aerosol-cloud and aerosol-radiation interactions depend on several factors such as the physico-chemical properties, geographical and temporal variability, and vertical distribution of atmospheric aerosols. Of particular importance are cloud condensation nuclei (CCN) and black carbon (BC) particles as a subset of the atmospheric aerosol population. CCN are a prerequisite for cloud droplet formation, and variations in CCN loading can modify cloud properties. BC can efficiently absorb solar radiation, induce local heating and inhibit cloud formation. In order to determine the effects of CCN and BC on clouds, precipitation, radiation and the Earth’s energy budget, atmospheric loading and spatio-temporal distribution of aerosols are highly relevant. Thus this dissertation addresses and helps to elucidate the spatio-temporal variation and co-variability of CCN and BC with extensive field measurement data from aircraft and ground-based measurements. The data analyses focus on anthropogenic pollution, wildfire emissions and volcanic aerosols. In the Anthropocene, the distribution and abundance of atmospheric aerosols have changed drastically. Major sources of anthropogenic particulate pollution are the combustion of fossil fuels and biofuels as well as emissions from open biomass burning. The ubiquitous presence of anthropogenic air pollution, especially over continental regions in the Northern Hemisphere, hampers the assessment of anthropogenic influence on aerosol and climate due to a lack of unperturbed reference measurements. The abrupt reduction in human activities during the first COVID-19 lockdown created unprecedented atmospheric conditions that allowed us to investigate and quantify changes in the tropospheric composition in response to changes in anthropogenic emissions. The results reflect a strong and immediate influence of human activities on air quality, the role of BC as a major air pollutant in the Anthropocene, and close links between the atmospheric burdens of CCN and BC. Measurement data from five aircraft missions in polluted environments reveal characteristic relationships between CCN and BC in urban haze from Europe and East Asia, highly aged biomass burning smoke over the tropical Atlantic and the Amazon rainforest, and lightly aged biomass burning smoke over Europe, Brazil, and Asia. Over Europe and Asia, the vertical distribution of CCN in the lower troposphere up to altitudes about 5 km is highly sensitive to regional anthropogenic emissions. Over the tropical Atlantic ocean, the vertical distribution is strongly influenced by the longrange transport of mineral dust and biomass burning smoke, but volcanic eruptions also contribute to the aerosol load

Overview: On the transport and transformation of pollutants in the outflow of major population centres – observational data from the EMeRGe European intensive operational period in summer 2017

Megacities and other major population centres (MPCs) worldwide are major sources of air pollution, both locally as well as downwind. The overall assessment and prediction of the impact of MPC pollution on tropospheric chemistry are challenging. The present work provides an overview of the highlights of a major new contribution to the understanding of this issue based on the data and analysis of the EMeRGe (Effect of Megacities on the transport and transformation of pollutants on the Regional to Global scales) international project. EMeRGe focuses on atmospheric chemistry, dynamics, and transport of local and regional pollution originating in MPCs. Airborne measurements, taking advantage of the long range capabilities of the High Altitude and LOng Range Research Aircraft (HALO, https://www.halo-spp.de, last access: 22 March 2022), are a central part of the project. The synergistic use and consistent interpretation of observational data sets of different spatial and temporal resolution (e.g. from ground-based networks, airborne campaigns, and satellite measurements) supported by modelling within EMeRGe provide unique insight to test the current understanding of MPC pollution outflows. In order to obtain an adequate set of measurements at different spatial scales, two field experiments were positioned in time and space to contrast situations when the photochemical transformation of plumes emerging from MPCs is large. These experiments were conducted in summer 2017 over Europe and in the inter-monsoon period over Asia in spring 2018. The intensive observational periods (IOPs) involved HALO airborne measurements of ozone and its precursors, volatile organic compounds, aerosol particles, and related species as well as coordinated ground-based ancillary observations at different sites. Perfluorocarbon (PFC) tracer releases and model forecasts supported the flight planning, the identification of pollution plumes, and the analysis of chemical transformations during transport. This paper describes the experimental deployment and scientific questions of the IOP in Europe. The MPC targets – London (United Kingdom; UK), the Benelux/Ruhr area (Belgium, the Netherlands, Luxembourg and Germany), Paris (France), Rome and the Po Valley (Italy), and Madrid and Barcelona (Spain) – were investigated during seven HALO research flights with an aircraft base in Germany for a total of 53 flight hours. An in-flight comparison of HALO with the collaborating UK-airborne platform Facility for Airborne Atmospheric Measurements (FAAM) took place to assure accuracy and comparability of the instrumentation on board. Overall, EMeRGe unites measurements of near- and far-field emissions and hence deals with complex air masses of local and distant sources. Regional transport of several European MPC outflows was successfully identified and measured. Chemical processing of the MPC emissions was inferred from airborne observations of primary and secondary pollutants and the ratios between species having different chemical lifetimes. Photochemical processing of aerosol and secondary formation or organic acids was evident during the transport of MPC plumes. Urban plumes mix efficiently with natural sources as mineral dust and with biomass burning emissions from vegetation and forest fires. This confirms the importance of wildland fire emissions in Europe and indicates an important but discontinuous contribution to the European emission budget that might be of relevance in the design of efficient mitigation strategies. The present work provides an overview of the most salient results in the European context, with these being addressed in more detail within additional dedicated EMeRGe studies. The deployment and results obtained in Asia will be the subject of separate publications.The HALO deployment during EMeRGe was funded by a consortium comprising the German Research Foundation (DFG) Priority Program HALO-SPP 1294, the Institute of Atmospheric Physics of DLR, the Max Planck Society (MPG), and the Helmholtz Association. Flora Kluge, Benjamin Schreiner, and Klaus Pfeilsticker acknowledge the support given by the DFG through the project nos. PF 384-16, PF 384-17, and PG 385-19. Ralf Koppmann and Marc Krebsbach acknowledge DFG funding through project no. KR3861_1-1. Katja Bigge acknowledges additional funding from the Heidelberg Graduate School for Physics. Johannes Schneider, Katharina Kaiser, and Stephan Borrmann acknowledge funding through the DFG (project no. 316589531). Lisa Eirenschmalz and Hans Schlager acknowledge support by DFG through project MEPOLL (SCHL1857/4-1). Anna B. Kalisz Hedegaard would like to thank DAAD and DLR for a Research Fellowship. Hans Schlager acknowledge financial support by the DLR TraK (Transport and Climate) project. Michael Sicard acknowledges support from the EU (GA nos. 654109, 778349, 871115, and 101008004) and the Spanish Government (ref. nos. CGL2017-90884-REDT, PID2019-103886RB-I00, RTI2018-096548-B-I00, and MDM-2016-0600). Midhun George, Yangzhuoran Liu, M. Dolores Andrés Hernández, and John Phillip Burrows acknowledge financial support from the University of Bremen. FLEXPART simulations were performed on the HPC cluster Aether at the University of Bremen, financed by DFG within the scope of the Excellence Initiative. Anne-Marlene Blechschmidt was partly funded through the CAMS-84 project. Jennifer Wolf acknowledges support from the German Federal Ministry for Economic Affairs and Energy – BMWi (project Digitally optimized Engineering for Services – DoEfS; contract no. 20X1701B). Theresa Harlass thanks DLR VOR for funding the young investigator research group “Greenhouse Gases”. Mariano Mertens, Patrick Jöckel, and Markus Kilian acknowledge resources of the Deutsches Klimarechenzentrum (DKRZ) granted by the WLA project ID bd0617 for the MECO(n) simulations and the financial support from the DLR projects TraK (Transport und Klima) and the Initiative and Networking Fund of the Helmholtz Association through the project “Advanced Earth System Modelling Capacity” (ESM). Bruna A. Holanda acknowledges the funding from Brazilian CNPq (process 200723/2015-4).Peer ReviewedArticle signat per 53 autors/es: M. Dolores Andrés Hernández (1), Andreas Hilboll (2), Helmut Ziereis (3), Eric Förster (4), Ovid O. Krüger (5), Katharina Kaiser (6,7), Johannes Schneider (7), Francesca Barnaba (8), Mihalis Vrekoussis (2,18), Jörg Schmidt (9), Heidi Huntrieser (3), Anne-Marlene Blechschmidt (1), Midhun George (1), Vladyslav Nenakhov (1,a), Theresa Harlass (3), Bruna A. Holanda (5), Jennifer Wolf (3), Lisa Eirenschmalz (3), Marc Krebsbach (10), Mira L. Pöhlker (5,b), Anna B. Kalisz Hedegaard (3,2), Linlu Mei (1), Klaus Pfeilsticker (11), Yangzhuoran Liu (1), Ralf Koppmann (10), Hans Schlager (3), Birger Bohn (12), Ulrich Schumann (3), Andreas Richter (1), Benjamin Schreiner (11), Daniel Sauer (3), Robert Baumann (3), Mariano Mertens (3), Patrick Jöckel (3), Markus Kilian (3), Greta Stratmann (3,c,) Christopher Pöhlker (5), Monica Campanelli (8), Marco Pandolfi (13), Michael Sicard (14,15), José L. Gómez-Amo (16), Manuel Pujadas (17), Katja Bigge (11), Flora Kluge (11), Anja Schwarz (9), Nikos Daskalakis (2), David Walter (5), Andreas Zahn (4), Ulrich Pöschl (5), Harald Bönisch (4), Stephan Borrmann (6,7), Ulrich Platt (11), and John P. Burrows (1) // (1) Institute of Environmental Physics, University of Bremen, Bremen, Germany; (2) Laboratory for Modeling and Observation of the Earth System, Institute of Environmental Physics, Bremen, Germany; (3) Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Physik der Atmosphäre, Oberpfaffenhofen, Germany; (4) Atmospheric Trace Gases and Remote Sensing, Karlsruhe Institute of Technology, Institute of Meteorology and Climate Research, Karlsruhe, Germany; (5) Multiphase Chemistry Department, Max Planck Institute for Chemistry, Mainz, Germany; (6) Institute for Atmospheric Physics, Johannes Gutenberg University, Mainz, Germany, (7) Particle Chemistry Department, Max Planck Institute for Chemistry, Mainz, Germany; (8) National Research Council of Italy, Institute of Atmospheric Sciences and Climate (CNR-ISAC), Rome, Italy; (9) Leipzig Institute for Meteorology, Leipzig University, Leipzig, Germany; (10) Institute for Atmospheric and Environmental Research, University of Wuppertal, Wuppertal, Germany; (11) Institute for Environmental Physics, University of Heidelberg, Heidelberg, Germany, (12) Institute of Energy and Climate Research IEK-8, Forschungszentrum Jülich, Jülich, Germany; (13) Consejo Superior de Investigaciones Científicas, Institute of Environmental Assessment and Water Research, Barcelona, Spain; (14) CommSensLab, Department of Signal Theory and Communications, Universitat Politècnica de Catalunya, Barcelona, Spain; (15) Ciències i Tecnologies de l’Espai-Centre de Recerca de l’Aeronàutica i de l’Espai/Institut d’Estudis Espacials de Catalunya), Universitat Politècnica de Catalunya, Barcelona, Spain; (16) Department of Earth Physics and Thermodynamics, University of Valencia, Burjassot, Spain; (17) Atmospheric Pollution Unit, Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (Ciemat), Madrid, Spain; (18) Climate and Atmosphere Research Center (CARE-C), The Cyprus Institute, Nicosia, Cyprus anow at: Flight Experiments, Deutsches Zentrum für Luft- und Raumfahrt (DLR), Oberpfaffenhofen, GermanyPostprint (published version

Water uptake of subpollen aerosol particles: Hygroscopic growth, cloud condensation nuclei activation, and liquid-liquid phase separation

Pollen grains emitted from vegetation can release subpollen particles (SPPs) that contribute to the fine fraction of atmospheric aerosols and may act as cloud condensation nuclei (CCN), ice nuclei (IN), or aeroallergens. Here, we investigate and characterize the hygroscopic growth and CCN activation of birch, pine, and rapeseed SPPs. A high-humidity tandem differential mobility analyzer (HHTDMA) was used to measure particle restructuring and water uptake over a wide range of relative humidity (RH) from 2 % to 99.5 %, and a continuous flow CCN counter was used for size-resolved measurements of CCN activation at supersaturations (S) in the range of 0.2 % to 1.2 %. For both subsaturated and supersaturated conditions, effective hygroscopicity parameters, κ, were obtained by Köhler model calculations. Gravimetric and chemical analyses, electron microscopy, and dynamic light scattering measurements were performed to characterize further properties of SPPs from aqueous pollen extracts such as chemical composition (starch, proteins, DNA, and inorganic ions) and the hydrodynamic size distribution of water-insoluble material. All investigated SPP samples exhibited a sharp increase of water uptake and κ above ∼95 % RH, suggesting a liquid–liquid phase separation (LLPS). The HHTDMA measurements at RH >95 % enable closure between the CCN activation at water vapor supersaturation and hygroscopic growth at subsaturated conditions, which is often not achieved when hygroscopicity tandem differential mobility analyzer (HTDMA) measurements are performed at lower RH where the water uptake and effective hygroscopicity may be limited by the effects of LLPS. Such effects may be important not only for closure between hygroscopic growth and CCN activation but also for the chemical reactivity, allergenic potential, and related health effects of SPPs

Strong particle production and condensational growth in the upper troposphere sustained by biogenic VOCs from the canopy of the Amazon Basin

Nucleation and condensation associated with biogenic volatile organic compounds (BVOCs) are important aerosol formation pathways, yet their contribution to the upper-tropospheric aerosols remains inconclusive, hindering the understanding of aerosol climate effects. Here, we develop new schemes describing these organic aerosol formation processes in the WRF-Chem model and investigate their impact on the abundance of cloud condensation nuclei (CCN) in the upper troposphere (UT) over the Amazon Basin. We find that the new schemes significantly increase the simulated CCN number concentrations in the UT (e.g., up to -1/4 400 cm-3 at 0.52 % supersaturation) and greatly improve the agreement with the aircraft observations. Organic condensation enhances the simulated CCN concentration by 90 % through promoting particle growth, while organic nucleation, by replenishing new particles, contributes an additional 14 %. Deep convection determines the rate of these organic aerosol formation processes in the UT through controlling the upward transport of biogenic precursors (i.e., BVOCs). This finding emphasizes the importance of the biosphere-atmosphere coupling in regulating upper-tropospheric aerosol concentrations over the tropical forest and calls for attention to its potential role in anthropogenic climate change

African smoke particles act as cloud condensation nuclei in the wintertime tropical North Atlantic boundary layer over Barbados

The number concentration and properties of aerosol particles serving as cloud condensation nuclei (CCN) are important for understanding cloud properties, including in the tropical Atlantic marine boundary layer (MBL), where marine cumulus clouds reflect incoming solar radiation and obscure the low-albedo ocean surface. Studies linking aerosol source, composition, and water uptake properties in this region have been conducted primarily during the summertime dust transport season, despite the region receiving a variety of aerosol particle types throughout the year. In this study, we compare size-resolved aerosol chemical composition data to the hygroscopicity parameter κ derived from size-resolved CCN measurements made during the Elucidating the Role of Clouds–Circulation Coupling in Climate (EUREC4A) and Atlantic Tradewind Ocean-Atmosphere Mesoscale Interaction Campaign (ATOMIC) campaigns from January to February 2020. We observed unexpected periods of wintertime long-range transport of African smoke and dust to Barbados. During these periods, the accumulation-mode aerosol particle and CCN number concentrations as well as the proportions of dust and smoke particles increased, whereas the average κ slightly decreased (κ=0.46±0.10) from marine background conditions (κ=0.52±0.09) when the submicron particles were mostly composed of marine organics and sulfate. Size-resolved chemical analysis shows that smoke particles were the major contributor to the accumulation mode during long-range transport events, indicating that smoke is mainly responsible for the observed increase in CCN number concentrations. Earlier studies conducted at Barbados have mostly focused on the role of dust on CCN, but our results show that aerosol hygroscopicity and CCN number concentrations during wintertime long-range transport events over the tropical North Atlantic are also affected by African smoke. Our findings highlight the importance of African smoke for atmospheric processes and cloud formation over the Caribbean.</p

Effects of transport on a biomass burning plume from Indochina during EMeRGe-Asia identified by WRF-Chem

The Indochina biomass burning (BB) season in springtime has a substantial environmental impact on the surrounding areas in Asia. In this study, we evaluated the environmental impact of a major long-range BB transport event on 19 March 2018 (a flight of the High Altitude and Long Range Research Aircraft (HALO; https://www.halo-spp.de, last access: 14 February 2023) research aircraft, flight F0319) preceded by a minor event on 17 March 2018 (flight F0317). Aircraft data obtained during the campaign in Asia of the Effect of Megacities on the transport and transformation of pollutants on the Regional to Global scales (EMeRGe) were available between 12 March and 7 April 2018. In F0319, results of 1 min mean carbon monoxide (CO), ozone (O$_3$), acetone (ACE), acetonitrile (ACN), organic aerosol (OA), and black carbon aerosol (BC) concentrations were up to 312.0, 79.0, 3.0, and 0.6 ppb and 6.4 and 2.5 µg m$^{−3}$, respectively, during the flight, which passed through the BB plume transport layer (BPTL) between the elevation of 2000–4000 m over the East China Sea (ECS). During F0319, the CO, O$_3$, ACE, ACN, OA, and BC maximum of the 1 min average concentrations were higher in the BPTL by 109.0, 8.0, 1.0, and 0.3 ppb and 3.0 and 1.3 µg m$^{−3}$ compared to flight F0317, respectively. Sulfate aerosol, rather than OA, showed the highest concentration at low altitudes (<1000 m) in both flights F0317 and F0319 resulting from the continental outflow in the ECS. The transport of BB aerosols from Indochina and its impacts on the downstream area were evaluated using a Weather Research Forecasting with Chemistry (WRF-Chem) model. The modeling results tended to overestimate the concentration of the species, with examples being CO (64 ppb), OA (0.3 µg m$^{−3}$), BC (0.2 µg m$^{−3}$), and O$_3$ (12.5 ppb) in the BPTL. Over the ECS, the simulated BB contribution demonstrated an increasing trend from the lowest values on 17 March 2018 to the highest values on 18 and 19 March 2018 for CO, fine particulate matter (PM$_{2.5}$), OA, BC, hydroxyl radicals (OH), nitrogen oxides (NO$_x$), total reactive nitrogen (NO$_y$), and O$_3$; by contrast, the variation of J(O$^1$D) decreased as the BB plume\u27s contribution increased over the ECS. In the lower boundary layer (<1000 m), the BB plume\u27s contribution to most species in the remote downstream areas was <20 %. However, at the BPTL, the contribution of the long-range transported BB plume was as high as 30 %–80 % for most of the species (NO$_y$, NO$_x$, PM$_{2.5}$, BC, OH, O$_3$, and CO) over southern China (SC), Taiwan, and the ECS. BB aerosols were identified as a potential source of cloud condensation nuclei, and the simulation results indicated that the transported BB plume had an effect on cloud water formation over SC and the ECS on 19 March 2018. The combination of BB aerosol enhancement with cloud water resulted in a reduction of incoming shortwave radiation at the surface in SC and the ECS by 5 %–7 % and 2 %–4 %, respectively, which potentially has significant regional climate implications

Black carbon aerosol reductions during COVID-19 confinement quantified by aircraft measurements over Europe

The abrupt reduction in human activities during the first lockdown of the COVID-19 pandemic created unprecedented atmospheric conditions. To quantify the changes in lower tropospheric air pollution, we conducted the BLUESKY aircraft campaign and measured vertical profiles of black carbon (BC) aerosol particles over western and southern Europe in May and June 2020. We compared the results to similar measurements of the EMeRGe EU campaign performed in July 2017 and found that the BC mass concentrations (MBC) were reduced by about 48%. For BC particle number concentrations, we found comparable reductions. Based on ECHAM/MESSy Atmospheric Chemistry (EMAC) chemistry-transport model simulations, we found differences in meteorological conditions and flight patterns responsible for about 7% of the MBC reductions. Accordingly 41% of MBC reductions can be attributed to reduced anthropogenic emissions. Our results reflect the strong and immediate positive effect of changes in human activities on air quality and the atmospheric role of BC aerosols as a major air pollutant in the Anthropocene

Black carbon aerosol reductions during COVID-19 confinement quantified by aircraft measurements over Europe

The abrupt reduction in human activities during the first lockdown of the COVID-19 pandemic created unprecedented atmospheric conditions. To quantify the changes in lower tropospheric air pollution, we conducted the BLUESKY aircraft campaign and measured vertical profiles of black carbon (BC) aerosol particles over Western and Southern Europe in May and June 2020. We compared the results to similar measurements of the EMeRGe EU cam�paign performed in July 2017 and found that the BC mass concentrations (MBC) were reduced by about 47%. For BC particle number concentrations, we found comparable reductions

Numerical simulation of the impact of COVID-19 lockdown on tropospheric composition and aerosol radiative forcing in Europe

Aerosols influence the Earth\u27s energy balance directly by modifying the radiation transfer and indirectly by altering the cloud microphysics. Anthropogenic aerosol emissions dropped considerably when the global COVID-19 pandemic resulted in severe restraints on mobility, production, and public life in spring 2020. We assess the effects of these reduced emissions on direct and indirect aerosol radiative forcing over Europe, excluding contributions from contrails. We simulate the atmospheric composition with the ECHAM5/MESSy Atmospheric Chemistry (EMAC) model in a baseline (business-as-usual) and a reduced emission scenario. The model results are compared to aircraft observations from the BLUESKY aircraft campaign performed in May–June 2020 over Europe. The model agrees well with most of the observations, except for sulfur dioxide, particulate sulfate, and nitrate in the upper troposphere, likely due to a biased representation of stratospheric aerosol chemistry and missing information about volcanic eruptions. The comparison with a baseline scenario shows that the largest relative differences for tracers and aerosols are found in the upper troposphere, around the aircraft cruise altitude, due to the reduced aircraft emissions, while the largest absolute changes are present at the surface. We also find an increase in all-sky shortwave radiation of 0.21 ± 0.05 W m⁻² at the surface in Europe for May 2020, solely attributable to the direct aerosol effect, which is dominated by decreased aerosol scattering of sunlight, followed by reduced aerosol absorption caused by lower concentrations of inorganic and black carbon aerosols in the troposphere. A further increase in shortwave radiation from aerosol indirect effects was found to be much smaller than its variability. Impacts on ice crystal concentrations, cloud droplet number concentrations, and effective crystal radii are found to be negligible

Cloud droplet number closure for tropical convective clouds during the ACRIDICON CHUVA campaign

The main objective of the ACRIDICON-CHUVA campaign in September 2014 was the investigation of aerosol-cloud-interactions in the Amazon Basin. Cloud properties near cloud base of growing convective cumuli were characterized by cloud droplet size distribution measurements using a cloud combination probe and a cloud and aerosol spectrometer. In the current study, an adiabatic parcel model was used to perform cloud droplet number closure studies for several flights in differently polluted air masses