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Dimethyl sulfide (DMS) influences climate via cloud condensation nuclei (CCN) formation resulting from its oxidation products (mainly methanesulfonic acid, MSA, and sulfuric acid, H2SO4). Despite their importance, accurate prediction of MSA and H2SO4from DMS oxidation remains challenging. With comprehensive experiments carried out in the Cosmics Leaving Outdoor Droplets (CLOUD) chamber at CERN, we show that decreasing the temperature from +25 to -10 °C enhances the gas-phase MSA production by an order of magnitude from OH-initiated DMS oxidation, while H2SO4production is modestly affected. This leads to a gas-phase H2SO4-to-MSA ratio (H2SO4/MSA) smaller than one at low temperatures, consistent with field observations in polar regions. With an updated DMS oxidation mechanism, we find that methanesulfinic acid, CH3S(O)OH, MSIA, forms large amounts of MSA. Overall, our results reveal that MSA yields are a factor of 2-10 higher than those predicted by the widely used Master Chemical Mechanism (MCMv3.3.1), and the NOxeffect is less significant than that of temperature. Our updated mechanism explains the high MSA production rates observed in field observations, especially at low temperatures, thus, substantiating the greater importance of MSA in the natural sulfur cycle and natural CCN formation. Our mechanism will improve the interpretation of present-day and historical gas-phase H2SO4/MSA measurements. publishedVersion

Long-term exposure to ambient ozone is linked with respiratory-related mortality, while the emerging climate change is projected to pose double-edged challenges for ozone air quality. Here, we calculate the impact of emissions- and climate-change under SSP3-7.0 scenario on ozone-related mortality on a global scale, using historical (experiment histSST) and future simulations (experiments ssp370SST and ssp370pdSST) from three CMIP6 Earth System Models (ESMs) (GFDL-ESM4, EC-Earth3-AerChem, and UKESM1-0-LL). The ssp370SST experiment follows time-varying SSTs, while the SSP370pdSST follows a present-day climatology for SSTs. The chronic obstructive pulmonary disease mortality attributable to ozone pollution is estimated following the Global Burden Disease (GBD) 2019 approach, by using the ozone season daily maximum 8-hour mixing ratio (OSDMA8), the baseline mortality rate (from the GBD), and the SSP3-7.0 present and future gridded population. An increase in ozone-related mortality of approximately 2.5 million people per year globally is projected at the end of the century (2090) with respect to 2000 due to emissions and population changes. The climate-change footprint on ozone-related mortality exhibits large variability among the ESMs; yet, over India and China all ESMs project an increase of ozone-related mortality in the future, highlighting the importance of the ozone penalty due to global warming in regions with strong anthropogenic sources.

A multitude of biogeochemical feedback mechanisms govern the climate sensitivity of Earth in response to radiation balance perturbations. One feedback mechanism, which remained missing from most current Earth System Models applied to predict future climate change in IPCC AR6, is the impact of higher temperatures on the emissions of biogenic volatile organic compounds (BVOCs), and their subsequent effects on the hydroxyl radical (OH) concentrations. OH, in turn, is the main sink term for many gaseous compounds including methane, which is the second most important human-influenced greenhouse gas in terms of climate forcing. In this study, we investigate the impact of this feedback mechanism by applying two models, a one-dimensional chemistry-transport model, and a global chemistry-transport model. The results indicate that in a 6 K temperature increase scenario, the BVOC-OH-CH4 feedback increases the lifetime of methane by 11.4% locally over the boreal region when the temperature rise only affects chemical reaction rates, and not both, chemistry and BVOC emissions. This would lead to a local increase in radiative forcing through methane (ΔRFCH4) of approximately 0.013 Wm−2 per year, which is 2.1% of the current ΔRFCH4. In the whole Northern hemisphere, we predict an increase in the concentration of methane by 0.024% per year comparing simulations with temperature increase only in the chemistry or temperature increase in chemistry and BVOC emissions. This equals approximately 7% of the annual growth rate of methane during the years 2008–2017 (6.6 ± 0.3 ppb yr−1) and leads to an ΔRFCH4 of 1.9 mWm−2 per year.

The Erasmus+ ClimEd (2021-2023; http://climed.network; “Multilevel Local, Nation- and Regionwide Education and Training in Climate Services, Climate Change Adaptation and Mitigation”) project is aimed at the development of competency-based curricula for continuous comprehensive training of specialists in the field of climate services and additional education in climate change for decision-makers, experts in climate-dependent economic sectors, and public.Some of the goals and objectives of the project are closely related to the Pan-Eurasian EXperiment (PEEX; www.atm.helsinki.fi/peex), and especially with multi-disciplinary, -scale and -component study climate change at resolving major uncertainties in the Earth system science and global sustainability issues.The ClimEd Trainings (http://climed.network/events/climed-trainings), in total 7, will be carried out during the project and will be focused on training the faculty/ teaching/ research staff and postgraduates at the ClimEd partner institutions and collaborating organizations in advanced educational and information-and-communication technologies for building a flexible multi-level integrated practice-based education system in the field of Climate Services, Climate Change Adaptation and Mitigation.Due to COVID pandemic situation, the originally planned face-to-face first trainings (in Estonia, Ukraine, and Finland) were converted into online training. Such online trainings were divided into 3 consecutive blocks: (i) online lecturing, (ii) home-work-assignments (HWAs) as group projects with established internal communication between the member of the groups and with an option of zoom-consulting during remote work, and (iii) final oral presentations (projects’ defenses) of HWAs with evaluation and feedback, discussions, and awarding certificates (corresponding to ECTS credits) with achieved learning outcomes. The majority of HWAs are based on the ClimEd main themes linking climate change vs. agriculture, energy, technical design and construction, urban economy, water management, health care; although other themes of interest can be selected by groups. Trainings also include questionnaires distributed among participants: evaluation of the training, and evaluation of own learning outcomes. Technically, the Moodle system, Zoom-hosting, e-evaluations, etc. are actively utilized in such trainings. All materials of the trainings are always publicly accessible online at the ClimEd project website as well as long-term stored at the Moodle system for each training.The outcomes/ summaries – including the lecture topics and learning outcomes, information resources, themes of group projects, feedbacks and training results, established network-community of the training participants (trainees and lecturers and teachers of HWAs) – of the online training approach will be presented for the ClimEd Trainings. Summaries are available for: 1st training “Competence-Based Approach to Curriculum Development for Climate Education”; 19 Apr – 12 May 2021; http://climed.network/events/climed-trainings/climed-training-1-online); 2nd – “Adaptation of the Competency Framework for Climate Services to conditions of Ukraine” (29 Jun – 26 Aug 2021; http://climed.network/events/climed-trainings/climed-training-2-online); 3rd – “Digital tools and datasets for climate change education” (26 Oct – 12 Nov 2021; http://climed.network/events/climed-trainings/climed-training-3-online); and 4th “Developing learning courses in climate services considering needs of different users” (7–11 February 2022; http://climed.network/events/climed-trainings/climed-training-4).

Strong, ongoing high latitude-warming is causing changes to vegetation composition and plant productivity, modifying plant emissions of Biogenic Volatile Organic Compounds (BVOCs). In the sparsely populated high latitudes, climatic feedbacks resulting from BVOCs as precursors of atmospheric aerosols could be more important than elsewhere on the globe. Here, we quantitatively assess the linkages between vegetation changes, BVOC emissions and secondary organic aerosol (SOA) under different climate scenarios and show that warming-induced vegetation changes determine the spatial patterns of BVOC impacts on SOA. The northward advances of boreal needle-leaved trees and shrubs result in an increase of up to 45% in regional SOA optical depth, causing a cooling feedback. In contrast, areas dominated by temperate broad-leaved trees show a large decline in monoterpene emissions and SOA formation, causing a warming feedback. We highlight the necessity of considering vegetation shifts when assessing radiative feedbacks on climate following the BVOC-SOA pathway.

The pressure to increase forest and land carbon stocks simultaneously with increasing forest based biomass harvest for energy and materials emphasizes the need for dedicated analyses of impacts and possible trade-offs between these different mitigation options including also forest related biophysical factors, surface albedo and the formation of biogenic Secondary Organic Aerosols (SOA). We analyzed the change in global radiative forcing (RF) due to changes in these climatic agents as affected by the change in state of Finnish forests under increased or decreased harvest scenarios from a baseline. We also included avoided emissions due to wood material and energy substitution. Increasing harvests from baseline (65% of Current Annual Increment) decreased the total carbon sink (carbon in trees, soil and harvested wood products) at least for 50 years. When we coupled this change in carbon with other biosphere responses, surface albedo and aerosols, decreasing harvests from the baseline produced the largest cooling effect during 50 years. Accounting also for the avoided emissions due to increased wood use, the RF responses of the two lowest harvest scenarios were within uncertainty range. Our results show that the effects of forest management on SOA formation should be included in the analyses trying to deduce the net climate impact of forest use. The inclusion of the rarely considered SOA effects enforces the view that the lower the harvest, the more climatic cooling boreal forests provide. These results should act as a caution mark for policy makers who are emphasizing the increased utilization of forest biomass for short-living products and bioenergy as an efficient measure to mitigate climate change.

Although much efforts have been put on studying air pollution, our knowledge on the mechanisms of frequently occurred intense haze episodes in China is still limited. In this study, using three years of measurements of air pollutants at three different height levels on a 325-meter Beijing meteorology tower, we found that a positive particulate matter-boundary layer feedback mechanism existed at three vertical observation heights during intense haze polluted periods within the mixing layer. This feedback was characterized by a higher loading of PM2.5 with a shallower mixing layer. Measurements showed that the feedback was related to the decrease of solar radiation, turbulent kinetic energy and thereby suppression of the mixing layer. The feedback mechanism can explain the rapid formation of intense haze episodes to some extent, and we suggest that the feedback mechanism should be considered in air quality models for better predictions.

Highly oxygenated multifunctional compounds (HOM) play a key role in the growth of new particles during new particle formation (NPF) events, but their quantitative roles in different environments of the globe haven’t been well studied yet. In this study, the HOM concentrations and NPF events at a remote boreal forest site in Finland (SMEAR II) and a sub-urban site in the polluted eastern China (SORPES) were simulated with the MALTE-BOX model, and their roles in NPF at the two distinctly different environments are discussed. We found that sulfuric acid and HOM organonitrate concentrations in the gas phase are significantly higher but other HOM monomers and dimers from monoterpene oxidation are lower at SORPES compared to SMEAR II. The model can simulate the NPF events at SMEAR II with a good agreement but underestimate the growth of new particles at SORPES, indicating a dominant role of sulfuric acid and HOM originated from oxidation of aromatics in the polluted environment. This study highlight the needs of molecular-scale measurements in improving the understanding of NPF mechanisms in the polluted areas like eastern China.

Aerosol-cloud interaction is examined using four years of data from the MODIS/Terra (morning orbit) and MODIS/Aqua (afternoon orbit) satellites. Aerosol optical depth (AOD) and cloud properties retrieved from both sensors are used to explore in a statistical sense the morning-to-afternoon variation of cloud properties in conditions with low and high AOD, over both land and ocean. The results show that the morning-to-afternoon variation of cloud properties during the 3 hours between the Terra and Aqua overpasses have similar patterns (increase or decrease) over land under both low and high AOD conditions. The variation in d(Cloud_X), defined as the mean change in cloud property Cloud_X between the morning and afternoon overpasses in high AOD conditions minus that in low AOD conditions, is different over land and ocean. This applies to cloud droplet effective radius (CDR), cloud fraction (CF) and cloud top pressure (CTP), but not to cloud optical thickness (COT) and cloud liquid water path (CWP). The effects of initial cloud fraction and meteorological conditions on the change in CF are also explored, showing that upward motion of air parcels can enhance the cloud cover much more when AOD is high than when it is low. In contrast, the increase of cloud cover with increasing relative humidity is much stronger in a relatively clean atmosphere with low AOD than in a more polluted atmosphere. Meanwhile, stable atmospheric conditions favour the development of a low cloud cover, especially when AOD is high. Overall, the analysis of the diurnal variation of cloud properties provides a better understanding of aerosol-cloud interaction over land and ocean.

A multi-layer gas dry deposition model has been developed and implemented into a 1-dimensional chemical transport model SOSAA (a model to Simulate the concentrations of Organic vapours, Sulphuric Acid and Aerosols) to calculate the dry deposition velocities for all the gas species included in the chemistry scheme. The new model was used to analyse in-canopy sources and sinks, including gas emissions, chemical production and loss, dry deposition and turbulent transport of 12 featured biogenic volatile organic compounds (BVOCs) or groups of BVOCs (e.g., monoterpenes, isoprene+2-methyl-3-buten-2-ol (MBO), sesquiterpenes and oxidation products of mono- and sesquiterpenes) in July, 2010 at the boreal forest site SMEAR II (Station to Measure Ecosystem-Atmosphere Relations II). According to the significance of modeled monthly averaged individual source and sink terms inside the canopy, the selected BVOCs were classified into five categories: (1) most of emitted gases are transported out of the canopy (monoterpenes, isoprene+MBO), (2) chemical reactions remove a significant portion of emitted gases (sesquiterpenes), (3) bidirectional fluxes occur since both emission and dry deposition are crucial for the in-canopy concentration tendency (acetaldehyde, methanol, acetone, formaldehyde), (4) gases removed by deposition inside the canopy are compensated by the gases transported from above the canopy (acetol, pinic acid, β-caryophyllene's oxidation product BCSOZOH), and finally (5) the chemical production is comparable to the sink by deposition (isoprene's oxidation products ISOP34OOH and ISOP34NO3). Most of the simulated sources and sinks were located above about 4 m for oxidation products and above about 8 m for emitted species except formaldehyde. In addition, soil deposition (including deposition onto understory vegetation) contributed 11–61 % to the overall in-canopy deposition. The emission sources peaked at about 14–16 m which was higher than 10 m where the maximum of dry deposition onto overstorey vegetation was located. This study provided a method to enable the quantification of the exchange between atmosphere and biosphere for numerous BVOCs, which could be applied in large-scale models in future. With this more explicit canopy exchange modeling system this study analysed both the temporal and spatial variations of individual in-caonpy sources and sinks, as well as their combined effects on driving BVOCs exchange. Twelve featured BVOCs or BVOC groups were analyzed in this study, more compounds could also be investigated similarly by being classified into the five categories.

Aerosol effects on summertime low warm clouds over the Yangtze River Delta (YRD) are examined using co-located MODIS, CALIOP and CloudSat observations. By taking the vertical locations of aerosol and cloud layers into account, we use simultaneously observed aerosol and cloud data to investigate relationships between cloud properties and the amount of aerosol particles (using aerosol optical depth, AOD, as a proxy). Also, we investigate the impact of aerosol types on the variation of cloud properties with AOD. Finally, we explore how meteorological conditions affect these relationships using ERA Interim Reanalysis data. This study shows that the relation between cloud droplet effective radius (CDR) and AOD depends on the aerosol abundance, with a different behaviour for low and high AOD (i.e. AOD 0.3). Cloud fraction (CF) is found to be little dependent on the AOD when aerosol and cloud physically interact, but has a positive relation in case of well-separated clouds. Cloud optical Thickness (COT) is found to decrease when AOD increases, which may be due to radiative effects and retrieval artefacts caused by absorbing aerosol. Conversely, cloud top pressure (CTP) tends to increase with elevated AOD, indicating that the aerosol is not always prone to expand the vertical extension. Furthermore, separation of cases with either polluted dust or smoke aerosol shows that COT and CF are smaller for clouds mixed with smoke aerosol which is ascribed to the higher absorption efficiency of smoke than dust. The variation of cloud properties with AOD is analysed for different values of relative humidity (RH) and boundary layer thermodynamic and dynamic conditions, showing that high relative humidity and upward motion of air parcels can enhance the strength of aerosol-cloud interaction, especially pronounced in heavily polluted conditions than in moderately polluted conditions. Meteorological conditions play a weak role in the COT-AOD and CTP-AOD relationships throughout the range of AOD. Overall, the interpretation of the observed relationships between cloud properties and AOD requires that ambient environmental conditions are considered in addition to the aerosol and cloud parameters.

Eddy covariance fluxes of formic acid, HCOOH, were measured over a boreal forest canopy in spring/summer 2014. The HCOOH fluxes were bidirectional, but mostly upward during daytime, in contrast to studies elsewhere that reported mostly downward fluxes. Downward flux episodes were explained well by modeled dry deposition rates. The sum of net observed flux and modeled dry deposition yields an upward “gross flux” of HCOOH, which could not be quantitatively explained by literature estimates of direct vegetative/soil emissions nor by efficient chemical production from other volatile organic compounds (VOC), suggesting missing or greatly underestimated HCOOH sources in the boreal ecosystem. We implemented a vegetative HCOOH source into the GEOS-Chem chemical transport model to match our derived gross flux, and evaluated the updated model against air- and space-borne observations. Model biases in the boundary layer were substantially reduced based on this revised treatment, but biases in the free troposphere remain unexplained.

The East Pacific wavetrain (EPW) refers to here the intense stationary wave activity detected in the troposphere over the East Pacific and North America in 45 northern winters from 1958 to 2002. The EPW is generated in the lower troposphere over the East Pacific, propagating predominantly eastward into North America and slightly upward then eventually into the stratosphere. The intensity of the EPW varies from year to year and exhibits apparent decadal variability. For the period 1958–1964, the EPW was in its second maximum, and it was weakest for the period 1965–1975, then it was strongest for the period 1976–1987. After 1987, the EPW weakened again.

A large amount of biogenic volatile organic compounds (BVOCs) are emitted from boreal forests. Once emitted, BVOCs can be oxidized in the air, participate in particle formation and growth and thus indirectly affect local, regional and global climate. BVOCs act as a bridge between the biosphere and the atmosphere including atmospheric chemistry in both gas and particle phases. In this thesis we studied the in-canopy sources and sinks of BVOCs, the roles of BVOCs in gas and particle phases, as well as the impact of aerosol dynamics on the vertical aerosol fluxes in the planetary boundary layer. Several findings in this thesis are shown below: (1) By using a newly implemented gas dry deposition model in a one-dimensional chemical transport model SOSAA (model to Simulate the concentrations of Organic vapours, Sulphuric Acid and Aerosols) we simulated the in-canopy source and sink terms of 12 featured BVOCs. According to the strength of individual terms, BVOCs were classified into five categories: Cemis in which most of the emitted gases are transported out of the canopy, Cemis-chem in which most of the emitted gases are quickly oxidized inside the canopy, Cemis-depo in which emissions are comparable to deposition, Cdepo in which the dominant deposition sink leads to downward fluxes and Cchem-depo in which the chemical production compensates a part of deposition. (2) High upward fluxes of formic acid over a boreal forest were observed. The required unknown precursors and emission sources were quantified to explain the missing sources inside the canopy. (3) The simulated O3 concentration change due to chemical reactions related to BVOCs was in average less than 10% of the deposition sink. (4) The highly oxidized multifunctional organic molecules (HOMs) play a dominant role in the growth of new particles over the sub-Arctic forest region at the Pallas Atmosphere-Ecosystem Supersite and account for ∼ 75% of total SOA mass during new particle formation events. (5) The modelled vertical aerosol fluxes above the canopy caused by aerosol dynamics were comparable or sometimes exceeded that caused by particle dry deposition. This introduced large biases between measured flux and the particle dry deposition flux. The findings (1), (2), (3), (5) were obtained over the boreal forest at SMEAR (Station for Measuring ecosystem-Atmosphere Relations) II. This thesis provides a new numerical tool to analyse detailed sources and sinks of BVOCs, which can be applied in other ecosystems and further implemented in large-scale models.

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