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Atmospheric Gas-to-Particle conversion

Periodic Reporting for period 2 - ATM-GTP (Atmospheric Gas-to-Particle conversion)

Reporting period: 2018-12-01 to 2020-05-31

Atmospheric Gas-to-Particle conversion (ATM-GTP) is a 5-year project focusing on one of the most critical atmospheric processes relevant to global climate and air quality. It is especially focused on the first steps of atmospheric aerosol particle formation and growth. The project concentrates on the currently lacking environmentally-specific knowledge associated with atmospheric aerosols, the nano-scale gas-to-particle conversion (GTP). The main scientific objective of ATM-GTP is to create a deep understanding on atmospheric GTP taking place at the sub-5 nm size range. The project is carrying out atmospheric measurements in heavily-polluted Chinese mega cities like Beijing and in pristine environments like Siberia and Nordic high-latitude regions. We also aim to find out how nano-GTM is associated with air quality-climate interactions and feedbacks. We are interested in quantifying the effect of nano-GTP on the COBACC (Continental Biosphere-Aerosol-Cloud-Climate) feedback loop that is important in Arctic and boreal regions. Our approach enables to point out the effective reduction mechanisms of the air pollution by a factor of 5-10 and to make reliable estimates of the global and regional aerosol loads, including anthropogenic and biogenic contributions to these loads. We can estimate the future role of Northern Hemispheric forests in reducing the global radiative forcing via new understanding of the feedbacks. The project is carried out by the world-leading scientist in atmospheric aerosol science, being also one of the founders of terrestrial ecosystem meteorology, together with his research team. The project uses data from novel ground based stations including SMEAR (Stations Measuring Ecosystem Atmospheric Relations) stations, related modelling platforms and regional data from Russia and China. The work is carried out in synergy with several national, Nordic and EU research-innovation projects.

We lack a holistic scientific understanding of atmospheric nano-GTP and its connection with air quality and climate. Key ways forward are multi-platform measurement campaigns and long-term comprehensive observations in different atmospheric environments (Hari et al. 2016) both coupled to multi-scale modeling tools. In this way we are able to understand the role of nano-GTP a) in the interactions and feedbacks associated with urban pollution to be ready to make targeted strategies for pollution control, and b) in the global aerosol load and its role in several feedback loops. One such feedback loop is the COBACC feedback loop.

Importance for society:
ATM-GTP provides crucial information on the atmospheric processes, feedback and interactions taking place in the Northern High latitudes and mega city environments. This new information is needed for the adaptation and mitigation plans and strategies and for the climate policy making as well as to reduce air pollution.

Objectives and hypothesis. The overlying scientific objective of ATM-GTP is to attain a deep understanding of atmospheric gas-to-particle conversion occurring in the sub-5 nm size range (nano-GTP), and to determine how nano-GTP is associated with air quality-climate interactions and feedbacks. The specific objectives are:
1. To quantify the contribution to nano-GTP from key neutral and ion-mediated processes (production of gaseous precursors, atmospheric oxidation, clustering, initial steps of cluster/aerosol growth, boosting growth / activation of clusters by of multiple vapors).
2. To quantify the non-linear physical and chemical atmospheric processes affecting and interacting with nano-GTP in heavily-polluted environments.
3. To quantify the non-linear processes governing nano-GTP in pristine environments like Siberia and Arctic areas.
4. To quantify the effects of biogenic and anthropogenic emissions on nano-GTP, their interactions, and their relative contributions to global aerosol number loads in present-day and future climates.
5. To quantify the effect of nano-GTP on the COBACC (COntinental Biosphere-Aerosol-Cloud-Climate) feedback loop.
Via producing new secondary aerosol particles, nano-GTP affects local, regional and global aerosol loadings and alters aerosol size distributions and Cloud Condensation Nuclei (CCN) concentrations. In polluted conditions the main concern is air quality, whereas in pristine conditions the interest lies more in the changing climate. Since GTP – particularly in the sub-5 nm size range – is a key element in understanding atmospheric chemistry and nanophysics, we can formulate the following hypothesis: By quantifying the processes, interactions and feedbacks related to our specific objectives, we will be able a) to determine the most efficient steps towards significantly reducing secondary air pollution (in some cases by a factor of 5−10), b) to estimate the potential that the biosphere in Northern Hemisphere has in reducing global radiative forcing via the quantified feedbacks, and c) to estimate anthropogenic and biogenic contributions to global and regional aerosol loadings, particularly related to pollution in the arctic/boreal regions in a changing climate.
WP1: Process level understanding of nano-GTP

We have performed several laboratory experiments at the CLOUD (Cosmic Leaving OUtdoor Droplets) chamber at CERN, Switzerland and found out and confirmed several processes like the interplay of sulphuric acid, amines, ammonia and extreme low volatile organics on clustering, nucleation and subsequent growth (Lehtipalo et al. 2018). Actually, the hypothesis on size dependent growth rate of freshly formed aerosol particles are further confirmed. In addition, we studied the effect of temperature on the pure biogenic new particle formation from alpha-pinene, simulating pristine, pre-industrial times (Simon et al. 2020). We also introduced different biogenic vapors to study their synergistic effect in new particle formation to simulate for example Amazonia (Heinritzi et al. Submitted) and the free troposphere above it (Dada et al. 2020a In Prep) as well as the boreal forest in Hyytiälä (Lehtipalo et al. 2018). Indeed, we found that isoprene attenuates the particle formation rate and the early growth of freshly formed particles (Heinritzi et al. Submitted), while sesquiterpenes enhance the formation and growth due to its longer carbon chain and thus lower volatility (Dada et al. 2020b, in Prep). We additionally simulated the addition of SO2 and NOx to biogenic freshly formed particles from alpha-pinene, which are pollutant related trace gases to understand the occurring mechanism (Yan et al. 2020, Under Review Science Advances). We found that at positive temperatures sulphuric acid formed from the oxidation of SO2, is completely sterile in the absence of stabilizing bases (Yan et al. 2020, Under Review Science Advances), while NOx attenuated the biogenic particle formation rate. On the other hand, at negative temperatures we found that sulphuric acid contributes to biogenic particle formation (Dada et al. 2020a In Prep). In order to make studies from different chamber experiments comparable and repeatable, we developed a protocol from scientists to follow when studying sub 3 nm particle formation and growth in chamber experiments (Dada et al. 2020, Accepted Nature Protocols).

References:

Lehtipalo, K., Yan, C., Dada, L., Bianchi, F., Xiao, M., Wagner, R., Stolzenburg, D., Ahonen, L. R., Amorim, A., Baccarini, A., Bauer, P. S., Baumgartner, B., Bergen, A., Bernhammer, A.-K. Breitenlechner, M., Brilke, S., Buchholz, A., Mazon, S. B., Chen, D., Chen, X., Dias, A., Dommen, J., Draper, D. C., Duplissy, J., Ehn, M., Finkenzeller, H., Fischer, L., Frege, C., Fuchs, C., Garmash, O., Gordon, H., Hakala, J., He, X., Heikkinen, L., Heinritzi, M., Helm, J. C., Hofbauer, V., Hoyle, C. R., Jokinen, T., Kangasluoma, J., Kerminen, V.-M. Kim, C., Kirkby, J., Kontkanen, J., Kürten, A., Lawler, M. J., Mai, H., Mathot, S., Mauldin, R. L., Molteni, U., Nichman, L., Nie, W., Nieminen, T., Ojdanic, A., Onnela, A., Passananti, M., Petäjä, T., Piel, F., Pospisilova, V., Quéléver, L. L. J., Rissanen, M. P., Rose, C., Sarnela, N., Schallhart, S., Schuchmann, S., Sengupta, K., Simon, M., Sipilä, M., Tauber, C., Tomé, A., Tröstl, J., Väisänen, O., Vogel, A. L., Volkamer, R., Wagner, A. C., Wang, M., Weitz, L., Wimmer, D., Ye, P., Ylisirniö, A., Zha, Q., Carslaw, K. S., Curtius, J., Donahue, N. M., Flagan, R. C., Hansel, A., Riipinen, I., Virtanen, A., Winkler, P. M., Baltensperger, U., Kulmala, M., and Worsnop, D. R.: Multicomponent new particle formation from sulfuric acid, ammonia, and biogenic vapors, Science Advances, 4, eaau5363, 10.1126/sciadv.aau5363 2018.

Simon, M., Dada, L., Heinritzi, M., Scholz, W., Stolzenburg, D., Fischer, L., Wagner, A. C., Kürten, A., Rörup, B., He, X.-C. Almeida, J., Baalbaki, R., Baccarini, A., Bauer, P. S., Beck, L., Bergen, A., Bianchi, F., Bräkling, S., Brilke, S., Caudillo, L., Chen, D., Chu, B., Dias, A., Draper, D. C., Duplissy, J., El Haddad, I., Finkenzeller, H., Frege, C., Gonzalez-Carracedo, L., Gordon, H., Granzin, M., Hakala, J., Hofbauer, V., Hoyle, C. R., Kim, C., Kong, W., Lamkaddam, H., Lee, C. P., Lehtipalo, K., Leiminger, M., Mai, H., Manninen, H. E., Marie, G., Marten, R., Mentler, B., Molteni, U., Nichman, L., Nie, W., Ojdanic, A., Onnela, A., Partoll, E., Petäjä, T., Pfeifer, J., Philippov, M., Quéléver, L. L. J., Ranjithkumar, A., Rissanen, M., Schallhart, S., Schobesberger, S., Schuchmann, S., Shen, J., Sipilä, M., Steiner, G., Stozhkov, Y., Tauber, C., Tham, Y. J., Tomé, A. R., Vazquez-Pufleau, M., Vogel, A., Wagner, R., Wang, M., Wang, D. S., Wang, Y., Weber, S. K., Wu, Y., Xiao, M., Yan, C., Ye, P., Ye, Q., Zauner-Wieczorek, M., Zhou, X., Baltensperger, U., Dommen, J., Flagan, R. C., Hansel, A., Kulmala, M., Volkamer, R., Winkler, P. M., Worsnop, D. R., Donahue, N. M., Kirkby, J., and Curtius, J.: Molecular understanding of new-particle formation from alpha-pinene between −50 °C and 25 °C, Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2019-1058 in review, 2020.

Heinritzi, M., Dada, L., Simon, M., Stolzenburg, D., Wagner, A. C., Fischer, L., Ahonen, L. R., Amanatidis, S., Baalbaki, R., et al.: Molecular understanding of the suppression of new-particle formation by isoprene, Submitted, 2020.

Dada L. et al. Pure biogenic new particle formation involving Sesquiterpenes, 2020a, In Prep

Dada L. et al. Molecular insights on multicomponent new particle formation, 2020b, In Prep

Yan, C., Nie, W., Vogel, A. L., Dada, L., Lehtipalo, K., Stolzenburg, D., Wagner, R., et al.: Size-dependent influence of NOx on the growth rates of organic aerosol particles, Under Review Science Advances, 2020.

Dada L., Lehtipalo K., Kontkanen J., Nieminen T., Baalbaki R., Ahonen L., Duplissy J., Yan C., Chu B., Petäjä T., Lehtinen K., Kerminen V-M., Kulmala M., Kangasluoma J. : Formation and Growth of sub-3-nm aerosol particles in experimental chambers, Nature Prot., Accepted, 2020

WP 2: GTP in polluted environments: China activities - Major achievements:

New particle formation in polluted megacities has been a controversial topic as the sink is too high for it to occur according to theory (Kulmala et al. 2017, Du et al. In Prep). Together with several Chinese institutes, we were able to identify the precursors that drive new particle formation in Shanghai, using state-of-the-art instrumentation and publish our results in Science (Yao et al. 2018). In order to extend the studied area from MegaCity to GigaCity, we established a comprehensive measurement station in the center of Beijing (Lu et al. 2019 and Zhou et al. 2019), the basic observations continued for two years. Beside, the new station is now equipped with several state-of-the-art instruments making the station one of the lead stations around the world. The new auxiliary instrumentation includes APi-TOFs (Atmospheric Pressure Time of Flight Spectrometer) equipped with several inlets (Chemical Ionization and FIGAERO), PSM (Particle Size Magnifier), CPC (Condensational Particle Counter), NAIS (Neutral and Air Ion Spectrometer), MARGA(Monitor for AeRosols and Gases in Ambient air), SMPS (Scanning Mobility Particle Sizer), ACSM (Aerosol Chemical Speciation Monitor), Aethalometer, TEOM(Tapered element oscillating microbalance), Filter measurements, metal analyzers, trace gases monitors, and meteorology weather stations. These longer term observations serve looking into gas to particle conversion not only concerning NPF but also mass formation and heterogenous reactions resulting in air pollution, particularly haze episodes. Measuring the composition of clusters, the nature of gases present as well as the mass chemical composition we are able to identify the mechanisms which govern pollution formation in such environments (Figure 1). Moreover, we were able to measure the gas phase concentration of ammonia and amines which seem to be the major component in stabilizing sulfuric acid, the major driver of NPF in urban environments, and using positive matrix factorization together with our collaborators in china and elsewhere, we identified that traffic seems to be the major source of these stabilizing bases. The summary of the two years of observations in Beijing brought about a conclusion on the new particle formation cycle, by which the following sequence occurs: 1) New sub 3 nm clusters form due to gas to particle transformation of sulfuric acid and amines concurrent with sunrise (Deng et al. in prep), 2) with the aid of sulfuric acid and anthropogenic volatile organic compounds these sub 3 nm particles grow into nucleation mode (Yan et al. submitted), 3) when reaching nucleation mode, these freshly formed particles known as NPF particles get mixed with primary particles emitted from traffic and other anthropogenic activities in urban environments such as cooking (Cai et al. submitted; Kontkanen et al. in Prep), 4) all together primary and NPF particles are subject to semi and low volatility organic compounds present in the air which condense on their surfaces resulting into their growth into mass relevant sizes also known as pollution. Depending on the meteorology, the haze or pollution either resides for up to 4 days or gets ‘washed out’ by northerly clean winds. Therefore, our results serve as influence for policy makers who intend to enforce laws for conquering air pollution in mega cities (Yan et al. submitted). In addition to looking into the gas to particle formation mechanism, our measurements of highly oxygenated molecules were utilized for comparison with other Chinese megacities in order to estimate their formation mechanisms and therefore their volatiles and thus their contributions to new particle formation and growth in urban environments (Nie et al. In prep).
To Combine our knowledge from atmospheric measurements and Process level understanding of nano-GTP, we performed multiple experiments in the CLOUD chamber at CERN where we injected anthropogenic VOCs (naphthaline, trimethyl benzene and toluene) in the presence and absence of the traditional sulfuric and ammonia, and found that those compounds can nucleate in the absence of any sulfuric acid and ammonia, and also contribute to the growth of nano particles (Xiao et al. submitted). Finally, we introduced Nitric acid to the chamber, and found out that atmospherically relevant concentrations of HNO3 together with ammonia is capable of growing the particles beyond few nm per hour, and was found in the particle phase (Wang et al., under review in Nature) concurrent with our observations in Beijing, where nitrate explains the majority of the mass formed (Daellenbach et al. In prep).
Figure 1: The main mechanisms of NPF and subsequent particle growth. The initial stages of NPF are dominated by formation of sulfuric acid–DMA clusters, with additional contribution by ammonia. Growth of >3 nm particles is mainly due to anthropogenic low volatile organic compounds and after 20/25 nm nitrates contribute significantly. Heterogeneous chemistry, including reactive uptake of aerosol precursors, is crucial for the production of secondary aerosol mass.
Figure 2: A schematic summarizing of key species and processes of NPF in Beijing. Stationary (combustion) sources emit SO2 while vehicles emit NOx and VOCs but also NH3 and amines. Gas-phase sulfuric acid (H2SO4), produced from oxidation of SO2, forms stable clusters with the amines. These clusters grow at first entirely by co-condensation of sulfuric acid and bases (amines and ammonia), along with cluster collisions. Gas-phase oxidation of VOCs produces mainly SVOCs and LVOCs, because NO from traffic suppresses ELVOC formation; these vapors contribute to (even dominate) the growth of particles from a few nanometers to several tens of nanometers.

References:
Kulmala, M., Kerminen, V. M., Petaja, T., Ding, A. J., and Wang, L.: Atmospheric gas-to-particle conversion: why NPF events are observed in megacities?, Faraday Discuss, 200, 271-288, 10.1039/c6fd00257a 2017.

Du W., Dada L., Yan C., Cai J. et al. Understanding new particle formation under high condensation sink conditions, 2020, In Prep.

Yao, L., Garmash, O., Bianchi, F., Zheng, J., Yan, C., Kontkanen, J., Junninen, H., Mazon, S. B., Ehn, M., Paasonen, P., Sipilä, M., Wang, M., Wang, X., Xiao, S., Chen, H., Lu, Y., Zhang, B., Wang, D., Fu, Q., Geng, F., Li, L., Wang, H., Qiao, L., Yang, X., Chen, J., Kerminen, V.-M. Petäjä, T., Worsnop, D. R., Kulmala, M., and Wang, L.: Atmospheric new particle formation from sulfuric acid and amines in a Chinese megacity, Science, 361, 278-281, 10.1126/science.aao4839 2018.

Lu, Y., Yan, C., Fu, Y., Chen, Y., Liu, Y., Yang, G., Wang, Y., Bianchi, F., Chu, B., Zhou, Y., Yin, R., Baalbaki, R., Garmash, O., Deng, C., Wang, W., Liu, Y., Petäjä, T., Kerminen, V. M., Jiang, J., Kulmala, M., and Wang, L.: A proxy for atmospheric daytime gaseous sulfuric acid concentration in urban Beijing, Atmos. Chem. Phys., 19, 1971-1983, 10.5194/acp-19-1971-2019 2019.

Zhou, Y., Dada, L., Liu, Y., Fu, Y., Kangasluoma, J., Chan, T., Yan, C., Chu, B., Daellenbach, K. R., Bianchi, F., Kokkonen, T., Liu, Y., Kujansuu, J., Kerminen, V. M., Petäjä, T., Wang, L., Jiang, J., and Kulmala, M.: Variation of size-segregated particle number concentrations in winter Beijing, Atmos. Chem. Phys. Discuss., 2019, 1-31, 10.5194/acp-2019-60 2019.

Deng, C., Fu, Y., Dada, L., Yan, C., Cai, R., Yang, D., Zhou, Y., Yin, R., Lu, Y., Li, X., Fan, X., Nie, W., Kontkanen, J., Kangasluoma, J., Chu, B., Ding, A., Kerminen, V.-M. Paasonen, P., Worsnop, D. R., Bianchi, F., Liu, Y., Zheng, J., Wang, L., Kulmala, M., and Jiang, J.: Seasonal characteristics of new particle formation and growth in urban Beijing, In Prep., 2020.

Yan, C. et al.: The synergistic role of sulfuric acid, dimethylamine and oxidized organics governing new-particle formation in Beijing,2020 Submitted (Science Advances).

Cai, J., Chu, B., Yao, L., Yan, C., Heikkinen, L. M., Zheng, F., Fan, X., et al.: Chemical and physical properties of primary particle emissions during the non-heating season in Beijing, In Prep., 2020.

Kontkanen J., Paasonen P., Kulmala M.: A New Method to Determine the Size Distribution of Particle Number Emissions in Urban Environments Based on Measured Particle Size Distributions2020, in Prep,

Xiao M , Hoyle C., Dada L., Doninik Stolzenburg , Andreas Kuerten , Mingyi Wang , Houssni Lamkaddam , Olga Garmash ,et al. The driving factors of new particle formation and growth in the polluted boundary layer, 2020, In Review, Nature Comm.

Wang M., Kong W., Marten R., He X., Chen D, Pfeifer J. et al. , Runaway growth of new atmospheric particles by nitric acid and ammonia condensation, Under Review in Nature, 2020

Daellenbach K. R., Cai J. , Krechmer J., Yan C., et al.: Long-term analysis of sources contributing to PM2.5 in Beijing, In Prep. 2020

WP3 GTP in pristine environments: RUSSIA activities - Major achievements:
we quantified two steps of the COBACC feedback loop (aerosol – solar radiation – photosynthesis) using data sets from five stations in boreal and hemiboreal forests (Ezhova et al., 2018a). The COBACC loop includes nano-GTP effect via aerosol component. Of the five stations, two sites are located in Finland, one site is in Estonia and two sites are in Russia. Currently, the data from these five stations form the largest possible set of simultaneous atmospheric observations on trace gases, meteorology, solar radiation and aerosols, conducted in boreal and hemiboreal forests in Eurasia. We showed that the maximum observed aerosol load can lead to an increase in gross primary production (GPP) of a forest ecosystem by 6-14% on clear days as compared to clean atmosphere conditions (low aerosol load). The increase is due to the effect of diffuse radiation fertilization. Furthermore, we showed that optically thin clouds might further increase GPP of an ecosystem by 11-30% as compared to clean atmosphere, clear-sky conditions. Therefore, clouds play an important role in the COBACC fee
dback loop and require further investigation. In particular, to understand GTP effect on COBACC feedback loop, aerosol-cloud interactions and aerosol role for the cloud formation in boreal forests should be clarified and quantified. We gave a theoretical description of the condensation sink (CS) – one of the two major parameters controlling nano-GTP, and provided a map allowing simple estimates of aerosol modes’ contribution to the CS (Ezhova et al., 2018b). We showed that smallest particles’ (cluster mode) contribution to the CS does not exceed few percent under atmospherically relevant conditions. We developed and tested a theoretical approach to describe joint dynamics of aerosol population and condensing vapors.
Task GTP observations in Siberia (pristine). The long-term measurement campaign in Siberia started in July 2019. The measurements are performed in collaboration with the Institute of Atmospheric Optics, Siberian Branch of the Russian Academy of Science (Tomsk, Russia). Two instruments (PSM and NAIS) have been installed at the background station Fonovaya located ca. 70 km from Tomsk, West Siberia. Fig. 3.1 shows the example of the first results from these instruments corresponding to the NPF event on 22.09.2019. These two instruments are part of the full set including state-of-the-art instruments necessary for the detailed study of the chemical and physical properties of an aerosol population: DMPS, NAIS, PSM and CI-API-TOF. CI-API-TOF and DMPS were shipped later and the start of new measurements is planned for January-March 2020.
Task 3.2-3.3. Background NPF/GTP in pristine environments. Integrated analysis of GTP in pristine environments. In order to understand better the conditions at Fonovaya, we have performed the preliminary analysis of the existing data (2015-2018) and compared the results to those from SMEAR II (Finland) and SMEAR Estonia. The aerosol data set at Fonovaya was obtained from Diffusion Aerosol Spectrometer (DAS) and Optical Particle Counter (OPC). The main results can be summarized as follows. Similar to the results for SMEAR stations, the NPF events in Siberia are more frequent when the sky is clear. However, the total number of events is considerably lower (Fig. 3.2) especially in summer and autumn. The number of NPF events peaks in March, similar to SMEAR stations where the seasonal distribution NPF has a peak in March-April (Fig. 3.2). The concentrations of trace gases, such as sulfur dioxide, nitrogen dioxide and nitrogen oxide are higher at Fonovaya during NPF events as compared to non-event days, pointing at the importance of anthropogenic factor for GTP in Siberia. In addition, the concentrations of trace gases on average are an order of magnitude higher in Siberia than at SMEAR II and SMEAR Estonia stations.

• Demakova, A., E. Ezhova, O. Garmash, M. Arshinov, B. Belan, T. Petäjä, and M. Kulmala Experimental research and analysis of atmospheric aerosol and its precursors in Siberian boreal forest/ Proceedings of The Center of Excellence in Atmospheric Science (CoE ATM) Annual Seminar 2019, Helsinki, 25-26 November 2019, Report series in aerosol science No 226 (2019), P. 208-209.

Fig. 3.1. The first results from the state-of-the-art aerosol instruments NAIS and PSM displaying NPF event at Fonovaya station, Siberia, on 22.09.2019. Particles of different polarity, NAIS (a), ions of different polarity, NAIS (b), particle number distribution at the smallest sizes, PSM (c), number concentration of the smallest particles in different size bins, PSM (d).

Fig. 3.2. Seasonal distribution of event, non-event and undefined days at Fonovaya (a), SMEAR Estonia (b) and SMEAR II (c).

WP 4. Task 4.2 On the COBACC feedback loop. We quantified two steps of the COBACC feedback loop (aerosol – solar radiation – photosynthesis) using data sets from five stations in boreal and hemiboreal forests (Ezhova et al., 2018a). The COBACC loop includes nano-GTP effect via aerosol component. Of the five stations, two sites are located in Finland, one site is in Estonia and two sites are in Russia. Currently, the data from these five stations form the largest possible set of simultaneous atmospheric observations on trace gases, meteorology, solar radiation and aerosols, conducted in boreal and hemiboreal forests in Eurasia. We showed that the maximum observed aerosol load can lead to an increase in gross primary production (GPP) of a forest ecosystem by 6-14% on clear days as compared to clean atmosphere conditions (low aerosol load). The increase is due to the effect of diffuse radiation fertilization. Furthermore, we showed that optically thin clouds might further increase GPP of an ecosystem by 11-30% as compared to clean atmosphere, clear-sky conditions. Therefore, clouds play an important role in the COBACC feedback loop and require further investigation. In particular, to understand GTP effect on COBACC feedback loop, aerosol-cloud interactions and aerosol role for the cloud formation in boreal forests should be clarified and quantified. We gave a theoretical description of the condensation sink (CS) – one of the two major parameters controlling nano-GTP, and provided a map allowing simple estimates of aerosol modes’ contribution to the CS (Ezhova et al., 2018b). We showed that smallest particles’ (cluster mode) contribution to the CS does not exceed few percent under atmospherically relevant conditions. We developed and tested a theoretical approach to describe joint dynamics of aerosol population and condensing vapors.

• Ezhova, E., Ylivinkka, I., Kuusk, J., Komsaare, K., Vana, M., Krasnova, A., Noe, S., Arshinov, M., Belan, B., Park, S-B., Lavric, J. V., Heimann, M., Petäjä, T., Vesala, T., Mammarella, I., Kolari, P., Bäck, J., Rannik, U., Kerminen, V-M., Kulmala, M. Direct effect of aerosols on solar radiation and gross primary production in boreal and hemiboreal forests// 2018. Atmos. Chem. Phys. V. 18, P. 17863-17881.

• Ezhova E., Kerminen V.-M. Lehtinen K., Kulmala M. A simple model for the time evolution of the condensation sink in the atmosphere for intermediate Knudsen numbers// 2018. Atmos. Chem. Phys., V. 18, P. 2431-2442.
During the first half of the project the main results beyond the state of the art are
1) the major fraction of haze particles are secondary (made via atmsopheric processes) origin: over 85% of mass and over 65 5 of number. This is particularly true in Chinese megacities

2) The new particle formation is more rare in Siberia than theoretically predicted

Before the end of the project we expect to answer main sceitific questions and publish our fresh results in high impact journals.
Figure 3.2, see figure text above
Figure 3.1., see figure text above
Figure 2., see figure text above
Figure 1. see figure text above