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  • Kerminen, Veli-Matti; Chen, Xuemeng; Vakkari, Ville; Petäjä, Tuukka; Kulmala, Markku; Bianchi, Federico (2018)
    This review focuses on the observed characteristics of atmospheric new particle formation (NPF) in different environments of the global troposphere. After a short introduction, we will present a theoretical background that discusses the methods used to analyze measurement data on atmospheric NPF and the associated terminology. We will update on our current understanding of regional NPF, i.e. NPF taking simultaneously place over large spatial scales, and complement that with a full review on reported NPF and growth rates during regional NPF events. We will shortly review atmospheric NPF taking place at sub-regional scales. Since the growth of newly-formed particles into larger sizes is of great current interest, we will briefly discuss our observation-based understanding on which gaseous compounds contribute to the growth of newly-formed particles, and what implications this will have on atmospheric cloud condensation nuclei formation. We will finish the review with a summary of our main findings and future outlook that outlines the remaining research questions and needs for additional measurements.
  • Dada, Lubna; Chellapermal, Robert; Mazon, Stephany Buenrostro; Paasonen, Pauli; Lampilahti, Janne; Manninen, Hanna E.; Junninen, Heikki; Petäjä, Tuukka; Kerminen, Veli-Matti; Kulmala, Markku (2018)
    Atmospheric new-particle formation (NPF) is a worldwide-observed phenomenon that affects the human health and the global climate. With a growing network of global atmospheric measurement stations, efforts towards investigating NPF have increased. In this study, we present an automated method to classify days into four categories including NPF events, non-events and two classes in between, which then ensures reproducibility and minimizes the hours spent on manual classification. We applied our automated method to 10 years of data collected at the SMEAR II measurement station in Hyytiala, southern Finland using a Neutral cluster and Air Ion Spectrometer (NAIS). In contrast to the traditionally applied classification methods, which categorize days into events and non-events and ambiguous days as undefined days, our method is able to classify the undefined days as it accesses the initial steps of NPF at sub-3 nm sizes. Our results show that, on similar to 24% of the days in Hyytiala, a regional NPF event occurred and was characterized by nice weather and favourable conditions such as a clear sky and low condensation sink. Another class found in Hyytiala is the transported event class, which seems to be NPF carried horizontally or vertically to our measurement location and it occurred on 17% of the total studied days. Additionally, we found that an ion burst, wherein the ions apparently fail to grow to larger sizes, occurred on 18% of the days in Hyytiala. The transported events and ion bursts were characterized by less favourable ambient conditions than regional NPF events and thus experienced interrupted particle formation or growth. Non-events occurred on 41% of the days and were characterized by complete cloud cover and high relative humidity. Moreover, for regional NPF events occurring at the measurement site, the method identifies the start time, peak time and end time, which helps us focus on variables within an exact time window to better understand NPF at a process level. Our automated method can be modified to work in other measurement locations where NPF is observed.
  • Artaxo, Paulo; Hansson, Hans-Christen; Andreae, Meinrat O.; Bäck, Jaana; Alves, Eliane Gomes; Barbosa, Henrique M. J.; Bender, Frida; Bourtsoukidis, Efstratios; Carbone, Samara; Chi, Jinshu; Decesari, Stefano; Despres, Viviane R.; Ditas, Florian; Ezhova, Ekaterina; Fuzzi, Sandro; Hasselquist, Niles J.; Heintzenberg, Jost; Holanda, Bruna A.; Guenther, Alex; Hakola, Hannele; Heikkinen, Liine; Kerminen, Veli-Matti; Kontkanen, Jenni; Krejci, Radovan; Kulmala, Markku; Lavric, Jost; de Leeuw, Gerrit; Lehtipalo, Katrianne; Machado, Luiz Augusto T.; McFiggans, Gordon; Franco, Marco Aurelio M.; Meller, Bruno Backes; Morais, Fernando G.; Mohr, Claudia; Morgan, William; Nilsson, Mats B.; Peichl, Matthias; Petäjä, Tuukka; Prass, Maria; Poehlker, Christopher; Poehlker, Mira L.; Poeschl, Ulrich; Von Randow, Celso; Riipinen, Ilona; Rinne, Janne; Rizzo, Luciana; Rosenfeld, Daniel; Silva Dias, Maria A. F.; Sogacheva, Larisa; Stier, Philip; Swietlicki, Erik; Soergel, Matthias; Tunved, Peter; Virkkula, Aki; Wang, Jian; Weber, Bettina; Maria Yanez-Serrano, Ana; Zieger, Paul; Mikhailov, Eugene; Smith, James N.; Kesselmeier, Juergen (2022)
    This review presents how the boreal and the tropical forests affect the atmosphere, its chemical composition, its function, and further how that affects the climate and, in return, the ecosystems through feedback processes. Observations from key tower sites standing out due to their long-term comprehensive observations: The Amazon Tall Tower Observatory in Central Amazonia, the Zotino Tall Tower Observatory in Siberia, and the Station to Measure Ecosystem-Atmosphere Relations at Hyytiala in Finland. The review is complemented by short-term observations from networks and large experiments. The review discusses atmospheric chemistry observations, aerosol formation and processing, physiochemical aerosol, and cloud condensation nuclei properties and finds surprising similarities and important differences in the two ecosystems. The aerosol concentrations and chemistry are similar, particularly concerning the main chemical components, both dominated by an organic fraction, while the boreal ecosystem has generally higher concentrations of inorganics, due to higher influence of long-range transported air pollution. The emissions of biogenic volatile organic compounds are dominated by isoprene and monoterpene in the tropical and boreal regions, respectively, being the main precursors of the organic aerosol fraction. Observations and modeling studies show that climate change and deforestation affect the ecosystems such that the carbon and hydrological cycles in Amazonia are changing to carbon neutrality and affect precipitation downwind. In Africa, the tropical forests are so far maintaining their carbon sink. It is urgent to better understand the interaction between these major ecosystems, the atmosphere, and climate, which calls for more observation sites, providing long-term data on water, carbon, and other biogeochemical cycles. This is essential in finding a sustainable balance between forest preservation and reforestation versus a potential increase in food production and biofuels, which are critical in maintaining ecosystem services and global climate stability. Reducing global warming and deforestation is vital for tropical forests.