Browsing by Subject "CCN"

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  • Pajunoja, Aki; Lambe, Andrew T.; Hakala, Jani; Rastak, Narges; Cummings, Molly J.; Brogan, James F.; Hao, Liqing; Paramonov, Mikhail; Hong, Juan; Prisle, Nonne L.; Malila, Jussi; Romakkaniemi, Sami; Lehtinen, Kari E. J.; Laaksonen, Ari; Kulmala, Markku; Massoli, Paola; Onasch, Timothy B.; Donahue, Neil M.; Riipinen, Ilona; Davidovits, Paul; Worsnop, Douglas R.; Petaja, Tuukka; Virtanen, Annele (2015)
    Aerosol climate effects are intimately tied to interactions with water. Here we combine hygroscopicity measurements with direct observations about the phase of secondary organic aerosol (SOA) particles to show that water uptake by slightly oxygenated SOA is an adsorption-dominated process under subsaturated conditions, where low solubility inhibits water uptake until the humidity is high enough for dissolution to occur. This reconciles reported discrepancies in previous hygroscopicity closure studies. We demonstrate that the difference in SOA hygroscopic behavior in subsaturated and supersaturated conditions can lead to an effect up to about 30% in the direct aerosol forcinghighlighting the need to implement correct descriptions of these processes in atmospheric models. Obtaining closure across the water saturation point is therefore a critical issue for accurate climate modeling.
  • Deng, Yange; Kagami, Sara; Ogawa, Shuhei; Kawana, Kaori; Nakayama, Tomoki; Kubodera, Ryo; Adachi, Kouji; Hussein, Tareq; Miyazaki, Yuzo; Mochida, Michihiro (2018)
    The formation of biogenic secondary organic aerosols (BSOAs) in forest environments is potentially important to cloud formation via changes of the cloud condensation nuclei (CCN) activity of aerosols. In this study, the CCN activation of submicrometer aerosols and their chemical compositions and size distributions were measured at a midlatitude forest site in Japan during the summer of 2014 to assess the hygroscopicity of the organic aerosols and their contributions to the local CCN concentrations. The mean number concentrations of the condensation nuclei and CCN at supersaturation (SS) conditions of 0.11-0.80% were 1,238 and 166-740cm(-3), respectively. Organic aerosols and sulfate dominated the submicrometer aerosol mass concentrations. The particle hygroscopicity increased with increases in particle diameters. The hygroscopicity parameter for the organics, (org), was positively correlated with the atomic O to C ratio. The product of (org) and the volume fraction of OA was 0.12, accounting for 38% of the water uptake by aerosol particles. The hygroscopicity parameter of the locally formed fresh BSOA was estimated to be 0.09. The contribution of OA to the CCN number concentration, which was assessed by subtracting the CCN concentration of the hypothetical inorganic aerosols from that of the ambient aerosols, was 50-182cm(-3) for the SS range of 0.11-0.80%. The increase of the CCN number concentrations per 1-g/m(3) increase of the BSOA was 23-299cm(-3) at 0.11-0.80% SS. The contribution of the BSOA to the CCN number concentration can be enhanced by new particle formation. Plain Language Summary Some of the particles suspended in the atmosphere can absorb water vapors around them and act as nuclei to form cloud droplets. These particles are called cloud condensation nuclei (CCN), the quantification of which is important for climate forcing prediction. The ability of a particle to absorb water is referred to as hygroscopicity, which is governed by the chemical composition. Volatile organic vapors emitted by vegetation (i.e., biogenic volatile organic compound) after chemical reactions in the atmosphere can either condense onto existing particles or participate in the formation of new particles and thus change the aerosol chemical composition. The aerosol component originated from biogenic volatile organic compounds, named biogenic secondary organic aerosol (BSOA), is an important constituent of CCN on a global scale. However, the hygroscopicity of BSOA and its contribution to CCN are not understood well. We performed measurements of the hygroscopicity and chemical composition of aerosol particles in a forest in Japan. Based on the observation, we calculated the hygroscopicity of the BSOA formed in the forest and quantified the contribution of the BSOA to the CCN number concentrations. An enhancement of the contribution of BSOA to the CCN number concentrations by new particle formation is suggested, which is an important subject of future studies.
  • Lee, Shan-Hu; Gordon, Hamish; Yu, Huan; Lehtipalo, Katrianne; Haley, Ryan; Li, Yixin; Zhang, Renyi (2019)
    New particle formation (NPF) represents the first step in the complex processes leading to formation of cloud condensation nuclei. Newly formed nanoparticles affect human health, air quality, weather, and climate. This review provides a brief history, synthesizes recent significant progresses, and outlines the challenges and future directions for research relevant to NPF. New developments include the emergence of state-of-the-art instruments that measure prenucleation clusters and newly nucleated nanoparticles down to about 1 nm; systematic laboratory studies of multicomponent nucleation systems, including collaborative experiments conducted in the Cosmics Leaving Outdoor Droplets chamber at CERN; observations of NPF in different types of forests, extremely polluted urban locations, coastal sites, polar regions, and high-elevation sites; and improved nucleation theories and parameterizations to account for NPF in atmospheric models. The challenges include the lack of understanding of the fundamental chemical mechanisms responsible for aerosol nucleation and growth under diverse environments, the effects of SO2 and NOx on NPF, and the contribution of anthropogenic organic compounds to NPF. It is also critical to develop instruments that can detect chemical composition of particles from 3 to 20 nm and improve parameterizations to represent NPF over a wide range of atmospheric conditions of chemical precursor, temperature, and humidity. Plain Language Summary In the atmosphere, invisible to the human eye, there are many microscopic particles, or nanoparticles, that affect human health, air quality, and climate. We do not fully understand the chemical processes that allow these fine particles to form and be suspended in the air nor how they influence heat flow in Earth's atmosphere. Laboratory experiments, field observations, and modeling simulations have all shown different results for how these particles behave. These inconsistencies make it difficult to accurately represent the processes of new particle formation in regional and global atmospheric models. Scientists still need to develop instruments that can measure the smallest range of nanoparticles and to find ways to describe particle formation that allow for differences in temperature, humidity, and level of pollution.
  • Kolehmainen, Sonja (Helsingin yliopisto, 2019)
    Polioenkefalomalasia eli PEM on keskushermosto-oireita aiheuttava sairaus naudoilla ja muilla eläinlajeilla. PEM:n diagnosointi elävältä eläimeltä on hyvin haastavaa, ja tämän kirjallisuuskatsauksen tavoitteena oli selvittää, onko kustannustehokkaita ja luotettavia diagnosointimenetelmiä saatavilla. PEM:n hoidossa käytettävän tiamiinin hinta on tällä hetkellä hyvin korkea, ja monien tuottajien taloudellinen tilanne Suomessa on huono. Tämän vuoksi laadukkaiden diagnosointimenetelmien kehittäminen olisi tärkeää, jotta tarpeettomia hoitoja ei aloitettaisi. Työn toinen tavoite oli koota yhteen PEM:n patofysiologiaa ja selvittää, mitä sairastuneiden eläinten aivoissa tapahtuu. Tässä työssä on käsitelty tiamiinia, tiaminaasia ja tiamiinianalogeja sekä rikkiä polioenkafalomalasian patofysiologiassa. PEM:n aiheuttajana on jo pidempään tiedetty olevan tiamiinin puute. Tiamiinia tarvitaan solujen energia-aineenvaihdunnassa osana sitruunahappokiertoa. Vasikat ovat riippuvaisia ravinnosta saatavasta tiamiinista, kun taas aikuisella naudalla pötsin mikrobit tuottavat yleensä riittävän määrän tiamiinia. Pötsin mikrobit voivat kuitenkin tuottaa liikaa tiamiinia pilkkovaa tiaminaasia. Tiedetään myös, että rehun liian korkea rikkipitoisuus voi aiheuttaa PEM:lle tyypillisiä oireita ja muutoksia aivoissa. Rikin vaikutuksia PEM:in kehittymiseen on tutkittu erityisesti 2000-luvulla. Tutkimusten mukaan ravinnon korkea rikkipitoisuus ei kuitenkaan yksiselitteisesti aiheuta polioenkefalomalasiaa. PEM-potilaan tyypillisiä oireita ovat sokeus, syömättömyys ja ataksia. Hoitamattomana sairaus johtaa kuolemaan. PEM:n hoidosta ei ole tehty yhtään kliinistä tutkimusta, mutta kirjallisuuden suosittelema hoito on 10-20 mg/kg tiamiinia injektioina kolmesti päivässä vähintään kolmen päivän ajan. Osa potilaista, jotka ovat sairastuneet PEM:an liian korkean rehun rikkipitoisuuden takia, vastaa tiamiinihoitoon, mutta osalle eläimistä hoito ei ole tehokas. Sairauden ehkäisemisessä on tärkeää huolehtia, että vasikat saavat ravinnostaan riittävästi tiamiinia, ja että ravinnon rikkipitoisuus pysyy suositelluissa rajoissa. Tämä kirjallisuuskatsauksen perusteella voidaan todeta, että PEM:n patofysiologian osalta on vielä monia epäselviä asioita. PEM:n diagnosointiin ei myöskään ole käytettävissä yhtä aikaa sekä luotettavaa että kustannustehokasta diagnosointimenetelmää eläville eläimille. Kuolleelta eläimeltä sairauden diagnosointi on kuitenkin helpompaa. Kliinisen työn kannalta tärkeä johtopäätelmä on, että lääkkeiden hintojen vertailun perusteella Neuramin on PEM:n hoitoon paras ja kannattavin vaihtoehto Suomessa saatavilla olevista valmisteista.
  • Hong, J.; Kim, J.; Nieminen, T.; Duplissy, J.; Ehn, M.; Äijälä, M.; Hao, L. Q.; Nie, W.; Sarnela, N.; Prisle, N. L.; Kulmala, M.; Virtanen, A.; Petäjä, T.; Kerminen, V. -M. (2015)
    Measurements of the hygroscopicity of 15145 nm particles in a boreal forest environment were conducted using two Hygroscopicity Tandem Differential Mobility Analyzer (HTDMA) systems during the Pan-European Gas-Aerosols-climate interaction Study (PEGASOS) campaign in spring 2013. Measurements of the chemical composition of non-size segregated particles were also performed using a high-resolution aerosol mass spectrometer (HR-AMS) in parallel with hygroscopicity measurements. On average, the hygroscopic growth factor (HGF) of particles was observed to increase from the morning until afternoon. In case of accumulation mode particles, the main reasons for this behavior were increases in the ratio of sulfate to organic matter and oxidation level (O : C ratio) of the organic matter in the particle phase. Using an O : C dependent hygroscopic growth factor of organic matter (HGF(org)), fitted using the inverse Zdanovskii-Stokes-Robinson (ZSR) mixing rule, clearly improved the agreement between measured HGF and that predicted based on HR-AMS composition data. Besides organic oxidation level, the influence of inorganic species was tested when using the ZSR mixing rule to estimate the hygroscopic growth factor of organics in the aerosols. While accumulation and Aitken mode particles were predicted fairly well by the bulk aerosol composition data, the hygroscopicity of nucleation mode particles showed little correlation. However, we observed them to be more sensitive to the gas phase concentration of condensable vapors: the more sulfuric acid in the gas phase, the more hygroscopic the nucleation mode particles were. No clear dependence was found between the extremely low-volatility organics concentration (ELVOC) and the HGF of particles of any size.
  • Ovaska, Aino (Helsingin yliopisto, 2021)
    Cloud condensation nuclei (CCN) participate in controlling the climate, and a better understading of their number concentrations is needed to constrain the current uncertainties in Earth’s energy budget. However, estimating the global CCN concentrations is difficult using only localised in-situ measurements. To overcome this, different proxies and parametrisations for CCN have been developed. In this thesis, accumulation mode particles were used as a substitute for CCN, and continental proxy for number concentration of N100 was developed with CO and temperature as tracers for anthropogenic and biogenic emissions. The data utilised in the analysis contained N100 measurements from 22 sites from 5 different continents as well as CO and temperature from CAMS reanalysis dataset. The thesis aimed to construct a global continental proxy. In addition to this, individual proxies for each site (the site proxy) and proxies trained with other sites’ data (the site excluded proxy) were developed. The performance of these proxies was evaluated using a modified version of K-fold cross-validation, which allowed estimating the effect of dataset selection on the results. Additionally, time series, seasonal variation, and parameter distributions for developed proxies were analysed and findings compared against known characteristics of the sites. Global proxy was developed, but no single set of parameters, that would achieve the best performance at all sites, was found. Therefore, two versions of global proxy were selected and their results analysed. For most of the sites, the site proxy performed better than the global proxies. Additionally, based on the analysis from the site excluded proxy, extrapolating the global proxy to new locations produced results with varying accuracy. Best results came from sites with low concentrations and occasional anthropogenic transport episodes. Additionally, some European rural sites performed well, whereas in mountainous sites the proxy struggled. Comparing the proxy to literature, it performed generally less well or similarly as proxies from other studies. Longer datasets and additional measurement sites could improve the proxy performance.
  • Hakala, Jani; Mikkilä, Jyri; Hong, Juan; Ehn, Mikael; Petäjä, Tuukka (2016)
    The aim of this study was to provide a description and characterize the performance of a volatility hygroscopicity tandem differential mobility analyzer (VH-TDMA) by calibration measurements. In our investigations, we used the two calibration standards most often used by the TDMA community: ammonium sulfate ((NH4)(2)SO4) and sodium chloride (NaCl) particles. The hygroscopic growth factors, volatility factors, and the hygroscopic growth factors of the nonvolatile particle core were measured in different relative humidity and thermal denuder temperature conditions. The measured hygroscopic growth and deliquescence relative humidities for ammonium sulfate and sodium chloride particles are in line with theory and results from previous measurements, as are the measurements for volatility and hygroscopicity of the particle core. We summarize the measurement campaigns, where the VH-TDMA has been deployed, and show the instrument is capable of measuring high quality data of atmospheric particle properties in various environments, in the laboratory and in the field.